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Ž .Lithos 46 1999 367–392

Emplacement, petrological and magnetic susceptibilitycharacteristics of diverse magmatic epidote-bearing granitoid

rocks in Brazil, Argentina and Chile

A.N. Sial a,), A.J. Toselli b,1, J. Saavedra c,2, M.A. Parada d, V.P. Ferreira a

a NEG-LABISE, Department of Geology, Federal UniÕersity of Pernambuco, Recife, P.O. Box 7852, 50732-970, Brazilb Instituto Superior de Correlacion Geologica, UniÕersidad Nacional de Tucuman, Miguel Lillo, 205, San Miguel de Tucuman 4000,´

Argentinac Consejo Superior de InÕestigaciones Cientıficas, Instituto de Recursos Naturales y Agrobiologia, Apartado 257, Salamanca 37080, Spain´

d Department of Geology, UniÕersity of Chile, Casilla 13518, Correo 21, Santiago, Chile

Received 1 December 1997; accepted 16 July 1998

Abstract

Ž . Ž .Magmatic epidote mEp -bearing granitoids from five Neoproterozoic tectonostratigraphic terranes in Northeastern NEŽ .Brazil, Early Palaeozoic calc-alkalic granitoids in Northwestern NW Argentina and from three batholiths in Chile have

been studied. The elongated shape of some of these plutons suggests that magmas filled fractures and that dyking wasprobably the major mechanism of emplacement. Textures reveal that, in many cases, epidote underwent partial dissolutionby host magma and, in these cases, may have survived dissolution by relatively rapid upward transport by the host magma.In plutons where such a mechanism is not evident, unevenly distributed epidote at outcrop scale is armoured by biotite ornear-solidus K-feldspar aggregates, which probably grew much faster than epidote dissolution, preventing completeresorption of epidote by the melt. Al-in-hornblende barometry indicates that, in most cases, amphibole crystallized at PG5kbar. Kyanite-bearing thermal aureoles surrounding plutons that intruded low-grade metamorphic rocks in NE Brazil support

Žpluton emplacement at intermediate to high pressure. mEp show overall chemical variation from 20 to 30 mol% mole. Ž .percent pistacite Ps and can be grouped into two compositional ranges: Ps and Ps . The highest Ps contents are20 – 24 27– 30

in epidotes of plutons in which hornblende solidified under P-5 kbar. The percentage of corrosion of individual epidotecrystals included in plagioclase in high-K calc-alkalic granitoids in NE Brazil, emplaced at 5–7 kbar pressure, yieldedestimates of magma transport rate from 70 to 350 m yeary1. Most of these plutons lack Fe–Ti oxide minerals and Feq3 is

Ž .mostly associated with the epidote structure. Consequently, magnetic susceptibility MS in the Neoproterozoic granitoids inNE Brazil, as well as Early Palaeozoic plutons in Argentina and Late Palaeozoic plutons in Chile, is usually lowŽ y3 . Ž .-0.50=10 SI , which is typical behavior of plutons which crystallized under low fO ilmenite-series granitoids ,2

Ž . Ž .although Fer FeqMg ratios in hornblende 0.40–0.65 indicate crystallization under high fO . Mesozoic to Tertiary2

calc-alkalic plutons in Chile, however, exhibit iron oxide minerals and MS values )3.0=10y3 SI, typical of magnetite-

) Corresponding author. E-mail: [email protected]; [email protected] E-mail: [email protected] E-mail: [email protected].

0024-4937r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0024-4937 98 00074-7

( )A.N. Sial et al.rLithos 46 1999 367–392368

series granitoids crystallized under higher oxygen fugacity. In NE Brazil, Argentina and Chile, it seems that mEp is morecommon in Precambrian to Palaeozoic ilmenite-series granitoids, while its occurrence in magnetite-series granitoids is morerestricted to Mesozoic to Tertiary granitoids. q 1999 Elsevier Science B.V. All rights reserved.

Keywords: Magmatic epidote; Barometry; Magnetic susceptibility; Magma transport rate; Oxygen fugacity

1. Introduction

Although it has been known since the last centurythat epidote occurs as a magmatic phase in granitic

Ž .rocks Keyes, 1893 , it was only after experimentsŽ .by Naney 1983 , which demonstrated that epidote

could be stable above the solidus in granite andgranodiorite, that its occurrence became a matter of

Ž .petrologic interest Zen and Hammarstrom, 1984 . Itwas accepted by that time that the occurrence of

Ž .magmatic epidote mEp in granitic rocks, at moder-Ž .ate to high pressure 6–8 kbar , was partly a function

of magma composition and partly of depth of em-placement. Other factors controlling naturally occur-ring mEp, however, are still debated, since plutonsof apparently similar chemical composition, crystal-lized at similar pressure, may or may not carry mEp.The combination of recent experiments on epidote

Ž .dissolution kinetics Brandon et al., 1996 and on itsŽstability in granitic melts Schmidt and Thompson,

.1996 suggests that epidote can be a powerful toolfor estimating intrusion conditions such as crystal-lization depth, oxygen fugacity and upward transportrate of melt.

Ž .Brandon et al. 1996 reacted epidote with naturalgranodioritic glass at pressures above and below thestability limit of mEp. At high pressure experimentsŽ .1150 Mpa, 7808C there was no evidence of reac-tion between epidote and the granitic melt, whereas

Ž .low pressure experiments 450 MPa, 7508C resultedin epidote with irregular rims due to dissolution.These authors modelled epidote dissolution in graniticmagmas as a relatively fast process and concludedthat the presence of mEp in calc-alkalic granitoidsimplies fast upward transport probably via dykingrather than diapirism.

Ž .Schmidt and Thompson 1996 studied the stabil-ity of epidote in calc-alkalic magmas and demon-

strated that, at water-saturated conditions and fO2

buffered by NNO, epidote has a wide magmaticstability field in tonalite, with a minimum pressure ofabout 5 kbar. Experiments performed with fO2

buffered by HM show that the stability field ofepidote is enlarged down to 3 kbar pressure.

In this study, mEp-bearing granitoid plutons fromŽ .northeast Brazil, Northwestern NW Argentina and

Chile were selected with the aim of identifying thosefeatures which mEp in diverse mEp-bearing grani-toids have in common and how these features help tounderstand intrusion conditions.

2. Geological setting and petrography

Distinguishing magmatic from secondary epidotein granitoids is not always straightforward. Toachieve this, the textural criteria described by Zen

Ž .and Hammarstrom 1984 including, among others,chemical zonation of epidote, the presence of allan-ite-rich core, embayed contacts with plagioclase and

Ž .quartz, wormy almost myrmekitic contacts, as wellŽ .as chemical criteria Tulloch, 1979 based on the

Ž . Žpistacite Ps content of epidote Ps s molarw 3q Ž 3q .x .Fe r Fe qAl =100 , have been adopted inthe present study. mEp typically has -0.2% TiO2

by weight, whereas secondary epidote replacing bi-Ž .otite has )0.6% TiO Evans and Vance, 1987 . In2

all of the plutons in the present study, modal abun-Ž .dances of mEp are low F5 vol.% .

( )2.1. Northeastern NE Brazil

mEp-bearing granitoids of Neoproterozoic age arewidespread in NE Brazil. They have been identified

( )A.N. Sial et al.rLithos 46 1999 367–392 369

within five Neoproterozoic tectonostratigraphic ter-w Ž . Ž .ranes Serido ST , Cachoeirinha–Salgueiro CST ,´

Ž . Ž .Riacho do Pontal RPT , Alto Pajeu APT and the´

Ž .xMacurure MT ; and belong to calc-alkalic, high-K´calc-alkalic, shoshonitic and trondhjemitic seriesŽ .Ferreira et al., 1997; Fig. 1 . Whole-rock chemical

Fig. 1. Simplified geological map of Northeast Brazil, indicating locations of Neoproterozoic mEp-bearing granitoids, distributed in fiveŽ .tectonostratigraphic terranes I: Serido, II: Cachoeirinha–Salgueiro, III: Riacho do Pontal, IV: Alto Pajeu, and V: Macurure terranes .´ ´ ´


data for these plutons are presented and discussed inŽ . Ž .Sial 1986, 1990 and Sial and Ferreira 1988 .

mEp exhibits four textural relationships in theseŽ .rocks: 1 embayed or in vermicular contact with

Ž .unaltered plagioclase; 2 rimmed by biotite, withŽ .zoned allanite core, 3 enclosing patches of horn-

Ž .blende, and 4 partially enclosed by biotite, in theinterstices of K-feldspar aggregates. All of thesetextural types are found in each of the above-men-tioned series of granitoids, with the exception of thetype 4 which is restricted to the high-K calc-alkalicgroup.

Calc-alkalic mEp-bearing granitoids are found inthe ST, CST, RPT and MT. In the latter two, grani-toids exhibit similar textural relationships and geo-chemical characteristics.

