structure and petrography op the piety hill...
TRANSCRIPT
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Structure and petrography of thePiety Hill area, Pima County, Arizona
Item Type text; Thesis-Reproduction (electronic); maps
Authors Broderick, Jon Palmer, 1941-
Publisher The University of Arizona.
Rights Copyright © is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.
Download date 16/07/2018 05:28:43
Link to Item http://hdl.handle.net/10150/551945
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STRUCTURE AND PETROGRAPHY OP THE PIE T Y H ILL AREA,
PIMA COUNTY, ARIZONA
b y
J o n P . B r o d e r i c k
A T h e s i s S u b m i t t e d t o t h e F a c u l t y o f t h e
DEPARTMENT OF GEOLOGY
I n P a r t i a l F u l f i l l m e n t o f t h e R e q u i r e m e n ts F o r t h e D e g re e o f
MASTER OF SCIENCE
I n t h e G r a d u a t e C o l l e g e
THE UNIVERSITY OF ARIZONA
1 9 6 7
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STATEMENT BY AUTHOR
T h i s t h e s i s h a s b e e n s u b m i t t e d i n p a r t i a l f u l f i l l m e n t o f r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t The U n i v e r s i t y o f A r i z o n a a n d i s d e p o s i t e d i n t h e U n i v e r s i t y L i b r a r y t o b e m ade a v a i l a b l e t o b o r r o w e r s u n d e r r u l e s o f t h e L i b r a r y .
B r i e f q u o t a t i o n s f ro m t h i s t h e s i s a r e a l l o w a b l e w i t h o u t s p e c i a l p e r m i s s i o n , p r o v i d e d t h a t a c c u r a t e a c k n o w le d g m e n t o f s o u r c e i s m a d e . R e q u e s t s f o r p e r m i s s i o n f o r e x t e n d e d q u o t a t i o n f ro m o r r e p r o d u c t i o n o f t h i s m anus c r i p t i n w h o le o r i n p a r t may b e g r a n t e d b y t h e h e a d o f t h e m a jo r d e p a r t m e n t o r t h e D ean o f t h e G r a d u a te C o l l e g e w hen i n h i s ju d g m e n t t h e p r o p o s e d u s e o f t h e m a t e r i a l i s i n t h e i n t e r e s t s o f s c h o l a r s h i p . I n a l l o t h e r i n s t a n c e s , h o w e v e r , p e r m i s s i o n m u s t b e o b t a i n e d f ro m t h e a u t h o r .
SIGNED:
APPROVAL BY THESIS DIRECTOR
T h is t h e s i s h a s b e e n a p p r o v e d o n t h e d a t e show n b e lo w :
_________________________ / / - ~R» L . D u B o is
P r o f e s s o r o f G e o lo g yD a te
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ACKNOWLEDGMENTS
T he a u t h o r w i s h e s t o e x p r e s s h i s g r a t i t u d e t o t h e
f a c u l t y m em b ers o f t h e D e p a r tm e n t o f G e o lo g y o f t h e
U n i v e r s i t y o f A r i z o n a who m ade m any h e l p f u l s u g g e s t i o n s
r e g a r d i n g t h e i n t e r p r e t a t i o n o f t h e g e o lo g y o f t h e P i e t y
H i l l a r e a .
S p e c i a l t h a n k s a r e d u e D r . R o b e r t L . D u B o is f o r
h i s a d v i c e a n d h i s t im e s p e n t i n t h e f i e l d . A c k n o w le d g m e n t
i s a l s o m ade t o D r . J o h n W. A n th o n y a n d D r . J o h n M.
G u i l b e r t who h a v e r e a d t h e m a n u s c r i p t a n d o f f e r e d m any
h e l p f u l s u g g e s t i o n s .
i l l
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TABLE OF CONTENTS
P a g e
L IS T OF ILLUSTRATIONS................................................................................... v i
ABSTRACT.........................................................................................................................v i i
INTRODUCTION........................................................................................................... 1
P u r p o s e o f S t u d y .................L o c a t i o n ......................................T o p o g ra p h y a n d D r a in a g e M e th o d o f I n v e s t i g a t i o n P r e v i o u s W o rk .........................
GEOLOGIC SETTING..................................................................................................... 6
PETROGRAPHY.................................................................................................................. 9
I n t r o d u c t i o n .................................................................................................. 9M e ta m o rp h ic R o c k s .................................................................................... 10
C a t a l i n a G n e i s s ............................................................................ 10G e n e r a l S t a t e m e n t o f A p a c h e G ro u p ............................ 12P i o n e e r F o r m a t i o n .............................................. 13
G n e i s s i c f a c i e s .............................................................. 19D r i p p i n g S p r i n g Q u a r t z i t e ................................................. 21
B a r n e s C o n g lo m e r a te M em ber.............. .................. 21D r i p p i n g S p r i n g Q u a r t z i t e .................................... 23
B o l s a Q u a r t z i t e . . . . ................................................................. 24S c h i s t f a c i e s o f B o l s a Q u a r t z i t e .............. 2 ?L im e s to n e f a c i e s o f B o l s a Q u a r t z i t e . . . 28
A b r lg o L i m e s t o n e ......................................................................... 29M a r t i n F o r m a t io n - E s c a b r o s a L i m e s t o n e ........... 33
I g n e o u s R o c k s ........................................................................................... 3 7L a m p ro p h y re D i k e s ................................................................... 3 7
A l lu v iu m ........................................................................................................... 38
STRUCTURAL GEOLOGY.............................................................................................. 40
G e n e r a l S t a t e m e n t .................................................................................... 40F a u l t s .............................................................................................................. 4 0F o l i a t i o n ................................................................................... 45
INTERPRETATION OF METAMORPHISM.............................................................. 4 ?
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VTABLE OF CONTENTS ( c o n t i n u e d ) P a g e
GEOLOGIC HISTORY................................................................................................ 52
REFERENCES................................................................................................................ 55
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L IS T OF ILLUSTRATIONS
F i g u r e P a g e
1 . LOCATION MAP...................................................................................... 2
2 . CARBONACEOUS VARIETY OF PIONEER FO R M A T IO N .... 18
P l a t e
1 . GEOLOGIC MAP OF THE PIETY H ILL AREA,PIMA COUNTY, ARIZONA.............................................. i n p o c k e t
2 . GEOLOGIC CROSS-SECTIONS OF THE PIETYH ILL AREA, PIMA COUNTY, ARIZONA.................i n p o c k e t
v i
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ABSTRACT
T he P i e t y H i l l a r e a i s l o c a t e d o n t h e e a s t e r n
f l a n k o f t h e S a n t a C a t a l i n a M o u n ta i n s , n o r t h e a s t o f T u c s o n ,
A r i z o n a . T he r o c k s c o n s i s t p r e d o m i n a n t l y o f m e ta m o rp h o s e d
P r e c a m b r l a n a n d P a l e o z o i c s e d i m e n t a r y r o c k s . L a m p ro p h y re
d i k e s t r a n s e c t t h e P r e c a m b r l a n a n d P a l e o z o i c r o c k s t h r o u g h
o u t t h e a r e a . F l a t - l y i n g , u n m e ta m o rp h o s e d , C e n o z o ic
a l l u v i u m o v e r l i e s t h e m e ta m o r p h ic r o c k s i n t h e e a s t .
T he c o r e o f t h e S a n t a C a t a l i n a R an g e i s c o m p o se d
o f a g r a n i t i c - g n e i s s i c c o m p le x t h a t fo r m e d p a r t l y f ro m
g r a n i t e i n t r u s i o n a n d p a r t l y f ro m g r a n i t i z a t i o n o f s e d i
m e n ta r y r o c k s . T he g r a n i t i c r o c k o f t h e s o u t h w e s t p o r t i o n
o f t h e P i e t y H i l l a r e a i s r e l a t e d t o t h e g r a n i t i c - g n e i s s i c
c o m p le x a n d w as p r o b a b l y i n t r u d e d d u r i n g p o s t - C r e t a c e o u s
t im e c a u s i n g c o n t a c t m e ta m o r p h ic p h e n o m e n a a t i t s m a r g i n s .
R e g i o n a l m e ta m o rp h is m a t t h i s sam e t im e a f f e c t e d m uch o f
t h e S a n t a C a t a l i n a r a n g e . C o n t a c t a n d r e g i o n a l m e ta m o rp h is m
a r e s u p e r im p o s e d i n t h e P i e t y H i l l a r e a .
F a u l t i n g , a n d a s s o c i a t e d f o l d i n g , a r e t h e m o s t
p r o m i n e n t t y p e o f s t r u c t u r a l d e f o r m a t i o n . T he o l d e s t
d i s c e m a b l e f a u l t s a r e o f p o s t - C r e t a c e o u s a g e a n d a r e
u p t h r u s t s o r g r a v i t y g l i d e f e a t u r e s . H ig h a n g l e , n o r t h w e s t
t r e n d i n g , n o r m a l f a u l t s fo r m e d n e x t , a n d t h e n h i g h a n g l e ,
e a s t - w e s t t r e n d i n g n o r m a l f a u l t i n g o c c u r r e d .
v i i
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TillR e c e n t e r o s i o n h a s d i s s e c t e d t h e l a n d s u r f a c e t o
c r e a t e t h e p r e s e n t t o p o g r a p h y .
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INTRODUCTION
P u r p o s e o f S tu d y
T he p u r p o s e o f t h i s s t u d y i s t o d e s c r i b e t h e r o c k
t y p e s p r e s e n t i n t h e P i e t y H i l l a r e a , a n d t o d e t e r m i n e
t h e i r a r e a l d i s t r i b u t i o n a n d s t r u c t u r a l r e l a t i o n s . A m a jo r
g o a l i s t o d e t e r m i n e t h e p r e - m e ta m o r p h ic e q u i v a l e n t s o f t h e
v a r i o u s r o c k s i n o r d e r t o c o r r e l a t e t h e s t r a t i g r a p h i c
s e c t i o n w i t h o t h e r a r e a s . An a t t e m p t i s m ade t o d e t e r m i n e
t h e p e t r o l o g i c h i s t o r y o f t h e r o c k s o f t h e a r e a .
L o c a t i o n
T he a r e a c o v e r e d b y t h i s r e p o r t i s l o c a t e d o n t h e
s o u t h e a s t e r n f l a n k o f t h e S a n t a C a t a l i n a M o u n ta in s i n
n o r t h e a s t P im a C o u n ty , A r i z o n a ( F i g u r e 1 ) . T he m a p p ed
a r e a i s a p p r o x i m a t e l y f o u r s q u a r e m i l e s a n d i n c l u d e s
s e c t i o n s 31 a n d 3 2 , a n d p a r t s o f 2 8 , 2 9 , 3 0 , a n d 33 o f
T . 1 2 S . , R . 1 8 E . a n d p a r t s o f s e c t i o n s 2 5 a n d 3 6 o f T .
1 2 S . , R . 1 ? E . G i l a a n d S a l t R i v e r B a s e a n d M e r i d i a n .
I t i s sho w n o n t h e B e l l o t a R a n c h Q u a d r a n g l e , 1 9 5 7 . ( 1 :
6 2 , 5 0 0 ) , U . S . G e o l o g i c a l S u r v e y T o p o g r a p h ic Map S e r i e s .
T he T a n q u e V e rd e - R e d i n g to n R o a d i s t h e m a jo r
r o u t e o f a c c e s s i n t o t h e a r e a . The m a p p ed a r e a i s t h i r t y -
f i v e m i l e s e a s t - n o r t h e a s t o f T u c s o n v i a t h e R e d i n g to n
1
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2
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O ra c le San .. \kfanue/J^_
S A N T A
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• F O R E S TTanque
V erdeTUCSON SA G U A R O NATL. MONUMENT
ScaleA R IZO N A 10 miles
LOCATION M AP
P IE T Y H IL L THESIS A R E A
F I G U R E I
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3
R o a d . T he a r e a I s a c c e s s a b l e b y a u t o m o b i l e t h r o u g h o u t t h e
y e a r e x c e p t d u r i n g b r i e f p e r i o d s o f e x t r e m e r u n o f f f ro m
m e l t i n g snow i n e a r l y s p r i n g .
T o p o g ra p h y a n d D r a in a g e
T he l a n d s c a p e o f t h e P i e t y H i l l a r e a c o n s i s t s
m a in ly o f s m o o th , r o u n d e d h i l l s a n d r a t h e r s t e e p - s i d e d
v a l l e y s . P i e t y H i l l , l o c a t e d i n t h e w e s t e r n p a r t o f t h e
a r e a ( P l a t e I ) i s t h e p o i n t o f maximum e l e v a t i o n a t
f e e t a b o v e s e a l e v e l . T he t o p o g r a p h i c r e l i e f i n t h e a r e a
m ap p ed i s a p p r o x i m a t e l y 1 0 7 0 f e e t .
T he s t r e a m c h a n n e l s a r e d r y e x c e p t f o r b r i e f
p e r i o d s a f t e r sum m er th u n d e r s h o w e r s o r d u r i n g p e r i o d s o f
m e l t i n g snow i n t h e h i g h e r m o u n ta in s i n e a r l y s p r i n g .
T he p a t t e r n o f t h e s t r e a m s o v e r t h e g r a n i t i c r o c k o n t h e
s o u t h a n d w e s t i s d e n d r i t i c . T he s t r e a m s o f t h e r e m a i n d e r
o f t h e a r e a f lo w o v e r m e ta m o r p h ic r o c k s a n d h a v e a p a r a l l e l
t o s u b p a r a l l e l p a t t e r n i n tw o d i r e c t i o n s . Some o f t h e s e
s t r e a m s f lo w n o r t h - n o r t h w e s t , b u t m o s t f lo w e a s t - n o r t h e a s t .
D r a in a g e f ro m t h e s o u t h e r n q u a r t e r o f t h e a r e a
g o e s s o u t h i n t o Y o u tc y C a n y o n , t h e n S o z a C an y o n w h ic h
f l o w s i n t o t h e S a n P e d r o R i v e r t o t h e e a s t . T he r e m a i n d e r
o f t h e m a p p ed a r e a d r a i n s t o t h e e a s t a n d t h e n n o r t h t o
j o i n B uehm an C anyon d r a i n a g e w h ic h f l o w s i n t o t h e S a n
P e d r o R i v e r a t R e d i n g t o n .
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4
M e th o d o f I n v e s t i g a t i o n
T he p r o b le m w as f i r s t a p p r o a c h e d b y f i e l d m a p p in g
b e g u n i n O c t o b e r 1965 . a n d c o m p le te d i n M a rc h 1966#
E n l a r g e d a e r i a l p h o t o g r a p h s t a k e n b y t h e U . S . F o r e s t
S e r v i c e , 1 9 5 8 , w e re u s e d a s a b a s e map f o r i n i t i a l f i e l d
m a p p in g . T he s c a l e o f t h e e n l a r g e d p h o t o s w a s 1 : 5 , 4 0 0 .
T he f i e l d d a t a w as s u b s e q u e n t l y t r a n s f e r r e d t o a s i m i l a r l y
e n l a r g e d p o r t i o n o f t h e B e l l o t a R a n c h Q u a d r a n g l e .
A p e t r o g r a p h i c s t u d y , i n v o l v i n g e x a m i n a t i o n o f
s i x t y t h i n s e c t i o n s , w as m ade i n a n a t t e m p t t o i n t e r p r e t
t h e p e t r o g e n e s i s o f t h e r o c k s , e s p e c i a l l y i n r e l a t i o n t o
t h e m e ta m o rp h is m o f t h e a r e a .
P r e v i o u s W ork
T he g e o lo g y o f t h e P i e t y H i l l a r e a h a s n o t b e e n
s p e c i f i c a l l y r e p o r t e d o n p r e v i o u s l y . T he a r e a w as i n
c l u d e d o n a g e n e r a l i z e d g e o l o g i c map o f t h e U . S .
G e o l o g i c a l S u r v e y T o p o g r a p h ic Map S e r i e s , T u c s o n Q u ad
r a n g l e , s c a l e 1 : 1 2 5 ,0 0 0 , 1 9 0 4 , b y M o o re , T o lm a n , a n d
o t h e r s ( 1 9 4 9 ) • T h i s map w as o f l i t t l e v a l u e b e c a u s e , i n
t h e l i g h t o f t h i s s t u d y , t h e r o c k s o f M o o r e 's map h a v e
b e e n i n a c c u r a t e l y c o r r e l a t e d w i t h r e g a r d t o a g e . The
L o w e r P a l e o z o i c r o c k s o f M oore a n d o t h e r s a r e i n t e r p r e t e d
t o b e P r e c a m b r i a n , a n d t h e C r e t a c e o u s r o c k s o f M oore a r e
i n t e r p r e t e d t o b e P a l e o z o i c i n a g e a s a r e s u l t o f t h e
p r e s e n t s t u d y .
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5
R o b e r t G . R a a b e (1 9 5 9 ) m ade a s t r u c t u r a l a n d p e t r o
g r a p h i c s t u d y o f t h e B u l l o c k C an y o n - B uehm an C an y o n a r e a ,
o n e m i l e n o r t h w e s t o f t h e a r e a o f t h i s r e p o r t . R a a b e
d e s c r i b e d t h e P r e c a m b r i a n A p a c h e G ro u p m e ta m o rp h o s e d s e d i
m e n ta r y r o c k s a n d som e o f t h e m e ta m o rp h o s e d P a l e o z o i c
r o c k s t h a t a r e a l s o f o u n d i n t h e P i e t y H i l l a r e a .
J o h n J . M cK enna ( I 9 6 6 ) m ade a s t u d y o f t h e P a l e o z o i c
s e d i m e n t a r y r o c k s o f B uehm an C an y o n i n a tw e l v e s q u a r e m i l e
a r e a o n t h e n e c k o f b e d r o c k p r o t r u d i n g i n t o t h e S a n P e d r o
R i v e r v a l l e y n e a r R e d i n g t o n . T he s o u t h e r n b o u n d a r y o f
M cKenna* s map i s tw o a n d o n e - h a l f m i l e s t o t h e n o r t h o f
t h e a r e a o f s t u d y o f t h i s r e p o r t .
T he M in e t a R id g e a r e a w a s m ap p ed b y R a n d a l l T .
Chew ( I 9 5 2 ) . T h i s a r e a l i e s o n e m i l e t o t h e s o u t h e a s t o f
t h e p r e s e n t s t u d y . Chew w as m a in ly c o n c e r n e d w i t h t h e
C e n o z o ic s e d i m e n t a r y r o c k s a n d t h e r e f o r e h i s w o rk w as n o t
o f m uch v a l u e t o t h e p r e s e n t s t u d y .
M aung Myo M in , a g r a d u a t e s t u d e n t a t t h e U n i v e r s i t y
o f A r i z o n a , i s c u r r e n t l y m a k in g a s t r u c t u r a l a n d p e t r o
g r a p h i c s t u d y o f t h e g r a n i t i c a n d m e ta m o r p h ic r o c k s i n
t h e c o n t i g u o u s a r e a t o t h e w e s t .
F r e d e r i c k L . P e i r c e (1 9 5 8 ) a n d H a r o l d D. P i l k i n g t o n
( I 9 6 2 ) d i d e x t e n s i v e s t r u c t u r a l a n d p e t r o g r a p h i c w o rk i n
t h e m e ta m o rp h o s e d s e d i m e n t a r y r o c k s o f t h e S a n t a C a t a l i n a
M o u n ta in s t o t h e n o r t h w e s t .
