U-Pb and Sm-Nd geochronology of the neoproterozoic granitic-gneissic Dom Feliciano belt, Southern Brazil

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U-Pb and Sm-Nd Geochrotiology of the Neoproterozoic Granitic-Gneissic Dom Feliciano Belt, Southern Brazil MARLY BABINSKI’, FARID CHEMALE JR.2, W.R. VAN SCHMUS3, LEO AFtiNEO and LUIZ CARLOS DA SILVA4

HARTMANN

1. Instituto de Geocihcias,

Universidade de Sao Paulo, Cx. Postal 11348, CEP 05522-970, Sb Paulo, SP, Brazil. E-mail: [email protected] 2. Instituto de GeociCncias, Universidade Federal do Rio Grande do Sul, Cx. Postal 15001, CEP 91501-970 Porto Alegre, RS, Brazil 3. Department of Geology, University of Kansas, Lawrence, KS, 66045 USA 4. CPRM/Brazilian Geological Survey, Rua Banco da Provincia, 105, CEP 90840-030 Porto Alegre, RS, Brazil (Received June 1996; accepted April 1997)

Abstract -The Brasiliano Cycle in southern Brazil and Uruguay is represented by three major NE-SW trending geotectonic units: the Vila Nova belt, Tijucas belt and Dom Feliciano belt. The Vila Nova belt is located in western part of Rio Grande do Sul State; its evolution took place between 900 and 700 Ma and it corresponds to one of the few areas with juvenile accretion during the Neoproterozoic in Brazil. The Tijucas belt, situated between the Vila Nova and Dom Feliciano belts, consists of a rift-related Mesoproterozoic (?) volcano-sedimentary sequence which was strongly deformed during the Brasiliano cycle. The Dom Feliciano belt is located along the eastern coast of southern Brazil and Uruguay and is a typical granite-gneiss-migmatite terrane. This belt is a key area for understanding West Gondwana assembly during Neoproterozoic and Early Paleozoic times, because of its direct connection to the Gariep and Damara belts in southern Africa. The present study defines the main tectonic phases of the ca. 600 Ma Dom Feliciano event in the Sb Feliciano belt. U-Pb zircon data for flat-lying gneisses yield ages between 610 i 5 Ma and 616 + 2 Ma, which we believe correspond to the approximate age of thrusting. The strike-slip deformation (main transcurrent phase) is well dated by U-Pb zircon ages for the syn-transcurrent granites (Arroio Moinho Granite, 595 f 1 Ma; Encruzilhada do Sul Granite, 594 2 5 Ma). These results indicate a relatively rapid evolution, from about 620 Ma (upper limit for the age of the gneiss) to 594 Ma (syn-trancurrent granites), for the known thrust related and strike-slip related tectonic phases of the Dom Feliciano belt. Sm-Nd results can be considered in three major groups. The first group (I) includes Brasiliano gneisses, granitoids, and one anorthosite with To, ages of ca. 2.0 Ga and very negative z&600) values. They may represent either direct melting of Transamazonian (Paleoproterozoic) basement or extensive contamination with older material of Paleoproterozoic to Archean age. The second group (II) includes granitoids and gneisses with To, model ages from I .3 I to 1.4I Ga. The third group (III) comprises samples with To, ages between 1.58 to 1.75 Ga. For groups II and III it is clear these rocks or their protoliths represent pre-Brasiliano continental crust. Unlike Group I rocks, groups II and 111granites and gneisses may also contain a small fraction of a juvenile Brasiliano material. However, we have not yet found any sample from the Dom Feliciano belt with a Neoproterozoic To, age and positive a,+, value at 600 Ma that could be considered largely juvenile. Based on results from the Vila Nova belt, in which the main erogenic process developed between 753 and 704 Ma, we conclude that the Vila Nova belt was stable for over 100 Ma before the Dom Feliciano event reached its peak. It is probable that the collage of terranes in the Dom Feliciano belt and the region comprised by the lijucas and Vila Nova belts were assembled during the Dom Feliciano event (ca. 600 Ma). 0 1997 Elsevier Science Ltd Resumo - 0 ciclo Brasiliano no sul do Brasil e Uruguai t representdo por tres unidades geotectonicas principais, corn orienta$io NE-SW Cinturb Vila Nova, Cinturao Tijucas e Cintur8o Dom Feliciano. 0 Cinturiio Vila Nova localiza-se na parte oeste do Estado do Rio Grande do Sul; sua evolu@o ocorreu no interval0 entre 900 e 700 Ma e corresponde a uma das poucas areas, no Brasil, corn acres@o de material juvenil neoproterozoico. 0 Cinturao Tijucas esta situado entre OScinturoes Vila Nova e Dom Feliciano e consiste de uma sequ&ncia vulcano-sedimentar mesoproteroz6ica (?) que foi fortemente deformada durante o ciclo Brasiliano. 0 Cinturb Dom Feliciano, localizado ao longo da costa sudeste do Brasil e Uruguai, B urn tipico terreno graniticogn&issico-migmatftico. Este cinturb t uma area-chave para compreender a colagem do Gondwana Ocidental durante o Neoproteroz6ico e Paleozdico Inferior, ja que possui uma conexb direta corn OScintur8es Gariep e Damara no sul da Africa. 0 presente trabalho define as principais fases tectonicas do evento Dom Feliciano (ca. 600 Ma) no Cinturb Dom Feliciano. Dados U-Pb em zirc&es de gnaisses corn folia@o de baixo ;ingulo fomeceram idades entre 610 2 5 Mae 616 + 2 Ma, as quais correspondem a idade da tect6nica tangential. A deforma@o direcional (principal fase transcorrente) foi datada atraves de idades U-Pb em zircoes de granitos sin-transcorrentes (Granito Arroio Moinho, 595 f I Ma; Granito Encruzilhada do Sul, 594 * 5 Ma). Estes resultados indicam uma evolu@o relativamente rapida, de 620 Ma (limite superior para a idade dos gnaisses) a 595 Ma (granitos sin-trancorrentes). para as fases tectonicas conhecidas (tangential e direcional) no Cintur8o Dom Feliciano. OS dados Sm-Nd podem ser divididos em tr& grupos principais. 0 primeiro (I) inclui gnaisses, granit6ides e urn anortosito brasilianos corn idade modelo To, de ca. 2,0 Ga e valores muito negativos de ~~~(600).Eles podem ter sido gerados a partir da fusao direta do embasamento transamazdnico (paleoproteroz6ico) ou terem sofrido uma intensa contamina@io corn material mais amigo de idade paleoproterozdica a arqueana. 0 Segundogrupo (II) inclui granitoides e gnaisses corn idades modelo To, entm I ,3 1 e I .41 Ga. O.terceiro grupo (III) d constituido por amostras corn idades modelo To, entre I ,58 e I ,75 Ga. OS prot6htos das rochas dos grupos II e 111.claramente, representam crosta continental pm-brasiliana. Porem, difetentemente das rochas do grupo 1, as rochas dos grupos