Plutons in the CST intrude low-grade metaŽ . Ž .marine turbidites Fig. 1 , and are typically roundto elongate in shape, containing calcic amphiboleand biotite as the main mafic phases. mEp occurs aslarge crystals, up to 2 mm long, and is substantially

Ž .less abundant when clinopyroxene diopside–saliteis present. This is consistent with experiments by

Ž .Schmidt and Thompson 1996, p. 470 , on water-saturated tonalitic melts, which demonstrate that‘‘melting of epidote above the clinopyroxene-in re-action is directly related to the appearance ofclinopyroxene, that is, with increasing temperaturemodal increase in clinopyroxene is directly propor-

Žtional to modal epidote decrease’’ epidote q.hornblendeqH Osclinopyroxeneq liquid .2

Around two of these plutons, kyanite-bearingblack-spotted thermal aureoles are developed and

Žcharacterized by fine-grained mica foliation Caby.and Sial, 1996 . According to the petrogenetic grid

Ž .of Xu et al. 1994 , the assemblage garnet, kyanite,staurolite, muscovite with Si-3.1, biotite, plagio-clase and quartz observed in these aureoles suggest T

Ž .around 6708C and Ps7.5"0.5 kbar Fig. 2 . Quartzand rutile inclusions in garnet attest to peak P(9

Ž .kbar during garnet growth Bohlen et al., 1983 .Two types of amphibole-rich clots are observed in

the mEp-bearing granitoids in the CST. The firsttype consists of deep-green calcic amphibole aggre-

Ž .gates fractionated from the host magma and thesecond one, which exhibits a fabric, is fine-grained,angular, and up to 15 cm long. This second type iscomposed of actinolitic amphibole, with margins of

Mg-hornblende, and regarded as fragments from thesource picked up by the granodioritertonalite mag-

Ž .mas Sial et al., 1995 . Often, the second type isarmoured by a layer of biotite and amphibole whichprevented further interaction with the host magma.

ŽmEp-bearing calc-alkalic plutons in the ST Fig..1 intruded intermediate to high-grade metasedimen-

tary rocks. These occur as tonalitic dykes and sheetsŽ .modal epidote up to 5% per volume and as elon-gated granodioritic plutons. In the Rio Piranhas base-ment, to the west of the ST, calc-alkalic to high-K

Ž .calc-alkalic plutons 1, 6 and 7, Fig. 1 also containmEp.

Ž .In the MT Fig. 1 , calc-alkalic granodiorites totonalites intruded intermediate-grade metasedimentslocally generating thermal aureoles with stauroliteq

Žcordieriteqgarnet porphyroblasts McReath et al.,.1993 . The calc-alkalic plutons of the MT, late to

post-kinematic according to Davison and SantosŽ .1989 , are similar in textures, mineralogy and geo-chemical characteristics to those of the CST. Themetaluminous Gloria Norte and Coronel Joao Sa˜ ´plutons are among the better known and these con-tain amphibole-rich clots which are similar in size,mineralogy and textures to those described in theCST mEp-bearing plutons.

High-K calc-alkalic metaluminous mEp-bearingŽgranitoids are mainly found in the APT Brejinho,

Tavares, Caldeirao Encantado, Conceicao das Cre-˜ ˜.oulas and Riacho do Ico plutons; Fig. 1 ; and one of´

Ž .these plutons is found in the ST Sao Rafael . They˜intrude gneisses to migmatites in the APT and mi-caschists and gneisses in the ST. These granites

Žconsist of coarse-grained porphyritic K-feldspar.megacrysts in places up to 10 cm long granodiorite

and granite with subordinate quartz monzodiorite toquartz monzonite. mEp accounts for up to 1.5% pervolume. Locally, quartz diorite synplutonic dykes areobserved in outcrops where co-mingling and partialmixing of granodiorite and quartz diorite magmastook place.

mEp was observed in only one shoshonitic mon-zogranite in NE Brazil, at the eastern portion of the

Ž .Teixeira batholith Fig. 1 next to the northern mar-gin of the APT. Among the mafic minerals, ferro-edenite is the main phase which, in places, formsagglomerates. Primary epidote is found as euhedralto subhedral crystals included in biotite or, less


Fig. 2. P–T plot for mineral assemblages in high-pressure, kyanite-bearing thermal aureoles observed around mEp-bearing granodioritesŽ . Ž .e.g., Angico Torto and Santo Antonio Creek plutons in the Cachoeirinha–Salgueiro terrane, NE Brazil Caby and Sial, in preparation .

often, at the borders of amphibole, in a texturalrelationship similar to that described by Zen and

Ž .Hammarstrom 1984 . Some epidote grains have al-lanite cores.

mEp is also observed in two leucocratic trond-hjemitic tonalite to granodiorite plutons: the Palmeirapluton, which intruded gneisses of the APT, and theSerrita pluton that intruded medium-grained

Žmetapelites of the Salgueiro Group in the CST Fig..1 . These plutons exhibit magmatic foliations, and

are almost totally devoid of enclaves. Mafic mineralsoccupy less than 10% per volume and epidote is

Ž .present in low abundance -1% as both primaryand secondary phases.

2.2. NW Argentina

In NW Argentina, mEp-bearing granitoids areŽmainly identified in two regions Toselli et al., 1997;

.Fig. 3 namely in the Pampean Ranges that corre-spond to a series of large N–S trending, tilted faultblocks, composed of Early Palaeozoic granitoids,

Ž .and in the Famatina geological province FGP , lo-cated between the Western and Eastern PampeanRanges, composed of Neoproterozoic to Early Cam-


Fig. 3. Simplified geological map of northwest Argentina, indicating locations of occurrence of Early Paleozoic magmatic epidote-bearing˜Ž .granitoids along the Tafi Megafracture 1: Loma Pelada, El Infiernillo, Nunorco Grande, La Angostura, El indio, and 2: Cafayate and in the˜

ŽFGP 5: Paiman–Copacabana, Cerro Toro, Nunorco, Sanogasta, Cerro Blanco, Paganzo; 6: San Agustin and 7: Serra de los Llanos˜ ˜.batholiths . These two granitic belts are separated by a set of Early Paleozoic cordierite-bearing granitoids.

brian metamorphic rocks overlain by younger marinesedimentary rocks.

In the Pampean Ranges, the NNW-trending TafiŽ .Megafracture Baldis et al., 1975 , active since Early

Ž . Ž .Fig. 4. Geological maps of the three areas of occurrence of calc-alkalic mEp-bearing granitoids in Chile: a High Andes Cordillera, bŽ .Southern Coastal batholith and c North Patagonian batholith.


Palaeozoic times, and of continental extension, is theboundary between the Cumbres de Calchaquies inthe northeast and the Sierra de Aconquija in thesouthwest. Along this megafracture, a group of lateto post-tectonic mEp-bearing calc-alkalic granitoids

˜ŽEl Infiernillo, Loma Pelada, Nunorco Grande, La˜.Angostura and El Indio; Fig. 3 was emplaced into

low- to medium-grade metamorphic rocks. AnotherŽ .mEp-bearing pluton Cafayate pluton , similar in age

and composition, is found to the north of the TafiŽMegafracture Rapela, 1976; Rapela and Shaw, 1979;

.Rapela et al., 1982 .The Infiernillo pluton is essentially homogeneous,

and is composed of granular tonalite cut by a fewdykes of two-mica granodiorite, with mEp and

õpaques. The Loma Pelada and Nunorco Grande˜plutons, although separated by intervening metamor-phic rocks, are perhaps part of a single pluton com-posed of biotite–muscovite granodiorite, and mus-covite granite, with tourmaline-bearing pegmatiticdykes. The Loma Pelada, Infiernillo and Cafayateplutons were emplaced at relatively shallow depths,developing thermal contact aureoles in the surround-ing metasedimentary rocks containing muscovite,staurolite and cordierite. La Angostura tonalite andEl Indio granodiorite plutons were emplaced andcrystallized at a late to post-tectonic stage, forming atypical calc-alkalic series.

mEp has been recognized in the following plutonsof the FGP: Cerro Toro, Paganzo, Cerro Blanco, San

Ãgustin, Narvaez, Nunorco–Sanogasta, Copacabana˜ ãnd Paiman. The granitoid plutons of the FGP in-truded Neoproterozoic–Early Cambrian metamor-phic rocks and have been dated between 500 and 400

Ž .Ma Rapela et al., 1991; Toselli et al., 1997 .˜The Narvaez, Copacabana, Paiman and Nunorco–˜

Sanogasta plutons intruded rather low-grade meta-˜morphic rocks, locally developing andalusite andcordierite hornfels. The Cerro Toro, Cerro Blancoand Paganzo plutons, however, intruded muscovite–cordierite–sillimanite gneisses and migmatites, sug-gesting somewhat deeper emplacement.

The metaluminous characteristics of the mEp-bearing plutons in the FGP, where muscovite isvirtually absent, contrasts with the peraluminouscharacter of the mEp-bearing granitoids in the Pam-pean Ranges. Whole-rock chemical data for mEp-bearing plutons in the FGP and Tafi Megafracture

Ž .are described by Toselli et al. 1997 . All belong tothe calc-alkalic series.

