Structural and geochronological constraints on the evolution of the Juréia Massif, Registro Domain, State of São Paulo, Brazil

EARTH SCIENCES

Structural and geochronological constraints on the evolution of the Juréia Massif, Registro Domain, State of São Paulo, Brazil

Cláudia R. Passarelli^I; Miguel A.S. Basei^{I, *} ; Hélcio J. Prazeres-Filho^I; Oswaldo Siga-Jr.^I; Gergely A.J. Szabó^I; Joaquim Marco-Neto^II

^IInstituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, Cidade Universitária, 05508-080 São Paulo, SP, Brasil

^IIInstituto Florestal, Estação Ecológica de Juréia-Itatins, Estrada do Guaraú, 4164, Caixa Postal 159, 11750-000 Peruíbe, SP, Brasil

^{Correspondence to}

ABSTRACT

The Juréia Massif, southeastern São Paulo State (Brazil), is part of the Registro Domain, limited to the north by the Cubatão-Itariri Shear System and to the south by the Serrinha Shear Zone. Mostly composed of migmatitic granitegneiss rocks, represents a Paleoproterozoic terrane (1.9–2.2 Ga) strongly deformed during the Neoproterozoic (750–580 Ma). The present tectonic scenario was established at the end of the Neoproterozoic, as a result of collages associated with the formation of Western Gondwana. The Ponta da Juréia, our study area within the Juréia Massif, is constituted by paragneisses (garnet-muscovite-biotite gneisses). The monazite U-Pb age of 750 Ma is related to a main regional metamorphic event that reached the high amphibolite facies, recorded in rocks from the Itatins Complex and Cachoeira Sequence as well, which also belongs to the Registro Domain. The paragneissic rocks of this study are affected by the E-W-trending Serrinha Shear Zone, registering a predominantly dextral movement. Biotite K-Ar ages of 482 ± 12 Ma may represent later movements and reflect the younger ages of reactivation of the major lineaments and juxtaposition of the tectonic blocks involved.

Key words: tectonic domain, shear zone, gneissic rocks, U-Pb geochronology.

RESUMO

O Maciço da Juréia, localizado na porção sul-oriental do Estado de São Paulo, está inserido no Domínio Registro, limitado a norte pelo Sistema de Cisalhamento Cubatão-Itariri e a sul pela Zona de Cisalhamento Serrinha. Composto em sua maior parte por rochas granito-gnáissico migmatíticas, representa um terreno Paleoproterozóico (1.9-2.2 Ga) fortemente afetado durante o Neoproterozóico (750-580 Ma). Na área em questão, no final do Neoproterozóico estabeleceu-se o quadro tectônico atualmente observado, como resultado de colagens associadas à formação do Gondwana Ocidental. A Ponta da Juréia, porção estudada do Maciço da Juréia, é constituída por paragnaisses, onde predomina granada-muscovita-biotita gnaisses.A idade U-Pb obtida em monazitas, em torno de750 Ma, é associada à principal fase de metamorfismo regional,que atingiu o fácies anfibolito alto, também registrado nas rochas do Complexo Itatins e da Sequência Cachoeira, igualmente pertencentes ao Domínio Registro. As rochas paragnáissicas estudadas apresentam-se afetadas pela Zona de Cisalhamento Serrinha, de direção principal em torno de E-W, com movimentação predominante dextral. Apresentam idade K-Ar em biotita de 482 ±12 Ma que pode representar movimentações tardias desta zona de cisalhamento, e refletir a época mais jovem possível para a movimentação que ocorre ao longo dos grandes lineamentos e justaposição dos blocos tectônicos envolvidos.

Palavras-chave: domínio tectônico, zonas de cisalhamento, rochas gnáissicas, método U-Pb.

INTRODUCTION

The southeastern portion of the State of São Paulo (Brazil), part of the southern sector of Ribeira Belt inthe Mantiqueira Province (Almeida et al.1981) consists of four major tectonic domains limited by importantshear zones, with mainly E-W or NE/SW trends related to Neoproterozoic tectonic events.

The Registro Domain, a polydeformed and metamorphosed block composed of metasedimentary andgranite-gneiss-migmatitic rocks, occurs between theCubatão-Itariri and the Serrinha (SSZ) Shear Zones (Figure 1). The Juréia Massif, the aim of this work, is partof this domain, and is located between the towns ofPeruíbe and Iguape. It forms the highest hills south of the Itatins Massif.

