Ž . Lithos 46 1999 367–392 Emplacement, petrological and magnetic susceptibility characteristics 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, Brazil b Instituto Superior de Correlacion Geologica, UniÕersidad Nacional de Tucuman, Miguel Lillo, 205, San Miguel de Tucuman 4000, ´ Argentina c 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 NE Ž . 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 was probably the major mechanism of emplacement. Textures reveal that, in many cases, epidote underwent partial dissolution by 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 or near-solidus K-feldspar aggregates, which probably grew much faster than epidote dissolution, preventing complete resorption of epidote by the melt. Al-in-hornblende barometry indicates that, in most cases, amphibole crystallized at P G5 kbar. Kyanite-bearing thermal aureoles surrounding plutons that intruded low-grade metamorphic rocks in NE Brazil support Ž pluton 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 are 20 – 24 27 – 30 in epidotes of plutons in which hornblende solidified under P -5 kbar. The percentage of corrosion of individual epidote crystals included in plagioclase in high-K calc-alkalic granitoids in NE Brazil, emplaced at 5–7 kbar pressure, yielded estimates of magma transport rate from 70 to 350 m year y1 . Most of these plutons lack Fe–Ti oxide minerals and Fe q3 is Ž . mostly associated with the epidote structure. Consequently, magnetic susceptibility MS in the Neoproterozoic granitoids in NE Brazil, as well as Early Palaeozoic plutons in Argentina and Late Palaeozoic plutons in Chile, is usually low Ž y3 . Ž . -0.50 =10 SI , which is typical behavior of plutons which crystallized under low f O ilmenite-series granitoids , 2 Ž . Ž . although Fer Fe qMg ratios in hornblende 0.40–0.65 indicate crystallization under high f O . Mesozoic to Tertiary 2 calc-alkalic plutons in Chile, however, exhibit iron oxide minerals and MS values )3.0 =10 y3 SI, typical of magnetite- ) Corresponding author. E-mail: [email protected]; [email protected]1 E-mail: [email protected]. 2 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
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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-
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 .´ ´ ´
( )A.N. Sial et al.rLithos 46 1999 367–392370
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
( )A.N. Sial et al.rLithos 46 1999 367–392 371
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-
( )A.N. Sial et al.rLithos 46 1999 367–392372
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.
( )A.N. Sial et al.rLithos 46 1999 367–392 373
( )A.N. Sial et al.rLithos 46 1999 367–392374
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
˜opaques. 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
˜Agustin, Narvaez, Nunorco–Sanogasta, Copacabana˜ ˜and 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
( )A.N. Sial et al.rLithos 46 1999 367–392 375
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,
.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 .
( )A.N. Sial et al.rLithos 46 1999 367–392376
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
( )A.N. Sial et al.rLithos 46 1999 367–392 377
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
.
( )A.N. Sial et al.rLithos 46 1999 367–392378
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.
( )A.N. Sial et al.rLithos 46 1999 367–392 379
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,
( )A.N. Sial et al.rLithos 46 1999 367–392380
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
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-
( )A.N. Sial et al.rLithos 46 1999 367–392 381
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
( )A.N. Sial et al.rLithos 46 1999 367–392382
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
.
( )A.N. Sial et al.rLithos 46 1999 367–392 383
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
( )A.N. Sial et al.rLithos 46 1999 367–392384
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
( )A.N. Sial et al.rLithos 46 1999 367–392 385
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.
( )A.N. Sial et al.rLithos 46 1999 367–392386
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-
( )A.N. Sial et al.rLithos 46 1999 367–392 387
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
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nodi
orit
eto
tona
lite
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c-al
kali
c0.
7062
712
y3.
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y3.
812
1.4
Ž.
pre-
And
ean
Ž.Ž
.Ž
.Ž
.S
outh
ern
Coa
stal
bath
olit
hS
anto
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ingo
308"
15R
b–
Sr
13G
rano
dior
ite
toto
nali
tean
dgr
anit
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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
( )A.N. Sial et al.rLithos 46 1999 367–392388
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
6.0
675
to70
025
to26
Mac
urur
eq
10.0
0.20
Am
phib
olit
efa
cies
5.0
to5.
565
5to
680
20to
24L
ate
coll
isio
nal
´6.
0to
6.5
660
to67
0
()
BA
rgen
tina
Taf
iM
egaf
ract
ure
q10
.00.
30G
reen
schi
stto
Hor
nble
nde-
free
Hor
nble
nde-
free
23to
24co
llis
iona
lam
phib
olit
efa
cies
0.13
Ž.
Fam
atin
aG
eolo
gica
lS
yste
m12
.0A
mph
ibol
ites
faci
es6.
5to
7.5
1667
0to
680
27to
28In
ner
Cor
dill
eran
Ž ort
oam
phib
olit
es,
mag
mat
icar
c.
mic
asch
isti
sm
igm
atit
esŽ
.O
rtoa
mph
ibol
ite
5.0
1666
0to
680
Ž.
Am
phib
olit
efa
cies
5.5
to6.
516
680
to69
0A
mph
ibol
ite
faci
esŽ g
arne
t–bi
otit
e–gn
eiss
es, .
amph
ibol
ite
and
mar
ble
()
CC
hile
Hig
hA
ndes
Cor
dill
era
0.30
Gne
isse
sof
the
Chi
leni
a4.
5to
5.5
645
to65
523
to24
Com
pres
sion
alsu
bduc
tion
Ž.
pre-
And
ean
Ter
rane
accr
eted
toG
ondw
ana
duri
ngL
ate
Dev
onia
nor
Ear
lyC
arbo
nife
rous
Sou
ther
nC
oast
alba
thol
ith
8.0
to13
.0G
reen
schi
st4.
0to
4.5
660
to68
0C
ompr
essi
onal
subd
ucti
onŽ
.pr
e-A
ndea
nto
amph
ibol
ite
faci
esN
orth
Pat
agon
ian
bath
olit
h50
.0L
owgr
ade
5.0
to6.
065
0to
660
Intr
a-ar
cst
rike
slip
faul
tŽ
.Ž
.A
ndea
nm
etas
edim
enta
ryro
cks
Liq
uine
-Ofq
uiF
ault
Zon
e˜
For
note
sto
Tab
le3
see
next
page
.
( )A.N. Sial et al.rLithos 46 1999 367–392 389
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 .
( )A.N. Sial et al.rLithos 46 1999 367–392390
.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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