2.3. Chile

Six calc-alkalic, metaluminous, mEp-bearingtonalites and granodiorites have been identified inthe Carboniferous Southern Coastal batholith andHigh Andes Cordillera of central Chile, and, furthersouth in the Cretaceous to Tertiary North Patagonian

Ž .batholith Fig. 4c . The Carboniferous plutons arepetrographically similar to mEp-bearing granitoids inNE Brazil, except that the amount of mEp is lowerand secondary epidote is commonly observed. Theybelong to the calc-alkalic series and a review anddetailed discussion on Pre-Andean to Andean grani-toids, including the plutons in this, study may be

Ž .found in Parada 1990 .Small amounts of mEp are present in the Car-

boniferous granitoids. They occur within plagioclasecrystals or partially surrounded by biotite crystals.Zoned allanite cores in epidote are also observed insome Carboniferous granites of the High AndesCordillera. In the North Patagonian batholith, amphi-bole is commonly replaced by epidote of ambiguousorigin in the 10 Ma-old Queulat quartz diorite whilesmall epidote grains, included in hornblende, showoptical and textural characteristics suggestive of anigneous origin.

3. Amphibole barometry

It has been demonstrated that total Al content ofhornblende in intermediate calc-alkalic rocks varies

Žlinearly with crystallization pressure Hammarstrom.and Zen, 1986 and an empirical barometric equation

was proposed. The empirical calibration of thisbarometer is essentially identical to that of Hollister

Ž .et al. 1987 who reduced the 3 kbar error to 1 kbar.Ž .Johnson and Rutherford 1989 and Thomas and

Ž .Ernst 1990 added experimental calibrations to thisbarometer. Results differ slightly from empirical cal-ibrations and uncertainties were reduced to 0.5 kbar.

Ž .Schmidt 1992 recalibrated this barometer usingepidote-bearing tonalite and made it applicable up to


Ž .13 kbar, while Johnson and Rutherford 1989 usedCO –H O fluid, Schmidt used an H O-saturated2 2 2

fluid.The presence of mEp in calc-alkalic plutons is

Ž .indicative of low CO activity Ghent et al., 19912

and, in principle therefore, the calibration by Schmidtwould be expected to be the most appropriate formEp-bearing plutons. However, other factors con-trolling the chemistry of hornblende should be takeninto account as pointed by Anderson and SmithŽ . Ž .1995 and Anderson 1996 . According to theseauthors, temperature, f H O and total pressure have2

an important influence on mafic silicate mineralchemistry, although fO is the main controlling2

factor. These authors demonstrated that this barome-ter fails by yielding elevated pressures for low-fO2

plutons with iron-rich hornblende coexisting with thefull barometric assemblage. With increasing fO ,2

Ž .the Fer FeqMg ratio for hornblende and biotitemarkedly decreases, independent of the FerMg ratio

Žof the whole rock Anderson and Smith, 1995; An-.derson, 1996 .

The calibration of the Al-in-hornblende barometerŽ .by Anderson and Smith 1995 has been used here

only with the appropriate mineral assemblage toŽ .buffer Al-in-hornblende and when the Fer FeqMg

ratios for hornblende are in the range 0.40–0.65,indicating high fO . Representative microprobe2

analyses of hornblende rims from the main plutonsunder consideration are shown in Table 1. In eachpluton, at least three grains of hornblende wereanalyzed.

3.1. NE Brazil

Pressure estimates for mEp-bearing calc-alkalicgranitoids in the CST, using the Al-in-hornblende

Ž .geobarometer by Anderson and Smith 1995 , are inŽ t .the 5–8.5 kbar range Al varies from 1.81 to 2.48 ,

Ž .including clinopyroxene-bearing plutons Fig. 5 .Unfortunately, no regional P–T data are availablefor metasedimentary rocks near mEp-bearing plutonsin this terrane. The presence of the assemblage kyan-ite–staurolite–garnet in contact aureoles of two plu-tons, however, seems to confirm the Al-in-hornb-lende barometry.

mEp-bearing calc-alkalic plutons in this terraneshare similar petrographic and mineralogical charac-teristics and probably experienced similar crystalliza-tion histories. Therefore, liquidus temperatures at thedepth of emplacement of these CST plutons probablyvaried very little from pluton to pluton. In this way,these plutons, offer a good opportunity to test the

Žapplication of the zircon saturation method Watson.and Harrison, 1983; Watson, 1987 and of estimating

liquidus temperatures. As long as most zircons arenot restitic, xenocrystic or cumulate in origin, andare early-crystallized, these calculations provide theonly information on minimum liquidus temperaturesthat may be comparable to conditions of melt forma-tion.

Liquidus temperature estimates obtained for CSTŽ .mEp-bearing plutons 785–8508C , assuming that all

the requirements of this method are satisfied, whenplotted against corresponding Al-in-hornblende pres-

Ž .sure estimates Fig. 6 show a reasonable alignment.As the magmas under consideration were relativelyhydrated, these temperature estimates appear to berealistic.

In the calc-alkalic mEp-bearing plutons in theMT, the Al-in-hornblende method yielded pressureestimates of 5 and 6 kbar. The metamorphic assem-blages in the host metagreywackes yield poorly-con-strained pressure estimates that suggest maximum

Ž .pressures around 5.5 kbar McReath et al., in press .In the APT, amphibole crystallization pressure

estimates for the mEp-bearing granitoids are in theŽ5–8 kbar range Palmeira trondhjemitic tonalite,

Teixeira shoshonitic monzogranite, high-K calc-alk-alic Brejinho, Tavares, Conceicao das Creoulas and˜

.Caldeirao Encantado plutons . In all of the studied˜plutons of the APT, liquidus temperature estimatesby the Zr saturation method, are in the 785–8508Crange, similar to the temperature range found in the

Ž .CST and MT mEp-bearing plutons Fig. 6 .Al-in-hornblende from amphiboles from four

calc-alkalic and one high-K calc-alkalic mEp-bearingplutons in the ST, yielded pressures in the 3.5–4.5kbar range. Pressures obtained from hornblendes ofthe Sao Rafael pluton, one of the largest mEp-bearing˜granitoids in this terrane, are in agreement withpressure estimates for the nearby metamorphic coun-

Žtry rocks of the Serido Group 3–4 kbar; Lima,´.1987 .


Tab

le1

Rep

rese

ntat

ive

elec

tron

mic

ropr

obe

anal

yses

ofam

phib

ole

rim

sfr

omm

agm

atic

epid

ote-

bear

ing

gran

itoi

dsin

this

stud

y

NE

Bra

zil

Ter

rane

Ser

ido

Cac

hoei

rinh

a–S

algu

eiro

Alt

oP

ajeu

´´

Plu

ton

Sao

Raf

ael

Boa

Ven

tura

St.

Ant

onio

Cre

ekP

enaf

orte

Ped

raB

ranc

aB

reji

nho

Tav

ares

Cri

oula

s˜

Sam

ple

KS

R-3

6K

SR

-4M

BV

-20

SE

R-4

5S

ER

-47

SE

R-7

7S

ER

-86

PB

-33

ITIM

-50

TV

-7T

V-2

RC

C-0

4

Poi

nt3

311

15A

nA

nA

nA

n2

3A

B2R

1R24

R33

R

SiO

45.6

644

.33

44.0

847

.56

44.0

042

.00

44.8

043

.50

42.6

742

.33

42.3

042

.50

44.9

040

.98

42.0

140

.95

2

TiO

0.57

0.66

0.68

0.52

0.80

1.25

1.40

1.00

1.06

0.66

0.40

0.45

0.40

0.58

0.80

0.65

2

Al

O8.

328.

4412

.08

9.72

12.9

012

.55

14.6

012

.40

11.5

512

.02

12.8

013

.80

9.17

11.2

912

.22

12.8

12

3

FeO

17.9

118

.15

13.9

913

.32

18.6

018

.20

14.6

018

.70

17.2

916

.86

20.0

020

.30

18.6

321

.29

21.0

320

.51

MnO

0.41

0.37

0.35

0.33

0.30

0.01

0.35

0.25

0.35

0.41

0.00

0.00

0.46

0.46

0.41

0.44

MgO

11.0

511

.25

10.9

112

.30

9.00

8.90

10.7

08.

208.

468.

138.

407.

809.

787.

547.

497.

07C

aO11

.08

11.6

511

.40

11.5

111

.40

12.7

410

.60

11.2

012

.62

12.6

912

.90

12.3

511

.93

11.5

311

.58

11.5

6N

aO

1.20

1.32

1.73

1.40

1.70

1.00

1.60

1.60

1.44

1.45

0.55

0.45

1.32

1.26

1.23

1.18

2

KO

0.97

0.95

1.50

1.11

1.40

1.45

0.90

1.60

1.71

1.69

1.40

1.40

1.06

1.59

1.75

1.44

2

Tot

al97

.37

97.2

496

.72

96.6

610

0.17

97.9

999

.22

98.2

197

.15

96.2

498

.77

99.0

497

.65

96.5

896

.77

96.6

1

Num

ber

ofca

tion

son

the

basi

sof

23ox

ygen

sS

i6.

