THE QUIRINO COMPLEX: A TRANSAMAZONIAN MAGMATIC ARC (?) OF THE CENTRAL SEGMENT OF THE BRASILIANO/PAN-AFRICAN RIBEIRA BELT, SE BRAZIL.

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1 C. S. Valladares et al. 49 THE QUIRINO COMPLEX: A TRANSAMAZONIAN MAGMATIC ARC (?) OF THE CENTRAL SEGMENT OF THE BRASILIANO/PAN-AFRICAN RIBEIRA BELT, SE BRAZIL. CLAUDIA SAYÃO VALLADARES 1 SHEILA SOUZA DIANA RAGATKY ABSTRACT: Claudia Sayão Valladares, Sheila Souza and Diana Ragatky; The Quirino Complex: a Transamazonian Magmatic Arc (?) of the Central Segment of the Brasiliano/Pan-African Ribeira Belt, SE Brazil; Revista Universidade Rural - Série Ciências Exatas e da Terra. V. 21, N 1 p.x-x.this paper presents new geochemical and Sm-Nd isotopic data of the Quirino Complex from the NW of the Rio de Janeiro state. The Quirino Complex constitutes the basement unit of the Paraíba do Sul Klippe, part of the Oriental Terrane, envisaged as a portion of the Congo plate. The rocks of this complex occur as extensive bodies of homogeneous gneisses with hornblende and/or biotite varying in composition from tonalitic/granodioritic to granitic rocks and including ultramafic, mafic and calc-silicate (tremolite rich) enclaves. Geochemical studies discriminate two calcalkaline suites: one of medium-k and another of high-k. The 147 Sm/ 144 Nd ratios of and are typical of crustal rocks and the Sm-Nd isotopic data yields Archaean (3280 Ma) and Palaeoproterozoic (2213 Ma) T DM consistent with U-Pb published zircon ages. The geochemical and isotopic data suggest, in part, tectonic correlation of the Quirino Complex with arc magmatic calc-alkaline granitoids, generated during the Transamazonian orogeny, reworking partially, Archaean crust. During the Brasiliano/ Pan African orogeny these granitoids were submitted to upper amphibolite facies metamorphism. KEY WORDS: Ribeira belt-palaeoproterozoic rocks-quirino Complex-geochemistry- Sm-Nd isotopic data. INTRODUCTION The crustal structure of the Ribeira belt (Cordani et al., 1973), in southeastern Brazil, can be defined in its central segment by two major tectono-stratigraphic terranes (Heilbron et al. 2000): a) the Occidental Terrane is interpreted as a reworked margin of the São Francisco Plate and comprises an autochthonous domain, the Andrelândia nappe system, and the Juiz de Fora thrust system; b) the Oriental terrane is envisaged as part of the Congo Plate and encompasses the Paraíba do Sul Klippe, the Costeiro and the Cabo Frio domains (Fig. 1). Three major lithological associations were recognised and mapped in the central segment of the Ribeira belt: a) a reworked Palaeoproterozoic/Archaean basement; b) different deformed Palaeoproterozoic to Neoproterozoic cover successions; and c) Neoproterozoic granitoid rocks. 1 Departamento de Geologia Regional e Geotectônica, Faculdade de Geologia, Universidade do Estado do Rio de Janeiro (UERJ). Rua São Francisco Xavier, 524, sala A Maracanã, Rio de Janeiro, RJ, CEP Telefone (Fax): 0055 (021) , tel , Brasil. vallada@uerj.br Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002

2 50 The Quirino Complex: A Transamazonian Magmatic Figure 1- Tectonic Map from the central segment of Ribeira belt (simplified from Almeida, 2000). ANS = Andrelândia Nappe System; JFTS- Juiz de Fora Thrust System; PSK- Paraíba do Sul Klippe; OrT- Oriental Terrane; PSSZ- Paraíba do Sul Shear Zone; CTB- Central Tectonic Boundary. 1- Cenozoic cover; 2- Alkaline intrusions; 3- Late-collisional granites; 4- D3 shear zones; 5- Oblique Shear Zones.

