n plomosa mountains geologic map azgs...
TRANSCRIPT
Qal
Qal
Qal
Qoal
Qoal
Qoal
Qoal
Qoal
Qeol
Qeol
Qeol
Ns
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Nv
Nv
Nv
Nv
Nv
Nv
Nv
Nv
Nv
Nv
Nv
TXg
TXg
TXg
TXg
TXg
TXg
TXg
KXgn
Nd
Nd
Nd
Nd
KXgn
KXgn
KXgn
KXhg
KXgn
KXhg
KXhg
KXhg
MzPzq
Nica
Nic
Nic
Nica
Nic
Nic
Nica
Nic
Nic
Nic
MzPzs
MzPzs
MzPzs
MzPzs
MzPzs
MzPzs
Ncgr
Ncgs
Ncgt
PlQcgm
PlQcgs
PlQcgs
K osPG
K osPG
K osPG
K osPG
K amPG
K amPG
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DU
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27
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26
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1
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1334
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21
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1813
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2620
13 13
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32
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30
13
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1614
10
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23
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65
16
24 80
10
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162610
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8
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913
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3
3
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4441
5766
7
8
153
219
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18
25
12
17
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21
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12
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13
83
27
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56
10
1617
26
8 41
435
1223
2425
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32
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7
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1916
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2121
1818
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31
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A’
B’
C’
D’
E’
A
C
D
E
B
0217-P47
15-5-P9
0217-P43
1015-P57
1016-P145
0316-P80a0316-P80b
0316-P81a0316-P81b
0316-P710316-P71x
0217-P470217-P47
1116-P12
114°
6’0”
W
114°
5’0”
W
114°
4’0”
W
33°56’0”N
33°55’0”N
33°54’0”N
33°53’0”N
33°52’0”N
33°51’0”N
114°
6’0”
W
114°
7’0”
W
114°
8’0”
W11
4°8’
0”W
33°51’0”N
33°52’0”N
33°53’0”N
33°54’0”N
33°55’0”N
33°56’0”N
326000326000
324000 324000
322000 322000
320000 320000
318000 318000
316000 316000
1840
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Elev
atio
n (m
)
(NE) A’A (SW)
Qoal
TXgNic MzPzq
K osPG
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0
Elev
atio
n (m
)
(NE) B’B (SW)
Qoal Ns
TXgKXgn
KXgn
KXhgNic
Nic
Nic
K osPG
K amPG
K osPG
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0
Elev
atio
n (m
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(SE) C’C (NW)
Qoal TXgMzPzqNic
Nic
K osPG
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Elev
atio
n (m
)
(SE) D’D (NW)
QoalMzPzs
TXg
KXgnNicK osPG
K amPG
500
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Elev
atio
n (m
)
(SE) E’E (NW)
Nv
KXgnKXgn
Ncgs Ns
?
Cross-sections through the footwall of the Plomosa detachment fault
Mylonitic foliation form lines
Metachert layers
Plomosa detachment fault
1
1
N
All footwall faults (poles) and slickenlines
Squares = poles to fault planes (with blue contour). e1 = T/P: 227,41Circles = slickenlines (with red contour). e1 = T/P: 048, 41
Fault planes, slickenlines, shortening axes (P) and extension axes (T) of normal faults
N N
n = 10 n = 26
Orocopia amphibolite gneissic foliation Meter-scale fold axes in mylonitic units
Dashed line = average foliation plane (S/D: 037, 52 SE)
n = 53
N
fault planes: n = 13slickenlines: n = 11
Plomosa detachment fault principal slip planes, poles, and slickenlines