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II e III podem comer uma pequena proporciio de material juvenil de idade brasiliana. Entretanto. mio foram encontradas Cinturao Dom Feliciano que apresentassem idades modelo To, neoproterozoicas e valores posrttvos de +,,(600).

rochas do

Corn base nos dados obtidos no CinturHo Vila Nova, onde o process0 orogenetico principal ocorreu entrr 7.53 e 704 Ma, C possivel concluir que o Cinturao Vila Nova estava estdvel por mais de 100 Ma antes que o evento Dom Feliciano atingisse o seu pica. fi prowivel que a colagem dos terrenos do Cinturb Dom Feliciano e da regilo compreendida pelos cinturoes Tijucas e Vila Nova ocorreu durante o evento Dom Feliciano (ca. 600 Ma).

GEOLOGICAL

INTRODUCTION The NE-SW trending Dom Feliciano belt is exposed along the eastern coast of southern Brazil and Uruguay (Fig. I), comprising a typical granite-gneiss-migmatite terrane. This belt, ca. 800 km long and 150 km wide, is considered one of the key areas for understanding West Gondwana assembly during Neoproterozoic to Early Paleozoic times, because it is the direct connection to the Gariep and Damara Belts in southern Africa. Several studies have been developed in the Dom Feliciano belt, focusing on its lithologic, structural, geochemical and geocronological aspects (e.g., Silva and Dias, 198 1; Basei, 1985; Frantz and Remus 1986, Fragoso-Cesar et al., 1986; Fragoso-Cesar, 1991; Mantovani et al., 1987; Phillip et al. 1993; Fernandes et al., 1992), and these have been used to support different tectonic models, ranging from a juvenile Brasiliano magmatic arc to Paleo- to Mesoproterozoic crustal material reworked during the Brasiliano orogeny. The purposes of this work are: (a) to present better constraints on the chronostratigraphy of the Dom Feliciano belt using U-Pb zircon analyses on some gneissic. migmatitic and granitic rocks, and (b) to identify the sources of the rocks using Sm-Nd isotopic data. ~.._~

SETTING

The study area is part of the Mantiqueira province (MP; Fig. 1) which consists of Archean to Early Paleozoic units formed during at least three main erogenic cycles, locally called Jequit (Archean), Transamazonian (Paleoproterozoic; ca. 2.1 Ga) and Brasiliano (Neoproterozoic to Early Paleozoic; 0.6-0.5 Ga) (Schobbenhaus et ul., 1984; Almeida and Hasui, 1984). The Mantiqueira province was strongly affected by Brasiliano tectonic activity, which resulted mainly in NE-SW trending structures, multiple granitic intrusions, and reworking of Archean to Transamazonian granite-gneiss terranes and some Mesoproterozoic sequences. The Dam Feliciano belt is part of the southern segment of the Mantiqueira Province (Almeida and Hasui, 1984) and represents a predominantly granitic-gneissicmigmatitic terrane in Uruguay and southern Brazil ( Rio Grande do Sul, RS, and Santa Catarina, SC, states; Fig. 1). To the east it is covered by Mesozoic and younger units. To the west this belt is limited by the NE-SW trending Tijucas belt (Fig. lb), which mainly consists of Mesoproterozoic volcano-sedimentary rocks that were deformed at greenschist to lower amphibolite facies conditions during the

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Fig. I. Geological sketch map of the southern part of the Mantiqueira province (after Chemale et ul.. 1995)

U-Pb and Sm-Nd Geochronology

of the Neoproterozoic

Brasiliano Cycle. In the Tijucas Belt granite-gneissic rocks belonging to Paleoproterozoic to Archean basement are also exposed. The contact between these belts is tectonic, and it is well exposed in the Porto Belo region as the km-wide Major Gercino transcurrent zone (Bitencourt, 1997), a large NE-SW trending strike-slip shear zone. The tectonic framework of Precambrian to Early Paleozoic units in southern Brazil (Fig. 1) includes: (a) Paleoproterozoic granulite complexes (the Santa Maria Chico complex in Rio Grande do Sul and the Santa Catarina complex in Santa Catarina); (b) a Paleoproterozoic granitegreeenstone greenstone terrane in Uruguay; (c) the Vila Nova belt, which is represented by tonalitic to granodioritic gneisses and volcano-sedimentary rocks, a maficultramafic unit, and foliated granites formed between 750 and 700 Ma (Chemale et al., 1995; Babinski et al., 1996); and (d) the late-erogenic to post-erogenic plutonicvolcanic-sedimentary Seival association, which is related to the 600 Ma Dom Feliciano event. Structural studies in the Dom Feliciano belt (FragosoCesar, 1991; Fernandes et al., 1992) defined two main structural events, each one consisting of two or more phases. Event 1 is related to SW-NE verging thrusts that, after strong crustal shortening, evolved to Event 2, a

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Dom Feliciano

Belt, Southern Brazil 265

transpressive deformation which gave rise to NE-SW trending, oblique to strike-slip, shear zones. Such transcurrent shear zones are mostly sinistral in the Dom Feliciano belt (Fernandes er al., 1992), but in some places, as in the Porto Belo region, a dextral displacement has been recognized (Bitencourt, 1997).

Geology of the Dom Feliciuno Belt The Dom Feliciano belt consists mainly of syn-thrust granites and migmatitic gneisses, strike-slip related granites, and late to post-tectonic granites, all formed between 650 Ma and 500 Ma (Basei, 1985; Chemale et al., 1997). Sm-Nd results for composite samples (Mantovani et al., 1987) and Pb-Pb zircon dating in this belt (Chemale et al., 1994b) indicate crustal reworking. The following lithostratigrafic units for the Dom Feliciano belt have been described (Figs. 2 and 3): Chart& gneisses, Capivarita anorthosite, syn-tangential Pinheiro Machado and Camborid complexes, Piquiri syenite, strike-slip related granites, late to post-tectonic granites, post-tectonic Passo da Fabiana gabbros, and post-tectonic Asperezas rhyolite. The Ghana gneisses correspond to paragneisses and orthogneisses metamorphosed in upper amphibolite facies

52"OO

Phanerozoic cover Piquiri Syenite Encruzilhada do Sul suite Sin-transcurrent granites Pinheiro Machado Complex Porongos group Capivarita anorthosite Char3 gneisses Dorsal do CanguGu shear zone Strike-slip shear zone Sample location Highway Town/City

20

I_.-.