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GEOLOGIC SETTING
T he S a n t a C a t a l i n a M o u n ta in s a r e i n l a r g e p a r t
c o m p o se d o f s e d i m e n t a r y r o c k s t h a t h a v e b e e n u p l i f t e d ,
i n t r u d e d , a n d m e ta m o r p h o s e d . T he o l d e s t know n r o c k i n t h e
r a n g e i s t h e P r e c a m b r i a n C a t a l i n a G n e i s s o f g r a n i t i c com
p o s i t i o n ( P e i r c e , 1 9 5 8 ; D u B o is , 1 9 5 9 a ) . T he O l d e r
P r e c a m b r i a n P i n a l S c h i s t o v e r l i e s t h e o l d e r g r a n i t e a n d
i s t h e o l d e s t know n s e d i m e n t a r y r o c k o f t h e r a n g e . An
a n g u l a r u n c o n f o r m i t y s e p a r a t e s t h e P i n a l S c h i s t f ro m t h e
Y o u n g e r P r e c a m b r i a n A p a c h e G ro u p s e d i m e n t a r y r o c k s . The
A p a c h e G ro u p i s c o m p o se d o f c o n g l o m e r a t e , q u a r t z i t e , a n d
s h a l y - s c h i s t o s e r o c k d e p e n d in g o n t h e d e g r e e o f m e ta m o rp h is m .
P a l e o z o i c s e d i m e n t a r y r o c k s l i e w i t h a n g u l a r u n c o n f o r m i t y
u p o n t h e A p a c h e G ro u p . T he P a l e o z o i c s t r a t a c o n s i s t p r e
d o m in a n t ly o f l i m e s t o n e , w i t h som e s i l t s t o n e , s a n d s t o n e ,
a n d q u a r t z i t e . M o s t o f t h e know n P r e c a m b r i a n a n d P a l e o z o i c
s e d i m e n t a r y r o c k s a r e f o u n d n o r t h o f M o u n t Lemmon a n d w e s t
o f R e d i n g to n (M o o re a n d o t h e r s , 1 9 4 9 ) •
T he d e g r e e o f m e ta m o rp h is m o f t h e P r e c a m b r i a n
P i n a l S c h i s t a n d A p a c h e G ro u p a n d t h e o v e r l y i n g P a l e o z o i c
s t r a t a i s v a r i a b l e . T he f i r s t s t a g e o f m e ta m o r p h ic
a c t i v i t y , i n P r e c a m b r i a n t i m e , b e l o n g e d t o t h e lo w g r a d e
g r e e n s c h i s t f a c i e s (D u B o is , 1 9 5 9 a ) . A s e c o n d p e r i o d o f
6
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7
m e ta m o r p h ic a c t i v i t y o c c u r r e d i n p o s t - C r e t a c e o u s t i m e .
T h i s l a t e r s t a g e o f m e ta m o rp h is m c a u s e d t h e d e v e lo p m e n t
o f t h e s t a u r o l i t e - q u a r t z s u b f a c i e s o f t h e a l m a n d i n e -
a m p h i b o l i t e f a c i e s i n t h e a r e a o f M oun t Lemmon ( F y f e ,
T u r n e r , a n d V e rh o o g e n , 1 9 5 8 ) a s r e p o r t e d b y D u B o is ( 1 9 5 9 a ) •
On t h e e a s t f l a n k o f t h e S a n t a C a t a l i n a s a n d a l s o n o r t h
o f M oun t Lemmon t h e m e ta m o rp h is m w as o f l o w e r g r a d e , a n d
i s a s s i g n e d t o t h e g r e e n s c h i s t f a c i e s . I n t h e n o r t h e a s t
p a r t o f t h e r a n g e , i n P e p p e r s a u c e C an y o n ( S to y a n o w , 1 9 3 6 ) ,
a n d a l s o w e s t o f R e d i n g to n (M cK enna , 1 9 6 6 ) t h e P r e -
c a m b r ia n a n d P a l e o z o i c r o c k s a r e r e l a t i v e l y u n m e ta m o rp h o s e d .
C r e t a c e o u s s t r a t a c o n s i s t i n g o f c o n g l o m e r a t e ,
s a n d s t o n e , a n d l i m e s t o n e b e d s l i e u n c o n f o r m a b ly u p o n t h e
P a l e o z o i c s t r a t a (M cK en n a , I 9 6 6 ) . T he C r e t a c e o u s s t r a t a
a r e i n t u r n u n c o n f o r m a b ly o v e r l a i n b y T e r t i a r y s e d i m e n t a r y
r o c k s a s r e p o r t e d i n t h e M in e t a R id g e a r e a (C h ew , 1 9 5 2 ) .
I n m any p l a c e s p o r t i o n s o f t h e s t r a t i g r a p h i c
c o lu m n h a v e b e e n re m o v e d b y t h r u s t f a u l t i n g o r g r a v i t y
g l i d i n g , o r n o r m a l f a u l t i n g .
D u r in g t h e p o s t - C r e t a c e o u s P e r i o d t h e g r a n i t i c
b a s e m e n t r o c k o f t h e S a n t a C a t a l i n a R an g e w as m o b i l i z e d
a n d a p e r i o d o f r e g i o n a l me tam o r p h l s m a n d g r a n i t i z a t i o n
o f o v e r l y i n g s e d i m e n t a r y r o c k s o c c u r r e d . T he d e g r e e o f
g r a n i t i z a t i o n a n d m e ta m o rp h is m v a r i e d i n i n t e n s i t y t h r o u g h
o u t t h e r a n g e . A g n e i s s i c t e x t u r e w i t h a w e l l d e v e lo p e d
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8
n o r t h e a s t - t r e n d i n g l i n e a t i o n w as d e v e lo p e d f ro m t h e M o u n t
Lemmon a r e a s o u th w a r d to w a r d t h e R in c o n M o u n ta in s (D u B o is , ;1 9 5 9 b ) . Some a r e a s o f g r a n i t i c c o m p o s i t i o n l a c k a r e c o g
n i z a b l e l i n e a t i o n o r f o l i a t i o n . T h e s e a r e a s m ay b e p o r t i o n s
o f t h e P r e c a m b r i a n g r a n i t e b e d r o c k t h a t w e re r e m o b i l i z e d
a n d r e i n t r u d e d d u r i n g p o s t - C r e t a c e o u s t i m e . O t h e r
i n t r u s i v e r o c k s s u c h a s q u a r t z d l o r l t e , d i a b a s e , a n d
q u a r t z l a t i t e a r e f o u n d i n v a r i o u s p a r t s o f t h e r a n g e .
P e g m a t i t e s a r e a l s o f o u n d .
T h e r e a r e b r o a d a n t i c l i n a l a n d s y n c l i n a l s t r u c t u r e s
i n t h e g n e i s s l c a n d s e d i m e n t a r y r o c k s o f t h e S a n t a C a t a l i n a
M o u n ta i n s . T he f o l d s t r u c t u r e s p r e s e n t i n t h e g n e i s s l c
g r a n i t e a r e i n t e r p r e t e d b y D u B o is ( 1 9 5 9 b ) a s r e m n a n t s o f
a p r e - e x i s t i n g s t r u c t u r a l p a t t e r n t h a t w a s p r e s e n t i n t h e
s e d i m e n t a r y r o c k s p r i o r t o t h e g r a n i t i z a t i o n a n d m e ta
m o rp h ism t h a t o c c u r r e d d u r i n g p o s t - C r e t a c e o u s t i m e .
F a u l t i n g i s a common f e a t u r e o f t h e r a n g e . E a s t -
w e s t - t r e n d i n g a n d n o r t h - s o u t h - t r e n d i n g h i g h - a n g l e n o r m a l
f a u l t s a r e com m on. T he M o g u l F a u l t a t t h e n o r t h e n d o f
t h e r a n g e i s a n e x a m p le o f t h e e a s t - w e s t - t r e n d i n g t y p e .
L o w - a n g le t h r u s t f a u l t s h a v e b e e n o b s e r v e d o n t h e e a s t
f l a n k o f t h e r a n g e w e s t o f R e d i n g to n ( R a a b e , 1 9 5 9 ) •
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PETROGRAPHY
I n t r o d u c t i o n
T he C a t a l i n a G n e i s s i s p a r t o f t h e C a t a l i n a
g n e i s s i c c o m p le x a n d a p p e a r s t o b e i n t r u s i v e w h e re i t
o c c u r s i n t h e w e s t a n d s o u t h w e s t p o r t i o n s o f t h e P i e t y
H i l l a r e a . C o n t a c t m e ta m o r p h ic e f f e c t s a r e p r o n o u n c e d n e a r
t h i s m a s s .
Y o u n g e r P r e c a m b r l a n m e ta m o rp h o s e d s e d i m e n t a r y r o c k s
o f t h e A p a c h e G ro u p o u t c r o p i n a f a u l t e d b l o c k e a s t o f
P i e t y H i l l . T he S c a n lo n C o n g lo m e r a te M em ber i s a b s e n t
a l t h o u g h t h e P i o n e e r F o r m a t io n a n d D r i p p i n g S p r i n g
Q u a r t z i t e , i n c l u d i n g t h e B a r n e s C o n g lo m e r a te M em ber, a r e
p r e s e n t .
P a l e o z o i c r o c k s t h a t c r o p o u t i n t h e P i e t y H i l l
a r e a a r e t h e B o l s a Q u a r t z i t e , A b r ig o L i m e s to n e , a n d u n
d i f f e r e n t i a t e d M a r t i n F o r m a t io n - E s c a b r o s a L i m e s to n e .
H o r i z o n t a l l y s t r a t i f i e d C e n o z o ic a l l u v i u m c r o p s o u t i n
t h e e a s t .
R e g i o n a l d e f o r m a t i o n a n d a c c o m p a n y in g m e ta m o rp h is m
h a v e c a u s e d r e c r y s t a l l i z a t i o n t o s u c h a n e x t e n t t h a t
r e c o g n i z a b l e f o s s i l r e m a i n s a r e v e r y s p a r s e .
U n m e ta m o rp h o se d l a m p r o p h y r e d i k e s a r e s c a t t e r e d
t h r o u g h o u t t h e a r e a a n d i n t r u d e r o c k s a s y o u n g a s
M i s s i s s i p p i a n .
9
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1 0
M e ta m o rp h ic R o c k s
C a t a l i n a G n e i s s
C a t a l i n a G n e i s s i s t h e nam e g i v e n b y D u B o is ( 1 9 5 9 a )
t o t h e g r a n i t l c - g n e i s s i c r o c k s f o r m in g t h e c o r e o f t h e
S a n t a C a t a l i n a M o u n ta i n s . I n t h e P i e t y H i l l a r e a t h e
C a t a l i n a G n e i s s h a s a c o m p o s i t i o n t h a t r a n g e s f ro m g r a n i t e
t o q u a r t z m o n z o n i te a n d a f a b r i c t h a t r a n g e s f ro m m a g m a tic
t o c r y s t a l l o b i a s t i c . G r a n i t e w o u ld b e a m o re e n c o m p a s s in g
te r m t h a n g n e i s s f o r t h e P i e t y H i l l a r e a r o c k s b u t n o
nam e c h a n g e s w i l l b e m ade i n t h i s s t u d y . T he C a t a l i n a
G n e i s s o f t h e P i e t y H i l l a r e a c r o p s o u t i n t h e w e s t a n d
s o u t h w e s t p o r t i o n o f t h e a r e a m a p p e d . M o s t o f t h e r o c k o f
t h i s u n i t i n t h e P i e t y H i l l a r e a l a c k s s t r u c t u r e . L o c a l l y
t h e g r a n i t i c r o c k h a s a t r u e g n e i s s i c s t r u c t u r e i n a r e a s
o f c o n t a c t w i t h m e t a s e d i m e n t a r y r o c k s .
T he a u t h o r f e e l s t h a t t h i s g r a n i t i c m a ss w as i n t r u d e d
d u r i n g a p o s t - C r e t a c e o u s p e r i o d o f r e g i o n a l m e ta m o rp h is m .
E v id e n c e f o r a n i n t r u s i v e o r i g i n i s m a n i f o l d . C o n t a c t s o f
t h i s g r a n i t i c m a ss w i t h t h e m e t a s e d i m e n t a r y r o c k s a r e i r r e g
u l a r a n d t r a n s e c t s e d i m e n t a r y s t r u c t u r e s . X e n o l i t h i c b l o c k s
o f s c h i s t a n d l i m e s t o n e a r e s i t u a t e d l o c a l l y n e a r t h e c o n t a c t .
N u m ero u s p e g m a t i t e d i k e s a n d a p o p h y s e s a r e c o n c e n t r a t e d i n
t h e P i o n e e r F o r m a t io n a t t h e g r a n i t i c c o n t a c t .
H ig h t e m p e r a t u r e e f f e c t s o f t h e i n t r u s i o n a r e
e v i d e n t . X e n o l i t h i c l i m e s t o n e b l o c k s h a v e b e e n c o n v e r t e d
t o s k a m w i t h d e v e lo p m e n t o f a b u n d a n t g a r n e t a n d e p i d o t e .
T he P i o n e e r F o r m a t io n i n c l o s e p r o x i m i t y t o t h e g r a n i t i c
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1 1
c o n t a c t s o u t h o f t h e R e d i n g to n R o a d , h a s u n d e r g o n e c o n t a c t
m e ta m o rp h is m e v i d e n c e d b y t h e d e v e lo p m e n t o f c o a r s e i d i o -
b l a s t l c c h i a s t o l i t e c r y s t a l s .
O u tc r o p s o f t h e C a t a l i n a G n e i s s w e a t h e r r e a d i l y
f o r m in g r o u n d e d h i l l s s e t o f f b y a d e n d r i t i c d r a i n a g e
p a t t e r n . F r e s h s a m p le s a r e d i f f i c u l t t o o b t a i n b e c a u s e
t h e f e l d s p a r c r y s t a l s a r e a l t e r e d n e a r t h e s u r f a c e a n d
s p e c im e n s a r e e x t r e m e l y f r i a b l e . On t h e w e a t h e r e d s u r f a c e
t h e C a t a l i n a G n e i s s i s v e r y p a l e o r a n g e (1 0 YR 8 / 2 -
G o d d a rd , 1 9 4 8 ) . T he f r e s h " g n e i s s " s u r f a c e i s w h i t e (N 9 )
w i t h l i g h t g r a y (N 7 ) q u a r t z c r y s t a l s .
G e n e r a l l y t h e r o c k i s a h o l o c r y s t a l l i n e p h a n e r i t e
w i t h g r a i n s i z e r a n g i n g f ro m f i n e t o c o a r s e . T he t e x t u r e
r a n g e s f ro m a l l o t r i o m o r p h i c g r a n u l a r t o h y p id io m o r p h ic
g r a n u l a r . T he g n e i s s i c v a r i e t y o f t h e C a t a l i n a G n e i s s
d i s p l a y s a f o l i a t i o n o f a l i g n e d b i o t i t e c r y s t a l s a n d t h e
f a b r i c i s e l o n g a t e s e r i a t e .
U n d e r t h e m ic r o s c o p e t h e g r a n i t i c r o c k i s s e e n t o
c o n t a i n 3 0 - 6 0 # q u a r t z , 2 0 # o r t h o c l a s e , 1 0 # m i c r o c l i n e ,
20 - 30# o l i g o c l a s e , 1 - 4 0 # b i o t i t e a n d g a r n e t .
Q u a r t z o c c u r s a s a n h e d r a l , m o d e r a t e l y - t o h i g h l y -
s t r a i n e d c r y s t a l s u p t o 7 mm l o n g . I n d i v i d u a l g r a i n s
d i s p l a y i r r e g u l a r s u t u r e d m a r g in s t h a t a r e i n t e r g r o w n
w i t h a d j a c e n t q u a r t z c r y s t a l s . O r t h o c l a s e i s t h e m o s t
a b u n d a n t f e l d s p a r i n t h e g n e i s s i c v a r i e t y . I t i s u p t o
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1 2
8 mm l o n g a s e u h e d r a l t o a n h e d r a l g r a i n s . C a r l s b a d t w i n n i n g
i s common. I n c i p i e n t a l t e r a t i o n t o c l a y ( K a o l i n i t e ? )
a n d s e r i c i t e i s w i d e s p r e a d . O r t h o c l a s e o c c a s i o n a l l y c o n
t a i n s i n c l u s i o n s o f p l a g i o c l a s e ( o l i g o c l a s e ) . M i c r o c l i n e
i s l o c a l l y t h e m o s t a b u n d a n t f e l d s p a r a s a n h e d r a l g r a i n s
u p t o 7 mm l o n g . M u s c o v i t e a n d b i o t i t e a s e u h e d r a l t o
s u b h e d r a l f l a k e s r e a c h 1 . 5 mm i n l e n g t h . S u b h e d r a l b i o t i t e
a n d m u s c o v i t e a r e t h e m i n e r a l s t h a t d e f i n e t h e f o l i a t i o n
i n t h e g n e i s s i c p a r t o f t h e C a t a l i n a G n e i s s . G a r n e t i s a
m in o r a c c e s s o r y m i n e r a l a s m in u te a n h e d r a l g r a i n s .
C u r r e n t t h o u g h t i n v o l v i n g t h e a g e o f t h e C a t a l i n a
G n e i s s s u g g e s t s t h a t a P r e C a m b r ia n g r a n i t i c r o c k w as s u b
j e c t e d t o m e ta m o rp h is m ( P e i r c e , 1 9 5 8 ; Dam on, E r i c k s o n , a n d
L i v i n g s t o n (1 9 6 3 ) a n d t h a t P a l e o z o i c s e d i m e n t a r y r o c k s w e re
g r a n i t i z e d t o fo rm t h e g n e i s s i c c o m p le x . Dam on, E r i c k s o n ,
a n d L i v i n g s t o n (1 9 6 3 ) h a v e d e t e r m i n e d K -A r d a t e s f o r m ic a s
i n t h e C a t a l i n a G n e i s s i c c o m p le x a n d c o n c lu d e d t h a t
M. . .m e ta m o rp h is m h a d t e r m i n a t e d b y U p p e r O l ig o c e n e - L o w er
M io c e n e t i m e . "
I n t h e P i e t y H i l l a r e a t h e f i e l d r e l a t i o n s , c o n t a c t
m e ta m o r p h ic e f f e c t s , a n d g e n e r a l l a c k o f s t r u c t u r e s u g g e s t
t h a t t h e g r a n i t i c m a t e r i a l w as m o b i l i z e d t o s u c h a n e x t e n t
t h a t t h e r o c k s w e re a c t u a l l y i n t r u s i v e .
G e n e r a l S t a t e m e n t o f A p a c h e G ro u p
T he A p a c h e G ro u p o f s e d i m e n t a r y r o c k s w as f i r s t
d e s c r i b e d b y R ansom e ( 1 9 0 3 ) » A c o m p le te s e c t i o n o f t h e
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A p a c h e G ro u p d o e s n o t c r o p o u t i n t h e P i e t y H i l l a r e a . A
q u a r t z - m i c a s c h i s t w i t h a g n e i s s i c f a c i e s s i m i l a r t o t h a t
d e s c r i b e d b y R a a b e ( 1 9 5 9 ) i s i n t e r p r e t e d a s t h e m e ta
m o rp h o s e d e q u i v a l e n t o f t h e P i o n e e r F o r m a t i o n . T he S c a n lo n
C o n g lo m e r a te M em ber o f t h e P i o n e e r F o r m a t io n d o e s n o t c r o p
o u t i n t h e t h e s i s a r e a . T he B a r n e s C o n g lo m e r a te M em ber
o f t h e D r i p p i n g S p r i n g Q u a r t z i t e a n d t h e o v e r l y i n g D r i p p i n g
S p r i n g Q u a r t z i t e c o n f o r m a b ly o v e r l i e t h e P i o n e e r F o r m a t i o n .
P i o n e e r F o r m a t io n
T he Y o u n g e r P r e c a m b r i a n P i o n e e r S h a l e w as o r i g i n a l l y
n am ed b y R ansom e ( 1 9 0 3 ) * T he nam e h a s s i n c e b e e n m o d i f i e d
b y S h r i d e ( 1 9 6 1 ) , a n d i s now c a l l e d t h e P i o n e e r F o r m a t i o n .