Solid lines = measured fault planes (poles = hollow circles)Dashed lines = planes from 3-point solution (poles = hollow squares) Gray line = cylindrical best �t to all poles (S/D: 137, 78.5 SW) Black square = calculated corrugation axis (e3 = T/P: 047, 11.5)
N
n = 95
Barite veins (poles)
Solid line = average plane �t to contour maximum (S/D: 033, 83 SE) Dashed line = average plane �t to e1: (S/D: 030, 80 SE)
N
n = 23
Carbonate veins and carbonate-cemented breccia zones (planes and poles)
Dashed line = average plane �t to e1: (S/D: 018, 76 E)
N
n = 42
Joints (planes and poles)
e1 = T/P 228, 13
1
N
n = 620
All mylonitic foliations (poles)
Dashed line = average foliation plane from e1: (S/D: 116, 10 SW)
1
2
3
NNic
n = 122
Mylonitic foliations in unit Nic (poles)
Solid line = cylindrical best �t. e3 = T/P: 139, 08Dashed line = average foliation plane from e1: (S/D: 099, 13 S)
Solid line = cylindrical best �t. e3 = T/P: 228, 19Dashed line = average foliation plane from e1: (S/D: 130, 19 SW)
1
2
3
N
n = 243
1
2
3
NKXgn
n = 214
Mylonitic foliations in unit KXgn (poles)
Solid line = cynlindrical best �t. e3 = T/P: 028, 05Dashed line = average foliation plane from e1: (S/D: 334, 05 NE)
N
n = 566
All mylonitic lineations
e1 = T/P: 220, 09
NNic
n = 122
Mylonitic lineations in unit Nic
e1 = T/P: 211, 11
N
n = 217
Mylonitic lineations in unit
e1 = T/P: 224, 19
NKXgn
n = 210
Mylonitic lineations in unit KXgn
e1 = T/P: 038, 05
1
2
3
NN
n = 32
Dikes (poles)Fault planes and slickenlines of fault zones with copper mineralization (mostly chrysocolla)
Circles = poles of dikes with measured dipsTriangles = poles of dikes assumed to be verticalSolid line = cylindrical best �t e3 = T/P: 132, 02. e1 = T/P: 222, 01Dashed line = average strike (312/132)
Structural data from the footwall of the Plomosa detachment fault
Average extension axis (e1) = 220, 03Average shortening axis (e3) = 108, 83Arrows indicate direction of hanging-wall movement
N
n = 79
Shortening axes (P) and extension axes (T) of all footwall faults with a known slip sense
fault planes: n = 191slickenlines: n = 167
N
Fault planes, slickenlines, shortening axes (P) and extension axes (T) of post-detachment faults
Arrows indicate direction of hanging-wall movement
N
fault planes: n = 13slickenlines: n = 11P&T axes: n = 7
Blue circles = shortening axes (P)Red circles = extension axes (T)
fault planes: n = 22slickenlines: n = 13
Arrows indicate direction of hanging-wall movement Solid: isoclinal/tight, recumbent/inclined folds. Hollow: open, upright folds.Squares: unit KXgn. Triangles: unit Nic. Diamonds: unit K osPG
K amPG
K osPG
K osPG
Mylonitic foliations in unit (poles)K osPG
K osPG
500 m 1 km0no vertical exaggeration
Evan D. Strickland, John S. Singleton, Andrew T.B. Griffin, and Nikki M. Seymour
N
1 km0 0.5
scale 1:10,000contour interval = 10 m
Coordinate reference system: NAD 1983 State Plane Arizona West FIPS 0203Datum: North American 1983Projection: Transverse Mercator
Elevation contours: derived from the digital elevation model USGS NED n34w114 1/3 arc-second 2013 1 x 1 degree ArcGrid, from the National Elevation Dataset.
Geologic Map of the Northern Plomosa Mountains Metamorphic Core Complex, Arizona
Qal
Qoal
Ncg
PlQcg
Qeol
The following upper-plate units are simplified from Spencer et al., September 2014, AZGS, Geologic map of the Bouse and Ibex Peak 7 1/2’ Quadrangles, La Paz County, Arizona - scale 1:24,000. Excludes upper Miocene to Quaternary units, and contacts of some units have been modified.
Ns Miocene sedimentary units - including conglomerates, sandstones, and limestones.
Miocene volcanic units - including hornblende dacite, pyroclastic tuff, and mafic volcanics.
Paleozoic and Mesozoic sedimentary units - including conglomerates, breccias, sandstones, limestones, and quartzites.
Paleoproterozoic to Tertiary granitic and gneissic rocks - including granite, mafic granitoid, gneissic leucogranite, very fine grained diorite, porphyritic biotite granite, and metamorphic rocks.