km

1

Fig. 2. Geological map of the Dom Feliciano belt in Rio Grande do Sul (after Chemale et al., 1995) with sample locations. A = Piquiri Syenite (RS-2), B = Encruzilhada do Sul Suite (RS-4) C = Capivarita Anorthosite (RS-S), D = Pinheiro Machado Complex (RS-7). E = Pinheiro Machado Complex (RS-9), F = CapIo do Leao Granite (RS-12), G = Arroio Moinho Granite (RS-13). SB = Santana da Boa Vista, PM = Pinheiro Machado, PG = Pantano Grande, PT = Pelotas, CO = Cordilheira Syn-trancurrent Granite, AM = Arroio Moinho Syn-trancurrent Granite

266

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Fig. 3. Geological map of the Santa Catarina schield (after Chemale el al., 199.5) with sample locations. H = Pedras Grandes Suite (SC42), I = Paulo Lopes monzogranite (SC-43). J = Guabimba leucogranite (SC-52), Camborili Complex (SC-54-I). conditions; they are exposed in the northern part of the area shown in Figure 2. Paragneisses are represented by aluminous, talc-silicate and quartzo-feldspathic gneisses with lenses of marbles and amphibolite. Banded granodioritic to tonalitic gneisses comprise the orthogneisses (Frantz et ul., 1984). Although there are no radiometric ages for the Ghana gneisses, field relationships indicate that they are the oldest stratigraphic unit of the Dom Feliciano belt (Frantz et al., 1984, Fernandes et al., 1990). The Capivarita anorthosite (Formoso, 1972) is a 170 km2 massive body within the Encruzilhada do Sul suite (Fig. 2). It has intercalations of banded amphibolite and some xenoliths of talc-silicate rocks (Ghana gneisses) as well as intrusions of Brasiliano granite. Its mineralogy is plagioclase-labradorite (> 90 %) with accessory quartz, sphene, and K-feldspar. It also formed in the upper amphibolite facies with greenschist facies retrograde metamorphism. However, there are no data available for the crystallization age of the anorthosite.

The Pinheiro Machado and Camboriu complexes are exposed in Rio Grande do Sul (Fig. 2) and Santa Catarina (Fig. 3) respectively; they have been interpreted as Brasiliano units with a strong component of older rocks (Chemale et cd., 1994b). These complexes are associations of gneiss, migmatite, and high-K talc-alkaline granite. The gneiss and migmatite show a flat-lying foliation that is mostly folded or cut by younger strike-slip structures. According to Fernandes et al. (1992) and Fragoso-Cesar (1991), this flat-lying fabric formed by a W- to NW-verging thrusting event. These structures formed around 600 Ma, during the Dom Feliciano event (Chemale et al., 1994a). In some places there are small blocks of preBrasiliano tonalitic-trondhjemitic-granodioritic gneiss (Basei, 1985) and supracrustal rocks such as talc-silicates, BIFs, quartzites, and amphibolites (Silva and Dias, 1981). Several NE-elongated granitic bodies displaying deformation related to the younger strike-slip deformation occur along the Dom Feliciano belt; they are commonly referred

U-Pb and Sm-Nd Geochronology

of the Neoproterozoic

to as syn-transcurrent or strike-slip related granites (Fragoso-Cesar, 1991, Fernandes et al., 1992, Phillip ef al., 1993). These granites intrude the Pinheiro Machado and Camboriu complexes, and they display both magmaticflow and solid-state foliation oriented at N40”E and N-S, with a sub-horizontal to horizontal stretching lineation. These bodies may be divided into a high-K talc-alkaline metaluminous suite (e.g. Monte Bonito, Arroio Moinho, QuitCria and Arroio Francisquinho metagranites) and a talc-alkaline to subalkaline peraluminous suite (Cordilheira leucogranites). These rocks have a direct relationship with the development of strike-slip megashear zones such as the Dorsal de Canguqu (Fernandes et al., 1990) and Major Gercino shear zones (Bitencourt, 1997). The Piquiri syenite is a hook-shaped, homogeneous, 130 km2 batholith (Jost et al., 1985) (Fig. 2). It consists of syenite with large K-feldspar phenocrysts (C 5 %), orthoclase, hornblende, and Ca-clinopyroxene; quartz, microcline, plagioclase, biotite, sphene, ilmenite, apatite and zircon occur as accessory minerals. A characteristic igneous banding is present in this unit. There is no radiometric age for the syenite, but it may be late- to posttranscurrent with respect to the Dom Feliciano event. Two of the most expressive granitic suites are the Encruzilhada do Sul suite in Rio Grande do Sul (Fig. 2) and the Pedras Grandes suite in Santa Catarina (Fig. 3). These granitic suites occur as large, irregular bodies intruded into the Pinheiro Machado and Camborid complexes. Petrographically their composition varies from syenite to monzogranite with a dominant syenogranitic facies. In Santa Catarina, the Pedras Grandes suite includes diverse magmatism, including deformed pre- and syn- strike-slip tectonic bodies in addition to the dominant late to posttectonic granites. U-Pb zircon dating of weakly foliated late-tectonic granite yields an age of ca. 600 Ma (Basei, 1985). The Passo da Fabiana gabbros are undeformed, mafic to ultramafic bodies varying from thousands of square kilometers to few square kilometers in area (Fragoso-Cesar et al., 1986) which are exposed near the cities of Pinheiro Machado and Dom Feliciano. A post-erogenic rhyolitic dyke swarm and isolated dykes of the Asperezas rhyolites cut units of the,Dom Feliciano Belt (Fragoso-Cesar, 1991). Sample Locations

and Description

Samples for geochronological studies were collected from several different localities (see Tables 1 and 2, Figures 2 and 3). We chose rocks from the main stratigraphic units of the Dom Feliciano belt in order to get a better approach to the chronostratigraphy as well as some additional information on regional crustal and mantle evolution. Details of their descriptions and locations are given in Appendix 1. ANALYTICAL

PROCEDURES

Isotopic analyses were done in the Isotope Geochemistry Lab, University of Kansas. Zircons were dissolved and