597

6.95

66.

510

6.35

06.

460

6.53

06.

508

6.50

76.

860

6.74

06.

380

6.37

06.

795

6.41

96.

400

6.34

9IV

Al

1.40

31.

044

1.49

01.

650

1.54

01.

470

1.49

21.

493

1.14

01.

260

1.62

01.

630

1.25

01.

581

1.60

01.

651

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

Ti

0.07

70.

057

0.09

00.

140

0.15

00.

110

0.12

20.

077

0.14

00.

150

0.04

00.

050

0.04

60.

068

0.09

20.

076

AlV

I0.

736

0.63

10.

740

0.59

00.

940

0.88

00.

584

0.68

40.

350

0.25

00.

660

0.81

00.

429

0.50

10.

593

0.68

72q

Fe

1.75

01.

629

2.28

02.

290

1.76

02.

350

2.20

52.

168

2.28

02.

200

2.52

02.

540

2.31

12.

667

2.71

42.

541

Mn

0.04

40.

041

0.04

00.

000

0.04

00.

030

0.04

50.

053

0.05

00.

050

0.00

00.

000

0.00

00.

000

0.05

30.

058

Mg

2.43

32.

681

1.96

02.

000

2.29

01.

830

1.92

31.

862

2.51

02.

550

1.89

01.

740

2.20

61.

761

1.70

11.

634

5.04

05.

039

5.11

05.

020

5.18

05.

200

4.88

94.

844

5.33

05.

200

5.11

05.

140

4.99

24.

997

5.15

34.

996

Ca

1.82

81.

804

1.79

02.

060

1.63

01.

800

2.06

22.

090

1.83

01.

760

2.08

01.

980

1.89

41.

818

1.89

01.

920

Na

0.50

10.

395

0.48

00.

290

0.44

00.

460

0.42

60.

431

0.33

00.

390

0.15

00.

130

0.38

70.

380

0.39

30.

355

K0.

286

0.20

70.

260

0.28

00.

170

0.30

00.

332

0.33

10.

170

0.18

00.

260

0.26

00.

340

0.38

22.

615

2.40

02.

530

2.63

02.

240

2.56

02.

820

2.85

22.

330

2.33

02.

490

2.37

02.

281

2.20

12.

623

2.65

7


Ž.

Tab

le1

cont

inue

d

NE

Bra

zil

Arg

enti

naC

hile

Ter

rane

Mac

urur

eF

amat

ina

Geo

logi

cal

Sys

tem

Hig

hA

ndes

Sou

thC

oast

alba

thol

iths

Nor

thP

atag

onia

bath

olit

hs´

aa

aP

luto

nG

lori

aN

orte

Cor

onel

Joao

Sa

Cer

roT

oro

Cer

roB

lanc

oS

ierr

ade

Pag

anzo

Gua

nta

San

toD

omin

goC

uest

aQ

ueul

at˜

´

Sam

ple

GN

-04

HJC

S47

6147

5749

7450

0349

4342

9918

31S

D-3

6S

D-4

0C

Q-4

8-B

CQ

-563

8

Poi

ntR

-1R

-205

-R1

05-R

2B

BB

BB

B1B

3B1B

2B1B

3B

SiO

44.2

544

.92

43.9

543

.18

42.9

242

.55

44.3

243

.58

42.2

241

.19

45.6

044

.84

45.5

845

.50

45.5

146

.19

2

TiO

1.33

1.58

0.91

1.14

0.91

0.83

0.94

1.72

1.45

1.15

0.84

0.77

1.13

0.51

1.00

1.03

2

Al

O9.

89.

6210

.811

.17

11.3

212

.24

9.09

9.51

10.0

211

.14

9.37

9.30

8.70

8.03

9.64

10.0

92

3

FeO

16.1

616

.68

14.6

117

.61

18.2

218

.99

17.9

320

.22

21.2

021

.83

18.2

217

.63

16.7

717

.29

16.5

516

.94

MnO

0.35

0.38

0.44

0.38

0.82

0.63

1.04

0.90

0.83

0.83

0.23

0.17

0.48

0.51

0.42

0.37

MgO

11.2

410

.61

9.59

9.33

9.86

9.37

10.5

59.

098.

077.

719.

8710

.73

11.0

111

.15

11.0

010

.46

CaO

11.5

11.5

411

.48

11.5

111

.91

11.4

011

.26

11.7

411

.20

11.5

712

.12

12.2

611

.97

11.9

011

.69

11.4

7N

aO

1.64

1.61

1.37

1.16

1.20

1.12

1.15

1.21

1.32

1.11

0.75

0.76

1.12

1.20

1.14

0.95

2

KO

1.29

1.14

1.38

1.51

0.99

0.95

0.93

1.15

1.22

1.29

0.90

0.90

0.81

0.72

0.45

0.48

2

Tot

al97

.56

98.0

897

.53

96.9

998

.15

98.0

897

.21

98.9

297

.53

97.8

297

.90

97.4

097

.57

99.2

197

.40

97.9

8

Num

ber

ofca

tion

son

the

basi

sof

23ox

ygen

sS

i6.

643

6.70

56.

634

6.56

86.

475

6.43

36.

737

6.57

86.

520

6.38

06.

834

6.74

96.

829

6.88

66.

781

6.83

8IV

Al

1.35

71.

295

1.36

61.

435

1.52

51.

567

1.26

31.

421

1.48

01.

620

1.16

61.

251

1.17

11.

114

1.21

91.

162

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

8.00

08.

000

Ti

0.15

00.

177

0.10

30.

130

0.10

20.

090

0.10

00.

191

0.16

70.

130

0.09

50.

087

0.12

70.

058

0.11

30.

115

VI

Al

0.37

60.

395

0.55

40.

565

0.49

20.

612

0.36

40.

273

0.35

00.

410

0.48

80.

398

0.36

40.

317

0.48

00.

597

2qF

e2.

029

2.08

22.

207

2.24

02.

300

2.39

82.

276

2.56

02.

740

2.86

22.

283

2.21

92.

102

2.18

82.

071

2.09

3M

n0.

045

0.04

80.

056

0.04

90.

107

0.07

40.

127

0.10

90.

102

0.10

20.

029

0.02

20.

061

0.06

50.

053

0.04

6M

g2.

516

2.36

12.

158

2.11

52.

212

2.11

22.

390

2.05

01.

857

1.77

92.

205

2.40

82.

459

2.51

62.

454

2.30

85.

116

5.06

35.

078

5.09

95.

213

5.28

65.

257

5.18

35.

216

5.28

35.

100

5.13

45.

113

5.14

45.

023

5.04

6C

a1.

850

1.84

51.

857

1.87

51.

927

1.84

41.

828

1.90

41.

848

1.94

61.

899

1.84

71.

922

1.92

91.

875

1.81

9N

a0.

449

0.38

80.

362

0.32

20.

347

0.32

30.

337

0.34

60.

390

0.31

60.

291

0.22

20.

325

0.35

20.

331

0.25

6K

0.24

70.

217

0.26

60.

293

0.18

50.

173

0.17

20.

218

0.24

00.

242

0.17

20.

173

0.15

50.

139

0.08

60.

091

2.54

62.

450

2.48

52.

490

2.45

92.

340

2.33

72.

468

2.47

82.

504

2.36

22.

244

2.40

22.

420

2.29

22.

166

All

anal

yses

are

inw

t.%

and

all

are

for

rim

s.a

Ž.

Fro

mR

ossi

deT

osel

liet

al.

1991

.


Fig. 5. P–T plot for mEp-bearing granitoids, including appropriate P and T uncertainties, in NE Brazil, NW Argentina and Chile.Ž .Pressures have been estimated by the Al-in-hornblende Anderson and Smith, 1995 calibration barometer and temperatures by

Ž .plagioclase–hornblende pairs thermometer of Holland and Blundy, 1994 . Dashed line at 5 kbar is for minimum P of epidote stability inŽ .water-saturated tonalitic melts under fO buffered by NNO. Epidote compositional ranges mol% Ps have been added for comparison with2

corresponding pressure ranges.


Ž .Fig. 6. A P –T plot for mEp-bearing granitoids in NE Brazil;Ž . Ž .B for mEp-bearing granitoids in Argentina FGP and Chile.

ŽCurve 1: temperatures obtained from zircon saturation equation TŽ . Ž . .8C sy273q12,900r17.18-ln Zr ; Watson, 1987 , and pres-sures by Al-in-hornblende barometric calibration by SchmidtŽ .1992 . Curve 2: melting curve for excess H O granodiorite2

Ž . Ž .composition Piwinskii and Wyllie, 1968 . The symbol ) is forCST and MT mEp-bearing calc-alkalic granitoids, while symbolŽ .` is for APT high-K calc-alkalic granitoids.