I n t h e P i e t y H i l l a r e a t h e P i o n e e r F o r m a t io n i s p r e
d o m in a n t ly a s c h i s t u n i t t h a t i s a q u a r t z - m u s c o v i t e - s e r i c i t e -
b i o t i t e r o c k w i t h a w e l l d e v e lo p e d f o l i a t i o n e x e m p l i f i e d
b y p r e f e r r e d o r i e n t a t i o n o f m ic a c e o u s m i n e r a l s . T he
s c h i s t e x p o s u r e i s a l a r g e f a u l t b l o c k w h ic h h a s i t s l o n g
d im e n s io n p a r a l l e l t o t h e s t r i k e o f t h e f o l i a t i o n a t
a p p r o x i m a t e l y N 2 0 ° W. T he d i p i s q u i t e v a r i a b l e ; t h e
m o s t common d i r e c t i o n i s t o t h e s o u t h w e s t .
T he o u t c r o p p a t t e r n i s d e t e r m i n e d l a r g e l y b y t h e
d i f f e r e n t i a l r e s i s t a n c e o f t h e v a r i o u s c o m p o s i t i o n a l l a y e r s
o f t h e s c h i s t . Q u a r t z r i c h z o n e s t e n d to b e m o s t r e s i s t a n t
t o e r o s i o n . G e n e r a l l y t h e P i o n e e r F o r m a t io n fo r m s a
t o p o g r a p h y o f r o u n d e d h i l l s w i t h s m o o th s a d d l e s a n d s l o p e s .
13
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B o th t h e e a s t e r n a n d w e s t e r n c o n t a c t s o f t h e s c h i s t a r e
f a u l t e d t h r o u g h o u t m o s t o f t h e a r e a . I n t h e s o u t h w e s t ,
h o w e v e r , t h e P i o n e e r F o r m a t io n i s c o n f o r m a b ly o v e r l a i n b y
t h e B a r n e s C o n g lo m e ra te M em ber o f t h e D r i p p i n g S p r i n g
Q u a r t z i t e . I t i s t h e p r e s e n c e o f t h e B a r n e s C o n g lo m e r a te
t h a t i s t h e m o s t c o n c l u s i v e e v i d e n c e t h a t t h e s c h i s t u n i t
i s t h e P i o n e e r F o r m a t i o n . P e t r o g r a p h i c a n d l i t h o l o g i c
s i m i l a r i t y b e tw e e n w h a t B a a b e (1 9 5 9 ) c a l l e d P i o n e e r
F o r m a t io n a n d t h e s c h i s t o f t h e P i e t y H i l l a r e a i s
s u p p o r t i n g e v i d e n c e f o r w h a t t h i s a u t h o r h a s i d e n t i f i e d
a s t h e P i o n e e r F o r m a t i o n . S t r u c t u r a l c o m p l e x i t i e s h a v e
m ade i t i m p o s s i b l e t o m e a s u r e t h e t h i c k n e s s o f t h e
P i o n e e r F o r m a t i o n .
T he P i o n e e r F o r m a t io n i s e x t r e m e l y v a r i a b l e l i t h
o l o g i c a l l y . T he r o c k s r a n g e f ro m m ic a c e o u s q u a r t z i t e
t h r o u g h q u a r t z - m u s c o v i t e s c h i s t , c a r b o n a c e o u s s i l l i m a n i t e -
s e r i c i t e s c h i s t t o a g n e i s s i c f a c i e s w i t h a b u n d a n t
f e l d s p a r . T he c o l o r o f t h e r o c k i s a l s o v a r i a b l e . A
r u s t y a p p e a r a n c e o n w e a t h e r e d o u t c r o p s i s c h a r a c t e r i s t i c
o f t h i s f o r m a t i o n i n t h e a r e a m a p p e d . C o lo r s o f t h e f r e s h
a n d w e a t h e r e d r o c k s a r e a s f o l l o w s i M ic a c e o u s q u a r t z i t e
i s l i g h t g r a y (N 7 ) o n b o t h f r e s h a n d w e a t h e r e d s u r f a c e s ;
q u a r t z - m u s c o v i t e s c h i s t i s l i g h t o l i v e g r a y ( 5 Y 6 / 1 ) o n a
f r e s h s u r f a c e a n d d a r k r e d d i s h b ro w n (iO R 3 / 4 ) o n a
w e a t h e r e d s u r f a c e ; s i l l i m a n i t e - s e r i c i t e s c h i s t i s m edium
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d a r k g r a y (N *f) o n a f r e s h s u r f a c e a n d d a r k r e d d i s h b ro w n
(10R 3 / 4 ) t o m edium d a r k g r a y (N 4 ) o n a w e a t h e r e d s u r f a c e .
T he r u s t y q u a r t z - m u s c o v i t e s c h i s t t h a t i s m o s t
c h a r a c t e r i s t i c o f t h e P i o n e e r F o r m a t io n c o n t a i n s v a r i a b l e
q u a n t i t i e s o f q u a r t z a n d m ic a c e o u s m i n e r a l s . Q u a r t z
r a n g e s f ro m 3 5 $ t o 9 0 $ o f t h e r o c k . T he m ic a c e o u s m i n e r a l s
a r e m u s c o v i t e a n d s e r i c i t e w i t h l e s s e r a m o u n ts o f b i o t i t e
a n d c h l o r i t e . M u s c o v i t e - s e r i c i t e r a n g e s f ro m a b o u t 8 $ t o
5 0 $ ; b i o t i t e h a s n o t b e e n f o u n d t o e x c e e d 1 5 $ . C h l o r i t e
i s p r e s e n t u p t o 8 $ . A l l o t h e r c o n s t i t u e n t s s u c h a s
p l a g i o c l a s e f e l d s p a r a n d o p a q u e m i n e r a l s m ake u p l e s s t h a n
1 $ o f t h e t o t a l v o lu m e .
G r a in s i z e i s g e n e r a l l y f i n e t o v e r y f i n e . Q u a r t z
i s a lw a y s l e s s t h a n 1 mm a n d u s u a l l y a s f i n e a s 0 .1 -
0 . 2 mm. M u s c o v i te a n d b i o t i t e c r y s t a l s r a n g e f ro m 0 . 5 mm
i n l e n g t h t o l e s s t h a n 0 .1 mm. S e r i c i t e i s e x t r e m e l y f i n e .
T he s c h i s t u n i t m a i n t a i n s a d e f i n i t e f o l i a t i o n o f
p a r a l l e l t o s u b p a r a l l e l a l i g n e d m u s c o v i t e - s e r i c i t e c r y s t a l s
w h ic h i m p a r t t o t h e r o c k a l e p i d o b l a s t i c t e x t u r e . I n
som e s p e c im e n s t h e s e r i c i t e i s i n e l o n g a t e m a s s e s w h ic h
a r e p a r a l l e l t o t h e f o l i a t i o n , b u t t h e i n d i v i d u a l g r a i n s
a r e r a n d o m ly o r i e n t e d . T h i s i s a g l o m e r o b l a s t i c t e x t u r e .
T he q u a r t z g r a i n s a r e o r i e n t e d i n p a r a l l e l b a n d s
a d j a c e n t t o m u s c o v i t e - s e r i c i t e o r a r e p r e s e n t a s a m a t r i x
c o n t a i n i n g s m a l l ra n d o m m ic a f l a k e s a n d c u t b y a f o l i a t i o n
15
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o f o r i e n t e d m ic a . T he i n d i v i d u a l g r a i n s o f q u a r t z a r e
m o d e r a t e l y t o h i g h l y s t r a i n e d a n h e d r a l c r y s t a l s w i t h i n t e r
l o c k i n g b o u n d a r i e s t h a t a r e v a g u e b e c a u s e o f u n d u l a t o r y
e x t i n c t i o n . I n som e a r e a s t h e q u a r t z i s e l o n g a t e d p a r a l l e l
t o t h e f o l i a t i o n .
M u s c o v i te i s g e n e r a l l y i n s u b h e d r a l t o a n h e d r a l
c r y s t a l s t h a t o c c u r a s r a n d o m ly o r i e n t e d c o m p o n e n ts o f a
p r e d o m i n a n t l y q u a r t z m a t r i x o r a s i n t e r w o v e n c o n s t i t u e n t s
o f b a n d s i m p a r t i n g a f o l i a t i o n t o t h e r o c k . S e r i c i t e i s
s o f i n e g r a i n e d t h a t r e l a t i o n s o f i n d i v i d u a l g r a i n s a r e
r a r e l y d e t e r m i n a b l e . I n o n e p e c u l i a r v a r i e t y o f t h e
s c h i s t l a r g e k n o t s o f s e r i c i t e h a v e d e v e lo p e d i n w h ic h t h e
i n d i v i d u a l g r a i n s h a v e b e e n o r i e n t e d a t r i g h t a n g l e s t o
t h e s c h i s t o s i t y . B i o t i t e a n d c h l o r i t e a r e n o t a lw a y s
p r e s e n t i n t h e s c h i s t , b u t w hen p r e s e n t t h e y a r e u s u a l l y
o r i e n t e d p a r a l l e l o r s u b p a r a l l e l t o t h e f o l i a t i o n . The
v a r i e t y o f c h l o r i t e p r e s e n t i s p e n n i n i t e a s d i s t i n g u i s h e d
b y i t s p a r a l l e l e x t i n c t i o n , s m a l l 2V, a n d a n o m a lo u s i n t e r
f e r e n c e c o l o r s . M in o r p l a g i o c l a s e f e l d s p a r i s p r e s e n t i n
a few s e c t i o n s a s v e r y s m a l l tw in n e d a n d u n tw in n e d c r y s t a l s .
T he c o m p o s i t i o n i s i n t h e o l i g o c l a s e r a n g e a s d e t e r m i n e d
b y i t s e x t i n c t i o n a n g l e r e l a t i v e t o t h e a l b l t e l a w . O p aq u e
m i n e r a l s a r e r a n d o m ly s c a t t e r e d t h r o u g h o u t t h e r o c k a n d
c o n s i s t o f m a g n e t i t e , l i m o n i t e , c a r b o n a c e o u s m a t t e r , a n d
h e m a t i t e a f t e r p y r i t e .
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I n a d d i t i o n t o t h e q u a r t z - m u s c o v i t e - s e r l c l t e -
b i o t l t e s c h i s t , t h e r e i s a c a r b o n a c e o u s v a r i e t y t h a t i s
c h a r a c t e r i z e d b y l a r g e p o r p h y r o b l a s t s o f s e r i c i t e a n d
s i l l i m a n i t e t h a t a r e p s e u d o m o rp h o u s a f t e r c h i a s t o l i t e
( F i g u r e 2 ) . T he a r e a l d i s t r i b u t i o n o f t h i s s c h i s t i s
l i m i t e d t o e r r a t i c e x p o s u r e s i n t h e s o u t h e r n p o r t i o n o f
P i o n e e r F o r m a t io n o u t c r o p s s u c h a s t h o s e s o u t h o f t h e
R e d i n g to n R o a d o n t h e e a s t - w e s t t r e n d i n g r i d g e . C h i a s t o l i t e
c r y s t a l s w i t h t h e f a m i l i a r c a r b o n - c r o s s o c c u r i n tw o f o r m s .
One fo rm h a s t h e c h i a s t o l i t e d e v e lo p e d a s c i g a r s h a p e d
p o r p h y r o b l a s t s w i t h t h e l o n g d im e n s io n r e a c h i n g 1 2 mm a n d
a d i a m e t e r o f 2 . 5 mm. T h e o t h e r fo rm o f t h e m i n e r a l i s a s
l a r g e 10 mm b y 20 mm c r y s t a l s w i t h a s q u a r e ( a n d a l u s i t e )
c r o s s - s e c t i o n b u t a l s o c o n t a i n i n g t h e c a r b o n - c r o s s . T he
f i n e r v a r i e t y o f t h e c h i a s t o l i t e i s i n a p r e f e r r e d o r i e n
t a t i o n d u e t o i t s g r o w th p a r a l l e l t o t h e f o l i a t i o n . T h e r e
i s , h o w e v e r , n o p r e f e r r e d l i n e a r a r r a n g e m e n t w i t h i n l a y e r s .
T he c o m p o s i t i o n o f t h e c h i a s t o l i t e s c h i s t i s a s
f o l l o w s ; 50% q u a r t z , 20 % s e r i c i t e - m u s c o v i t e , 2-10%
s i l l i m a n i t e , 20% c a r b o n , a n d u p t o 8% b i o t i t e . T he
m a j o r i t y o f t h e s e r i c i t e - m u s c o v i t e a n d a l l o f t h e s i l l i
m a n i t e o c c u r a s r e p l a c e m e n t s w i t h i n t h e p s e u d o m o r p h e d
c h i a s t o l i t e c r y s t a l s .
Q u a r t z g r a i n s a r e a n h e d r a l a n d m o d e r a t e l y s t r a i n e d .
T he m a t r i x o f t h e r o c k i s c o m p o se d o f i n t e r l o c k i n g q u a r t z ,
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18
FIGURE 2 . CARBONACEOUS VARIETY OF PIONEER FORMATION
Porphyroblasts of serlcite and sillimanite pseudomorphous after chiastolite. 3X.
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19
m u s c o v i t e - s e r i c i t e , a n d b i o t i t e c r y s t a l s . T he q u a r t z
c r y s t a l s a r e a p p r o x i m a t e l y 0 .1 mm I n s i z e a n d a r e e x t e n d e d
p a r a l l e l t o t h e f o l i a t i o n . M u s c o v i t e - s e r i c i t e a n d b i o t i t e
a r e s u b h e d r a l t o a n h e d r a l a n d a r e g e n e r a l l y l e s s t h a n 0 . 5 mm
i n l e n g t h . T he m ic a c e o u s m i n e r a l s a n d t h e a b u n d a n t c a r b o n
a c e o u s m a t t e r i n t h e m a t r i x a r e r o u g h l y p a r a l l e l t o t h e
f o l i a t i o n , a l t h o u g h t h e y b e n d o r s w i r l a r o u n d t h e l a r g e
p o r p h y r o b l a s t s o f s e r i c i t e - s i l l i m a n i t e p s e u d o m o rp h o u s
a f t e r c h i a s t o l i t e .
G n e l s s l c f a c i e s . A g n e i s s i c f a c i e s o f t h e q u a r t z -
m ic a s c h i s t o c c u r s t h a t i s d i s t i n c t l y d i f f e r e n t f ro m o t h e r
P i o n e e r F o r m a t io n l i t h o l o g i e s a s d e s c r i b e d o n t h e p r e v i o u s
p a g e s . I t i s a m a p p a b le u n i t b y i t s e l f , a n d a s s u c h i s
i n c l u d e d w i t h t h e P i o n e e r F o r m a t io n i n t h i s s t u d y . A
c o r r e s p o n d i n g m em ber w a s s i m i l a r l y t r e a t e d b y R a a b e (1959 *
p . 2 0 ) .
T he g n e i s s i c f a c i e s i s d i s t i n g u i s h e d f ro m t h e r e s t
o f t h e P i o n e e r F o r m a t io n b e c a u s e o f i t s a b u n d a n t m i c r o -
c l i n e a n d i t s a u g e n t e x t u r e . T he a r e a o f o u t c r o p i s s m a l l
a n d i s l o c a t e d a l o n g t h e w e s t e r n m a r g in o f t h e s c h i s t i n
t h e v a l l e y t o t h e e a s t o f P i e t y H i l l . R e s i s t a n c e t o
e r o s i o n i s n o t g r e a t , a n d i s s i m i l a r t o t h e r e m a i n d e r o f
t h e P i o n e e r F o r m a t i o n . T he s t r i k e o f t h e g n e i s s i c f a c i e s
i s t o t h e n o r t h w e s t a n d t h e d i p i s 2 0 - 4 0 d e g r e e s s o u t h w e s t .
On a w e a t h e r e d o u t c r o p t h e r o c k i s d u s k y y e l l o w i s h b ro w n
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(1 0 YR 2 / 2 ) , a n d o n a f r e s h s u r f a c e I t i s l i g h t g r a y (N 7 )
w i t h o l i v e b l a c k ( 5 Y 2 / 1 ) b a n d s o f b i o t i t e .
T he g n e l s s i c f a c i e s i s b o u n d e d o n t h e w e s t b y t h e
B o l s a Q u a r t z i t e w i t h w h ic h i t i s i n f a u l t c o n t a c t . The
e a s t e r n m a r g in i s c o n f o r m a b le w i t h t h e r u s t y m ic a s c h i s t
o f t h e P i o n e e r F o r m a t i o n .
T he r o c k i s w e l l f o l i a t e d w i t h a b a n d e d t e x t u r e o f
q u a r t z a n d f e l d s p a r . M i c r o s c o p i c s t u d y sh o w s t h e r o c k t o
b e c o m p o se d o f 35-kO $ q u a r t z , 30% m i c r o c l i n e , 13% m u s c o v i t e
15% b i o t i t e , a n d 1% o r l e s s o f m a g n e t i t e , e p i d o t e , a n d
m i c r o p e r t h i t e . T he m i c r o s c o p i c t e x t u r e i s c a t a c l a s t i c
w i t h a u g e n o f m i c r o c l i n e f e l d s p a r . B ro a d b a n d s o f b i o t i t e
a n d m u s c o v i t e a r c h a r o u n d m i c r o c l i n e p o r p h y r o b l a s t s . F i n e
g r a i n e d s e r i c i t e , q u a r t z , a n d m a g n e t i t e a r e com m only
i n t e r m i x e d w i t h t h e m ic a b a n d s . O v a l l e n s e s o f i n t e r
l o c k i n g q u a r t z g r a i n s u p t o 7 mm l o n g a r e a b u n d a n t .
S h e a r i n g m ay h a v e c a u s e d t h e f i n e g r a i n s i z e o f q u a r t z ,
s e r i c i t e , a n d f e l d s p a r .
T h e re seem t o b e tw o s t a g e s o f q u a r t z p r e s e n t .
T he o l d e r v a r i e t y c o n s i s t s o f m o d e r a t e l y s t r a i n e d , a n h e d r a l
i n t e r l o c k i n g g r a i n s c o n t a i n i n g m u s c o v i t e i n c l u s i o n s . The
y o u n g e r v a r i e t y c o n s i s t s o f l a r g e r , s u b h e d r a l , u n s t r a i n e d
c r y s t a l s t h a t a r e f r e e o f i n c l u s i o n s . T he m i c r o c l i n e
p r e s e n t i s c h a r a c t e r i z e d b y p o l y s y n t h e t i c t w i n n i n g a n d
15 d e g r e e e x t i n c t i o n a n g l e . I t o c c u r s a s l a r g e a n h e d r a l
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c r y s t a l s , 6 . 5 mm m axim um d i a m e t e r , a n d c o n t a i n s m any
I n c l u s i o n s o f o l d e r q u a r t z , b l o t l t e , a n d m i c r o c l i n e .
T he b l o t l t e o c c u r s a s b o t h l o n g a n d s h o r t s u b h e d r a l
c r y s t a l s t h a t a r e p l e o c h r o i c i n s h a d e s o f b ro w n . T he
m i c r o p e r t h i t e o c c u r s a s s m a l l a n h e d r a l m a s s e s a r o u n d t h e
m a r g in s o f t h e l a r g e m i c r o c l i n e p o r p h y r o b l a s t s . F i n e
g r a i n s o f m a g n e t i t e a r e a s s o c i a t e d w i t h b l o t l t e c o n c e n
t r a t i o n s .