Nv
MzPzs
TXg
Bedrock contacts Faults
Plomosa detachment fault
Nic
KXgn
MzPzq
KXhg
Nd
Nica
Unit descriptions
Detachment fault
Approximate detachment fault
Approximate fault
Concealed fault
Concealed detachment fault
Alluvium contact
Bedrock contact
Approximate bedrock contact
FaultD
U
Symbols
name
Map trace or projected trend of dikes
Mylonitic foliation strike and dip
Bedding strike and dip
Fault plane dip direction and dip
Detachment plane calculated from 3-point solution
Slickenline trend and plunge
Open fold axis trend and plunge
Isoclinal/tight fold axis trend and plunge
Fold axial trace trend
Location of magnesian actinolite pods
Location of metachert
Location of L-tectonites
Location or contact of uncertainty
Zircon U-Pb geochronology sample
Mylonitic lineation trend and plunge
Horizontal lineation trend
Mylonitic marble foliation strike and dip
Vertical mylonitic foliation strike
Horizontal mylonitic foliation
30
27
64
13
?
27
4
7
72
24
Recent alluvial deposits: Poorly-sorted, unconsolidated, angular to subrounded sediment deposited within unvegetated to lightly vegetated active channels. Sediment is derived from the surrounding bedrock and consists primarily of sand, gravel, and cobbles with minor silt and sparse boulders. Channels are incised 0.5–6 m into bedrock and Qoal.
Aeolian deposits: Unconsolidated, moderately-vegetated, tan-colored, fine- to very-fine sand deposits consisting of ~97% quartz. Most sand is subangular to subrounded and well sorted. This unit is deposited on Qoal, contains scattered colluvium clasts, and has locally accumulated into dunes (typically on the flanks of colluvium mounds or bedrock slopes). Locally a weakly-consolidated, 1–3 mm thick crust is developed a few centimeters beneath the surface.
Older colluvium and alluvium: Mostly paleo-terraces composed of weakly-consolidated, clast-supported colluvium and alluvium with a silt matrix. Clasts are mostly angular to subangular, pebble to cobble in size with sparse boulders, and are commonly imbricated. Terraces are locally >6 m thick where incised by active channels. This unit is moderately vegetated in most areas, but lightly to scarcely vegetated where desert pavement is developed. On the northwest side of the range colluvium and alluvium terraces are locally moderately to well consolidated.
Pliocene to Quaternary(?) sandstone and conglomerate: Concealed mostly beneath Qoal, this unit is exposed within two main drainages in the southernmost map area, and is bounded on its SE side by the mapped NE-striking fault. There are two subunits: PlQcgs: The southernmost subunit, interpreted as the youngest, is a tan-colored, moderately-consolidated silty sandstone, with 5–20% pebble to boulder-sized (up to 30 cm) angular clasts of mylonite. PlQcgm: To the north is a well-consolidated, angular, clast-supported sedimentary breccia. Clasts are mostly pebble to cobble in size, and are sourced from the surrounding mylonitic gneisses (unit KXgn). Compared to Qoal this unit has much more sand and gravel in the matrix (up to 30–40%), is more well consolidated, and clasts have a higher degree of angularity.
Miocene(?) siltstone and conglomerates: Concealed mostly beneath Qoal, this unit is exposed within three drainages just NNE of the unit PlQcg. There are three subunits: Ncgt: The southernmost and youngest subunit is a moderately-consolidated, clast-supported, pale salmon to tan conglomerate, with a silty to sandy matrix. Clasts are mostly subangular, with 50–60% gravel to cobble in size (5–10% of the total volume are cobble clasts >10 cm in diameter), and sparse boulders 0.4–1 m in diameter. Clast lithologies include volcanic (including rhyolitic tuff and vesicular basalt), plutonic (medium-grained granite and diorite), and quartz-pebble conglomerate. This subunit lacks mylonite clasts, but is overlain by a sedimentary breccia consisting entirely of mylonite clasts, likely the same breccia as PlQcgm. Ncgr: The middle subunit is a moderately- to well-consolidated, matrix-supported, reddish-tan conglomerate, with a sand and pebble matrix (~60%), and mostly rounded to subrounded cobble-sized clasts (~30%). Clasts include volcanic and plutonic lithologies similar to those in subunit Ncgt, but also sparse, well-rounded pegmatitic granite boulders (up to 50 cm), and rare mylonite. Ncgs: The oldest and northernmost subunit is a well-consolidated (though fractured and friable) brownish-red and tan siltstone, with bedding ranging from 0.5 mm to ~5 cm thick. Resistant, cobble-sized oblate nodules are common, and sparse 1–2 cm thick manganiferous(?) to ferruginous sandstone layers are present.