Granitic-Gneissic

Dom Feliciano

Belt. Southern Brazil 267

Pb and U were separated using procedures modified after Krogh (1973, 1982) and Parrish (1987). All samples were total-spiked with a mixed 2osPb-2’“U tracer solution. Isotopic ratios were usually measured in dynamic mode using a VG Sector multi-collector mass spectrometer equipped with a Daly detector for large samples; this mode allows real-time internal calibration of the Daly gain during runs. We used single-collector mode with the Daly detector for smaller samples. Pb samples were analyzed on single Re filaments using silica gel and H,PO,; measured isotopic compositions were corrected for average mass discrimination of 0.12 + 0.05 percent per mass unit for Faraday data and 0.25 percent per mass unit for Daly data. These corrections were determined by analyses of NBS SRM-982 (equal-atom Pb), and monitored by analyses of NBS SRM983 (radiogenic Pb). Uranium was loaded on a single Re filament with H,PO, and a layer of colloidal carbon and analyzed as U+. Uranium fractionation was monitored by analyses of NBS SRM U-500 and averaged 0.1 percent per mass unit for Faraday data and 0.2 percent per mass unit for Daly data. Uncertainties in U/Pb ratios due to uncertainties in fractionation and mass spectrometry for typical analyses are 2 0.5%; in some instances weak signals cause uncertainties to range up to k 2%. Radiogenic 208Pb, 207Pb and 206Pb were calculated by correcting for modern blank Pb and for nonradiogenic original Pb corresponding to Stacey and Kramers (1975) model Pb for the approximate age of the sample. Data were corrected for average blanks of 5-10 pg total Pb and 5-10 pg total U. Uncertainties in radiogenic Pb ratios are typically f 0.1% unless the samples had an unusually low 206Pb/204Pb ratio, in which case uncertainties in the common Pb correction could cause greater uncertainties. Decay constants used were 0.155125 x 10e9 yeai’ for 238U and 0.98485 x 10m9year-’ for 235U (Steiger and Jager, 1977). Zircon data were regressed using the ISOPLOT program of Ludwig (1993). Model 1 regressions were accepted if probabilities of fit were better than 30%; Model 2 regressions were accepted if probabilities of fit were less than 30%. Uncertainties in concordia intercept ages are given at the 2-sigma confidence level. For Sm/Nd analyses, whole-rock powders were dissolved and REE were extracted using the general method of Patchett and Ruiz (1987). Isotopic compositions were measured with a VG Sector multi-collector mass spectrometer. Sm was loaded with H,PO, on a single Ta filament and typically analyzed as Sm+ in static multicollector mode. Nd was loaded with H,PO, on a single Re filament having a thin layer of AGW-50 resin beads and analyzed as Nd+ using dynamic mode. We collected 100 ratios with a 1V 144Nd beam, which typically yields internal precision of 10 ppm. External precision based on repeated analyses of our internal standard was f 30 ppm (2 o) during the course of these analyses; all ‘43Nd/‘44Nd ratios were adjusted for instrumental bias as determined by measurements of our internal Nd standard for periodic adjustment of collector positions; on this basis our analyses of La Jolla Nd average 0.511860 rt-0.000020 (2 0). During the course of these analyses Nd blanks were about 150 pg, with corresponding Sm blanks of 50 pg. Correction for blanks was

M. BABINSKI

Table I U/Pb zircon data ofgramte-gneissic

SIX (mg)

Fraction’ RS-4 Encruzilhada NM(-2) E. I. C M(-2) E, VPY, C M(-l)a E, VPY, C M(-l)b E, YPY, C M(0) E, UPY, F

er al.

samples from Rio Grande do Sul and Santa Catarina States

Concentration? Pb u (ppm) (ppm)

Observed Ratios’ Z”“Pb, ZX>Pb, XK’Pb, ?“7Pb Z’,XPb ‘“JPb

*““Pb/ z ‘H”

Atomic Ratios’ X’,Pb, L3.5”

LWPb, “‘“Pb

“‘“pb, *inu

Age? ZO-iPb, ?“7Pb, L‘5U ‘I,“Pb

do Sul Granite 0.023 0.013 0.026 0.013 0.024

23.95 45.99 44.34 60.64 74.24

228.6 482.4 469.2 670. I 855.3

4.183.7 1.523.2 14,559.j I ,939.9 24.749.6

15.5628 14.5.5.57 16.5224 14.9287 16.5965

5.01 197 4.99962 5.19012 5.94810 7.29340

0.09646 0.08872 0.0876X 0.08617 0.08432

0.81812 0.73118 0.72364 0.71106 0.69638

0 06151 0.05977 0.05986 0.05985 0.05990

594 548 542 533 522

607 557 553 54s 537

657 595 599 598 600

RS-13-H Arroio Moinho Granite NM(- I )a E,l/PY, C 0.132 NM(-1 )b E,VPY,C 0.033 M(- l)a E, VPY,C 0.099 M(-l)b E, PY, F 0.041 M(0) E, UPY,C 0.033 M( I ) E, VPYC 0.027

39 26 22.98 43.76 35.31 53.91 33.10

384.3 235.6 452.6 373.1 550.0 348.4

22.195.5 4.713.7 12,343. I 5.546.5 798.6 1.085.1

15.7179 16.0062 16.4704 16.1097 12.8982 13.8093

7.49441 7.23893 7.3 1922 6.00774 6.39558 5.89054

0.09920 0.09467 0.09386 0.08991 0.09103 0.09020

0.86494 0.78220 0.77318 0.74148 0.75055 0.74085

0.06324 0.05993 0.05975 0.0598 I 0.05980 0.05957

610 583 578 555 562 557

633 587 582 563 569 563

716 601 594 597 596 588

RS-7B Pinheiro Machado NM(-2)el, E, l/Y, C NM(-2)n I, En, UPY, C NM(-2)n2. En, 1. C M(-2) E, I, C M(0) E, VPY, C

Complex 0.098 0.042 0.037 0.073 0.054

35.16 47.24 32.49 38.72 3.5.08

344.9 469.0 324.4 383.5 350.7

16,175.4 20,169.l 13,029.O 12.593-S 4,726.0

16.3415 16.4700 16.3327 16.1790 I5 6143

7.92264 8.00798 X.37956 9.04878 9.59831

0.09987 0.09879 0.09867 0.10023 0.09969

0.83363 0.822 I3 0.82306 0.84207 0.84135

0.06054 0.06036 0.06050 0.06094 0.06121

614 607 607 616 613

616 609 610 620 620

623 616 621 637 647

RS-YA Pinheiro Machado M(-l)E,I.C M(0) E, UPY, C

Complex 0.016 0.030

38.45 47 78

383.8 485.6

3,786.7 7.592.4

15.23.51 15 5754

14.34754 14.62234

0.10300 0.10150

0.88667 0.87673

0.06244 0.06265

632 623

645 630

68’) 696

71.22 40 77 74.62 48.12 61.65 93.13

322.4 231.1 333 I 208.8 431.0 709.8

840.9 488.Y 313.3 932.0 2.424.2 761.5

6 0406 6 7504 5.5874 6.3356 8.5976 6.7934

7.44304 -1.45813 4.23723 5.17580 8.11794 5.68171

0.19472 0.14793 0. I7592 0.19920 0 13416 0.11335

4.062 I4 2.50320 3.37314 3.99860 2.06327 2.04634

0.15110 0 12273 0. I3907 0 14559 0 11154 0.13093

1147 X89 1045 1171 812 692

1647 1273 1498 1634 1137 1131

7361 IYY6 2216 2295 182.5 2111

X-54-I Camhoriti NM(-I) E. PY, F M(-I) E. VPY, C M(-I) E, PY, Met M(0)E/El, UPYSF M(0) E, PY. Met M(2) E. PY, Met