3.2. NW Argentina and Chile

Pressures of amphibole crystallization have beencalculated for some calc-alkalic granitoid plutons inthe FGP that intrude syntectonically intermediate tohigh-grade cordierite–sillimanite-bearing gneissesrmig-matites; namely the Cerro Toro, Cerro Blanco

Žand Sierra de Paganzo tonalites Rossi de Toselli et.al., 1991 . Calcic hornblendes in these plutons show

Al in the 1.60–2.20 range corresponding to pressuresŽ .of solidification of 6.5–7.5 kbar Cerro Toro pluton ,

Ž . Ž4.4 kbar Cerro Blanco pluton and 5.6 kbar Sierra.de Paganzo pluton .

All hornblendes from Chilean granitoids analyzedin this study, are Mg-hornblende. Those from theSanto Domingo pluton in the Southern Coastalbatholith yielded solidification pressures around 4.5kbar, between 5.5 and 6 kbar in the Late Tertiarygranitoids on the North Patagonian batholith, andbetween 4.5 and 5.5 kbar in the High Andes

ŽCordillera batholith Guanta and Pisco-Elqui plutons

. Ž .in the Elqui superunit . The Fer FeqMg ratios inhornblendes are in the 0.43–0.50 range.

In Fig. 6, pressure estimates obtained by horn-blende barometry in this study have been plottedagainst temperatures estimated by the revised cali-bration of the hornblende–plagioclase thermometerŽ .Holland and Blundy, 1994 . Plagioclase–hornblendepairs from Chilean and Argentinian mEp-bearinggranitoids yielded similar temperature ranges,whereas some more mafic granitoids in NE Brazildisplay a higher temperature range. Plutons in NEBrazil, except for those in the ST, were emplaced atpressures equivalent to, or slightly higher than, thosein the FGP in Argentina, whereas Chilean mEp-bearing plutons were emplaced at shallower depths.

4. Epidote chemistry

More than 100 microprobe analyses of epidotewere performed in this study. Cores and rims ofthree grains per pluton were usually analyzed. Com-positional ranges are shown in Fig. 7 and representa-tive core and rim analyses in Table 2.

4.1. NE Brazil

Microprobe data indicate that the mole percent Psof euhedral mEp in the high-K calc-alkalic Sao˜Rafael batholith in the ST lies in a narrow rangeŽ .Ps with some variation of Al and Fe contents27 – 29

from core to margin, indicated by the data in TableŽ .2. The Ps contents Ps are within the range25 – 29

Žreported to be typical for mEp Tulloch, 1979; Vyh-. Ž .nal et al., 1991 . Galindo 1993 reported epidotes in

the Prado pluton with a narrow compositional rangeŽ .Ps , equivalent to that observed in epidotes of28 – 29

the Sao Rafael pluton.˜mEp in calc-alkalic plutons in the CST has Ps

contents between 20 and 24, within the range ofŽ .epidote phenocrysts Ps in high-K calc-alkalic19 – 24

Ždykes of the of the Front Range of Colorado Dawes.and Evans, 1991 which are considered to be un-

equivocally mEp. Some examples described byŽ . Ž .Rogers 1988 , Owen 1991 and Farrow and Barr

Ž .1992 , also lie in this range. Typically, the CSTmEp have lower proportions of the Ps component,


Ž .Fig. 7. Histograms of mole percent mol% Ps in magmatic epidotes from NE Brazil, NW Argentina and Chile. The compositional ranges ofŽ . Ž .epidote from alteration of plagioclase and biotite are from Tulloch 1979 . Johnston and Wyllie 1988, Fig. 5, p. 42 observed values of

20–24, 28 mol% Ps for igneous epidote in rocks and 26–30 mol% Ps, in experiments.

higher Si, Al, Ca, Ti and lower Fe contents thanthose of the ST.

mEp from the shoshonitic Teixeira pluton andtrondhjemitic Palmeira pluton, in the APT, show a

Ž .narrow compositional variation Ps . Values for25 – 28

the trondhjemitic Serrita pluton in the CST are lowerŽ .Ps around 21 .

Ps contents of high-K calc-alkalic plutons in theŽ .APT show broader compositional variation Ps .21 – 29

In the Conceicao das Creoulas pluton, mEp grains˜

are usually zoned, with the Feq3 content increasingfrom core to rim. Ps content varies with epidote

Ž .textural types in the following way: a those in-cluded in feldspars exhibit compositions around Ps ,21

Ž .at their rims; b those surrounding allanite have rimŽ .composition of Ps , and c those rimmed by25 – 27

biotite display rim compositions of Ps .21 – 23

Epidotes in the ST plutons crystallized under adifferent oxygen fugacity buffer than epidotes in theCST plutons. Compositions for this mineral in grani-


Tab

le2

Rep

rese

ntat

ive

elec

tron

mic

ropr

obe

anal

yses

ofep

idot

ein

this

stud

y

NE

Bra

zil

Ter

rane

Ser

ido

Cac

hoei

rinh

a–S

algu

eiro

Alt

oP

ajeu

Mac

urur

e´

´´

aP

luto

nS

aoR

afae

lB

oaV

entu

raE

mas

Tav

ares

Cri

oula

sP

alm

eira

Tei

xeir

aG

lori

aN

orte

Cel

.Jo

aoS

a˜

˜´

Sam

ple

SR

-3M

BV

-23

E-5

7T

V-2

.1R

CC

-16-

AP

-6T

X-1

2G

N-4

H-1

1

Poi

ntC

ore

Rim

Cor

eR

imC

ore

Rim

Cor

eR

imC

ore

Rim

Cor

eR

imC

ore

Rim

Cor

eR

imC

ore

Rim

SiO

37.5

438

.00

38.4

438

.12

37.9

738

.22

38.3

838

.82

38.9

237

.49

38.1

538

.11

38.3

437

.73

38.2

938

.35

38.4

738

.23

2

TiO

0.09

0.05

0.20

0.15

0.10

0.12

––

0.00

0.13

0.09

0.02

0.11

0.01

0.12

0.12

0.14

0.20

2

Al

O22

.16

22.0

224

.33

23.8

023

.82

23.9

125

.67

23.7

725

.02

25.0

123

.26

24.2

23.9

924

.30

24.9

724

.73

26.4

26.6

82

3

Cr

O0.

000.

000.

050.

050.

020.

11n.

d.n.

d.0.

020.

000.

070.

030.

030.

000.

000.

080.

010.

042

3

MgO

0.02

0.00

0.05

0.04

0.07

0.15

0.02

0.02

0.14

0.00

0.00

0.00

0.01

0.00

0.09

0.12

0.03

0.03

CaO

23.3

423

.22

23.8

723

.90

23.8

424

.08

23.8

424

.45

24.1

723

.45

22.4

223

.47

23.1

923

.27

2.53

23.6

623

.71

23.3

2M

nO0.

100.

220.

220.

190.

090.

07n.

d.n.

d.n.

d.n.

d.0.

470.

250.

340.

000.

000.

040.

180.

12F

eO13

.85

13.7

510

.38

10.7

011

.45

11.1

39.

5711

.69

11.2

211

.76

12.9

812

.23

11.4

311

.56

10.5

510

.49

8.55

8.45

Na

On.

d.n.

d.0.

030.

000.

000.

00n.

d.n.

d.n.

d.n.

d.0.

000.

010.

000.

040.

030.

030.

000.

012

KO

0.00

0.00

0.01

0.01

0.00

0.01

0.00

0.00

n.d.

n.d.

0.00

0.00

0.00

0.01

0.00

0.00

0.00

0.01

2

Tot

al97

.11

97.2

997

.60

96.9

697

.36

97.8

097

.48

98.5

598

.37

98.0

397

.42

98.3

297

.44

96.8

797

.58

97.5

997

.53

97.1

0

Num

ber

ofca

tion

son

the

basi

sof

25ox

ygen

sS

i3.

102

3.10

43.

025

3.02

92.

903

2.92

93.

004

3.02

93.

030

2.96

73.

011

2.98

13.

018

2.98

63.

026

3.03

12.

881

2.87

1T

i0.

130.

009

0.00

60.

007

0.00

50.

003

––

––

0.00

50.

003

––

0.00

70.

007

––

Al

2.31

42.

284

2.23

52.

231

2.02

02.

001

2.36

62.

184

2.33

32.

331

2.16

22.

229

2.22

42.

265

2.32

42.

302

2.32

82.

871

Cr

0.00

30.

003

0.00

10.

009

0.00

00.

000

––

––

0.00

30.

001

––

0.00

00.

005

––

Mg

0.00

50.

150.

008

0.01

30.

002

0.00

30.

002

0.00

00.

006

0.00

00.

000

0.00

00.

001

0.00

00.

011

0.01

40.

003

0.00

3C

a2.

067

2.08

62.

035

2.04

51.

934

1.91

81.

999

2.01

71.

993

1.98

81.

895

1.96

71.

956

1.97

31.

992

2.00

41.

902

1.87

6M

n0.

140.

013

0.00

60.