3 C. S. Valladares et al. 51 The Quirino Complex (Valladares, 1996) represents the reworked Palaeoproterozoic basement of the Paraíba do Sul Klippe. This complex occurs as extensive bodies of homogeneous orthogneisses with hornblende and/or biotite of upper amphibolite facies metamorphism and yields tectonic contacts with the supracrustal rocks of the Paraíba do Sul Group, representing slices of basement rocks on the metasedimentary sequence. The orthogneisses vary in composition from tonalitic/granodioritic to granitic and includes ultramafic, mafic and calc-silicate (tremolite rich) enclaves. This paper presents new geochemical and geochronological (Sm-Nd) data for the orthogneisses of the Quirino Complex. These new data together with published mineral U-Pb geochronology (Valladares, 1996; Machado et al., 1996; Valladares et al., 1997), field and geochemical data (Valladares, 1996; Valladares et al. 1997; Vianna and Valladares, 1997, Souza and Valladares, 1999) support the presently proposed model of generation of these calc-alkaline granitoids during the Transamazonian orogeny ( Ga). These basement rocks were reworked during the Brasiliano/ Pan- African orogeny ( Ma) associated with the collision of the São Francisco-Rio de la Plata and Congo plates (Heilbron et al., 1999). SAMPLING AND ANALYTICAL PROCEDURES The new geochemical and Sm-Nd isotopic data refer to the gneissic rocks of the Quirino Complex on the NW of the Rio de Janeiro state, occuring between Nossa Senhora do Amparo and Três Rios cities (Fig. 1). For the geochemical studies 9 samples of tonalitic/granodioritic gneisses and 10 samples of granodioritic/granitic gneisses were selected. These 19 new analyses were interpreted together with 14 another data of the south of Volta Redonda 1: quadrangle published in Valladares (1996) and Valladares et al. (1997). The UTM coordinates of all of the 33 samples that were used in this paper are given on Table 1. Sm- Nd isotopic analyses were carried out on a sample of hornblende tonalitic gneiss (Conceição quarry near Valença, state of Rio de Janeiro, sample VAS-786B) and a sample of biotite granitic gneiss collected near the village of Bom Sucesso (sample 150B). These gneiss rocks are similar to the rocks described by Machado (1986) in Valença, state of Rio de Janeiro. All the new chemical analyses were carried out at ACT LABS (Canadá) for major, trace and rare earth elements, as well as the 14 chemical data of the south of Volta Redonda 1: quadrangle published in Valladares (1996) and Valladares et al. (1997), used in this paper. The major and some trace elements were measured using ICP fusion and total digestion. The trace elements with minor concentration and the rare earth elements were detected by (INAA). The abundance patterns of REE were done using the concentration values proposed by Boynton (1984) for chondrite normalization. The Sm-Nd isotopic analyses were carried out at the Laboratory of Geochronology of the University of Brasília (UnB), Brazil. Sm and Nd concentrations were determined by the isotope dilution method, using a mixed 149 Sm Nd spike. Measurements were done on a Finnigan MAT 262 mass spectrometer equipped with seven Faraday collectors. Sm and Nd data were acquired in the static mode. The elements were loaded as phosphates on double Re filament. Total procedure blank was minor of 0.2 ng for Nd. Values for La Jolla Nd standard 143 Nd/ 144 Nd = ± 7 (1σ). Nd isotopic compositions were normalized to 146 Nd/ 144 Nd = Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002