Complex 0.033 0.018 0.034 0.015 0.022 0.027

Notes for Table: 1:NM = nonmagnetic, M = magnetic, numbers in parentheses indicate side tilt used on Frantz separator at I .S amp power; E = hand-picked euhedral 3: I grains; El = hand-picked elongate grains; En = hand-picked euhedral needle grains; I = Colorless; PY = Pale yellow; C = internally clear; F = frosted; SF = slightly frosted; Met = metamict. 2: Total U and Pb concentrations corrected for analytIcal blank. 3: Not corrected for blank or non-radiogenic Pb. 4: Radiogenic Pb correctedfor blank and initial Pb; U corrected for blank. 5: Ages given in Ma using decay constants recommended by Steiger and Jiger (1977).

insignificant for Nd isotopic composition and generally insignificant for Sm/Nd concentrations and ratios. Sm/Nd ratios are correct to within + OS%, based on analytical uncertainties. Extrapolations to T,, for plutonic rocks can have large uncertantainties due to possible REE fractionation during magma genesis if they are much younger than their source terrains, as is the case for ca. 550-600 Ma Brasiliano granites intruding and presumably derived from Archean to Mesoproterozoic (?) basement in parts of the Dom Feliciano belt. As a result, we prefer to use 600 Ma as the main reference time for Nd compositions in the past, since we can extrapolate accurately to that time without worrying about possible fractionation of Sm/Nd during either magma genesis or high grade metamorphism. Because most felsic samples have similar Sm/Nd ratios (Table 2), this approach gives a quick estimate of the age of the crustal sources for volcanic and plutonic rocks, the protoliths of gneisses, or the provenance of sediments. To, results following the model of DePaolo (1981) are also presented in Table 2, but allowances must be made for absolute uncertainties (as opposed to relative precision) of f 0.2 Ga or more due to both analytical and geological factors.

U-PB ZIRCON

RESULTS

Six zircon samples from Rio Grande do Sul and one sample from Santa Catarina were analyzed (Table 1). RS-4 Encruzilhadu do Sul Granite. We analysed five zircon fractions from sample RS-4, the Encruzilhada do Sul granite (Table 1). Four fractions yielded good results which define a normal discordia with an upper intercept of 594 + 5 Ma (Fig. 4). We interpret the upper intercept from the chord defined by the four colinear fractions as the crystallization age of this granite. The one fraction plotting to the right of this upper intercept indicates the presence of xenocrystic zircons that were not completely avoided during preparation of this fraction. This fraction cannot be used to define an age of this inherited component because it was also probably affected by Pb-loss, so no meaningful chord can be drawn through it. RS-13-11: Syn-transcurrent Arroio Moinho Granite. We analysed 6 zircon fractions (Table 1) from RS- 13-11, the monzogranitic phase of the Arroio Moinho granite. Five fractions yielded good analyses which scatter along a normal discordia (Fig. 5). Fractions M(i), M(O), M(-l)a,

U-Pb and Sm-Nd Geochronology

of the Neoproterozoic

Table 2. Sm-Nd isotopic data from Dom Feliciano Belt whole-rock Sample Type

Sample # (KU)

Rio Grande do Sul Samples RS-2 Piquiri syenite RS-4 Syenogranite RS-5 Anorthosite RS-7A Diorite gneiss RS-7B Granodiorite gneiss RS-7C Syenogranite

RS-9A

Migmatiticgneiss

RS-9B RS-12 RS- 13-B

Syenogranite Metaluminous Monzogranite

Nd

Sm

ppm

ppm

91.28 183.26 2.02 33.06 29.60 32.86

14.32 29.26 0.32 6.65 5.54 4.76

Santa Catarina Samples SC-42-l Granodiorite SC-42-B Porphyritic leucogranite SC-43 Porphyritic monzogranite SC-52 Leucogranite SC-54-I Migmatitic gneiss

Dom Feliciano

Belt, Southern Brazil 269

samples 147Sm 144Nd

0.09487 0.09652 0.09434 0.12165 0.11320 0.08753

0.511678 0.511449 0.5 11480 0.511831 0.511928 0.511906

I %‘I

r2o

143Nd 144Nd

+ 8 + 8 *II i 9 + 7 + 8

%d2.1

(0)

(0.6 Ca)

T(DM)” Ga

-18.7 -23.2 -22.6 -15.7 -13.9 -14.3

-10.9 -15.5 -14.8 -10.0 -7.5 -5.9

1.75 2.08 2.00 2.01 1.69 1.37

0.13144

0.511914

+I2

-14.1

-9.1

2.09

24.14 45.03 45.06

3.39 12.53 6.87

0.0848 1 0.16827 0.09217

0.511853 0.512340 0.511995

+ 7 * 9 +8

-15.3 -5.8 -12.5

-6.7 -3.6 -4.5

1.41 2.37 1.31

58.77 18.87 58.69 45.73 57.10

9.98 4.79 9.60 6.38 6.54

0.10264 0.15340 0.09893 0.08436 0.0692 1

0.512032 0.512184 0.511853 0.511142 0.511001

2 8 + 8 & 9 + 9 ~8

-11.8 -8.9 -15.3 -29.2 -31.9

-4.6 -5.6 -7.8 -20.6 -22.2

1.39 2.18 1.58 2.25 2.16

7.44

granite

Granitic-Gneissic

1.62

today = 0.512638 with data normalized to ‘4nNd/‘44Nd = 0.72190. 1. Calculated assuming ““Nd/‘“Nd sNd(0) = ((‘43Nd/‘44Nd[sample, now]/0.512638) - I) x 104. 2. ENd = ((‘4’Nd/““‘Nd[sample, 600 Ma]/‘43Nd/‘“Nd[CHUR. 600 Ma]) - I) x IO“. 3. Based on UlPb zircon ages of Dom Feliciano Event. 4. Calculated following model of DePaolo (198 I).

and M(-1)b define an upper intercept of 595 f 1 Ma if forced through the origin (an age of 593 +- 3 Ma is obtained if not forced through the origin, but it has a negative intercept). This chord includes two analyses of the same fraction, M(-1), and we believe it represents the true crystallization age for this rock. If NM(-1)b is included with the other four analyses, an upper intercept age of 604 f 9 Ma is obtained; this chord is slightly influenced by the second analysis of the least magnetic fraction, NM(-1)b. The first analysis of that fraction, NM(-l)a, shows a significant inherited component, and we believe it is likely that fraction NM(-1)b also contains a much smaller inherited component which causes this regression to yield an age slightly greater than the true crystallization age of 595 Ma.