005

0.00

70.

012

––

––

0.01

40.

012

––

0.00

00.

003

0.00

00.

000

Fe

0.70

00.

725

0.68

60.

663

0.80

70.

799

0.62

60.

762

0.62

50.

700

0.85

60.

799

0.75

10.

764

0.63

00.

620

0.53

50.

530

Na

0.00

50.

000

––

––

––

––

0.00

00.

000

0.00

00.

000

––

––

K0.

000

0.00

10.

000

0.00

00.

000

0.00

00.

000.

000

––

0.00

00.

000

0.00

00.

000

––

––

Ps

2324

2323

2828

2127

2224

2827

2724

2121

2018


Ž.

Tab

le2

cont

inue

d

NW

Arg

enti

naC

hile

Taf

iM

egaf

ract

ure

Fam

atin

aH

igh

And

esS

outh

ern

Coa

stal

bath

olit

hN

orth

Pat

agon

ian

bath

olit

h

bP

luto

nC

afay

ate

Infi

erni

llo

Cer

roT

oro

Sie

rra

Chi

cade

Cor

doba

Gua

nta

San

toD

omin

goC

uest

ade

Que

ulat

Sam

ple

CA

F47

-2C

CT

-40

EP

-3G

UA

SD

-1C

Q

Poi

ntC

ore

Rim

Cor

eR

imC

ore

Rim

Cor

eR

imC

ore

Rim

Cor

eR

imC

ore

Rim

SiO

40.5

237

.49

38.0

838

.30

37.4

738

.40

37.7

837

.69

38.0

438

.22

37.6

738

.12

38.0

537

.58

2

TiO

0.09

0.15

0.05

0.20

0.13

0.12

0.13

0.12

0.02

0.00

0.02

0.18

0.04

0.00

2

Al

O22

.44

23.0

123

.73

23.6

822

.74

22.9

922

.58

23.0

323

.96

2370

23.5

323

.60

23.4

724

.09

23

Cr

O0.

060.

020.

000.

150.

000.

12–

–0.

040.

000.

000.

000.

060.

002

3

MgO

0.10

0.00

0.06

0.04

0.11

0.06

0.02

0.05

0.05

0.27

0.09

0.11

0.02

0.00

CaO

22.2

223

.10

23.7

123

.63

23.1

323

.54

23.1

323

.45

23.5

923

.10

23.7

823

.57

23.7

23.5

8M

nO0.

380.

660.

380.

040.

440.

380.

340.

260.

220.

270.

220.

200.

160.

20F

eO10

.99

12.0

111

.41

11.6

912

.80

12.9

513

.53

13.4

811

.80

11.4

712

.02

18.3

011

.93

11.3

4N

aO

0.00

0.19

0.16

0.07

0.18

0.05

––

0.19

0.20

0.04

0.00

0.04

0.12

2

KO

0.00

0.02

0.00

0.00

0.00

0.02

––

0.00

0.00

0.00

0.02

0.00

0.00

2

Tot

al96

.80

96.5

397

.52

97.8

097

.00

97.6

497

.73

97.7

797

.91

97.2

397

.33

98.0

897

.54

97.2

1

Num

ber

ofca

tion

son

the

basi

sof

25ox

ygen

sS

i3.

214

3.02

43.

031

3.03

13.

086

3.03

63.

020

3.00

03.

018

3.04

63.

011

3.02

13.

031

3.00

3T

i0.

005

0.00

90.

003

0.01

20.

008

0.00

70.

010

0.01

00.

001

0.00

00.

001

0.01

10.

002

0.00

0A

l2.

096

2.18

62.

224

2.20

72.

156

2.14

12.

130

2.16

02.

239

2.22

42.

215

2.20

32.

201

2.26

7C

r0.

004

0.00

10.

000

0.00

90.

000

0.00

7–

–0.

003

0.00

00.

000

0.00

00.

004

0.00

0M

g0.

012

0.00

00.

007

0.00

50.

013

0.00

70.

000

0.01

00.

006

0.03

20.

011

0.01

30.

002

0.00

0C

a1.

888

1.99

52.

022

2.00

41.

995

1.99

41.

980

1.98

02.

005

1.97

22.

037

2.00

12.

028

2.04

5M

n0.

025

0.04

50.

026

0.02

70.

030

0.02

50.

020

0.01

00.

015

0.01

80.

015

0.01

30.

011

0.01

4F

e0.

655

0.72

80.

683

0.69

60.

775

0.77

00.

820

0.81

00.

729

0.71

80.

722

0.73

30.

718

0.68

1N

a0.

000

0.00

00.

023

0.01

10.

028

0.00

0–

––

–0.

006

0.00

0.00

60.

019

K0.

030

0.00

20.

000

0.00

00.

009

0.00

2–

––

–0.

000

0.00

20.

000

0.00

0P

s24

2423

2427

2728

2724

2424

2424

23

Ana

lyse

sin

wt.

%.

Tot

alF

em

easu

red

asF

eO.

aŽ

.F

rom

Gal

indo

1993

.b

Ž.

Fro

mB

elen

Per

ezet

al.

1996

.


Žtoids in the ST lie between the Ps and Ps NNO25 33

and HM buffer curves, respectively, according to.Liou, 1973 . In the CST granitoids, epidote crystal-

lized under fO close to the NNO buffer curve.2

In the Macurure terrane, mEp in the Gloria Norte´and Coronel Joao Sa plutons displays compositions˜ ´in the Ps and Ps ranges, respectively.20 – 22 19 – 25

4.2. NW Argentina

Compositions of mEp in the Ps range are23 – 26Žobserved in plutons of the Tafi Megafracture In-

.fiernillo and Cafayate plutons . In the FGP, epidotesfrom the Cerro Toro pluton display compositions

Ž .around Ps while Belen Perez et al. 1996 reported26

compositions in the 26–28 mol% Ps range for epi-dotes in the Sierra Chica de Cordoba pluton, inwhich up to 3% modal epidote is present. All epidotegrains analysed in this study have less than 0.20% byweight of TiO , and are usually chemically zoned2

with rims slightly Fe, Ca enriched in relation to theircores.

4.3. Chile

mEp from the Guanta, Las Terneras and PiscoElqui plutons in the Elqui superunit of the HighAndes Cordillera have compositions in the Ps to20

Ps range, while the Santo Domingo pluton have24

compositions varying around Ps . Epidote related to24

hornblende, in the Tertiary Cuesta de Queulat pluton,has a compositional range from Ps to Ps .20 24

5. Magnetic susceptibility

Ž .Ishihara 1977 proposed that granites can beŽ .subdivided into magnetite series high fO and2

Ž .ilmenite-series low fO with the boundary approx-2

imately between the NNO and QFM buffers. Themagnetite content of rocks is easily determined by

Ž .magnetic susceptibility MS measurements which isa qualitative means of estimating the oxygen fugac-ity of granitoids. In this study, the digital kappameterKT-5, a field portable MS meter was used; measure-ments are reported in SI units. The MS data obtained

from mEp-bearing granitoids from NE Brazil, Ar-gentina and Chile are presented in Fig. 8.

Almost all Neoproterozoic mEp-bearing plutonsin NE Brazil, Early Palaeozoic equivalent granitoids

Žin Argentina Infiernillo, Loma Pelada and Anguinan. Žplutons and Late Palaeozoic in Chile Guanta and

.Las Terneras , in which opaque phases are almostŽ y3 .absent, low MS f0.3=10 SI was recorded. All

of these plutons correspond, in terms of MS, toŽ . Žilmenite-series granitoids of Ishihara 1977 MS

values-3=10y3 SI, the limit between ilmenite-and magnetite-series granitoids of Takahashi et al.,

.1980 . In contrast, granitoids from two plutons inŽ .Chile Pisco Elqui and Santo Domingo and three in

˜Ž .Argentina El Indio, Nunorco and Cerro Toro con-˜tain some rectangular magnetite and have much

Ž y3 .higher MS values 3 to 10=10 SI , departingfrom values obtained in natural and experimentalmEp-bearing granitoids. In granitoids from the Ter-tiary Queulat pluton in Chile primary magnetite isfound in greater amounts; these having the highest

Ž y3 .MS values 40 to 50=10 SI .Magnetite-seriesrilmenite-series volcanic rocks

increase drastically from the Mesozoic to Recent inŽ .Japan Ishihara, 1977 . Schmidt and Thompson

Ž .1996 concluded from experiments that magnetite issignificantly more abundant in epidote-free than inepidote-bearing granitoid intrusions. From these ob-servations and this study, it can be inferred that mEpoften occurs in Precambrian to Palaeozoic ilmenite-series granitoids. Its occurrence in magnetite-seriesgranitoids, with some exceptions, is more restrictedto Mesozoic to Tertiary granitoids, usually in loweramounts as suggested by the experiments.

In this study, most epidote-bearing granitoids ap-parently belong to the ilmenite-series granitoids, andare therefore of low oxygen fugacity magmas. How-ever, epidote and hornblende compositions demon-

Žstrate that oxygen fugacity was higher between NNO.and HM buffers than that required for the ilmenite-Ž .series granitoids between NNO and QFM buffers .