D r i p p i n g S p r i n g Q u a r t z i t e
T he r o c k s e q u i v a l e n t t o t h e D r i p p i n g S p r i n g
Q u a r t z i t e a s o r i g i n a l l y n a m e d b y H ansom e (1 9 0 3 ) w e r e f o u n d
t o c o n f o r m a b ly o v e r l i e t h e B a r n e s C o n g lo m e r a te , a nam e
a l s o p r o p o s e d b y H a n so m e . S h r i d e (1 9 6 1 ) h a s s u g g e s t e d
t h a t t h e b a s a l c o n g lo m e r a t e o f t h e D r i p p i n g S p r i n g Q u a r t z i t e
b e c a l l e d t h e B a r n e s C o n g lo m e r a te M em ber i n s t e a d o f d e l e
g a t i n g i t f o r m a t i o n a l s t a t u s .
B a r n e s C o n g lo m e r a te M em ber. T he B a r n e s C o n g lo m e r a te
m em ber h a s b e e n r e c o g n i z e d i n t h e P i e t y H i l l a r e a a s a
s t r e t c h e d q u a r t z p e b b l e c o n g lo m e r a t e c o n f o r m a b ly o v e r l y i n g
t h e P i o n e e r F o r m a t io n a n d u n d e r l y i n g t h e q u a r t z i t e p o r t i o n
o f t h e D r i p p i n g S p r i n g Q u a r t z i t e . T he c o n g l o m e r a t e c r o p s
o u t f o r 1 1 0 0 f e e t a l o n g s t r i k e a s t h e r e s i s t a n t b a c k b o n e
o f a n o r t h w e s t t r e n d i n g r i d g e s o u t h o f t h e R e d i n g t o n R o ad
a n d s o u t h e a s t o f P i e t y H i l l . T he a v e r a g e t h i c k n e s s i s
2 1
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2 2
t h i r t y - f i v e t o f o r t y f e e t . T he s t r i k e i s N 6 0 ° W a n d t h e
a v e r a g e d i p i s 5 ^ d e g r e e s s o u t h w e s t .
M e g a s c o p i c a l l y t h e c o n g lo m e r a t e c o n s i s t s o f l o n g
s t r e t c h e d q u a r t z i t e p e b b l e s i n a m a t r i x o f q u a r t z a n d m ic a .
T he p e b b l e s a r e s t r e t c h e d a s m uch a s f o u r t o f i v e t i m e s
t h e i r t h i c k n e s s a n d h a v e I m p a r t e d a d e f i n i t e f o l i a t i o n t o
t h e r o c k . T h i s f o l i a t i o n i s p a r a l l e l t o t h a t o f t h e
a d j a c e n t P i o n e e r F o r m a t io n a n d t h e o v e r l y i n g r o c k s o f t h e
D r i p p i n g S p r i n g Q u a r t z i t e . T he c o l o r o f t h e c o n g lo m e r a t e
i s v a r i a b l e f ro m y e l l o w i s h g r a y ( 5 Y 8 / 1 ) t o a r e d d i s h
g r a y t h a t i s n o t f o u n d o n t h e R o ck C o lo r C h a r t .
T he B a r n e s C o n g lo m e r a te M em ber i s c o m p o se d o f 87 -
90% q u a r t z , 8 - 1 0 ^ m u s c o v i t e - s e r i c i t e , 2% b i o t i t e , a n d 1%
o p a q u e m i n e r a l s , p r o b a b l y h e m a t i t e a n d m a g n e t i t e .
T h e q u a r t z i t e p e b b l e s a r e c o m p o se d o f a p p r o x i m a t e l y
97% q u a r t z a n d 2% s e r i c i t e w h ic h i s a l i g n e d p a r a l l e l t o
t h e f o l i a t i o n . V e ry f i n e g r a i n e d o p a q u e m i n e r a l s , p r o b a b l y
i r o n o x i d e s , a r e a l s o c o n c e n t r a t e d i n t h e q u a r t z i t e p e b b l e s .
Q u a r t z g r a i n s w i t h i n t h e p e b b l e s a r e u s u a l l y l e s s t h a n
0 . 5 mm a n d n e v e r m o re t h a n 1 mm i n d i a m e t e r . T he g r a i n s
a r e c h a r a c t e r i z e d b y v e r y i r r e g u l a r m a r g i n s . B o u n d a r i e s
a r e m o d e r a t e l y i n t e r g r o w n a n d c r y s t a l s a r e h i g h l y s t r a i n e d
g i v i n g u n d u l a t o r y e x t i n c t i o n . T he c r y s t a l s a r e a n h e d r a l
a n d a r e e l o n g a t e d w i t h t h e i r l o n g e s t d im e n s io n p a r a l l e l
t o t h e l o n g a x i s o f t h e p e b b l e s .
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23
S u r r o u n d i n g t h e q u a r t z i t e p e b b l e s i s u s u a l l y a
t h i n l a y e r o f b ro w n b i o t i t e , s e r i c i t e , a n d s t r e a k s o f
l i m o n l t e . T he m a t r i x i s c o m p o se d o f a n h e d r a l , s l i g h t l y
e l o n g a t e d q u a r t z c r y s t a l s t h a t a r e g e n e r a l l y l e s s t h a n
0 .2 5 mm i n d i a m e t e r , a r e m u t u a l l y i n t e r g r o w n , a n d a r e
s l i g h t l y s t r a i n e d . M u s c o v i t e - s e r i c i t e o c c u r s a s o r i e n t e d
s u b h e d r a l c r y s t a l s u p t o 0 .2 5 ram i n l e n g t h a n d a s sw arm s
o r m a s s e s .
D r i p p i n g S p r i n g Q u a r t z i t e . T he B a r n e s C o n g lo m e r a te
M em ber g r a d e s u p w a rd i n t o a c a l c i u m r i c h q u a r t z i t e i n t h e
P i e t y H i l l a r e a . T h i s q u a r t z i t e , t h e D r i p p i n g S p r i n g
Q u a r t z i t e , c r o p s o u t s o u t h w e s t o f t h e B a r n e s C o n g lo m e r a te
M em ber a n d d i p s t o t h e s o u t h w e s t f i f t y t o e i g h t y d e g r e e s .
T he q u a r t z i t e i s l e s s r e s i s t a n t a n d fo r m s a s l o p i n g t o p o
g r a p h y aw ay f ro m t h e r i d g e - f o r m i n g B a r n e s . T he C a t a l i n a
G n e i s s c u t s o f f t h e D r i p p i n g S p r i n g Q u a r t z i t e a t i t s o n l y
e x p o s u r e s o t h a t t h e m axim um t h i c k n e s s e x p o s e d i s a b o u t
o n e h u n d r e d f e e t .
M e g a s c o p i c a l l y t h e q u a r t z i t e c o n s i s t s o f b a n d e d
q u a r t z w i t h m any a l t e r e d p o r p h y r o b l a s t s o f g r o s s u l a r i t e ( ? )
g a r n e t a r r a n g e d i n a p l a n a r o r i e n t a t i o n . The c o l o r o f t h e
r o c k i s d a r k y e l l o w i s h b ro w n ( 1 0 YR 4 / 2 ) o n t h e w e a t h e r e d
s u r f a c e , a n d m ed ium g r a y (N 5 ) o n t h e f r e s h s u r f a c e .
T he r o c k c o n s i s t s o f 65% q u a r t z , 15-20% g a r n e t ,
15% e p i d o t e , 2 - 3 ^ c a l c i t e , a n d l e s s t h a n 1% o p a q u e m i n e r a l s .
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T he q u a r t z o c c u r s a s s t r o n g l y i n t e r g r o w n e l o n g a t e g r a i n s
t h a t a r e m o d e r a t e l y s t r a i n e d a n d a n h e d r a l i n f o r m . The
g r a i n s a r e u p t o 1 mm i n l e n g t h a n d o r i e n t e d p a r a l l e l t o
t h e f o l i a t i o n . T he g a r n e t o c c u r s a s l a r g e , 0 .9 - 2 .3 mm
i n d i a m e t e r , i d i o b l a s t i c c r y s t a l s t h a t a p p e a r t o b e a l t e r e d
i n h a n d s p e c im e n . I n t h i n s e c t i o n t h e g a r n e t s a r e f u l l o f
h o l e s a n d c o n t a i n i n c l u s i o n s o f e p i d o t e , q u a r t z , a n d
o p a q u e s . Z o n in g h a s b e e n o b s e r v e d i n a t l e a s t o n e g a r n e t
c r y s t a l . T w in n in g h a s c a u s e d t h e o c c u r r e n c e o f a n o m a lo u s
a n i s o t r o p i s m i n a fe w c a s e s .
E p i d o t e o c c u r r i n g a s a n h e d r a l t o s u b h e d r a l g r a i n s
w i t h a n a v e r a g e l e n g t h o f 0 . 5 mm i m p a r t a n e m a t o b l a s t i c
t e x t u r e p a r a l l e l t o t h e f o l i a t i o n . T he e p i d o t e g r a i n s
m ake s w i r l s a r o u n d t h e l a r g e g a r n e t p o r p h y r o b l a s t s .
C a l c i t e e x i s t s a s n a r r o w d i s c o n t i n u o u s b a n d s p a r a l l e l t o
t h e f o l i a t i o n .
B o l s a Q u a r t z i t e
T he B o l s a Q u a r t z i t e w as o r i g i n a l l y n a m ed b y R ansom e
(1 9 0 4 ) a s t h e b a s a l C a m b ria n q u a r t z i t e e x p o s e d n e a r B i s b e e ,
A r i z o n a . T he T ro y Q u a r t z i t e o f t h e C a t a l i n a M o u n ta i n s , a s
d e s i g n a t e d b y R an so m e (1 9 1 6 ) a n d S to y a n o w ( 1 9 3 6 ) , h a s b e e n
r e d e s i g n a t e d B o l s a b y S h r i d e ( 1961 ) a n d i s c o r r e l a t e d w i t h
t h e B o l s a t o t h e s o u t h o n t h e b a s i s o f s i m i l a r t e x t u r e s
a n d worm c a s t s . T he q u a r t z i t e o f t h e P i e t y H i l l a r e a i s
c o n s i d e r e d t o b e B o l s a b e c a u s e o f i t s c o n g l o m e r a t i c
24
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t e x t u r e , l i t h o l o g i c s i m i l a r i t y t o B o l s a e l s e w h e r e , a n d t h e
p r e s e n c e o f r o c k s e q u i v a l e n t t o t h e A b r ig o L im e s to n e i n
c o n f o r m a b le r e l a t i o n u p w a r d .
L i t h o l o g i c a l l y t h e B o l s a i s a m a s s i v e , h a r d , g r a y -
w h i t e q u a r t z i t e w i t h c o n g l o m e r a t e , l i m e s t o n e , a n d s c h i s t
d e v e lo p e d l o c a l l y . T he o u t c r o p s o f t h e B o l s a a r e w id e
s p r e a d i n t h e a r e a m a p p ed a s a r e s u l t o f r e p e t i t i o n b y
f a u l t i n g . T he e x t r e m e r e s i s t a n c e o f t h e q u a r t z i t e t o
w e a t h e r i n g i s e v i d e n c e d b y i t s p r e s e n c e o n h i l l s a n d
r i d g e s w h e r e v e r i t i s e x p o s e d . G e n e r a l l y t h e s t r i k e o f
t h e f o r m a t i o n i s n o r t h w e s t w i t h v a r i a b l e d i p s t o t h e
n o r t h e a s t . The m a s s iv e n a t u r e o f t h e B o l s a m a k es i t
v e r y d i f f i c u l t t o o b t a i n o r i e n t a t i o n s . T he t h i c k n e s s a s
d e t e r m i n e d f ro m g e o l o g i c c r o s s - s e c t i o n s i s a p p r o x i m a t e l y
3 5 0 f e e t .
M e g a s c o p i c a l l y t h e B o l s a i s a v e r y f i n e - g r a i n e d
q u a r t z i t e t h a t o c c a s i o n a l l y c o n t a i n s p e b b l e s t h a t r a n g e
f ro m 2 mm t o 6 cm i n s i z e a n d m ay b e r o u n d e d o r s t r e t c h e d .
I n o u t c r o p t h e q u a r t z i t e i s m a s s i v e l y b e d d e d a n d w e a t h e r s
t o b l o c k y f r a g m e n t s . T he w e a t h e r e d s u r f a c e i s g e n e r a l l y
i r o n s t a i n e d p r o d u c i n g m o d e r a t e r e d d i s h b ro w n ( 1 0 YR 4 / 6 )
t o g r a y i s h o r a n g e p i n k ( 5 YR 7 / 2 ) c o l o r s . T he f r e s h
s u r f a c e r a n g e s f ro m p a l e y e l l o w i s h b ro w n (1 0 YR 6 / 2 ) t o
g r a y i s h o r a n g e p i n k ( 5 YR 7 / 2 ) i n c o l o r .
I n t h i n s e c t i o n t h e q u a r t z ! t i c p o r t i o n o f t h e
B o l s a c o n t a i n s 5 0 - 9 7 $ q u a r t z , 1 - 4 5 $ m u s c o v i t e - s e r i c i t e ,
2 5
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26
u p t o 10% m l c r o c l i n e a n d o r t h o c l a s e f e l d s p a r a n d l e s s e r
a m o u n ts o f b l o t l t e , e p i d o t e , c l i n o z o i s i t e , a n d o p a q u e s .
T he t e x t u r e o f t h e r o c k r a n g e s f ro m c o n g l o m e r a t i c , w i t h
p e b b l e s f o r m in g a c r u d e l y - b e d d e d a r r a n g e m e n t , t o e q u i -
g r a n u l a r w i t h n o a p p a r e n t s t r u c t u r e . O c c a s i o n a l l y som e
q u a r t z o r m ic a i s e l o n g a t e p r o d u c i n g a s u b p a r a l l e l
f o l i a t i o n .
T he q u a r t z g r a i n s t h a t c o m p r i s e t h e p e b b l e s i n t h e
B o l s a c o n s i s t o f m o d e r a t e l y t o h i g h l y s t r a i n e d a n h e d r a l
c r y s t a l s . G r a in b o u n d a r i e s a r e i n t e r l o c k i n g w i t h s e c o n d a r y
o v e r g r o w t h s . I n d i v i d u a l g r a i n s r a n g e f ro m 0 . 2 t o 5 am i n
d i a m e t e r . M a t r i x q u a r t z c o n s i s t s o f u n s t r a i n e d t o m o d e r
a t e l y s t r a i n e d a n h e d r a l g r a i n s . M a r g in s a r e s e c o n d a r i l y
i n t e r g r o w n o n som e c r y s t a l s a n d o t h e r s a r e i n t e r l o c k i n g
w i t h s h a r p c o n t a c t s . T he q u a r t z sh o w s l i t t l e p r e f e r r e d
o r i e n t a t i o n , b u t o c c a s i o n a l l y t h e l a r g e r g r a i n s a r e e l o n g a t e
p a r a l l e l t o m ic a o r i e n t a t i o n . M any o f t h e q u a r t z g r a i n s
c o n t a i n I n c l u s i o n s o f f i n e l y c r u s h e d o p a q u e m i n e r a l s i n a
l i n e a r a r r a n g e m e n t .
M u s c o v i t e a n d s e r i c i t e a r e v a r i a b l e i n t h e i r
a b u n d a n c e a n d r e l a t i o n s w i t h t h e o t h e r r o c k c o n s t i t u e n t s .
M u s c o v i t e o c c u r s i n a ra n d o m p a t t e r n a n d a l s o i n a s u b
p a r a l l e l a r r a n g e m e n t . G r a i n s a r e a n h e d r a l t o s u b h e d r a l i n
f o r m . A v e r a g e l e n g t h o f s u b h e d r a l c r y s t a l s i s 0 .3 mm.
I n som e s p e c im e n s s e r i c i t e i s v e r y a b u n d a n t a n d f i l l s a l l
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2 7
i n t e r g r a n u l a r s p a c e i n a r a n d o m ly o r i e n t e d m a n n e r . The
s e r i c i t e i s p r o b a b l y a n a l t e r a t i o n p r o d u c t o f t h e f e l d s p a r .
B o th m i c r o c l i n e a n d o r t h o c l a s e f e l d s p a r a r e p r e s e n t i n
m in o r a m o u n ts . The g r a i n s a r e o f t e n c lo u d y d u e t o i n c i p i e n t
a l t e r a t i o n . O p aq u e m i n e r a l s , p r e d o m i n a n t l y h e m a t i t e
p s e u d o m o rp h o u s a f t e r p y r i t e , a r e g e n e r a l l y a r r a n g e d i n
b a n d s p a r a l l e l t o b e d d i n g . I n d i v i d u a l c r y s t a l s a r e
e u h e d r a l t o s u b h e d r a l i n s h a p e a n d a v e r a g e 0 .3 mm i n s i z e ,
w i t h a m axim um o f 1 .0 mm. E p l d o t e a n d c l i n o z o i s i t e a r e
m in o r a c c e s s o r y m i n e r a l s t h a t o c c u r a s s m a l l a n h e d r a l t o
s u b h e d r a l g r a i n s i n a fe w o f t h e s p e c im e n s c o l l e c t e d .
S c h i s t f a c i e s o f B o l s a Q u a r t z i t e . A n a r r o w
s c h i s t o s e f a c i e s o f t h e B o l s a Q u a r t z i t e c r o p s o u t o n t h e
s o u t h e a s t f l a n k o f P i e t y H i l l ( P l a t e I ) . T h i s r o c k t y p e
fo r m s a t o p o g r a p h i c lo w i n o u t c r o p . The m ic a c e o u s m i n e r a l s
c a u s e t h i s u n i t t o w e a t h e r m uch m o re r a p i d l y t h a n t h e
s u r r o u n d i n g q u a r t z i t e .
T he s c h i s t i s c o m p o se d o f 4 0 - 4 5 # q u a r t z , 3 5 #
p e n n i n l t e , 15 - 20# m u s c o v i t e , a n d 5 # h e m a t i t e a f t e r p y r i t e .
T he c h l o r i t e a n d m u s c o v i t e o c c u r a s s u b h e d r a l c r y s t a l s
a n d l i e i n a s u b p a r a l l e l a r r a n g e m e n t g i v i n g t h e r o c k a
l e p i d o b l a s t i c t e x t u r e . Q u a r t z fo r m s t h e m a t r i x m a t e r i a l .
T he I n d i v i d u a l q u a r t z g r a i n s a r e 0 . 2 mm i n l e n g t h , e l o n g a t e ,
s l i g h t l y s t r a i n e d , a n d a n h e d r a l i n f o r m . Some s t r e t c h e d
p e b b l e s o f q u a r t z i t e w i t h i n t e r l o c k i n g , a n h e d r a l g r a i n s
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2 8
a n d s e c o n d a r y q u a r t z o v e r g r o w t h s a r e p r e s e n t . T he p e b b l e s
a r e s t r e t c h e d so t h a t t h e i r l e n g t h i s t h r e e t i m e s t h e i r
w i d t h .
L im e s to n e f a c i e s o f B o l s a Q u a r t z i t e . L e n s e s o f
g r a y t o w h i t e r e c r y s t a l l i z e d l i m e s t o n e a r e v e r y common i n
t h e B o l s a Q u a r t z i t e o f t h e P i e t y H i l l a r e a ( P l a t e I ) .
T h e s e l e n s e s a r e g e n e r a l l y q u i t e t h i n a n d e x t e n d a l o n g
s t r i k e f o r a b o u t tw o h u n d r e d f e e t o r l e s s .
On a w e a t h e r e d s u r f a c e t h e l i m e s t o n e i s p a l e
y e l l o w i s h b ro w n (1 0 YR 6 / 2 ) i n c o l o r a n d o n a f r e s h s u r f a c e
l i g h t g r a y (N 7 ) • I n o u t c r o p , b e d d i n g s t a n d s o u t p r i m a r i l y
d u e t o d i f f e r e n t i a l w e a t h e r i n g .