I

0.104

I

i

I

I

RS-7B and RS-9A: migmatitic gneisses of the Pinheiro Machado Complex. We analysed zircons from RS-7B, a migmatitic gneiss from the Pinheiro Machado complex. Five analyses (Table 1) cluster near concordia at about 620 Ma (Fig. 6a). They all show small effects due to both inheritance and Pb-loss, so that we could not define a unique discordia. The single fraction with the least apparent Pb inheritance, NM(-2)nl, yields a Pb/Pb age of 616 f. 2 Ma, while two other fractions NM(-2)n2 and NM(-2)el (shaded, Fig. 6a) are consistent with an average age of 623 + 2 Ma (regression forced through zero). Two other fractions, M(0) and M(2), show significantly more influence of an inherited component. In any case, since both Pb-loss

Fs 13-11

;

-

Rs4

1I i

T=595+1Ma 0.080

I

1

4 J 0.64

I

/

I

I 0.76

I

I

I

I 0.88

207pb/235u 0.76

0.88

207pb/235u Fig. 4. Concordia Diagram for Encruzilhada do Sul rocks (RS-4). Chord shown is a regression forced through the origin (t = 0) and four co-linear points. The fifth point to the right of the upper end of discordia probably includes an inherited component.

Fig. 5. Concordia diagram for syn-trancurrent Arroio Moinho granite (RS-13-U). The 595 * 1 Ma discordia shown is for the four fractions least likely to have any inheritance. Fraction NM(-1)b was excluded from this regression because fraction NM(-1)a definitely shows inheritance, and NM(-1)b may also have a slight amount of inheritance; if NM(-1)b is included with the other four analyses, an upper intercept age of 604 f 9 Ma is obtained.

270

et al.

M. BABINSKI

natives, and we prefer to set the interval between 610 2 5 Ma and 6 16* 2 Ma as the best estimate for the age of this unit (6 13 + 6 Ma).

0.84

0.80

_~_

0.88

207pb/235U __~_

I

650

I "1

0.097

,I

FLS-7B t

1 /:

’ 0.82

640 /

RS-9A

1

0.84

I

4

/a

SC-54-I: Migmatitic gneiss of Camboriri Complex. We analysed 6 fractions horn SC-54-1, migmatitic gneiss of the Camborili complex (Table 1). Fractions M(O)a. M(O)b, M(-1)a and M(-l)b define a chord with an upper intercept apparent age of 2736 f 90 Ma and a lower intercept apparent age of 544 +- 45 Ma (Fig. 7). These data clearly demonstrate that this gneiss is part of the old basement. However, the age of that basement is not well defined, since Nd data from this locality indicate a Sm-Nd T model age of only 2.16 Ga (Table 2 and see further dz%ssion). The lower intercept age cannot be interpreted as the age of metamorphism because of the possible occurrence of indeterminate Pb-loss mechanisms (combined episodic Pb-loss during the Brasiliano orogeny and diffusive Pb-loss at other times). Fraction NM(-1) plots slightly below the upper end of the chord, which may reflect a slightly greater degree of recent Pb-loss. Fraction M(2) plots significantly below the lower end of chord, which probably reflects greater recent Pb-loss. It is not clear at this time if this rock was an Archean gneiss that experienced Sm-Nd fractionation during the Brasiliano orogeny, a Transamazonian (Paleoproterozoic) rock (as defined by the Sm-Nd model age) that also contains some Archean detrital zircons, or a Transamazonian rock in which the discordia was rotated to an older upper intercept by greater Pb-loss in the fractions with greater inheritance.

.~

0.86

0.88

SM-ND RESULTS

207pb/235U Fig. 6. (a) Concordia diagram for migmatitic gneiss RS-7B from Pinheiro Machado Complex. (b) Concordia Diagram formigmatitic gneiss RS-9A from Pinheiro Machado Complex. Regression line shown is a chord from the origin (t = 0) through the two shaded points. See text for discussion.

Capivarita Anorthosite (RS-5). The whole-rock sample yields a To, age of 2.00 Ga (Table 2), which is interpreted as the age of formation of the anorthosite from a depleted-mantle source. We do not believe that this age represents an inherited Nd signature from older crust, ___.

and inheritance effects are small, there is little doubt that this rock is late Neoproterozoic. We also analysed two fractions of RS9A, a migmatitic gneiss in outcrop RS-9 that is equivalent to RS7B. The zircons from RS-9A show greater effects of inheritance (Fig. 6b); if it is assumed that the inheritance in RS-7B is the same as that in RS-BA, a biotite-rich phase of the migmatitic gneiss, then we can use the combined data to set better limits on the age of these samples. A maximum age of 616k 2 Ma is given by the data from RS-7B fraction NM(-2)n 1, whereas a minimum age of 610 + 5 Ma is given by the lower intercept of a chord through RS7B fraction NM(-2)el and RS-9A fraction M(- 1). The 616 Ma age assumes that fraction NM(-2)nl from RS-7B has experienced Pb-loss but has no inherited component. The 6 10 Ma age assumes that data for fraction NM(-2)nl are still slightly influenced by an inherited component, but that fraction NM(-2)el from RS-7B has experienced less Pb-loss. At present we cannot choose between these alter-

1800

,

,A/: 0.301 I

,/

SC-54-I

I L

//

3

al g

1400

! / 0.221

,

1

/

7

r

g

.:~..~~~

1

2

3

4

5

207Pbl235U Fig. 7. Concordia diagram for gneiss from Camborili Complex (SC-54-l). The two discordia shown represent regressions through fractions which define a minimum age of610 c 5 Ma and a maximum age of 616 + 2 Ma. See text for further discussion.

U-Pb and Sm-Nd Geochronology

of the Neoproterozoic

because it is not feasible to produce an anorthosite from pre-existing continental crust.