Alteration zone: Pale-green to light-gray colored zone within unit Nic, associated with widespread sericitization, chloritization, and pervasive fractures covered in chlorite. This zone is conspicuous only in the northern half of the mapped footwall adjacent to the Plomosa detachment fault.
Miocene dikes: Mostly non-mylonitic NW-striking dikes ~0.2–3 meters wide, which are commonly exposed as linear piles of boulder- and cobble-sized angular clasts. The most common composition is rhyo-dacite with ~35–40% fine-grained phenocrysts of plagioclase (20%), biotite (7%), quartz (7%), and accessory hornblende (~0.5%). The remaining 60-65% groundmass consists primarily of plagioclase laths. Weathered surfaces of non-mylonitic dikes are pitted (0.2–1 cm wide pits). A few of the mapped dikes are phaneritic, mylonitic quartz diorites, which are likely late-stage intrusions of unit Nic.
Miocene intrusive complex: Dominantly appears as a bimodal composition of leucocratic and intermediate dikes, sills, and intrusive bodies. Leucocratic intrusions: fine- to medium-grained, mostly mylonitic biotite tonalite, granodiorite, and uncommon granite, which together make up ~60% of Nic. Commonly has up to 10% 1–2 cm feldspar porphyroclasts. In thin-section, feldspars are typically moderately to strongly sericitized, and plagioclase has very well defined oscillatory zoning and polysynthetic twinning. Biotite is usually partially to completely chloritized. Minor minerals include opaques (up to 5%), local muscovite (1–3%), and accessory apatite, titanite, zircon, and rutile. Intermediate intrusions: very fine- to medium-grained (but locally aphanitic or coarse-grained), hornblende-biotite diorite, with lesser quartz diorite, quartz monzodiorite, and rare quartz monzonite. This unit is typically nonmylonitic to protomylonitic, and hornblende abundance typically ranges from 10–40% (rarely up to 70%). Accessory mineralogy is similar to that in the leucocratic intrusions.The bulk of this unit appears as layered tabular bodies approximately parallel to mylonitic foliation, though nonmylonitic diorite/quartz diorite dikes locally cut across well foliated layers. Alternating layers of leucocratic and intermediate intrusions are commonly ~0.2–2 m thick, though leucocratic intrusions are locally as thin as 0.5–3 cm. In some locations, hornblende quartz diorites appear to have undergone magma mingling, with intermediate and more felsic compositions intermixed as centimeter- to decimeter-scale irregular ribbons. Local high-strain mylonitic hornblende-bearing biotite granodiorite is similar in appearance to the well-foliated gneiss of unit KXgn. This unit is locally highly brecciated and intensely chloritized.