6. Upward magma migration

Epidote textural relationships may provide a clueŽto understanding upward magma transport Brandon


Ž .Fig. 8. Histograms of magnetic susceptibility MS of some mEp-bearing granitoids in NE Brazil, NW Argentina and Chile in this study.There are 12 readings per representative outcrop per pluton.

.et al., 1996 . To illustrate this, mEp-bearing plutonsŽ .from the same terrane APT in NE Brazil, in which

epidote shares similar textural relationships, havebeen chosen to apply the parameters described by


Ž .Brandon et al. 1996 to estimate relative rate ofepidote dissolution in relation to upward magmamigration.

These plutons are elongate in a SW–NE directionand they probably filled fractures opened during thedevelopment of the Brasiliano orogeny in this region.This situation seems to support emplacement bydyking rather than by diapirism. To test this field-based assumption with possible conclusions to bedrawn from epidote textural relationships, four dif-ferent textural situations common to most of theseplutons are shown in Fig. 9.

In Fig. 9a, euhedral mEp has a chemically zonedallanite core and is wholly rimmed by biotite, whilein Fig. 9b, euhedral mEp with an allanite core iswholly rimmed by K-feldspar. In Fig. 9c, subhedral

epidote is included in plagioclase, whereas in Fig.9d, mEp was partially resorbed by the host magma inthat portion not rimmed by biotite.

In relation to Fig. 9a and b, mEp seems to havesurvived dissolution by the host magma because it

Žwas armoured by biotite examples where biotitearmour is, in turn, within interstices formed by K-

.feldspar aggregates are common or by K-feldspar.In both these examples, not only very rapid upwardtransport rate has been responsible for the epidotesurviving dissolution, but probably rapid near-solidus

Žof K-feldspar growth faster than epidote dissolution.rate contributed.

In relation to Fig. 9c and d, the magma transportrate was probably rapid enough to guarantee epidotesurvival to complete dissolution, supporting dyking

Fig. 9. Magmatic epidote textural relationships common to all of the studied high-K calc-alkalic plutons in the Alto Pajeu terrane, NE´Ž . Ž . Ž . Ž .Brazil. a Epidote armoured by biotite; b armoured by aggregates of K-feldspar; c partially resorpted, included in plagioclase and d

partially armoured by biotite, partially resorpted. Abbreviations are: alsallanite, bisbiotite, epsepidote, K-sparsK-feldspar, plagsŽ . Ž .plagioclase and qzsquartz. Dashed lines in c and d are an attempt to reconstruct original shape of epidote crystals indicating how much

of these crystals have been dissolved by the host magma.


as the probable mechanism of upward magma migra-tion for this and the other mEp-bearing plutons inthis area where similar epidote textural relationshipsare present.

Upward migration rates of host magmas can beestimated wherever partially dissolved epidote is ar-

Žmoured by plagioclase epidote and plagioclase cancoexist around 10 kbar in tonalitic magmas as exper-imentally demonstrated by Schmidt and ThompsonŽ .1996, Fig. 2, p. 467 and epidote has grown simulta-neously with K-feldspar at near-solidus conditionsand the corresponding pressure is known from Al-in-hornblende barometry.

In order to estimate the maximum rate of magmaascent in APT high-K calc-alkalic granitoids, thosehaving mEp with resorption textures armoured byplagioclase phenocrysts have been selected. Thedepth of emplacement of these granitoids, estimatedfrom Al-in-hornblende barometry, was about 5–7kbar, which is similar to the minimum pressure foroccurrence of mEp enclosed in K-feldspar. Using the

Žapparent diffusion coefficient of elements Si, Al, Ca.and Fe between tonalitic melt and epidote at 7508C

Ž y17 2 y1. Ž .5=10 m s given by Brandon et al. 1996 ,dissolution inwards of 0.15–0.20 mm of epidote

Ž .crystal margins Fig. 9c and d was completed in40–180 years. Therefore, a transport rate from pres-

Ž .sures around 10 to 6 kbar ;12 km of 70–350 myeary1 is required.

Survival of mEp in hornblende-free granitoidsemplaced in the Pampean Ranges, Argentina, can beexplained by rapid magma upward transport alongthe Tafi Megafracture, active during Palaeozoic gran-itoid emplacement. For mEp-bearing granitoids inthe Famatina geological system, however the possi-bility of rapid upward transport of epidote is notobvious.

Structural control of upward magma migration byfaults is obvious in most Chilean plutons underconsideration. Those plutons in the Elqui superunitare elongated in the N–S direction and their em-placement was controlled by N–S trending faults,and same can be said for the Santo Domingo andCuesta de Queulat plutons. The Mesozoic granodior-ite at Puerto Chacabuco, although sharing similarpetrographicalrchemical characteristics with those inthe Elqui superunit, contains no epidote and it islikely that this magma did not migrate upwards

rapidly enough to prevent a complete dissolution ofepidote.

7. Discussion

ŽSeveral variables rock type, magma series, iso-topic data, MS, host metamorphic grade, mol% Ps of

.epidote, Al-in-hornblende barometry have beenlisted in Table 3 to permit assessment of commonfeatures of mEp occurring in diverse plutons ofvarious tectonic settings, as described in this study.

Epidote is more abundant in plutons of the calc-alkalic and high-K calc-alkalic magma series than inthe trondhjemitic and shoshonitic series. It is alsoshown in this study that low MS is the rule and thatmEp is present in plutons of late collisional, innerarc, compressional subduction and intra-arc slip faulttectonic settings. These plutons intruded low, inter-mediate or high grade metamorphic rocks.

With few exceptions, the absence of iron oxides isa major feature of these plutons. Schmidt and

Ž .Thompson 1996 observed that magnetite is themain Feq3-containing phase above epidote stability,whereas at lower temperatures Feq3 tends to enterepidote. In these plutons, it is probable true thatFeq3 and Ti have been accommodated by epidoteand titanite, respectively, obviating oxide saturation.

The fresh appearance of plagioclase in the plutonsin this study suggests that, in most cases, the rockshave been subjected to minimal weathering and sub-solidus alteration, supporting an igneous origin formost epidotes observed in these plutons. In theGuanta pluton, in Chile, plagioclase is sometimesrather more altered and the amount of secondaryepidote is high, but textural relationships and thecompositions of some epidote grains suggest a mag-matic origin.

Virtually all the textural features common to mEpŽ .described by Zen and Hammarstrom 1984 are pre-

sent in almost all the calc-alkalic and high-K calc-al-kalic plutons of NE Brazil. In some of these plutons,epidote encloses highly embayed hornblende, sug-gesting resorption of the hornblende and subsequentprecipitation of epidote in the magma. In other cases,when the proportion of biotite to hornblende in-creases, the modal abundance of epidote also in-


Tab

le3

Geo

logi

cal

and

geoc

hem

ical

feat

ures

ofre

pres

enta

tive

epid

ote-

bear

ing

gran

itoi

dpl

uton

sin

NE

Bra

zil,

Arg

enti

naan

dC

hile

Ž.

Ž.

Ter

rane

rge

olog

ical

syst

emP

luto

nA

geM

aR

ock

type

Mag

ma

seri

esS

ri´

Nd

TD

MG

a

()

AN

EB

razi

lŽ

.Ž.

Ž.

Ž.

Ser

ido

Sao

Raf

ael

Bat

holi

th57

5U

–P

b1

Por

phyr

itic

qzm

onzo

nite

togr

anit

eH

igh-

Kca

lc-a

lkal

ic0.

7130

y23

.0to

y18

.01

2.73

1´

˜

Ž.Ž.

Ž.

Ž.

Cac

hoei

rinh

a–S

algu

eiro

Boa

Ven

tura

633"

0.9

Rb

–S

r2

Gra

nodi

orit

eto

tona

lite

Cal

c-al

kali

c0.

7059

8y

2.0

toy

1.0

31.

20to

1.40

3E

mas

Ped

raB

ranc

aP

enaf

orte

St.

Ant

onio

Cre

ekˆ

Ž.Ž.

Ž.

Alt

oP

ajeu

Bre

jinh

o63

8"29

Rb

–S

r4

Por

phyr

itic

gran

odio

rite

tom

onzo

gran

ite

Hig

h-K

calc

-alk

alic

0.70

933

4y

3.6

toy

3.5

1.32

to1.

42´

Tav

ares

Por

phyr

itic

gran

odio

rite

Con

ceic

aoda

sC

riou

las

Por

phyr

itic

gran

odio

rite

tom

onzo

gran

ite

˜C

alde

irao

Enc

anta

doP

orph

yrit

icgr

anod

iori

te˜

Pal

mei

raL

euco

crat

icgr

anod

iori

teto

tona

lite

Tro

ndhj

emit

icy

14.6

toy

14.1

2.15

Tei

xeir

aQ

uart

zm

onzo

nite

toqu

artz

syen

ite

Sho

shon

itic

Mac

urur

eG

lori

aN

orte

600

Gra

nodi

orit

eto

tona

lite

Cal

c-al

kali

cy

4.2

1.46

´Ž

.Ž.