Granitic-Gneissic

Dom Feliciano Belt. Southern Brazil 27 1

magma

Pinheiro Machado and Camboriri Complexes. We analysed whole-rock samples RS-7A, RS-7B, RS-7C, RS-9A, and RS-9B from the Pinheiro Machado complex in Rio Grande do Sul (D, E, F, G, and H, respectively in Fig. 8) and samples SC-52 and SC-54-I from the Camboriu complex in Santa Catarina (N, 0, respectively in Fig. 9); all samples display the same flat-lying fabric. These seven samples cluster in three groups. The samples with the oldest To, ages (7A: 2.01 Ga, 9A: 2.09 Ga, SC-52: 2.25 Ga, and SC-54-I: 2.16 Ga) apparently represent the oldest protolith for rocks in these outcrops. However, since zircons from 9A are near the lower end of discordia at ca. 600 Ma, this gneiss either represents an early Brasiliano granitoid derived from Transamazonian basement or Transamazonian basement gneiss in which zircons were nearly completely reset during the Brasiliano orogeny. The typical igneous morphology of the zircons from 9A suggests that the former alternative is the best interpretation. The two Brasiliano 9B) have less negative To, ages than those of 9A) from the respective values are similar (Fig.

metagranite samples (RS-7C and e&600) and significantly younger the two gneiss samples (RS-‘IA and outcrops, even though their ~~~(0) 8). In this case the interpretation is

I

1

?

3

T GO Fig. 8. ~~~(600) diagram for rocks from Rio Grande do Sul in the Dom Feliciano Belt: A = RS-2; B = RS-4; C = RS-5; D = RS-7A; E = RS-7B; F = RS-7C; G = RS-9A; H = RS-9B; I = RS-12; J = RS- 13-B. Dashed lines represent extrapolations of Nd evolution prior to 600 Ma assuming no Sm/Nd fractionation during the Brasiliano orogeny.

0

1

3

T @a) Fig. 9. ~~~(600) diagram for rocks from Santa Catarina in the Dom Feliciano Belt: L = SC-42-l; K = SC-42-B; M = SC-43; N = SC-52; 0 = SC-54-l. Dashed lines represent extrapolations of Nd evolution prior to 600 Ma assuming no Sm/Nd fractionation during the Brasiliano orogeny.

more ambiguous. If it is assumed no REE fractionation occurred during magma genesis, then the protolith for the metagranites could have been Mesoproterozoic basement. However, 1.2 to 1.6 Ga basement has not been recognized in this region, so other possibilities must be considered. The most likely explanation is that magmas for 7C and 9B came from protolith with an age similar to that for 7A and 9A, but with slightly higher 147Sm/144Nd ratios (more mafic, deeper equivalents?). At 600 Ma the ~~~(600) for these protoliths would have been slightly less negative than for the exposed gneisses, 7A and 9A. During magma genesis significant REE fractionation then occurred, producing distinctly lower ‘47Sm/‘44Nd ratios and resulting in fortuitously similar ~~~(0) values for the granites (F, H; Fig. 8) and their host gneisses (D, G; Fig. 8). A second alternative is that the magma for 7C and 9B was derived from a source nearly identical to that for 9A and 7A, but that it was mixed with a small amount of fluid (magma’?) from a more juvenile source. In both cases the To, ages of ca. 1.4 Ga would be artifacts of the chemical changes that occurred during magma genesis. The migmatitic gneiss sample, RS-7B, could represent a rock intermediate between the extremes of the gneisses and granites, or it could have had a more complex history. In any case, the zircons from this sample also indicate that it, like RS-9A, represents granitoid derived from Transamazonian basement.

272

M. BABINSKI

Syn-tramcurrent and late- to post-tectonic granites. We also recognized three major groups in these rocks. Three samples show the oldest To, ages (RS-4: 2.08 Ga, RS- 12: 2.37 Ga, and SC-42-11: 2.18 Ga) that may represent the oldest protolith of the syn- to late- strike-slip related granites. The only sample with U/Pb zircon data, the Encruzilhada do Sul Granite (RS-4), contains evidence of inheritance of older Proterozoic zircon (Fig. 4). As we mentioned previously, the Encruzilhada do Sul granite has a high 87Sr/86Sr initial ratio and a metaluminous character. In addition, a Transamazonian model age (TDM) and very negative Ed,, values (Figs. 8a, 8b) indicate that these Brasiliano granites were derived from Paleoproterozoic basement. A second group represents samples with To, ages of ca. 1.3-l .4 Ga (RS- 13-B and SC-42-I) that may either correspond to remelting of older Transamazonian material similar to that for the first group, but with significant REE fractionation occuring during magma genesis, or to mixing between a Transmazonian basement source and a small amount of fluid from a more juvenile source. Two zircon fractions of the RS-13-B show Pb-inheritance (Fig. 5), but the data are insufficient to define the age of the protolith. A third group includes two samples with intermediate T or,,, values (RS-2: 1.75 Ga, and SC-43: 1.58 Ga), similar to the sample RS-7B. Like RS-7B, they may have had a more complex history; no zircon data are available for this group.

et al.

groups. The first of these (I) includes Brasiliano gneisses, granitoids, and one anorthosite with To, ages of 2.0 Ga (RS-4, RS-5, RS-9A, RS-12, SC-42-11, SC-52, and SC-54-I) and very negative EN, (600) values. The gneisses and granitoids may represent direct melting of a Transamazonian (Paleoproterozoic) basement, which was generated during the most important erogenic cycle that preceeded the Brasiliano orogeny in southern Brazil The second group (II) includes granitoids and gneisses wtth To, model ages from 1.31 to 1.41 Ga (RS-7C, RS-OB, RS-I3-II, SC-42-I). The third group (III) comprises samples with To, ages between 1.58 and 1.75 Ga (RS-2, RS-7B, SC-43). For both cases it is clear that these rocks or their protoliths represent pre-Brasiliano continental crust. However, unlike the case for Group I, Groups II and III may contain a small fraction of a juvenile Brasiliano material, although we have not yet found any sample from the Dom Feliciano belt with a Brasiliano T,, age and positive ~~~ value at 600 Ma. Comparison of these geochronological results with those from the Vila Nova belt, in which the main erogenic process was from 753 to 704 Ma (Chemale et al., 1994a), allows us to conclude that the Vila Nova belt was stable for over 100 Ma before the Dom Feliciano event reached its peak. It is probable that the collage of terranes in the Dom Feliciano belt and the region comprised by the Tijucas and Vila Nova belts was formed during the main tectonism of the Dom Feliciano event (ca. 600 Ma). Acknowledgements

DISCUSSION

AND CONCLUSIONS

-

from the U.S. National

The research was supported Science Foundation

in part by fundmg

and from CNPq in Brazil. We

wish to thank Mr. Allen Fetter and Mr. Elton Dantas for assistance during

The present study allows us to define precisely the main tectonic phases of the ca. 600 Ma Dom Feliciano event which affected the rocks in the Dom Feliciano belt. U-Pb zircon data for flat-lying gneisses yield ages of 6 10 f 5 Ma and 616 + 2 Ma, which we believe corresponds to the approximate age of thrusting. A whole-rock Rb/Sr isochron age of 783+29 Ma for outcrop RS-7 (Soliani Jr., 1986) may represent a mixed age. In this case, the characterization of a ca. 800 Ma magmatic arc for this region, as interpreted by Fragoso-Cesar (1991) and Fernandes et al. (1992), cannot be supported by our U-Pb zircon data.

the laboratory

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Dr

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The strike-slip deformation (main transcurrent phase) is well dated by the U-Pb zircon age of 595 f 1 Ma for the syn-transcurrent Arroio Moinho Granite, which shows parallel state-solid and magmatic flow foliation. Because the Encruzilhada do Sul granite has a similar zircon age (594 + 5 Ma), we assume that this granite is also a syntranscurrent granite and was probably formed in the transtensional enviroment along the main strike-slip Canguqu Shear zone, as concluded by Fragoso-Cesar (1991) based on field work.