Orocopia Schist: Biotite ± muscovite quartzo-feldspathic mylonitic schist. Mineralogy is dominantly quartz (26–50%) and plagioclase (24–50%), with biotite (8–34%, variably chloritized), locally muscovite (2–20%, generally ~10%), minor opaques (up to 4%, mostly graphite), accessory apatite (up to 1%), rutile, zircon, and local accessory garnet (up to 0.5%). Commonly has 1–5 mm poikiloblastic graphitic plagioclase porphyroblasts, which are dark gray in hand sample, locally with a bluish tint. In some samples a foliation defined by the graphite is preserved within the porphyroblasts. In plane-polarized light, the biotite is typically reddish brown, and rutile needles are common in areas where biotite has retrograded into chlorite. In outcrop this unit is often gray and flaggy, or is more resistant with a reddish-purple tint. The texture is generally homogenous, and the mylonitic foliation (defined by sheared micas and dynamically recrystallized quartz) commonly has a very well developed S-C’ fabric indicative of top-to-NE-directed shear. Mylonitic lineations are defined by quartz ribbons and streaks of mica. Locally the unit contains gray metasandstone layers 10–30 cm wide that have <10% total mica and >60% feldspar. 2–50 cm thick milky quartz lenses locally with up to ~10% feldspar are common throughout the unit.Scattered pods of course-grained green magnesian actinolite, 5 cm to 1.5 m wide, are present in the schist; locally, several smaller pods may be aligned parallel to the trend of mylonitic lineations. ~0.1–2 m-thick layers of actinolite-bearing schist with minor talc and rare talc schist are also present, which commonly include actinolite pods within them. In one location, a 0.5 m-wide tabular body of the actinolite is present.Mylonitic to protomylonitic leucocratic dikes and sills (unit Nic), 3 cm to 2 m thick, are common throughout this unit, but are greatest in abundance and thickness at the intrusive contact with unit Nic. The contact with the unit KXgn is abrupt and primarily marked by the unit .
Orocopia amphibolite (metabasalt?): Medium-grained hornblende amphibolite locally interlayered with Orocopia Schist and leucocratic mylonitic sills (unit Nic). Mineralogy is hornblende (60–80%), plagioclase (10–30%), quartz (~5%), titanite (up to 3%), and accessory opaques, biotite, chlorite, garnet, apatite, and clinopyroxene. Within this unit are abundant ~3–30 cm thick layers of quartzite (metachert), which are locally iscoclinally folded and commonly weathered to a rusty red color, or exposed as clear alternating white and dark-gray layers. The quartzite includes <1 mm wide Mn-rich garnets (2–15%, locally up to 40% in masses), opaque minerals (3–10%), hornblende (≤8%), locally minor actinolite (up to 9%), apatite (≤1%), and biotite (≤1%). The contact with this unit and unit KXgn is folded and varies from gently SE-dipping to subvertical.
Interlayered mylonitic quartzite and marble: Quartzite layers are typically 1–3 m-thick, and are light tan to pale green in color with minor chlorite. Marble layers are typically 0.5 m thick, but may be up to ~2 m thick. The marble is light gray to tan-brown with orangish-brown siliceous layers, mm- to cm-scale foliation, and is locally isoclinally folded. Mineralogy is dominated by calcite with up to 20% tremolite. Most quartzite is intensely fractured, whereas the marble primarily lacks brittle deformation. This unit is pervasively intruded by sills of the unit Nic, particularly in the southern half of the unit. Isolated, discontinuous layers of mylonitic marble exist south of the unit adjacent to the Plomosa detachment fault.
Mylonitic layered gneisses: Most commonly has alternating layers ~3–30 cm thick, composed of hornblende amphibolite, biotite-poor tonalite/granodiorite, and gray to tan-gray, well-foliated and lineated hornblende-bearing biotite tonalite/granodiorite. The well-foliated gneiss commonly appears as several meter-thick packages (locally >10 m), with 1 mm to 1.5 cm-thick layering defined by alternating felsic (up to 50% quartz, 40% plagioclase), and mafic (up to 50% hornblende, 15% biotite) compositions. Amphibolite and hornblende-rich tonalite/granodiorite may be several meters thick, and the amphibolite commonly is boudined or exhibits pinch-and-swell structures. The unit locally includes 1–10 cm thick leucogranitoid layers with recrystallized ribbons of quartz and feldspar. The SW portion of the gneissic unit commonly has an outcrop-scale “salt-and-pepper” appearance as viewed from a distance, which is fine-grained hornblende amphibolite adjacent to leucocratic biotite-poor tonalite/granodiorite, commonly interlayered with the well-foliated gneiss. Minor and accessory minerals of this unit include opaques (0.5–4%), chlorite (1–2%), and titanite (up to 2%), accessory apatite, and local accessory zircon. The unit is dominantly mylonitic within the map area, though locally there are 5–30 cm thick protomylonitic layers with feldspar porphyroclasts up to 4 cm long. Mylonitic lineations are typically defined by stretched quartz, aligned hornblende, and streaks of biotite. The fabric becomes predominantly protomylonitic towards the southern end of the map area, which is ~2 km NNE of a mylonitic front that demarcates the top of the zone of mylonitic fabrics. A nonmylonitic gneiss with a spotted appearance is found in the very SE portion of the unit, on the east side of the mapped NE-striking fault. It has white poikiloblastic plagioclase ~3 mm to 1 cm in diameter and a weakly-developed foliation defined by aligned hornblende and biotite, which is overgrown by randomly-oriented hornblende ≤0.5 cm long. Minor titanite up to 2 mm long and quartz are also present. This nonmylonitic gneiss occurs as several repeated layers that vary from 3–8 meters thick and are laterally continuous for ≥400 m.