4 52 The Quirino Complex: A Transamazonian Magmatic Table 1- Samples UTM coordinates. Sample X Y Sample X VR-223A BP-II-61A VR-150A/B BP-I VR-222A BP-I VR BP-I VR BP-II VR BP-M VR-5022B BP-M VR NSA-V VR NSA-V VR TR-PM VR-201A TR-MM-71A VR-5029B TR-MM VR-94A VAS-786B BP-IV PS-PM BP-IV-53A PS-PM BP-I-4(3) Note: VR-samples from Volta Redonda 1: quadrangle which the chemical data were published in Valladares (1996) and Valladares et al. (1997); BP- samples from Barra do Piraí 1: quadrangle; NSA- samples from Nossa Senhora do Amparo 1: quadrangle; TR- samples from Três Rios 1: quadrangle; VAS-samples from Vassouras 1: quadrangle; P S - samples from Paraíba do Sul 1: quadrangle. Geochemistry RESULTS The 19 new geochemical data from the Quirino orthogneisses, interpreted together with 14 analyses of these ortogneisses of the Volta Redonda area (samples discriminated in Figs. 2 to 9; chemical data published in Valladares 1996 and Valladares et al. 1997), discriminate two calc-alkaline suites (Figs. 2 and 3): one of medium-k (Fig. 4, Table 2) and another of high-k, (Fig.4, Table 3). The major element abundances indicate that these rocks bear characteristics of metaluminous to slightly peraluminous granitoids, with Shand s indice <1.1 (Fig. 5). The medium-k calc-alkaline suite comprises tonalitic to granodioritic gneisses (Figs. 6 and 7). The SiO 2 content varies between 59 and 68%, Na 2 O between 3 and 4,5% and K 2 O 2%, in avarage. The main characteristics are K 2 O/Na 2 O <1; Al 2 O 3 > 15%; CaO between 3-6%; Fe 2 O 3 between 4-9%, and Cr between 7-108ppm (Table 2, Fig. 8a). In terms of incompatible elements this suite displays ppm Rb, exception made to a sample of Volta Redonda that yields 195ppm of Rb; ppm Ba, exception made to the sample VAS-786B that yields ppm of Ba (not plotted on diagrams), ppm Zr and ppm Th (Table 2, Figure 8). Chondrite-normalized

5 C. S. Valladares et al. 53 REE patterns are moderately fractionated (La N /Yb N = 20-8), with flat HREE (Sm N /Lu N =2-5) patterns, and positive and negative Eu anomaly (Eu/Eu* = ). The La content is moderate (La N ca times chondrite), Table 2 and Figure 9a. The high-k calc-alkaline suite comprises predominantly granodioritic/adamellitic-granitic gneisses, Fig 6 and 7. The SiO 2 content varies between 56 and 72%, Na 2 O between 2 and 4%, K 2 O between 3-6%, in media 4%; and CaO between 2-7% (Table 3). This suite is enriched in incompatible elements, including LILE, REE and high field strength elements (HFSE), with 22,330-47,166ppm K, ppm Rb, ppm Ba, 0,2-7ppm U, ppm Zr and Th content ppm (Figure 8, Table 3). The granitic gneissic rocks from Volta Redonda area are strongly enriched in Zr and Th (Fig. 8b and 8c). Chondrite-normalized REE patterns are strongly fractionated with La N /Yb N = and Yb N =3 to 30, with enrichment in LREE (La N /Sm N = 1-7, Table 3, Fig. 9b). The La content is moderate to high (La N ca times chondrite) and Eu negative anomaly predominates (Eu/Eu* = ), exception made to the sample PS-PM-67 (Table 3). The Ocean Ridge Granite (ORG)- normalized incompatible element distribution patterns (spidergrams, Pearce et al. 1984) for both suites exhibit enrichment of large ion lithophile element (LILE) and decreasing values for the least incompatible elements, as well as negative anomalies of Nb and Ta. These features have been described for volcanic arc granites with envolvement of oceanic crust in a subduction environment. The envelope of multi-element patterns for both suites shows similarity with rocks from calc-alkaline series of active continental margins. The medium-k calc-alkaline rocks show similarity with the pattern of the Jamaica granodiorite of Pearce et al. (1984) and the high-k calc-alkaline suite show similarity with the pattern of the Chile granite of the same author (Figs. 10a and 10b). Figure 2 - TAS diagram (Irvine and Baragar, 1971) for the orthogneisses of Quirino Complex. Legend: asterisk and cross medium- K calc-alkaline suite; filled and openned circle - high K calc-alkaline suite. Cross and openned circle- samples of the south of Volta Redonda 1: quadrangle which the chemical data were published in Valladares (1996) and Valladares et al. (1997). Figure 3 - AFM diagram (Irvine and Baragar, 1971) for the orthogneisses of Quirino Complex. CA-TH: boundary between calc-alkaline and tholeiitic series. Same symbols as in Figure 2. Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002