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DePaolo, D.J., 1981. A neodymium and strontium isotopic study of the Mesozoic talc-alkaline granitic batholiths of the Sierra Nevada and Peninsular Ranges, California. Journul c$Gec@ysicul Research, 68, 10470-10488.

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APPENDIX Sample Location and Description Rio Grande do Sul State. Piquiri Syenite (RS-2) (quarry outcrop 13.2 km SW of Hwy. 290 on a road which leaves Hwy. 290 near km 257). This outcrop consists of red syenitic rocks with >60 percent K-feldpar (orthoclase). Hornblende and clinopyroxene are minor components; quartz, microcline, plagioclase, biotite, sphene, ilmenite, apatite and zircon are accessory minerals. A primary igneous foliation, which is marked by alignment of feldspars and mafic stringers, is the most conspicuous fabric of this syenite. Encruzilhada do Sul Suite (RS-4) (3OO25.22’ S; 52O28.03’ W; roadcut on road RS-233 between Pantano Grande and Encruzilhada do Sul at km 211.6, 11.5 km from town of Encruzilhada do Sul). This outcrop consists of subalkaline syenogranite. Mesoscopically the rocks do not show any deformation, although we recognized some hydrothermal alteration (epidote). Microscopically, the quartz and feldspar crystals display undulose extinction, indicating that this rock was subjected to some deformational process. Capivarite Anorthosite (RS-5) (3OO18.64’; 52O24.56’; outcrop 4.7 km from road RS-233 on a road which leaves RS-233 near km 198.9, 26.6 km from town Encruzilha do Sul). In this outcrop the anorthosite is associated with some lenses of talc-silicate rocks and amphibolite that have a flat-lying fabric formed in upper amphibolite conditions. We collected a sample of anorthosite (RS-5) which is composed of >90 % plagioclase (labradorite) with diopside, hornblende, sphene and quartz as accessory minerals. Pinheiro Machado Complex (RS-7) (31O37.43’ S; 53O23.13’ W; outcrop at the western entrance to town of Pinheiro Machado). This outcrop consists of at least four granitic phases: (a) blastomylonitic diorite that occurs as centimeter lenses (Sample RS-7A) is the oldest phase; (b) grey migmatitic granodioritic gneiss with flat-lying banding (foliation), stretched matic stringers and K-feldspar porphyroclasts (up to ca. 5 cm diameter) (RS-7B); (c) fine grained, deformed syenogranite which cuts the previous phase (RS-7C); and (d) 20 cm wide aplitic dykes oriented at N40’E and N-S, which is the youngest granitic phase. There are also meter-size xenoliths of quartzite and calcsilicate rocks.

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Pinheiro Machado Complex (RS-9) (3 l”36.70’; 53O17.22’ W; roadcut on Hwy Br-293, 9.3 km from Pinheiro Machado). This outcrop consists of polydeformed banded gneiss with some layers of the foliated grey, migmatititic granodioritic gneiss similar to that at the RS-7 outcrop. There are some Encruzilhada do Sul “dykcs” showing assimilation (forming biotite and amphibole) as well as a migmatitic phase. We collected biotite-rich migmatitic gneiss (sample RS-9A). a foliated metasyenogranite (RS-9B), and biotite-poor miglnatitic gneiss (RS-9C). The tectonic fabric is related to the tangential event, including folding of layering. A 2 m-thick quartz vein is present, injected into the gneisses; it is also strongly affected by the transcurrent fabric. CapEo do Letio Monzogranite (RS-12) (quarry outcrop at the Capso do Lego locality, - 3.0 km from Hwy Br-293, 83 km from Pinheiro Machado). This unit is an undeformed granitoid with garnet as an accessory mineral; it is metaluminous in composition, and it cuts the Pinheiro Machado Complex. Arroio Moinho Granite (RS-13) (31O30.79’ S; 152~36.27’ W; outcrop in a quarry along Hwy Br-392, 5 km SE of town of CanguGu). This unit is a strike-slip related granite. Two samples were collected from this outcrop: a pink syenogranitc facies (RS- 13-I) and a gray monzogranitic facies (RS- 13-11). The outcrop displays magmatic-flow and solid-state planar and linear fabrics related to the strike-slip deformation. Santa Catarina State. Pedras Grandes Suite (SC-42) (outcrop in quarry in TubaGo city, 400M W of km post 338 on Hwy Br-101). This outcrop consists of non-deformed

et al.

granites of this suite. We collected samples of two facies. One is a pink, coarse-grained, equigranular to porphyritic leuco-granite with accessory biotite (SC-42-11); it is the dominant granitic facies in the suite. The other facies is a mesocratic, medium-grained, gray granodiorite (SC-42-I) with abundant mafic clots. Some preferential alignment of mafic minerals can be observed, which is interpreted as magmatic flow structure. Some meter-size amphibolitc enclaves also occur in this unit. Paulo Lopes monzogrunite (SC-43) (outcrop in quarry in Paula Lopes town, along west side of Hwy Br- 101 at km 249.8). This is probably a strike-slip related body. It is characterized by megacrysts that may add up to 4&60%) of the rock volume; the megacrysts range from idiomorphic to rounded (porphyroclasts). The megacrysts (augen) are flattened and stretched parallel to a well-defined subvertical banding. The matrix is medium-grained, gray, and rich in biotite that may wrap around the porphyroclasts, forning pressure shadows. Cuabiruba metaleucogranite (SC-52) (Quarry alongside BR-101 in the Serra de Camborit’i, close to resort Balnekio Camborid). This is a fine to medium-grained, twomica peraluminous metaleucogranite that cuts migmatitic gneisses (SC-54); both units belong to the Camborili complex. Cumboriu’ Complex (SC-54-l) (outcrop in Cesarna Quarry in the Balnejrio Camborili). This unit consists of migmatitic gneisses with agmatitic structure comprised 01 fine-grained metagranite and pieces of banded gneiss. A Hat-lying fabric is recognized as the main deformational structure.