M i c r o s c o p i c a l l y t h e r o c k c o n t a i n s 9 0 - 9 8 # c a l c i t e ,
1 - 1 0 # q u a r t z , a n d l e s s t h a n 1# m u s c o v i t e . T he c a l c i t e
o c c u r s a s a n h e d r a l t o s u b h e d r a l c r y s t a l s t h a t a r e so m ew h a t
e l o n g a t e p a r a l l e l t o t h e b e d d i n g . T he a v e r a g e s i z e o f t h e
c a l c i t e i s 1 . 5 mm, h o w e v e r t h e i n d i v i d u a l g r a i n s r a n g e i n
s i z e f ro m l e s s t h a n 0 .1 mm t o 3 mm. P o l y s y n t h e t i c t w i n n i n g
i s p r o n o u n c e d i n t h e c a l c i t e .
Q u a r t z i s p r e s e n t a s m in u te a n h e d r a l f l a k e s b o t h
r a n d o m ly s c a t t e r e d t h r o u g h o u t t h e s p e c im e n a n d c o n c e n t r a t e d
i n n a r r o w b a n d s p a r a l l e l t o t h e b e d d i n g . I n d i v i d u a l q u a r t z
g r a i n s a r e 0 . 2 - 3 mm i n d i a m e t e r . M in o r r a n d o m ly
s c a t t e r e d s u b h e d r a l m u s c o v i t e g r a i n s a r e p r e s e n t t h r o u g h o u t
t h e m a t r i x .
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2 9
The B o l s a Q u a r t z i t e u s u a l l y l i e s u n c o n f o r m a b ly
o v e r t h e Y o u n g e r P r e c a m b r i a n A p a c h e G ro u p r o c k s , b u t i n
t h e P i e t y H i l l a r e a i t i s i n f a u l t c o n t a c t w i t h a l l u n d e r
l y i n g r o c k s . T he B o l s a com m only o v e r l i e s t h e M i s s i s s l p p i a n
E s c a b r o s a L i m e s t o n e . T he M id d le a n d L a t e C a m b ria n A b r ig o
L im e s to n e c o n f o r m a b ly o v e r l i e s t h e B o l s a . T he M id d le
C a m b ria n a g e o f t h e B o l s a h a s b e e n e s t a b l i s h e d b y F lo w e r
( 1 9 5 8 ) . No f o s s i l s w e re f o u n d i n t h e P i e t y H i l l a r e a , b u t
M cK enna ( 1966 ) f o u n d worm c a s t s a n d t u b e s i n t h e B uehm an
C an y o n a r e a .
A b r ig o L im e s to n e
T he A b r ig o L im e s to n e w as o r i g i n a l l y n a m ed b y
R ansom e (1 9 0 4 ) a s t h e l i m e s t o n e u n i t o v e r l y i n g t h e B o l s a
Q u a r t z i t e i n t h e B l s b e e a r e a o f s o u t h e a s t e r n A r i z o n a .
S to y a n o w (1 9 3 6 ) d e s c r i b e d t h e A b r ig o i n t h e S a n t a C a t a l i n a
M o u n ta in s a n d a t t e m p t e d t o s u b d i v i d e t h e o r i g i n a l A b r ig o
o f R an so m e i n t o s e v e r a l f o r m a t i o n s . T he A b r ig o L im e s to n e
i s c o m p o se d o f l i m e s t o n e , s a n d s t o n e , c o n g l o m e r a t e , a n d
s h a l e i n t h e S a n t a C a t a l i n a s a s c o m p a re d t o a p r e d o m in a n c e
o f l i m e s t o n e n e a r B l s b e e . S to y an o w * s (1 9 3 6 ) s u b d i v i s i o n
h a s n o t b e e n a c c e p t e d o f f i c i a l l y , so t h e A b r ig o o f t h e
S a n t a C a t a l i n a M o u n ta in s i s t e r m e d " L im e s to n e " i n s p i t e
o f i t s i n a c c u r a c y .
T he A b r ig o o f t h e P i e t y H i l l a r e a c o n s i s t s o f l i m e
s t o n e , q u a r t z i t e , a n d c a l c a r e o u s s a n d s t o n e . M e ta m o rp h ism ,
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3 0
p r o b a b l y d u e t o t h e h i g h t e m p e r a t u r e o f t h e i n t r u s i v e
C a t a l i n a G n e i s s , h a s c a u s e d d e v e lo p m e n t o f a c t i n o l i t e a n d
e p i d o t e i n t h e c a l c a r e o u s b e d s . T h e A b r lg o L im e s to n e c o n
f o r m a b ly o v e r l i e s t h e B o I s a Q u a r t z i t e a n d i s d i s c o n f o r m a b l y
o v e r l a i n b y t h e D e v o n ia n M a r t i n L i m e s t o n e . A b a n d o f
A b r lg o t r a n s e c t s t h e m a p p ed a r e a w i t h a n o r t h w e s t s t r i k e
a n d n o r t h e a s t d i p . T he A b r lg o i s a l s o p r e s e n t i n t h e a r e a
n o r t h o f P i e t y H i l l .
T he u p p e r c o n t a c t o f t h e A b r lg o i s a p p r o x im a te i n
i t s l o c a t i o n . T he c o n t a c t w as m ap p ed a t a l i t h o l o g i c
b r e a k b e tw e e n t h e t h i n l y b e d d e d s a n d s t o n e s a n d l i m e s t o n e s
o f t h e A b r lg o a n d t h e m o re m a s s i v e , r e l a t i v e l y p u r e l i m e
s t o n e o f t h e M a r t i n - E s c a b r o s a s e q u e n c e . No f o s s i l s w e re
f o u n d t o a i d i n t h e i n t e r p r e t a t i o n . T o p o g r a p h i c a l l y t h e
A b r lg o L im e s to n e i s a s l o p e - f o r m i n g u n i t a d j a c e n t t o t h e
r e s i s t a n t B o I s a Q u a r t z i t e .
T he A b r lg o i s e x t r e m e l y v a r i a b l e i n l i t h o l o g y a n d
a l s o i n c o l o r . T he w e a t h e r e d s u r f a c e r a n g e s f ro m d a r k
y e l l o w i s h b ro w n ( 1 0 YR 4 / 2 ) t o m ed ium g r a y (N 5 ) • F r e s h
s a m p le s r a n g e f r o m m ed ium g r a y (N 5 ) t o g r e e n i s h g r a y
( 5 G 6 / 1 ) . I n h a n d s p e c im e n t h e A b r lg o i s l a m i n a t e d t o
v e r y t h i n l y b e d d e d . B e d d in g i s d e f i n e d b y c o n c e n t r a t i o n
o f p a r t i c u l a r m i n e r a l s s u c h a s q u a r t z a n d e p i d o t e i n
p a r a l l e l b a n d s . T he m o s t t y p i c a l s p e c im e n o f A b r lg o w o u ld
c o n s i s t o f a l t e r n a t i n g q u a r t z a n d c a l c a r e o u s b a n d s . D i f f e r
e n t i a l w e a t h e r i n g o f c o n s t i t u e n t b e d s i s com m on.
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3 1
M i c r o s c o p i c a l l y t h i s f o r m a t i o n c o n t a i n s 0-99%
c a l c i t e , 15-60% q u a r t z , u p t o 15% e p i d o t e , 20% a c t i n o l i t e ,
1 - 1 5 $ c h l o r i t e , a n d m in o r a m o u n ts o f d i o p s i d e , m l c r o c l i n e
f e l d s p a r , m u s c o v i t e , a n d o p a q u e s . I n s p e c im e n s c o m p o se d
p r e d o m i n a n t l y o f c a l c i t e , w i t h som e q u a r t z , t h e r e i s
g e n e r a l l y n o d l s c e m a b l e m ic r o s t r u c t u r e . M o s t o f t h e
t h i n - b e d d e d A b r i g o , h o w e v e r , e x h i b i t s a f o l i a t e d a r r a n g e
m e n t o f m i n e r a l s i n t h i n s e c t i o n . E p i d o t e , m ic a , a c t i n o l i t e ,
a n d e l o n g a t e q u a r t z a n d c a l c i t e g i v e t h e r o c k a d e f i n i t e
p l a n a r s t r u c t u r e . I n t h e s t r u c t u r e l e s s l i m e s t o n e m e n t io n e d
a b o v e , t h e c a l c i t e r e a c h e s a maximum s i z e o f 1 .5 mm w i t h
a n a v e r a g e o f 1 mm. T he g r a i n s a r e a n h e d r a l a n d a r e
tw in n e d p o l y s y n t h e t l c a l l y . Q u a r t z i s r a n d o m ly s c a t t e r e d
t h r o u g h o u t t h e s p e c im e n a n d c o n s i s t s o f u n s t r a i n e d a n h e d r a l
g r a i n s t h a t a v e r a g e 0 .1 t o 0 . 2 mm i n s i z e .
The l a m i n a t e d , c a l c a r e o u s s a n d s t o n e b e d s a l s o
common i n t h e A b r ig o c o n t a i n p a r a l l e l b a n d i n g o f q u a r t z .
Two s i z e s o f q u a r t z a r e p r e s e n t : a v e r y f i n e g r a i n e d
v a r i e t y , l e s s t h a n 0 .1 mm, o f a n h e d r a l , h i g h l y s t r a i n e d
c r y s t a l s i n a n i n t e r l o c k i n g a g g r e g a t e ; a n d a l a r g e r s i z e d
q u a r t z , 0 .3 t o 0 . 4 mm l o n g , e l o n g a t e d t h r e e t o f o u r t i m e s
i t s w i d t h a n d o c c u r s a s s l i g h t l y s t r a i n e d a n h e d r a l c r y s t a l s
f o r m in g b a n d s u p t o 0 . 5 mm w id e . Some c r y s t a l s h a v e
s u t u r e d m a r g in s a n d s e c o n d a r y o v e r g r o w t h s .
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A n h e d r a l c a l c i t e w i t h a n a v e r a g e l e n g t h o f 0 .8 mm
o c c u r s m a in ly i n p u r e n a r r o w b a n d s a n d a l s o o c c u r s f i n e l y
i n t e r m i x e d w i t h o t h e r r o c k c o n s t i t u e n t s i n c e r t a i n l a y e r s .
W here f o u n d , a c t i n o l i t e c o n s i s t s o f s u b h e d r a l c r y s t a l s a n d
f i b r o u s a g g r e g a t e s . I n d i v i d u a l c r y s t a l s r a n g e u p t o 1 mm
i n l e n g t h , b u t a v e r a g e 0 . 5 mm. T he p l e o c h r o i c g r e e n c o l o r ,
c l e a v a g e , a n d t h e i n c l i n e d e x t i n c t i o n a n g l e a r e c h a r a c t e r
i s t i c o f a c t i n o l i t e . E p i d o t e a n d d i o p s i d e g r a i n s a r e
s m a l l , l e s s t h a n 0 .1 mm i n l e n g t h , b u t r e a c h a maximum o f
0 . 6 mm a n d c o n s i s t o f a n h e d r a l c r y s t a l s o r i e n t e d w i t h
t h e i r l o n g a x e s p a r a l l e l t o t h e b e d d i n g .
S u b h e d r a l p e n n i n i t e w i t h a n o m a lo u s i n t e r f e r e n c e
c o l o r s a n d m u s c o v i t e a r e o r i e n t e d i n a s u b p a r a l l e l
a r r a n g e m e n t c o n s i s t e n t w i t h t h e q u a r t z - e p i d o t e f o l i a t i o n .
S m a l l , a n h e d r a l , p o l y s y n t h e t i c a l l y tw in n e d g r a i n s o f
m l c r o c l i n e f e l d s p a r m ake u p l e s s t h a n 1 v o lu m e p e r c e n t
o f som e s p e c im e n s . L i m o n i t e p s e u d o m o rp h o u s a f t e r p y r l t e
i s p r e s e n t a s i n d i v i d u a l e u h e d r a l c r y s t a l s t h a t a r e
r a n d o m ly s c a t t e r e d t h r o u g h o u t t h e r o c k . T h e s e c r y s t a l s
r e a c h a m axim um s i z e o f 1 mm.
T he A b r ig o L im e s to n e i s M id d le a n d L a t e C a m b ria n
i n a g e a s h a s b e e n d e t e r m i n e d b y f o s s i l s i n o t h e r l o c a l i t i e s
( G i l l u l y , 1 9 5 6 ) t h a t h a v e n o t u n d e r g o n e s u c h e x t e n s i v e
m e ta m o rp h is m a s t h a t o f t h e P i e t y H i l l a r e a .
3 2
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3 3
M a r t i n F o r m a t io n - E s c a b r o s a L im e s to n e
B e c a u s e o f t h e l a c k o f f o s s i l s a n d p o o r e x p o s u r e s
t h e M a r t i n F o r m a t io n a n d t h e E s c a b r o s a L im e s to n e h a v e b e e n
g r o u p e d t o g e t h e r f o r m a p p in g p u r p o s e s i n t h e P i e t y H i l l
a r e a . M cK enna (1 9 6 6 ) w as a b l e t o d i f f e r e n t i a t e t h e tw o
f o r m a t i o n s t o t h e n o r t h w h e re m e ta m o rp h is m w as m uch l e s s
s e v e r e a n d f o s s i l s w e re p r e s e r v e d .
T he M a r t i n L im e s to n e a n d E s c a b r o s a L im e s to n e w e re
n am ed b y R ansom e (1 9 0 4 ) f o r r e s p e c t i v e D e v o n ia n a n d
M i s s i s s l p p i a n l i m e s t o n e s i n t h e B i s b e e a r e a . LeM one (1 9 5 9 )
a n d C o o p e r a n d S i l v e r (1 9 6 4 ) h a v e u s e d t h e nam e M a r t i n
F o r m a t io n r a t h e r t h a n M a r t i n L im e s to n e o w in g t o t h e
p r e s e n c e b f d o l o m i t e a n d c l a s t i c r o c k s i n t h e D e v o n ia n
s e c t i o n .
G e n e r a l l y t h e M a r t i n - E s c a b r o s a o f t h e P i e t y H i l l
a r e a c o n s i s t s o f l i m e s t o n e w i t h a s m a l l a m o u n t o f s a n d
s t o n e i n t h e l o w e r p o r t i o n . B e d d in g r a n g e s f ro m t h i n
b e d d e d t o v e r y t h i c k b e d d e d u p w a rd . E x p o s u r e s o f t h i s
u n i t a r e w i d e s p r e a d . Two p a r a l l e l b a n d s t r e n d n o r t h w e s t
t h r o u g h t h e a r e a a n d d i p n o r t h e a s t . Some d o l o m i t e a n d
m a s s iv e l i m e s t o n e o u t c r o p im m e d i a t e l y n o r t h a n d e a s t o f
P i e t y H i l l a n d a r e t h o u g h t t o b e M a r t i n - E s c a b r o s a a l s o .
T he e a s t e r n m o s t o f t h e tw o p a r a l l e l b a n d s m e n t io n e d a b o v e
l i e s i n p r o p e r s t r a t i g r a p h i c p o s i t i o n u p o n t h e A b r ig o
L i m e s to n e . T he o t h e r b a n d o f M a r t i n - E s c a b r o s a i s i n
f a u l t c o n t a c t w i t h t h e P r e c a m b r i a n P i o n e e r F o r m a t io n o n
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3 4
t h e w e s t a n d t h e C a m b ria n B o l s a Q u a r t z i t e o n t h e e a s t .
T he t o t a l t h i c k n e s s o f t h e M a r t i n - E s c a b r o s a i s n o t
e x p o s e d , b u t i n t h e n o r t h e a s t c o m e r o f t h e a r e a w h e re
t h e g r e a t e s t e x p o s u r e o c c u r s t h e t h i c k n e s s i s i n t h e o r d e r
o f 1 ,0 0 0 f e e t . T he lo w e r p o r t i o n o f t h e M a r t i n - E s c a b r o s a
i s a w e a k , s l o p e - f o r m i n g u n i t a n d t h e u p p e r p o r t i o n , w h ic h
i s m uch m o re m a s s i v e , f o r m s r e s i s t a n t c l i f f - l i k e e x p o s u r e s .
M e g a s c o p l c a l l y t h e M a r t i n — E s c a b r o s a i s a m edium
t o c o a r s e l y r e c r y s t a l l i z e d l i m e s t o n e t h a t i s l o c a l l y
m a r b l e i z e d . B row n c h e r t n o d u l e s a n d b a n d s a r e l o c a l l y
c o n c e n t r a t e d p a r a l l e l t o b e d d i n g . N e a r i n t r u s i v e la m p r o p h y r e
d i k e s t h e l i m e s t o n e i s a l t e r e d t o t r e m o l i t e - a c t i n o l i t e a n d
o t h e r c a l c i u m s i l i c a t e m i n e r a l s . T he c o l o r o f t h e M a r t i n -
E s c a b r o s a i s n e a r l y t h e sam e o n f r e s h a n d w e a t h e r e d s u r f a c e s
a n d r a n g e s f ro m m ed ium d a r k g r a y (N 4 ) t o m ed ium b l u i s h
g r a y ( 5 B 5 / 1 ) t o w h i t e (N 9 ) .
I n t h i n s e c t i o n t h e l i m e s t o n e r a n g e s f ro m n e a r l y
p u r e c a l c i t e t o c o m p le te r e c o n s t i t u t i o n t o c a l c - s i l i c a t e
m i n e r a l s s u c h a s t r e m o l i t e , d i o p s i d e , a n d w o l i a s t o n ! t e
l e a v i n g n o r e m n a n t c a l c i t e . T r e m o l i t e o c c u p i e s u p t o 6 5 $
a n d d i o p s i d e - h e d e n b e r g i t e u p t o 4 5 $ o f t h e t o t a l v o lu m e
i n e x t r e m e c a s e s . E p i d o t e fo r m s u p t o 2 0 $ a n d q u a r t z ,
m l c r o c l i n e , a n d m u s c o v i t e e a c h c o m p r i s e l e s s t h a n 5 $ o f
t h e r o c k . O c c a s i o n a l l y g a r n e t i s p r e s e n t u p t o 1 0 $ .
O t h e r m in o r m i n e r a l s i n c l u d e o r t h o c l a s e , s p e n e , s e r i c i t e ,
w o l l a s t o n i t e , z i r c o n , a n d o p a q u e s .
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3 5
A r e a s o f m a s s iv e c a l c i t e o r t r e m o l i t e a r e g e n e r a l l y
s t r u c t u r e l e s s . T h o s e t h a t a r e p r e d o m i n a n t l y c a l c i t e h a v e
a n i n t e r l o c k i n g t e x t u r e o f tw in n e d a n h e d r a l c r y s t a l s w h ic h
a v e r a g e 1 t o 2 mm i n s i z e . R o c k s c o m p o se d p r e d o m i n a n t l y
o f t r e m o l i t e h a v e a t e x t u r e c o n s i s t i n g o f r a d i a t i n g
a g g r e g a t e s o f t h e f i b r o u s m i n e r a l . I n d i v i d u a l s u b h e d r a l
c r y s t a l s r e a c h 3 * 5 mn i n l e n g t h . O c c a s i o n a l l y t r e m o l i t e
i s i n s u b p a r a l l e l a l i g n m e n t i m p a r t i n g a c r u d e f o l i a t i o n t o
t h e r o c k . C a l c i t e o c c a s i o n a l l y o c c u r s i n f i n e g r a i n e d
b a n d s a n d a s l a r g e e l o n g a t e a n h e d r a l c r y s t a l s w h ic h g i v e
t h e r o c k a s c h i s t o s i t y .