6 54 The Quirino Complex: A Transamazonian Magmatic Table 2 - New data from the medium-k calc-alkaline orthogneisses suite of the Quirino Complex. Sample BP-I-24 VAS-M-793 VAS-786B BP-I-4(3) BP-M-659 BP-I-40 NSA-V-66 SiO TiO Al 2 O Fe 2 O MnO MgO CaO Na 2 O K2O P 2 O LOI TOTAL Cr Ni Co Sc V Cu nd Pb Zn Rb Cs nd 0.4 nd nd Ba Sr Tl Ga Ta Nb Hf Zr Y Th U Be Mo Sn Sb W nd nd 2 nd 15.6 La Ce Pr Nd Sm Eu Gd Tb

7 C. S. Valladares et al. 55 Table 3 - New data from the high-k calc-alkaline orthogneisses suite of the Quirino Complex. Sample BP-IV-80 BP-II-61A BP-I-22 PS-PM-67 TR-PM-69A BP-IV-53A BP-II-26 BP SiO TiO Al 2O Fe2O MnO MgO CaO Na 2O K2O P 2O LOI TOTAL Cr Ni 60 nd nd 12 Co Sc V Cu nd Pb Zn Rb Cs 1.3 nd Ba Sr Tl Ga Ta Nb Hf Zr Y Th U Be Mo Sn Sb W 2 nd nd nd nd La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002

8 56 The Quirino Complex: A Transamazonian Magmatic Figure 4 - SiO 2 xk 2 O diagram with fields from calc-alkaline series. Same symbols as in Figure 1. Figure 5 - Shand s indice diagram (Maniar and Piccoli, 1989). Same symbols as in Figure 2. Figure 6 - O Connor s An-Ab-Or normative classificatory diagram for the orthogneisses of Quirino Complex. Same symbols as in Figure 2. Figure 7 - Chemical classification (Middlemost, 1985). Same symbols as in Figure 2.

9 C. S. Valladares et al. 57 Legend: / High - k cale-alkaline suite /+ Medium - K calc-alkaline suite Figure 8 - Variations diagrams of trace elements for the orthogneisses of Quirino Complex. Same symbols as in Figure 2.

10 58 The Quirino Complex: A Transamazonian Magmatic Figure 9 - Chondrite-normalized (Boynton, 1984) rare earth elements (REE) distribution patterns- A) for the medium-k calc-alkaline suite; B) for the high-k calc-alkaline suite. Lines - samples of the south of Volta Redonda 1: quadrangle which the chemical data were published in Valladares (1996) and Valladares et al. (1997). Figure 10 - Envelope of multi-element patterns normalized to Pearce et al. (1984) ORG values, with plote of volcanic arc granodioritic and granitic rocks, showing a comparation with active continental margins granitoids; A) for the medium-k calc-alkaline suite; B) for the high-k calc-alkaline suite. Sm-Nd isotopic data The only available Sm-Nd data (Table 4) show 147 Sm/ 144 Nd ratios of typical crustal rocks: and , suggesting no Sm/Nd crustal fractionation during the magma genesis. The ε Nd values have been recalculated for T=2.1 Ga based on U-Pb zircon crystallization ages for these rocks. The depleted mantle model Nd ages (T DM ) of 2.2 Ga were obtained on a sample of a granitic gneiss of the high calc-alkaline suite (sample VR-150B). The ε Nd 2.1 = value for this sample suggest juvenile Palaeoproterozoic source. A T DM of 3.2 Ga was obtained on a sample of a tonalitic