Ž.

Cel

.Jo

aoS

a62

7U

–P

b61

8"9.

50.

7083

75

y7.

4to

y4.

85

1.3

to1.

7˜

´Ž

.Ž.

Rb

–S

r5

()

BA

rgen

tina

Ž.Ž.

Ž.

Ž.

Taf

iM

egaf

ract

ure

Caf

ayat

e50

7"13

Rb

–S

r6

Ton

alit

eto

gran

odio

rite

Cal

c-al

kali

c0.

7043

y1.

0to

y3.

86

1.2

to1.

36

Ž.Ž.

Ž.

Infi

erni

llo

422

Rb

–S

r6

Ton

alit

e0.

7069

y3

to0

6Ž

.Ž.

Fam

atin

aG

eolo

gica

lS

yste

mC

erro

Tor

o45

6"14

Rb

–S

r7

Ton

alit

eto

gran

odio

rite

Cal

c-al

kali

c0.

7060

7to

y5.

0to

y7.

01.

7Ž.

0.70

961

8Ž

.Ž.

Cer

roB

lanc

o46

0to

400

Rb

–S

r8

Ž.Ž.

Sie

rra

deP

agan

zo45

7;40

4R

b–

Sr

9Ž

.Ž

.S

ierr

aC

hica

deC

ordo

ba49

4"11

Rb

–S

r10

()

CC

hile

Ž.Ž

.Ž

.Ž

.H

igh

And

esC

ordi

ller

aG

uant

a28

5"1.

5U

–P

b11

Gra

nodi

orit

eto

tona

lite

Cal

c-al

kali

c0.

7062

712

y3.

1to

y3.

812

1.4

Ž.

pre-

And

ean

Ž.Ž

.Ž

.Ž

.S

outh

ern

Coa

stal

bath

olit

hS

anto

Dom

ingo

308"

15R

b–

Sr

13G

rano

dior

ite

toto

nali

tean

dgr

anit

e0.

7057

–0.

7098

y1.

7to

y4.

214

0.9

–1.

514

Ž.

Ž.

pre-

And

ean

14Ž

.Ž

.Ž

.Ž

.Ž

.N

orth

Pat

agon

ian

bath

olit

hC

uest

ade

Que

ulat

14.6

"0.

4R

b–

Sr

15Q

z–di

orit

e0.

7036

715

y4.

915

0.31

815

Ž.

And

ean


Ž.

Tab

le3

cont

inue

d

18Ž

.d

O‰

Mag

neti

cH

ost

met

amor

phic

grad

eA

l-in

-hbl

Han

dB

Ps

epid

ote

Tec

toni

csm

owŽ

.Ž

.Ž

.su

scep

tibi

lity

Aan

dS

T8C

mol

%S

etti

ngy

3Ž

.Ž

.=

10S

IP

kbar

()

AN

EB

razi

lŽ

.S

erid

oq

7.5

toq

8.5

1.0

to4.

0A

mph

ibol

ite

faci

es3.

5to

4.5

1665

0to

700

27to

29L

ate

coll

isio

nal

´Ž m

ica

schi

sts

and

.li

mes

tone

san

dgn

eiss

esC

acho

eiri

nha–

Sal

guei

roq

11.0

toq

13.0

0.15

to0.

40G

reen

schi

stfa

cies

4.5

to6.

565

0to

720

20to

24L

ate

coll

isio

nal

Ž.

mar

ine

turb

idit

es;

kyan

ite-

bear

ing

ther

mal

aure

oles

4.5

to5.

078

0to

810

5.5

to6.

573

0to

740

6.5

to8

725

to73

06.

0to

7.0

730

to76

5A

lto

Paj

euq

10.0

toq

12.0

0.30

to0.

50H

igh-

grad

egn

eiss

es,

6.5

to7.

574

0to

760

20to

24L

ate

coll

isio

nal

´qu

arti

zite

s,an

dsc

hist

s5.

0to

7.0

660

to68

021

and

26to

270.

156.

5to

8.5

650

to71

521

to24

0.20

27to

290.

105.

0to

6.0

680

to70

027

to28

q8.

5to

q9.

55.

5to

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creases. In such cases, the textural relationship ofepidote to biotite suggests that these two phasescrystallized simultaneously, according to the reac-tion: plagioclase q amphibole q liquid ™ biotite qepidote. In the plutons of the Tafi Megafracture inArgentina, these relationships are not so clear andhornblende is virtually absent.

The overall compositional variation of epidoteŽ .20–30 mol% Ps is consistent with values proposed

Ž .by Johnston and Wyllie 1988, Fig. 5, p. 42 , and byŽ .Tulloch 1979 for mEp. There is a tendency, with

some exceptions, for 20–24 mol% Ps compositionsto occur in epidotes from plutons emplaced at, orabove, 5 kbar pressure, and compositions in the27–29 mol% Ps range to occur in plutons emplaced

Ž .at lower pressures Table 3 .Partially resorpted mEp crystals, in a large num-

ber of the studied plutons, suggest that this phasesometimes exceeded its stability field after crystal-lization but survived complete dissolution by thehost melt due to relatively rapid upward melt trans-port. Alternatively, epidote armoured by biotiteandror by near-solidus K-feldspar in high-K calc-al-kalic granitoids, also survived resorption by melt. Inthis latter case, it is assumed that K-feldspar crystal-lized much more rapidly than the time scales for

Ž 2epidote dissolution -10 years, according to Bran-.don et al., 1996 .

8. Conclusions

Our current knowledge of mEp-bearing granitoidsin NE Brazil, Argentina and Chile leads us to thefollowing conclusions.

Ž .1 Typically, Neoproterozoic mEp-bearing grani-toids in NE Brazil have low MS, consistent withexperiments which indicate that iron oxide mineralsand mEp are mutually exclusive. Similar behavior isobserved in Early Palaeozoic plutons in Argentinaand Late Palaeozoic granitoids in Chile, with only afew exceptions in which magnetite is present andMS values higher than 10=10y3 SI are observed.

Ž .2 mEp, recognized on textural grounds, can begrouped into Ps and Ps compositional20 – 23 27 – 29

ranges. Epidotes in the first group crystallizedbuffered by the NNO or in the QFM to NNO rangeat Pf5 kbar or above. In the second group, epidotecrystallized under P between 3 and 5 kbar and fO2

between the NNO and HM range. Al-in-hornblendebarometry, in some cases, yields pressure estimatescorresponding to variation in composition of coexist-ing epidote.

Ž .3 Preliminary estimates of upward migrationrates of high-K calc-alkalic magmas give valuesranging from -100 m yeary1 up to 350 m yeary1.

Ž . Ž4 The absence of epidote in granitoids high-Kcalc-alkalic plutons adjacent to the northern bound-

Notes to Table 3:Ž .A and S: Anderson and Smith 1995 .Ž .H and B: Holland and Blundy 1994 .

Italicized age is from regional geologic consideration.Ž . Ž .1 Ketcham et al. 1995 .Ž . Ž .2 Sial 1993 .Ž . Ž .3 Van Schmus et al. 1995 .Ž . Ž .4 Brasilino et al. 1997 .Ž . Ž .5 Castellana 1994 .Ž . Ž .6 Miller et al. 1991 .Ž . Ž .7 Saavedra et al. 1996 .Ž . Ž .8 Cisterna and Toselli 1991 .Ž . Ž .9 Saal et al. 1996 .Ž . Ž .10 Rapela et al. 1991 .Ž . Ž .11 Pankhurst et al. 1996 .Ž . Ž .12 Mpodozis and Kay 1992 .Ž . Ž .13 Herve et al. 1988 .´Ž . Ž .14 Parada et al. 1998 , this volume.Ž . Ž .15 Pankhurst et al. 1998 .Ž . Ž .16 Rossi de Toselli et al. 1991 .


.ary of the CST that otherwise are identical to mEp-Žbearing plutons described in this study high-K calc-

. Ž .alkalic plutons in the APT suggests that a hostmagma did not migrate upward sufficiently rapidly

Ž .to avoid complete dissolution of epidote or b near-solidus K-feldspar or biotite did not grow suffi-ciently rapidly to allow armouring of epidote before

Ž .its total dissolution, or c that magma did not meetthe required compositional or fO conditions to2

crystallize epidote.

Acknowledgements

This project was partially supported by grantsfrom the Program of Support to the Scientific and

ŽTechnological Development PADCTrFINEP, grant. Žno. 65.930.619-00 and from VITAE B-11487r

.3B001 to which we are thankful. We are alsograteful to Andrew Tulloch and to an anonymousreviewer for comments and suggestions made on anearlier version of this paper. This is the contributionno. 118 of the Laboratory Nucleus for Granite Stud-

Ž .ies NEG , Department of Geology, Federal Univer-sity of Pernambuco, Brazil.

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