H e d e n b e r g i t e a n d d i o p s i d e a r e a b u n d a n t c o m p o n e n ts
o f c e r t a i n r o c k s . C r y s t a l s a r e s u b h e d r a l a n d u p t o 3 mm
i n l e n g t h . H e d e n b e r g i t e a n d d i o p s i d e h a v e n o t b e e n
i d e n t i f i e d i n t h e sam e s p e c im e n . H e d e n b e r g i t e i s d i s t i n g
u i s h e d f ro m t r e m o l i t e b y a h i g h e r e x t i n c t i o n a n g l e , a n d
f ro m d i o p s i d e b y h i g h e r r e f r a c t i v e i n d i c e s . E p i d o t e
o c c u r s a s b o t h e u h e d r a l c r y s t a l s a n d a n h e d r a l f l a k e s . T he
e u h e d r a l c r y s t a l s o c c u r u p t o 1 . 5 mm i n l e n g t h . Q u a r t z
e x i s t s a s u n s t r a i n e d a n h e d r a l c r y s t a l s i n t e r g r o w n w i t h
c a l c i t e a n d w i t h g a r n e t . T he l a r g e s t q u a r t z g r a i n s a r e
0 . 5 mm i n d i a m e t e r . G a r n e t i s n o t a common c o n s t i t u e n t
o f t h e M a r t i n - E s c a b r o s a , b u t w hen f o u n d i t e x i s t s a s
f i n e g r a i n e d a n h e d r a l p a r t i c l e s t h a t a r e i n t e r g r o w n w i t h
q u a r t z a n d may b e r e m n a n t s o f f o r m e r p o r p h y r o b l a s t s .
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M i c r o c l i n e o c c u r s a s l a r g e a n h e d r a l c r y s t a l s (u p t o 8 mm
lo n g ) t h a t h a v e t h e c h a r a c t e r i s t i c p o l y s y n t h e t i c t w i n n i n g
a n d 1 5 ° e x t i n c t i o n a n g l e . M u s c o v i t e o c c u r s a s e u h e d r a l t o
a n h e d r a l f l a k e s a n d n e v e r e x c e e d s o f t h e r o c k . S p h e n e
i s a m in o r m e ta m o r p h ic a c c e s s o r y m i n e r a l t h a t f o r m s a s
e u h e d r a l t o s u b h e d r a l c r y s t a l s 0 .5 mm i n l e n g t h . O t h e r
m in o r c o n s t i t u e n t s a r e s e r i c i t e , o r t h o c l a s e , l i m o n i t e
p s e u d o m o rp h o u s a f t e r p y r i t e , w o l l a s t o n i t e , a n d a t r a c e o f
z i r c o n .
A p o o r l y p r e s e r v e d s p i r i f e r i d b r a c h i o p o d a n d a
p e l e c y p o d w e re f o u n d i n t h e e x t r e m e s o u t h e a s t p o r t i o n o f
t h e a r e a m a p p ed i n a m a s s iv e c l i f f - f o r m i n g l i m e s t o n e . D r .
D o n a ld L . B r y a n t o f t h e U n i v e r s i t y o f A r i z o n a e x a m in e d t h e
s p e c im e n s a n d s 6 i d t h a t c o u p l e d w i t h t h e r o c k t y p e , t h e
f o s s i l s a r e p r o b a b l y f ro m t h e M i s s i s s i p p i a n E s c a b r o s a
L i m e s to n e .
I n t h e B uehm an C an y o n a r e a , m ap p ed b y M cK enna
( 1 9 6 6 ) , t h e E s c a b r o s a L im e s to n e i s o v e r l a i n b y t h e
P e n n s y l v a n i a n B la c k P r i n c e L im e s to n e a n d t h e H o r q u i l l a
L i m e s to n e s u c c e s s i v e l y . T he M a r t i n - E s c a b r o s a i s t h e
y o u n g e s t P a l e o z o i c r o c k t y p e r e c o g n i z e d i n t h e P i e t y H i l l
a r e a . C r e t a c e o u s r o c k s a r e a b s e n t . F l a t - l y i n g C e n o z d ic
a l l u v i u m o v e r l i e s t h e P a l e o z o i c s t r a t a i n t h e e a s t e r n
p o r t i o n o f t h e P i e t y H i l l a r e a .
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3 7
I g n e o u s R o c k s
L a m p ro p h y re D ik e s
M a f ic d i k e s c o n s i s t i n g p r e d o m i n a n t l y o f p l a g i o -
c l a s e a n d h o m b l e n d e - a c t i n o l i t e a r e c l a s s i f i e d h e r e a s
l a m p r o p h y r e s . T h e s e d i k e s c r o p o u t i n n u m e ro u s l o c a l i t i e s
t h r o u g h o u t t h e P i e t y H i l l a r e a . Z o n e s o f s t r u c t u r a l
w e a k n e s s s u c h a s f a u l t s a r e common l o c a l i z i n g f a c t o r s i n
t h e e m p la c e m e n t o f t h e d i k e s .
I n o u t c r o p t h e d i k e s a r e d a r k g r e e n t o b l a c k a n d
h a v e a s a l t a n d p e p p e r a p p e a r a n c e . T h ey w e a t h e r so t h a t
o u t c r o p s a r e g e n e r a l l y c o v e r e d w i t h a t h i c k z o n e o f f r i a b l e
r o c k t h a t m ak es c o l l e c t i o n o f f r e s h s a m p le s d i f f i c u l t .
T he m o s t p r o m i n e n t d i k e i n t h e a r e a i s a f i f t y
f o o t w id e , n o r t h - s t r i k i n g f e a t u r e t h a t s t a n d s o u t p r o m in
e n t l y o n a n a e r i a l p h o t o g r a p h . T h i s d i k e c u t s a c r o s s t h e
A b r ig o a n d M a r t i n - E s c a b r o s a f o r m a t i o n s i n t h e n o r t h
c e n t r a l p a r t o f t h e a r e a a n d d i p s n e a r l y v e r t i c a l l y .
T he d i k e s a r e a h o l o c r y s t a l l i n e , f i n e - t o m e d iu m -
g r a i n e d r o c k w i t h a h y p i d io m o r p h ic g r a n u l a r t e x t u r e
a p p r o a c h i n g p a n l d i o m o r p h i c ^ g r a n u l a r . M i c r o s c o p i c a l l y t h e
d i k e s a r e c o m p o se d o f f ro m 10 - 70$ p l a g i o c l a s e ( a n d e s i n e -
o l i g o c l a s e ) , 3 0 - 6 0 $ h o r n b l e n d e a n d a c t i n o l i t e , u p t o 2 5 $
s e r i c i t e , 5 $ a u g i t e , a n d l e s s t h a n 1 $ e a c h o f h e m a t i t e
a f t e r p y r i t e , b i o t i t e , a n d a p a t i t e .
T he p l a g i o c l a s e i s v a r i a b l e i n a m o u n t b e c a u s e o f
i t s a l t e r a t i o n t o s e r i c i t e a n d c l a y . I n d i v i d u a l c r y s t a l s
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r a n g e u p t o 2 mm i n s i z e a n d c o n s i s t o f s u b h e d r a l i n t e r
l o c k i n g a n d o v e r l a p p i n g t a b u l a r l a t h s a n d a n h e d r a l
c r y s t a l f r a g m e n t s . T he h o r n b l e n d e i s p l e o c h r o i c g r e e n t o
b ro w n a n d o c c u r s a s e u h e d r a l c r y s t a l s u p t o 1 . 5 mm l o n g
a n d a s l o n g , 3 - 4 mm, p r i s m a t i c c r y s t a l s a n d a c i c u l a r
f r a g m e n t s . Some o f t h e h o r n b l e n d e i s p r o b a b l y u r a l i t e .
Some s p e c im e n s o f d i k e r o c k c o n t a i n a c t i n o l i t e r a t h e r
t h a n h o r n b l e n d e . I n d i v i d u a l c r y s t a l s a r e s u b h e d r a l t o
a n h e d r a l i n fo rm a n d r e a c h a maximum o f 2 . 5 mm i n l e n g t h .
A p a t i t e o c c u r s a s m in u te s i x - s i d e d p r i s m a t i c c r y s t a l s .
B i o t i t e a n d h e m a t i t e a f t e r p y r i t e a r e t h e r e m a i n i n g m in o r
c o n s t i t u e n t s o f t h e la m p r o p h y r e d i k e s .
T h e i r s t r u c t u r a l r e l a t i o n s a n d u n m e ta m o rp h o s e d
c h a r a c t e r s u g g e s t t h a t t h e d i k e s w e re p r o b a b l y e m p la c e d
a f t e r t h e m e ta m o rp h is m o f t h e a r e a , w h ic h , a c c o r d i n g t o
D am on, E r i c k s o n , a n d L i v i n g s t o n ( I 9 6 3 ) , w o u ld b e a f t e r
U p p e r O l ig o c e n e - L o w e r M io c e n e t i m e .
A l lu v iu m
I n t h e e a s t e r n p a r t o f t h e P i e t y H i l l a r e a i s a
h o r i z o n t a l l y s t r a t i f i e d a l l u v i u m . T h i s u n i t l i e s w i t h
a n g u l a r u n c o n f o r m i t y u p o n t h e P a l e o z o i c r o c k s a n d c o n s i s t s
o f u n c o n s o l i d a t e d f r a g m e n t s o f g r a n i t e , q u a r t z i t e , l i m e
s t o n e , s c h i s t , a n d v o l c a n i c r o c k s i n a m a t r i x o f s a n d
a n d c l a y .
3 8
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39
B ecau se o f th e u n c o n s o l id a te d an d u n d efo rm ed
n a tu r e o f t h i s a l lu v iu m i t i s p resu m ed to b e L a te C en o zo ic
i n a g e , p ro b a b ly Q u a te rn a ry , an d p r o b a b ly c o r r e l a t e s w i th
th e a l lu v iu m d e s c r ib e d by R aabe ( 1959) •
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STRUCTURAL GEOLOGY
G e n e ra l S ta te m e n t
T he p r e d o m i n a n t t y p e o f d e f o r m a t i o n i n t h e P i e t y
H i l l a r e a i s t h e r e s u l t o f f a u l t i n g a n d i t s a s s o c i a t e d
p h e n o m e n a . T h r u s t f a u l t i n g f ro m t h e e a s t o r g r a v i t y
g l i d i n g f ro m t h e w e s t h a s c a u s e d t h e C a m b ria n B o l s a
Q u a r t z i t e t o b e e m p la c e d u p o n t h e M i s s i s s i p p i a n E s c a b r o s a
L im e s to n e i n a t l e a s t tw o p a r a l l e l b o l t s i n t h e m ap p ed
a r e a .
N o rm a l f a u l t s w i t h s t r i k e s r a n g i n g f ro m N 2 0 ° W
t o N 6 5 ° W a n d d i p s a t a h i g h a n g l e t o t h e e a s t a n d w e s t
a r e p r e s e n t . A h o r s t s t r u c t u r e h a s b e e n fo r m e d e a s t o f
P i e t y H i l l w h e re t h e P r e c a m b r i a n A p a c h e G ro u p m e ta s e d im e n t s
h a v e b e e n u p l i f t e d a n d now c u t a c r o s s t h e P a l e o z o i c r o c k s .
A l o n g n o r t h w e s t d i p p i n g , N 7 5 ° E s t r i k i n g n o r m a l f a u l t
t r a n s e c t s t h e h o r s t s t r u c t u r e a n d t h e t h r u s t ( ? ) f a u l t .
M in o r d r a g o r f lo w f o l d s a r e p r e s e n t i n t h e A b r ig o
L im e s to n e a n d a r e p r o b a b l y t h e r e s u l t o f d i f f e r e n t i a l s l i p
a l o n g b e d d i n g p l a n e s d u r i n g t h e t h r u s t i n g .
F a u l t s
G r a v i t y g l i d i n g o r t h r u s t f a u l t i n g h a s p r o d u c e d a
s t r u c t u r a l s i t u a t i o n w h e re b y t h e C a m b ria n B o l s a Q u a r t z i t e
4 0
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h a s b e e n e m p la c e d u p o n t h e M i s s i s s l p p i a n E s c a b r o s a L im e
s t o n e . Two p a r a l l e l n o r t h w e s t - t r e n d i n g b e l t s o f B o l s a
c u t a c r o s s t h e t h e s i s a r e a . T he t h i r d m a jo r e x p o s u r e ,
t h a t o f P i e t y H i l l , i s t h o u g h t t o b e a down f a u l t e d
e x t e n s i o n o f t h e p r o m i n e n t n o r t h w e s t t r e n d i n g b a n d o f
B o l s a i n t h e c e n t e r o f t h e a r e a . I t a p p e a r s t h a t t h e
m a s s i v e , h a r d , B o l s a Q u a r t z i t e a n d t h e m a s s iv e E s c a b r o s a
L im e s to n e h a v e b e e n p r e f e r e n t i a l l y s e l e c t e d a s s u r f a c e s
o v e r w h ic h r e p e a t e d , i m b r i c a t e f a u l t s c o u l d o c c u r .
A n g u l a r , s i l i c a c e m e n te d q u a r t z i t e f r a g m e n t s
f o r m in g a f a u l t b r e c c i a a r e f o u n d a l m o s t e v e r y w h e r e f a u l t
c o n t a c t s a r e e x p o s e d . T he o r i e n t a t i o n o f t h e s u r f a c e o f
m o v em en t o f t h e v a r i o u s t h r u s t b l o c k s r a n g e s f ro m n e a r l y
h o r i z o n t a l t o a h i g h a n g l e n o r t h e a s t d i p . A t t i t u d e s o f
t h e B o l s a a r e e r r a t i c a n d o f t e n i m p o s s i b l e t o d e t e r m i n e
s o t h a t t h e f a u l t s u r f a c e i s b e s t l o c a t e d b y s t u d y i n g t h e
a r e a l e x t e n t o f e x p o s u r e s w i t h r e g a r d t o to p o g r a p h y a n d
a c t u a l t r a c i n g o f c o n t a c t s . T he b a n d o f B o l s a n e a r t h e
e a s t e r n m a r g in o f t h e P i o n e e r F o r m a t io n h a s a d i p o f
t w e n t y - f i v e t o t h i r t y d e g r e e s e a s t i n t h e s o u t h a n d f i f t y
t o s i x t y d e g r e e s e a s t i n t h e n o r t h . T he e x p o s u r e s o f
B o l s a i n t h e n o r t h e a s t p a r t o f t h e a r e a l i e n e a r l y h o r i
z o n t a l l y o v e r t h e M a r t i n - E s c a b r o s a . T he l i m e s t o n e t h a t
fo r m s t h e s u r f a c e o v e r w h ic h t h e m o v em en t o c c u r r e d h a s
e r r a t i c a t t i t u d e s i n p r o x i m i t y t o t h e f a u l t s . M in o r f o l d s
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4 2
c a u s e d b y d r a g o r f lo w a g e u n d e r t h e p r e s s u r e o f t h e o v e r
r i d i n g t h r u s t s h e e t fo r m e d i n b o t h t h e M a r t i n - E s c a b r o s a
a n d i n t h e A b r lg o L i m e s t o n e . T h e A b r ig o i n t e r l a y e r e d s a n d
s t o n e s a n d l i m e s t o n e s a r e t h e m o s t d e f o r m e d o f t h e r o c k s
a f f e c t e d . T he d r a g f o l d s o f t h e A b r lg o h a v e a g e n e r a l
c o n s i s t e n c y o f o r i e n t a t i o n . T h ey a r e o v e r t u r n e d t o t h e
n o r t h e a s t g i v i n g t h e a x i a l p l a n e s a N 3 0 ° - 5 0 ° W s t r i k e
a n d a d ip o f 4 0 ° - 7 0 ° SW. F o l d a x e s p l u n g e a s m uch a s
tw e n ty d e g r e e s i n a n o r t h w e s t d i r e c t i o n . S h e a r s e n s e
r e q u i r e d t o p r o d u c e s u c h f o l d s w o u ld h a v e t o i n v o l v e t h e
o v e r l y i n g s t r a t a m o v in g n o r t h e a s t r e l a t i v e t o t h e u n d e r
l y i n g s t r a t a . T h i s t y p e o f f o l d c o u l d h a v e fo r m e d i f t h e
l o w e r P a l e o z o i c s t r a t a w e re u p t h r u s t o v e r t h e M a r t i n -
E s c a b r o s a .
T he g r a v i t y g l i d i n g h y p o t h e s i s r e q u i r e s t h a t t h e
f a u l t b l o c k s g l i d e d f ro m t h e c r e s t a l p a r t o f t h e S a n t a
C a t a l i n a M o u n ta in s n o r t h e a s t w a r d i n t o t h e P i e t y H i l l a r e a .
I f g r a v i t y g l i d i n g w e re t h e m e c h a n is m o f e m p la c e m e n t i t
w o u ld b e e x p e c t e d t h a t t h e f a u l t p l a n e s w o u ld m a i n t a i n a
s h a l l o w d i p a n d n o t p l u n g e s t e e p l y do w n w ard a t t h e r e a r
o f t h e t h r u s t s h e e t ( d e S i t t e r , 1 9 6 4 , p . 2 5 5 ) • A l s o , d r a g
f o l d s w o u ld b e e x p e c t e d t o e x h i b i t s h e a r s e n s e o p p o s i t e t o
t h a t o c c u r r i n g i n t h e A b r lg o L i m e s t o n e . E v id e n c e se e m s t o
f a v o r t h e t h r u s t i n g h y p o t h e s i s , b u t t o c h o o s e w h ic h m ech
a n is m , t h r u s t i n g o r g l i d i n g , c a u s e d t h e s t r u c t u r a l r e l a t i o n s
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i n t h e P i e t y H i l l a r e a w o u ld b e u n w is e i n s u c h a l i m i t e d
s t u d y a s t h i s .
B e d d in g s l i p p a g e i n v o l v i n g n o r m a l o r r e v e r s e m ove
m e n t may h a v e o c c u r r e d a s a r e s u l t o f t h e t h r u s t i n g o r
g l i d i n g . F a u l t s o f t h i s t y p e a r e v e r y d i f f i c u l t t o
i d e n t i f y i n a s t r a t i g r a p h i c s e c t i o n t h a t i s p o o r l y d e f i n e d
b e c a u s e o f m e ta m o rp h is m o f o r i g i n a l s e d i m e n t a r y f e a t u r e s
a n d p o o r e x p o s u r e s . T h e s e b e d d i n g f a u l t s w o u ld b e s i m i l a r
t o l a g ty p e f a u l t s o f H i l l s ( I 9 6 3 , p . 1 9 1 ) w h e re n o r m a l
f a u l t s o c c u r o n t h e h a n g i n g w a l l o f a t h r u s t .
H ig h a n g l e n o r m a l f a u l t s t r e n d i n g n o r t h w e s t c u t
t h e p i e t y H i l l a r e a a n d a r e y o u n g e r t h a n t h e t h r u s t s . The
w ed g e o f A p a c h e G ro u p r o c k s i s b o u n d e d o n t h e e a s t a n d
w e s t b y N 2 0 ° W - s t r i k i n g n o r m a l f a u l t s . T he w e s t e r n f a u l t
d i p s w e s t a n d t h e e a s t e r n f a u l t d i p s e a s t c a u s i n g t h e
A p a c h e G ro u p m e ta s e d im e n t s t o b e u p l i f t e d r e l a t i v e t o t h e
s u r r o u n d i n g r o c k s a s a h o r s t . B o th o f t h e s e f a u l t s d i p
a t a v e r y h i g h a n g l e b e c a u s e t h e y a r e n o t o f f s e t b y to p o
g r a p h i c v a r i a t i o n s .