11 C. S. Valladares et al. 59 gneiss of the medium-k calc-alkaline suite (sample VAS-786B) with ε Nd 2.1 = , indicating a pre-existence of Archaean crust. This feature is consistent with the high 87 Sr/ 86 Sr value calculated for the crystallization age for this sample (2.1 Ga) of (D. Ragatky, unpublished data). The U-Pb geochronological published data (Machado et al. 1996; Valladares, 1996) on the same samples yield U-Pb zircon ages of 2185 ± 8 Ma (granitic orthogneiss of the high-k calc-alkaline suite - sample VR- 150B) and 2169 ± 3 Ma (tonalitic gneiss of the medium-k calc-alkaline suite - sample VAS-786B). These ages were defined by upper discordia intercepts suggesting that these are crystallisation ages. The tonalitic gneiss (sample VAS-786B) yields U-Pb zircon minimum ages of 2846 and 2981 Ma (Machado et al., 1996; Valladares, 1996), representing Archaean heritage. The lower intercepts in concordia diagrams yield ages of 605 ± 3 Ma and 571 ± 3 Ma, respectively, representing metamorphic ages related to the Brasiliano Orogeny. CONCLUSIONS Geochemical studies of the Quirino orthogneisses discriminate two calc-alkaline suites: one of medium-k and another of high-k. The medium-k calc-alkaline suite comprises tonalitic to granodioritic gneisses and the high-k calc-alkaline comprises predominantly granodioritic to granitic gneisses. Both suites show similarity with plutonic calc-alkaline rocks from active continental margins. The agreement between the 2185 ± 8 Ma crystallisation age (U-Pb zircon) and the 2213 Ma T DM age from the granitic gneiss (high-k suite) suggests Palaeoproterozoic juvenile crust accretion, compatible with the observed magmatic arc geochemical signature. For the tonalitic gneiss of the medium-k calc-alkaline suite the 2169 ± 3 Ma is interpreted as crystallisation age (U-Pb zircon). This sample displays a T DM of 3280 Ma, consistent with U-Pb zircon heritage ages of 2846 Ma and 2981 Ma and the high inicial 87 Sr/ 86 Sr value of , suggesting melt of an Archaean crust during the same event that generated juvenile crust on the Palaeoproterozoic. The few isotopic and geochronological data available for the granitoids from the Quirino Complex suggest that the Transamazonian orogeny generated juvenile crust and reworked, in part, Archaean crust. However, more isotopic data will be necessary to confirm the tectonic correlation of the Quirino Complex with a transamazonian arc magmatic setting. ACKNOWLEDGEMENTS Field work was financed by FAPERJ through research grant to C.V. (Proc. E- 26/ /99). The geochemical analyses were financed by FAPERJ and CNPq. Sm-Nd geochronogical analyses were carried out at the Laboratory of Geochronology of University of Brasilia (UnB), Brazil. Table 4 - Analytical Sm-Nd data from orthogneisses of the Quirino Complex. Sample Sm (ppm) Nd (ppm) 147 Sm/ 144 Nd 143 Nd/ 144 Nd (±s) VR-150B (24) VAS-786B (19) Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002

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13 C. S. Valladares et al. 61 VALLADARES, C.S.; FIGUEIREDO, M.C.; HEILBRON, M.; TEIXEIRA, W Geochemistry and Geochronology of Paleoproterozoic gneissic rocks of the Paraíba do Sul Complex, Barra Mansa Region, Rio de Janeiro, Brazil. Número Temático Geoquímica do Précambriano. Revista Brasileira de Geociências, 27 (1): VIANNA, S. M. & VALLADARES, C. S Estudo geoquímico das rochas ortognáissicas da Unidade Quirino (Complexo Paraíba do Sul), na região de Barra do Piraí, estado do Rio de Janeiro. In: SIMPÓSIO DE GEOLOGIA DO SUDESTE, 5, Penedo, RJ, Boletim de Resumos Expandidos, SBG/RJ, p Univ. Fed. Rural do Rio de Janeiro Revista Universidade Rural, Série Ciências Exatas e da Terra Vol. 21 (1): 49-61, 2002