Hornblende-rich gneiss: areas within unit KXgn composed mostly of medium-grained hornblende amphibolite (~70–90% hornblende) or hornblende-rich tonalite/granodiorite (~40–50% hornblende). This unit is distinguished from the unit by the presence of gneissic banding, and a lack of quartzite (metachert) layers.
Funding provided by 2016 USGS EDMAP grant G16AC00142
K osPG
K amPG
K amPG
K amPG
Arizona Geological SurveyContributed Map-17-AArizona Geological Survey
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Mylonitic Lineations
Nearest Neighbor Interpolations:Top-NE shear recorded in outcrop or thin section
+/- 20º to 40º from mean NE-SW direction+/- 40º to 90º from mean NE-SW direction
Mylonitic foliations
Strikes of barite veinsStrikes of carbonate veinsCopper mineralization(mostly chrysocolla and malachite)
La PazCounty
Map area
Arizona
200 km
15-5-P9(n=109)
0 200 400 600 800 1000 1200 1400 1600 1800 Ma0 200 400 600 800 1000 1200 1400 1600 1800 Ma
1015-P57(n=122)
0316-P71(n=144)
0 200 400 600 800 1000 1200 1400 1600 1800 Ma 0 200 400 600 800 1000 1200 1400 1600 1800 Ma
0316-P80a(n=110)
0316-P81b(n=111)
0 200 400 600 800 1000 1200 1400 1600 1800 Ma
1016-P145(n=127)
0 200 400 600 800 1000 1200 1400 1600 1800 Ma
Detrital zircon U-Pb age density plots of Orocopia Schist Ages >850 Ma are 207Pb/206Pb ages with <30% discordance. Ages <850 Ma are 206Pb 206/238U ages with <20% discordance.
All xenocrystic ages from intrusive samples(n=246)
0 200 400 600 800 1000 1200 1400 1600 1800 Ma
0 200 400 600 800 1000 1200 1400 1600 1800 Ma
1116-P12(n=160)
Sample name
0316-P80b
0316-P81a
0316-P71x
0217-P16
Granodiorite mylonitic sillNic
22.58 ± 0.55 Ma1 of 8 rejectedMSWD = 2.5
22.49 +0.81/-0.31 Ma2 of 8 rejected
22.71 +0.25/-0.25 Ma1 of 18 rejected
23.10 +0.28/-0.73 Ma1 of 10 rejected
20.45 +0.29/-0.20 Ma2 of 26 rejected
22.68 ± 0.27 Ma1 of 18 rejected
MSWD = 1.8
22.81 ± 0.49 Ma0 of 10 rejected
MSWD = 2.4
20.46 ± 0.15 Ma2 of 26 rejected
MSWD = 1.6
All xenocrystic(Paleogene through Proterozoic ages)
All xenocrystic(Paleogene through Proterozoic ages)
Nic
Nic
Nic
Nica
Nic
Granodiorite mylonitic dike
Granodiorite mylonitic dike
Dioritenonmylonitic
Granodioriteprotomylonitic
Granodioritemylonitic
N 3758338E 769383
N 3757321E 769528
N 3757544E 769283
N 3753950E 769064
N 3752598E 766960
N 3746181E 767928
(2.3 km south of map area)
Rock typeUnit UTM coordinates(zone 11 N)
206Pb/238U ages(<10% discordant)
Zircon U-Pb ages of intrusive samples
Weighted mean age
Tuff-Zirc age
0217-P43
0217-P47