O t h e r l e s s e x t e n s i v e n o r t h w e s t t r e n d i n g n o r m a l
f a u l t s a r e p r e s e n t . A n a r r o w f a u l t z o n e s t r i k e s a p p r o x i
m a t e l y N 5 0 ° W a n d d i p s a t a h i g h a n g l e s o u t h w e s t i n t h e
c e n t r a l p a r t o f S e c . 29» T . 12 S . , R . 18 E . A n a r r o w
w ed g e o f t h e B o l s a t h r u s t s h e e t h a s b e e n d o w n -d r o p p e d .
I n t h i s n a r r o w z o n e t h e B o l s a h a s b e e n m e ta m o rp h o s e d t o a
4 3
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4 4
q u a r t z - m i c a s c h i s t a s a r e s u l t o f t h e t e m p e r a t u r e s a n d
p r e s s u r e s o f d i s l o c a t i o n . T he s c h i s t o s i t y o f t h e r o c k i n
t h e f a u l t z o n e p a r a l l e l s t h e f a u l t a n d i s a c c o m p a n ie d b y
s l i c k e n s i d e s .
T he y o u n g e s t s t a g e o f f a u l t i n g a p p e a r s t o h a v e
r e s u l t e d i n h i g h a n g l e n o r m a l f a u l t s t h a t t r e n d n e a r l y
e a s t - w e s t . A w e l l e x p o s e d f a u l t o f t h i s t y p e i s l o c a t e d
s o u t h o f t h e R e d i n g t o n R o a d i n t h e c e n t r a l p o r t i o n o f t h e
a r e a ( P l a t e I ) . T he s t r i k e o f t h i s f a u l t r a n g e s f ro m
N 9 0 ° E t o N 7 5 ° E a n d t h e d i p i s n o r t h a t a h i g h a n g l e .
T h i s f a u l t t r a n s e c t s t h e t h r u s t f a u l t a n d t h e n o r t h w e s t
t r e n d i n g n o r m a l f a u l t s . T he n o r t h d ip i s w e l l d i s p l a y e d
b y o f f s e t s o n o p p o s i t e s i d e s o f t h e f a u l t w h ic h w e re c a u s e d
b y t h e n o r t h b l o c k m o v in g dow n r e l a t i v e t o t h e s o u t h b l o c k .
A w e l l d e f i n e d s i l i c i f i e d q u a r t z b r e c c i a i s e x p o s e d a l o n g
t h e f a u l t f o r t h r e e - q u a r t e r s o f a m i l e . To t h e w e s t t h e
f a u l t i s l o s t i n t h e h o m o g e n e o u s g r a n i t i c r o c k a n d i s a l s o
u n t r a c e a b l e i n t h e A b r ig o L im e s to n e t o t h e e a s t .
T h e r e a p p e a r s t o b e a s t r u c t u r a l c o n t r o l t h a t h a s
g o v e r n e d t h e e m p la c e m e n t o f t h e la m p r o p h y r e d i k e s . A l l
t h e d i k e s t r e n d N o r t h t o N 2 0 ° W. S e v e r a l d i k e s a r e
s i t u a t e d a l o n g t h e h i g h a n g l e n o r m a l f a u l t o n t h e e a s t e r n
m a r g in o f t h e h o r s t o f A p a c h e G ro u p r o c k s . T he m o s t
c o n s p ic u o u s d i k e o f t h e a r e a i s i n t h e w e s t e r n p a r t o f
s e c t i o n 2 9 . t r e n d s n o r t h , d i p s v e r t i c a l l y , a n d i s f i f t y
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4 5
t o s i x t y f e e t w id e . A lo n g s t r i k e t h i s d i k e e x t e n d s f o r
a t l e a s t o n e - h a l f m i l e n o r t h o f t h e map a r e a a s i n t e r p r e t e d
f ro m a e r i a l p h o t o g r a p h s . I t s s t r a i g h t n e s s s u g g e s t s a
b u r i e d s t r u c t u r a l c o n t r o l , p o s s i b l y i n P r e c a m b r i a n r o c k s .
F o l i a t i o n
T he g r a n l t i c - g n e i s s l c r o c k s o f t h e P i e t y H i l l a r e a
a r e g e n e r a l l y w i t h o u t f o l i a t i o n . C o n t a c t a r e a s r a r e l y
d i s p l a y a w e l l - d e v e l o p e d g n e i s s i c f o l i a t i o n w h ic h m ay
r e p r e s e n t f lo w a g e o f m a t e r i a l a t t h e c o o l e r m a r g in s o f t h e
i n t r u s i v e , t h a t i s , i f t h e g r a n i t i c m a s s w as m o b i l i z e d
s u f f i c i e n t l y t o b e h a v e a s a f l u i d .
T he P r e c a m b r i a n A p a c h e G ro u p m e t a s e d i m e n t s ,
e s p e c i a l l y t h e P i o n e e r F o r m a t i o n , a r e e r r a t i c i n d i p . The
s t r i k e i s g e n e r a l l y N 2 0 ° - 50° W a n d t h e d i p i s u s u a l l y
t o t h e s o u t h w e s t . T he f o l i a t i o n i s p a r a l l e l t o t h e
o r i g i n a l b e d d i n g b e c a u s e i t p a r a l l e l s t h e s e d i m e n t a r y
c o n t a c t s b e tw e e n i n d i v i d u a l f o r m a t i o n s o f t h e g r o u p . I n
p l a c e s t h e s c h i s t o s e r o c k o f t h e P i o n e e r F o r m a t io n d i s p l a y s
a c r e n u l a t i o n c l e a v a g e p e r p e n d i c u l a r t o t h e f o l i a t i o n .
T he P a l e o z o i c s t r a t a l i e i n a n g u l a r u n c o n f o r m i t y
u p o n t h e P r e c a m b r i a n A p a c h e G ro u p r o c k s a l t h o u g h a n o r m a l
u n f a u l t e d c o n t a c t i s n o t p r e s e n t i n t h e P i e t y H i l l a r e a .
G e n e r a l l y t h e P a l e o z o i c r o c k s s t r i k e N 3 0 ° - 5 0 ° W a n d
d i p n o r t h e a s t . B e d d in g d e f i n e d b y o r i g i n a l c o m p o s i t i o n a l
b a n d i n g h a s n o t b e e n so d e f o r m e d a s t o b e u n r e c o g n i z a b l e
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4 6
i n m o s t o f t h e s t r a t a . T he m a s s iv e B o l s a Q u a r t z i t e a n d
E s c a b r o s a L im e s to n e h a v e o b s c u r e b e d d i n g w h ic h i s som e
t i m e s u n r e c o g n i z a b l e .
T he B o l s a Q u a r t z i t e e x p o s e d o n P i e t y H i l l s t r i k e s
r o u g h l y N 9 0 ° E a n d d i p s s o u t h . T he g r a n i t e e x p o s e d
a r o u n d P i e t y H i l l s u g g e s t s t h a t i t u p l i f t e d t h e o v e r l y i n g
s t r a t a u p o n i n t r u s i o n .
T he y o u n g e s t r o c k s o f t h e a r e a a r e u n c o n s o l i d a t e d
a l l u v i u m w h ic h a r e h o r i z o n t a l a n d t h e r e f o r e l i e w i t h
a n g u l a r u n c o n f o r m i t y u p o n t h e P a l e o z o i c s t r a t a . A l th o u g h
t h e r e a r e n o C r e t a c e o u s s t r a t a i n t h e m ap p ed a r e a , M cK enna
( 1966 ) r e p o r t e d t h e i r p r e s e n c e n o r t h i n t h e B uehm an C anyon
a r e a . T he C r e t a c e o u s s t r a t a l i e w i t h a n g u l a r u n c o n f o r m i t y
u p o n t h e P a l e o z o i c s t r a t a a n d a r e i n t u r n a n g u l a r l y o v e r -
l a i n b y a l l u v i u m .
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INTERPRETATION OF METAMORPHISM
T he r o c k s o f t h e P i e t y H i l l a r e a h a v e u n d e r g o n e
a t l e a s t tw o s t a g e s o f m e ta m o rp h is m . B o th r e g i o n a l a n d
c o n t a c t m e ta m o rp h is m h a v e a f f e c t e d t h e s e d i m e n t a r y r o c k s ,
o f w h ic h t h e P r e C a m b r ia n A p a c h e G ro u p i s t h e m o s t h i g h l y
m e ta m o rp h o s e d .
R e g i o n a l m e ta m o rp h is m h a s i m p a r t e d i t s e f f e c t s t o
t h e P r e c a m b r i a n A p a c h e G ro u p r o c k s a n d t o a l e s s e r e x t e n t
t o t h e o v e r l y i n g P a l e o z o i c r o c k s . T he P i o n e e r F o r m a t io n
a n d p a r t s o f t h e B o l s a Q u a r t z i t e h a v e a d e f i n i t e s c h i s t o s e
s t r u c t u r e t h a t i s c h a r a c t e r i s t i c o f r e g i o n a l m e ta m o rp h is m .
E l o n g a t e q u a r t z g r a i n s w i t h u n d u l a t o r y e x t i n c t i o n a n d
o r i e n t e d m ic a c e o u s m i n e r a l s i n d i c a t e t h a t t h e r e g i o n a l
m e ta m o rp h is m w as a c c o m p a n ie d b y o r o c c u r r e d i n c o n j u n c t i o n
w i t h r e g i o n a l d e f o r m a t i o n . S t r e t c h e d p e b b l e s i n t h e B a r n e s
C o n g lo m e r a te M em ber o f t h e D r i p p i n g S p r i n g Q u a r t z i t e a r e
f u r t h e r e v i d e n c e o f t h e r e g i o n a l m e ta m o rp h is m a n d d e f o r m a
t i o n . T he q u a r t z g r a i n s o f t h e p e b b l e s a r e h i g h l y s t r a i n e d
a n d e l o n g a t e d p a r a l l e l t o t h e l o n g a x e s o f t h e p e b b l e s .
T he B o l s a Q u a r t z i t e c o n t a i n s som e e l o n g a t e q u a r t z
g r a i n s a n d o r i e n t e d m ic a w h ic h a r e i n d i c a t i o n s o f r e g i o n a l
m e ta m o rp h is m . I n t h e A b r ig o L im e s to n e a n d t h e M a r t i n -
E s c a b r o s a F o r m a t io n t r e m o l i t e , a c t i n o l i t e , a n d c a l c i t e a r e
4 ?
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4 8
com m only o r i e n t e d i n a c r u d e s c h i s t o s i t y w h ic h i n d i c a t e s
a c o n d i t i o n o f s t r e s s d u r i n g c r y s t a l l i z a t i o n .
C o n d i t i o n s o f r e g i o n a l m e ta m o rp h is m w e re t r a n s i
t i o n a l b e tw e e n t h e q u a r t z - a l b i t e - m u s c o v i t e - c h l o r i t e a n d
q u a r t z - a l b i t e - e p i d o t e - b i o t i t e s u b f a c i e s o f t h e g r e e n s c h i s t
f a c i e s o f F y f e , T u r n e r , a n d V e rh o o g e n ( 1 9 5 8 ) . T he q u a r t z o -
f e l d s p a t h i c r o c k s s u c h a s t h e B a r n e s C o n g lo m e r a te , P i o n e e r
F o r m a t i o n , a n d B o l s a Q u a r t z i t e c o n t a i n t h e c h a r a c t e r i s t i c
q u a r t z - m u s c o v i t e - e p i d o t e - m i c r o c l i n e a s s e m b l a g e . The c a l
c a r e o u s u n i t s s u c h a s t h e D r i p p i n g S p r i n g Q u a r t z i t e , A b r ig o
L i m e s to n e , a n d M a r t i n - E s c a b r o s a F o r m a t io n c o n t a i n t h e
c h a r a c t e r i s t i c t r e m o l i t e - a c t i n o l i t e - e p i d o t e - c a l c i t e -
c h l o r i t e - q u a r t z a s s e m b l a g e .
R e g i o n a l m e ta m o rp h is m o f t h e s e d i m e n t a r y s t r a t a
o f t h e S a n t a C a t a l i n a M o u n ta in s o c c u r r e d d u r i n g t h e f o r m a t i o n
o f t h e l a r g e g r a n i t i c - g n e i s s i c c o m p le x . A c c o r d i n g t o D u B o is
(1959 a , b ) , t h e g r a n i t i c - g n e i s s i c r o c k s f o r m in g t h e m a in
m a ss o f t h e m o u n ta in s w e re f o r m e d a s a r e s u l t o f r e c r y s t a l
l i z a t i o n a n d , l o c a l l y , r e m o b i l i z a t i o n o f a P r e c a m b r i a n
g r a n i t e a n d a l s o f ro m g r a n i t i z a t i o n o f p a r t o f t h e s e d i
m e n ta r y c o v e r o f t h e r a n g e .
R e g i o n a l m e ta s o m a t is m i n t r o d u c i n g p o t a s s i u m - r i c h
f l u i d s h a s b e e n s u g g e s t e d b y D u B o is (1 9 5 9 b ) a s h a v i n g
a c c o m p a n ie d t h e g r a n i t i z a t i o n a n d p r e s u m a b ly t h e m e ta
m o rp h ism a s w e l l . T he i d e a o f p o t a s s i u m m e ta s o m a t is m i s
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s u p p o r t e d b y t h e p e t r o g r a p h y o f t h e P i e t y H i l l a r e a . T he
C a t a l i n a G n e i s s o f t h e P i e t y H i l l a r e a c o n t a i n s e u h e d r a l
p o t a s h f e l d s p a r c r y s t a l s , som e o f w h ic h c o n t a i n i n c l u s i o n s
o f p l a g i o c l a s e . T h i s l a t t e r s t a g e o f p o t a s h f e l d s p a r
c o u l d b e a t t r i b u t e d t o m e ta s o m a t i c a c t i v i t y . O t h e r e v i d e n c e
o f p o t a s s i u m i n t r o d u c t i o n i n t h e P i e t y H i l l a r e a i s t h e
a b u n d a n c e o f m l c r o c l i n e i n som e o f t h e m e ta m o rp h o s e d s e d i
m e n ta r y r o c k s . T he g n e i s s i c f a c i e s o f t h e P i o n e e r F o r m a t io n
i s a p a r t i c u l a r e x a m p le o f t h i s . T he a lu m in u m s i l i c a t e
m i n e r a l s o f t h e P i o n e e r F o r m a t io n m ay h a v e b e e n a l t e r e d t o
m u s c o v i t e a s a r e s u l t o f p o t a s h i n t r o d u c t i o n . S u c h a l t e r
a t i o n i s a n i n t e r m e d i a t e s t e p w i t h p o t a s s i u m f e l d s p a r a s
t h e f i n a l p r o d u c t .
R e l i c t t e x t u r e s o r s t r u c t u r e s h a v e n o t b e e n f o u n d
i n t h e P i e t y H i l l a r e a t h a t m ig h t s u g g e s t w h e t h e r t h e
C a t a l i n a g r a n i t i c m a ss may h a v e o r i g i n a l l y b e e n a n i n t r u s i v e
r o c k o r a g r a n i t i z e d s e d i m e n t . The f i e l d r e l a t i o n s seem
t o s u g g e s t t h a t t h e C a t a l i n a G n e i s s w as m o b i le w hen i n t r o
d u c e d i n t o t h e P i e t y H i l l a r e a .
C o n t a c t m e ta m o rp h is m i s a r e s u l t o f t h e i n t r u s i o n
o f t h e a n c e s t r a l C a t a l i n a G n e i s s . T he e f f e c t s o f t h e
c o n t a c t m e ta m o rp h is m w e re s u p e r im p o s e d u p o n t h e e f f e c t s
o f r e g i o n a l m e ta m o rp h is m i n t h e P r e c a m b r i a n a n d P a l e o z o i c
s e d i m e n t a r y r o c k s . T e m p e r a tu r e c o n d i t i o n s r a n g e d f ro m lo w
t o m ed ium p r o d u c i n g m i n e r a l a s s e m b la g e s c h a r a c t e r i s t i c o f
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5 0
t h e a l b i t e - e p i d o t e - h o m f e l s f a c i e s o f F y f e , T u r n e r , a n d
V e rh o o g e n ( 1 9 5 8 ) •
T he m o s t s t r i k i n g f e a t u r e o f t h e c o n t a c t m e ta
m o rp h ism i s t h e d e v e lo p m e n t o f l a r g e i d i o b l a s t i c c r y s t a l s
o f c h i a s t o l i t e i n p a r t s o f t h e P i o n e e r F o r m a t i o n . A l l o f
t h e c h i a s t o l i t e h a s b e e n a l t e r e d s o t h a t o n l y p s e u d o m o r p h s
r e m a i n . T he p s e u d o m o r p h s c o n s i s t o f s l l l i m a n i t e a n d
s e r l c i t e i n som e s p e c im e n s a n d o f o n l y s e r i c i t e i n o t h e r s .
I t i s s u g g e s t e d t h a t t h e o r i g i n a l c h i a s t o l i t e w as c o n
v e r t e d t o s l l l i m a n i t e a n d s u b s e q u e n t l y t o s e r i c i t e . A
c h a n g e f ro m c h i a s t o l i t e t o s l l l i m a n i t e may h a v e b e e n
c a u s e d b y d e f o r m a t i o n a n d w o u ld n o t h a v e r e q u i r e d a
t e m p e r a t u r e i n c r e a s e . A c c o r d i n g t o D r . H . S . Y o d e r o f
t h e G e o p h y s i c a l L a b o r a t o r y ( p e r s o n a l c o m m u n ic a t io n )
s l l l i m a n i t e a n d a n d a l u s i t e c a n c o e x i s t u n d e r a l a r g e r a n g e
o f t e m p e r a t u r e s a n d s l l l i m a n i t e i s n o t n e c e s s a r i l y a h i g h
t e m p e r a t u r e p o ly m o r p h o f a n d a l u s i t e o r c h i a s t o l i t e .
T he p r e s e n c e o f g a r n e t ( g r o s s u l a r i t e ? ) i n t h e
D r i p p i n g S p r i n g Q u a r t z i t e i s a t t r i b u t e d t o t h e c o n t a c t
p h e n o m e n a . M in o r a m o u n ts o f w o l l a s t o n i t e a s s o c i a t e d w i t h
d i o p s i d e a n d h e d e n b e r g i t e i n t h e M a r t i n - E s c a b r o s a
F o r m a t io n s s u g g e s t t h a t t h e c o n t a c t m e ta m o rp h is m m ay h a v e
b e e n t h e m o s t i m p o r t a n t o f t h e tw o m e ta m o r p h ic e f f e c t s i n
t h e P i e t y H i l l a r e a .
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A n o th e r a l t e r n a t i v e t o e x p l a i n t h e c o a r s e r e c o n
s t i t u t i o n o f t h e M a r t i n - E s c a b r o s a t o t r e m o l i t e a n d o t h e r
c a l c iu m s i l i c a t e m i n e r a l s i n l o c a l a r e a s aw ay f ro m t h e
C a t a l i n a G n e i s s c o n t a c t z o n e w o u ld b e n e a r s u r f a c e l a m p r o
p h y r e d i k e s t h a t h a v e i m p a r t e d t h e i r own c o n t a c t a u r e o l e s
t o t h e c o u n t r y r o c k . I f t h i s w e re t h e c a s e , c o n t a c t m e ta
m o rp h ism a s s o c i a t e d w i t h t h e C a t a l i n a G n e i s s w as i m p o r t a n t
o n l y i n c l o s e p r o x i m i t y t o i t s m a r g i n s .
T he a s s o c i a t i o n o f g r o s s u l a r i t e a n d e p i d o t e i n t h e
D r i p p i n g S p r i n g Q u a r t z i t e a n d t h e q u a r t z - m u s c o v i t e -
c h i a s t o l i t e - s i l l i m a n i t e i n t h e P i o n e e r F o r m a t io n m a r g i n a l
t o t h e i n t r u s i v e c o n t a c t r e q u i r e t h a t t h e h i g h e s t g r a d e o f
c o n t a c t m e ta m o rp h is m b e t h e a l b i t e - e p i d o t e - h o m f e l s f a c i e s
r a t h e r t h a n t h e h o m b l e n d e - h o m f e l s f a c i e s .
T he s u p e r p o s i t i o n o f t h e r e g i o n a l a n d c o n t a c t
m e ta m o rp h is m w i t h t h e i r s i m i l a r t e m p e r a t u r e s a n d m i n e r a l
a s s e m b la g e s h a s m ade i t i m p o s s i b l e t o r e c o g n i z e m e ta m o r p h ic
i s o g r a d s .
5 1
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GEOLOGIC HISTORY
T he o l d e s t r o c k o f t h e P i e t y H i l l a r e a m ay b e t h e
C a t a l i n a G n e i s s , b u t b e c a u s e i t w as r e c o n s t i t u t e d d u r i n g
p o s t - C r e t a c e o u s t im e i t w i l l b e c o n s i d e r e d a p o s t - C r e t a c e o u s
r o c k h e r e .
T he Y o u n g e r P r e c a m b r l a n A p a c h e G ro u p r o c k s w e re
p r o b a b l y d e p o s i t e d a s s e d i m e n t s u p o n t h e O l d e r P r e c a m b r l a n
P i n a l S c h i s t w h ic h d o e s n o t c r o p o u t i n t h e m ap p ed a r e a .
R a a b e (1 9 5 9 ) r e p o r t e d a p o s s i b l e m e t a - e q u i v a l e n t o f t h e
P i n a l i n t h e B u l l o c k C an y o n - B uehm an C an y o n a r e a t o t h e
n o r t h w e s t . T he P i o n e e r F o r m a t io n r e p r e s e n t s a n o r i g i n a l
s e d i m e n t , p r o b a b l y a s h a l e , w i t h a c o m p o s i t i o n r i c h i n
a lu m in u m , i r o n , a n d c a l c i u m . T he B a r n e s C o n g lo m e r a te
M em ber o f t h e D r i p p i n g S p r i n g Q u a r t z i t e w as p r o b a b l y a
c o n g lo m e r a t e c o m p o se d p r e d o m i n a n t l y o f q u a r t z , b u t a l s o
c o n t a i n i n g i r o n a n d a lu m in u m . T he D r i p p i n g S p r i n g Q u a r t z i t e
a p p e a r s t o h a v e b e e n a c a l c i u m r i c h s a n d s t o n e .
A f t e r d e p o s i t i t l o n o f t h e A p a c h e G ro u p r o c k s t h e
a r e a w as u p l i f t e d a n d e r o d e d . I n M id d le C a m b ria n t im e s e a s
a d v a n c e d a c r o s s s o u t h e a s t e r n A r i z o n a f ro m M e x ic o a s p a r t
o f t h e S o n o r a n g e o s y n c l i n e (M cK ee, 1 9 5 1 ) • T he B o l s a
Q u a r t z i t e w as t h e f i r s t P a l e o z o i c s e d i m e n t d e p o s i t e d , a n d
i t c o n s i s t e d o f a b a s a l q u a r t z p e b b l e c o n g lo m e r a t e a n d
5 2
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q u a r t z i t e w i t h l o c a l l e n s e s o f l i m e s t o n e a n d s h a l e . S e d i
m e n t a t i o n c o n t i n u e d w i t h o u t a p p a r e n t i n t e r r u p t i o n t h r o u g h
L a t e C a m b ria n t i m e , d e p o s i t i n g t h e A b r ig o L im e s to n e u p o n
t h e B o l s a . The A b r ig o s e a p r o d u c e d a v a r i a b l e e n v i r o n m e n t
o f d e p o s i t i o n b e c a u s e l i m e s t o n e , s a n d s t o n e , s h a l e , a n d
s i l t s t o n e w e re l a i d d ow n . A t t h e e n d o f t h e C a m b ria n
p e r i o d t h e s e a r e g r e s s e d a n d a p e r i o d o f n o n d e p o s i t i o n
e n s u e d u n t i l M id d le D e v o n ia n t i m e . S e a s a g a i n a d v a n c e d
f ro m t h e s o u t h d e p o s i t i n g c a r b o n a t e s e d i m e n t s w i t h som e
e l a s t i c s a s t h e M a r t i n F o r m a t i o n . I n L o w e r M i s s i s s i p p l a n
t im e l i m e s t o n e a n d c h e r t w e re d e p o s i t e d a s t h e E s c a b r o s a
L i m e s to n e . A l th o u g h P a l e o z o i c r o c k s y o u n g e r t h a n E s c a b r o s a
h a v e n o t b e e n f o u n d t o c r o p o u t i n t h e P i e t y H i l l a r e a , i t
c a n b e a s s u m e d t h a t t h e y w e re d e p o s i t e d a n d re m o v e d e i t h e r
b y e r o s i o n o r f a u l t i n g . T h ey h a v e b e e n r e p o r t e d t o t h e
n o r t h i n t h e B uehm an C anyon a r e a (M cK en n a , 1 9 6 6 ) .
A t t h e e n d o f t h e P a l e o z o i c e r a t h e a r e a w as u p
l i f t e d a n d d e f o r m e d ; a n a n g u l a r u n c o n f o r m i t y fo r m e d w i t h
t h e n e x t b l a n k e t o f s e d i m e n t a r y s t r a t a d e p o s i t e d i n E a r l y
C r e t a c e o u s ( ? ) t im e i n t h e B uehm an C an y o n a r e a (M cK enna ,
1 9 6 6 ) . A l o n g p e r i o d o f d e f o r m a t i o n t h a t b e g a n i n p o s t -
C r e t a c e o u s t im e a n d c o n t i n u e d a t l e a s t u n t i l U p p e r O l ig o c e n e
L o w er M io c e n e t im e (D am on, E r i c k s o n , a n d L i v i n g s t o n , 1 9 6 3 )
s t r o n g l y a f f e c t e d t h e r o c k s o f t h e S a n t a C a t a l i n a M o u n ta in s
a n d t h e P i e t y H i l l a r e a . I t w as d u r i n g t h i s d e f o r m a t i o n a l
5 3
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p e r i o d t h a t m e ta m o rp h is m a n d f a u l t i n g o c c u r r e d . R e g i o n a l
m e ta m o rp h is m i n c o n j u n c t i o n w i t h t h e i n t r u s i v e a n d g r a n i t i -
z a t i o n p h e n o m e n a o f t h e g r a n t t i c - g n e i s s i c c o m p le x m i l d l y
m e ta m o rp h o s e d t h e r o c k s o f t h e P i e t y H i l l a r e a . C o n t a c t
m e ta m o rp h is m a s s o c i a t e d w i t h t h e i n t r u s i v e g r a n i t e w as
s u p e r im p o s e d u p o n t h e r e g i o n a l m e ta m o rp h is m .
T h r u s t f a u l t i n g o r g r a v i t y g l i d i n g o c c u r r e d n e x t
a n d w as f o l l o w e d b y n o r t h w e s t - s t r i k i n g , h i g h a n g l e n o r m a l
f a u l t i n g . T he l a s t s t a g e o f f a u l t i n g w as o n e o f h i g h
a n g l e n o r m a l f a u l t s s t r i k i n g n e a r l y e a s t - w e s t .
A p e r i o d o f i n t r u s i o n o f la m p r o p h y r e d i k e s
f o l l o w e d t h e p o s t - C r e t a c e o u s d e f o r m a t i o n . T h e s e d i k e s
a r e u n m e ta m o rp h o s e d .
C e n o z o ic a l l u v i u m , p r o b a b l y Q u a t e r n a r y , l i e s
h o r i z o n t a l l y i n t h e P i e t y H i l l a r e a a n d r e p r e s e n t s t h e
l a s t p e r i o d o f d e p o s i t i o n i n t h e a r e a . R e c e n t e r o s i o n
h a s d i s e c t e d t h e l a n d s u r f a c e d e v e l o p i n g t h e p r e s e n t
t o p o g r a p h y .
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REFERENCES
Chew, R . T . , 1 9 5 2 , G e o lo g y o f t h e M in e t a R id g e a r e a , P im a a n d C o c h i s e C o u n t i e s , A r i z o n a : U n iv . o f A r i z o n au n p u b l i s h e d m a s t e r 1s t h e s i s , 53 P»
C o o p e r , J . R . , a n d S i l v e r , L . T . , 1 9 6 4 , G e o lo g y a n d o r ed e p o s i t s o f t h e D ra g o o n Q u a d r a n g l e , C o c h i s e C o u n ty , A r i z o n a : U . S . G e o l . S u r v e y , P r o f . P a p e r 4 1 6 .
Dam on, P . E . , E r i c k s o n , R . C . , a n d L i v i n g s t o n , D. E . , 1 9 6 3 , K -A r d a t i n g o f b a s i n a n d r a n g e u p l i f t , C a t a l i n a M o u n ta i n s , A r i z o n a : N u c l e a r G e o p h y s ic s , N a t .A c a d . S c i . - N a t . R e s . C o u n c i l P u b . 1 0 7 5 , N u c l e a r S c i e n c e S e r i e s n o . 3 8 , p p . 1 1 3 - 1 2 1 .
d e S i t t e r , L . U . , 1 9 6 4 , S t r u c t u r a l g e o lo g y : New Y o rk ,M c G ra w -H il l , S e c o n d e d i t i o n , 551 p .
D u B o is , R . L . , 1 9 5 9 a . G e o lo g y o f t h e S a n t a C a t a l i n aM o u n ta in s : A r i z . G e o l . S o c . G u id e b o o k I I , p p . 1 0 ? -116.
__________ , 1 9 5 9 b , P e t r o g r a p h y a n d s t r u c t u r e o f a p a r t o ft h e g n e i s s i c c o m p le x o f t h e S a n t a C a t a l i n a M o u n ta i n s , A r i z o n a : A r i z . G e o l . S o c . G u id e b o o k I I ,p p . 117 - 1 2 6 .
F lo w e r , R . H . , 1 9 5 8 , C a m b r i a n - M i s s i s s i p p i a n b e d s o fS o u t h e r n New M e x ic o : R o s w e l l G e o l . S o c . , G u id e b o o kE l e v e n t h F i e l d C o n f .
F y f e , W. S . , T u r n e r , F . J . , a n d V e rh o o g e n , J . , 1 9 5 8 , M e ta m o rp h ic r e a c t i o n s a n d m e ta m o r p h ic f a c i e s :G e o l . S o c . A m e r ic a , M e m o ir.
G i l l u l y , J . , 1 9 5 6 , G e n e r a l g e o lo g y o f c e n t r a l C o c h i s eC o u n ty , A r i z o n a : U . S . G e o l . S u r v e y P r o f . P a p e r 2 8 1 .
G o d d a rd , E . N . ( C h a i r m a n ) , 1 9 4 8 , R o c k - C o lo r C h a r t , p r e p a r e d b y t h e R o c k - C o lo r C h a r t C o m m itte e , N a t . R e s .C o u n c il , W ash in g to n , D. C.
H i l l s , E . S . , 1 9 6 3 , E l e m e n ts o f s t r u c t u r a l g e o lo g y : NewY o rk , J o h n W ile y & S o n s , 4 8 3 p .
5 5
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L eM one, D . V . , 1 9 5 9 . T he D e v o n ia n s t r a t i g r a p h y o f C o c h i s e , P im a , S a n t a C ru z C o u n t i e s , A r i z o n a , a n d H id a lg o C o u n ty , New M e x ic o : U n lv . o f A r i z o n a u n p u b l i s h e dm a s t e r ' s t h e s i s , 108 p .
M cK ee, E . D . , 1 9 5 1 . S e d im e n ta r y b a s i n s o f A r i z o n a a n da d jo i n i n g a r e a s : G e o l. S o c . A m erica B u l l . , v . 6 2 ,p . 4 8 1 - 5 0 6 .
M cK enna, J . J . , 1 9 6 6 , B uehm an C anyon P a l e o z o i c S e c t i o n ,Pim a C o u n ty , A r iz o n a : U n lv . o f A r iz o n a u n p u b l is h e dm a s t e r 's t h e s i s , 57 P»
M oore, B. N . , Tolm an, C. P . , B u t l e r , B . S . , an d H e m o n , R .N . , 1 9 4 9 , G e o lo g y o f t h e T u c s o n q u a d r a n g l e , A r i z o n a : U . S . G e o l . S u r v e y , O pen F i l e R p t . , o n f i l e A r i z . B u r . M in e s , T u c s o n , A r i z o n a .
P e i r c e , P . L . , 1 9 5 8 , S t r u c t u r e a n d P e t r o g r a p h y o f p a r t o f t h e S a n t a C a t a l i n a M o u n ta in s : U n lv . o f A r i z o n au n p u b l i s h e d d o c t o r a l d i s s e r t a t i o n , 86 p .
P i l k i n g t o n , H . D . , 1 9 6 2 , S t r u c t u r e a n d p e t r o l o g y o f a p a r t o f t h e E a s t f l a n k o f t h e S a n t a C a t a l i n a M o u n ta i n s , P im a C o u n ty , A r i z o n a : U n lv . o f A r i z o n a u n p u b l i s h e dd o c t o r a l d i s s e r t a t i o n , 120 p .
R a a b e , R . G . , 1 9 5 9 . S t r u c t u r e a n d p e t r o g r a p h y o f t h eB u l l o c k C an y o n -B u eh m an C an y o n A r e a , P im a C o u n ty , A r i z o n a : U n lv . o f A r i z o n a u n p u b l i s h e d m a s t e r ' st h e s i s , 50 p .
R ansom e , F . L . , 1 9 0 3 . G eology o f th e G lobe C opper D i s t r i c t , A r iz o n a : U. S . G e o l. S u rv e y , P r o f . P a p e r 1 2 .
__________ , 1 9 0 4 , T he g e o lo g y a n d o r e d e p o s i t s o f t h e B l s b e eq u a d r a n g l e , A r i z o n a : U . S . G e o l . S u r v e y , P r o f .P a p e r 2 1 .
__________ , 1 9 1 6 , Some P a l e o z o i c s e c t i o n s i n A r i z o n a a n dt h e i r c o r r e l a t i o n : U. S . G e o l. S u rv e y , P r o f .P a p e r 9 8 k .
S h r l d e , A . F . , 1 9 6 1 , Some a s p e c t s o f y o u n g e r P r e c a m b r i a n g e o lo g y i n s o u t h e r n A r i z o n a : U n lv . o f A r i z o n au n p u b l i s h e d d o c t o r a l d i s s e r t a t i o n , 2 3 4 p .
S to y a n o w , A . A . , 1 9 3 6 , C o r r e l a t i o n o f A r i z o n a P a l e o z o i c F o r m a t i o n s : G e o l . S o c . A m e r ic a B u l l . , v . 4 ? ,p . 4 5 9 -5 4 0
56
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■2 -p /a le g
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E f 7 ? //O' Ce 7
J ?
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PLATE I
EXPLANATION
SEDIMENTARY ROCKS
Q U A T E R N A R Y Q al Al l uvl um
IGNEOUS ROCKS
T E R T I A R Y L a m p r o p h y r e Di ke s
METAMORPHIC ROCKS
P O S T - C R E T A C E O U S PK e gC a t a l i n a G n e i s s
P A L E OZ OI C
D M m eD e v o n i a n - M i s s i s s i p p i a n
M a r t i n F o r m a t i o n - E s c a b r o s a L i m e s t o n e U n d i f f e r e n t i a t e d
< •€ aC a m b r i a n
Ab r i g o L i m e s t o n e
C a m b r i a n
B o l s a Q u a r t z i t e
P C dsD r i p p i n g S p r i n g Q u a r t z i t e
Y O U N G E R P R E CAMBRI AN
A P A C H E G R O U P
P- Cds b B a r n e s C o n g l o m e r a t e M e m b e r
<
P - Cp P i o n e e r F o r m a t i o n
F a c i e s
SYMBOLS
C o n t a c t s , d a s h e d w h e r e a p p r o x i m a t e
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p- e dsDrip ping S p r i n g Q u a r t z i t e
Y O U N G E R P R E C A M B R I A N
A P A C H E G R O U P
P- Cds b B o r n e s C o n g l o m e r a t e M e m b e r
<
p-ep P i o n e e r F o r m a t i o n
Fa c i e s
SYMBOLS
C o n t a c t s , d a s h e d w h e r e a p p r o x i m a t e
F a u l t s , d a s h e d w h e r e a p p r o x i m a t e
U, u p t h r o w n s i d e D , d o w n t h r o w n
T h r u s t F a u l t
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2 5 © S t r i k e a n d d i p o f b e d s , h o r i z o n t a l
7
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GEOLOGIC MAP
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PIMA COUNTY, ARIZONAS C A L E 1 : 5 4 0 0
5 0 0 _ _ _ _ _ _ _ _ 0 ____________ 5 0 0 _________ 1 0 0 0 _ _ _ _ _ _ _ _ 1 5 0 0 _________ 2 0 0 0 Ft ,I E— I l— T \ i t i _ J
C O N T O U R I N T E R V A L 8 0 F E E TT O P O G R A P H Y FROM U. S. G E O L O G I C A L S U R V E Y B E L L O T A R A N C H Q U A D R A N G L E , 1 9 5 7
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A P P R O X I M A T E ME A N
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• x x
P K c g L i m e s t o n eF o c i e s _ _
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S c h i s t o s eF a c i e s
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A P P R O X I M A T E M E A N
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Jon R Broderick 1 9 6 5 - 6 6
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PLATE I
o
Q U A T E R N A R Y
T E R T l A R Y
P O S T - C R E T A C E O U S
P A L EOZOI C
Y O U N G E R P R E CAMBRI AN
A P A C H E G R O U P
UD
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©
EXPLANATION
SEDIMENTARY ROCKS
Al l uvl um
IGNEOUS ROCKS
L a m p r o p h y r e Di ke s
METAMORPHIC ROCKS
C a t a l i n a G n e i s s
D e v o n i a n - M i s s i s s i p p i a n
Ma r t i n F o r m a t i o n - E s c a b r o s a L i m e s t o n e
C a m b r i a nAb r i g o L i m e s t o n e
C a m b r i a n
B o l s a Q u a r t z i t e
D r i p p i n g S p r i n g Q u a r t z i t e
P- Gdsb B a r n e s C o n g l o m e r a t e M e m b e r
P i o n e e r F o r m a t i o n
G n e i s s i c F a c i e s
SYMBOLS
C o n t a c t s , d a s h e d w h e r e a p p r o x i m a t e
F a u l t s , d a s h e d w h e r e a p p r o x i m a t e
U, u p t h r o w n s i d e D , d o w n t h r o w n
T h r u s t F a u l t
S a w t e e t h o n u p p e r p l a t e
S t r i k e a n d d i p o f b e d s , h o r i z o n t a l
S t r i k e a n d d i p o f f o l i a t i o n
a n d p l u n g e o f l i n e a t i o n
5 0 0
GEOLOGIC MAP
OF THE
PIETY HILL AREA
PIMA COUNTY, ARIZONAS C A L E | : 5 4 0 0
5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 Ft ,
C O N T O U R I N T E R V A L 8 0 F E E TT O P O G R A P H Y FROM U. S. G E O L O G I C A L S U R V E Y B E L L O T A R A N C H Q U A D R A N G L E , 1 9 5 7
Geology By
Jon P. Broderick 1 9 6 5 - 6 6
A P P R O X I M A T E ME A N
A t t i t u d e o f a x i s a n d a x i a l p l a n e o f d r a g f o l d s
S m a l l p r o s p e c t p i t
D r a i n a g e , i n t e r m i t t e n t s t r e a m s
£ < ? ? ? / / f 6 7
U n d i f f e r e n t i a t e d
s i d e
b e d s
D E C L I N A T I O N , 1 9 5 7