The Juréia Massif is composed of amphibolite facies mylonitic paragneisses and was subjected to more than one episode of metamorphism and deformation. It is usual that the preserved mineral assemblages andmicrofabrics mainly record the latest metamorphic/tectonic event since these erase the record of the respective earlier events (Krohe and Wawrzenitz 2000). The Juréia rocks preserve an unusual P-T path.

Neoproterozoic III igneous and metamorphic ages are widely documented on the granite-gneissic domains of the southern Ribeira Belt (Siga Jr. et al. 1995, Machado et al.1996, Basei et al.1997, Harara et al.1997, Campos Neto 2000, Tupinambá et al. 2000, Hackspacher et al. 2000, Sato et al. 2001, Heilbron and Machado 2003, Passarelli et al.2004). Recent geochronological studies of upper amphibolite facies paragneiss from the Juréia Massif provide evidence for an earlier metamorphic event of Cryogenian age in the Brasiliano-Pan-African Cycle.

Ages of this period were previously recorded only in the Embu Complex (Vlach 2001, Cordani et al. 2002, Janasi et al.2003), in granites and juvenile volcanic rocks from the southern part of the Mantiqueira Province (Babinski et al.1996), and also as a magmatic-metamorphic event in the Brasília Belt (Ferreira et al. 1994, Pimentel et al. 2000).

In this paper we present a preliminary structural and petrographic characterization of rocks from the Ponta da Juréia, the results of the first analyses of U-Pb in monazite from these rocks, together with a discussion of their tectonic meaning and the differences from the neighboring gneissic migmatites.

GEOLOGICAL SETTING

Four major tectonic domains limited by important shear zones, characterize the southeastern portion of the State of São Paulo, Brazil. In radar images, the lineaments that correspond to the bordering shear zones are conspicuous (Figure 1). E-W-NE/SW trending lineaments, related to the Neoproterozoic tectonic events, predominate in the whole area. However, former NW trending lineaments can also be individualized, mainly observed in the Registro Domain, or even later ones, related to the Guapiara Structural Alignment (Almeida 1983).

The Embu Domain, to the north of the Cubatão Shear Zone (CSZ), is composed mainly of medium to high grade metasedimentary rocks, locally migmatized, intruded by pre-collisional peraluminous granites, and stretched out by E-NE trending shear zones (Cubatão - Itariri Shear System - CISS). Gneiss-migmatite rocks and related granites presenting E-NE structural fabrics predominate in the Mongaguá Domain, which is limited by the Cubatão and Itariri (ISZ) Shear Zones. The Juréia Massif is part of the Registro Domain, which is composed of metasedimentary and granitic rocks with migmatitic structures, between the Cubatão-Itariri and the Serrinha (SSZ) Shear Zones. It represents a Paleoproterozoic domain intensely affected by Neoproterozoic tectonic events. The domain has a NW-SE trending structure, which swings to E or NE under the influence of the CISS. Rocks of the Iguape Domain, limited to the north by the SSZ, include granites and low-grade metasediments with a dominantly NE structural orientation (Figure 2).

Migmatitic granite-gneiss rocks occupy the largest part of the Registro Domain and correspond to what Dantas et al.(1987) named Gneissic-Migmatitic Complex and Granitic Suite of the migmatitic facies.Likewise, the paragneisses cropping out in the Juréia Massif would correspond to the undifferentiated Gneissic-Migmatitic Complex of Silva (1981) and Silva et al. (1981).

The rocks from the outcrops of the studied area, Ponta da Juréia, were described for the first time by Morgental et al.(1973), as "gneissic leptinolites, with stretched quartz-feldspatic lenses" incorporated into the Undifferentiated Gneissic Migmatitic Complex (Morgental et al. 1975, Silva et al. 1978, 1981).

Hasui et al. (1981) related the Juréia Massif rocks tothat gneissic-migmatitic of Costeiro Complex, a terrene that would include all rocks that outcrop to thesouth of the Cubatão shear zone in the area.

The gneissic-migmatitic rocks are associated with granitic and metasedimentary rocks of the CachoeiraSequence (Silva et al.1981, Dantas et al.1987). The Juréia Massif rocks were correlated with the Cachoeira Sequence by Passarelli (2001), that comprise kinzigites and kinzigitic gneisses that crop out in the Itatins Massif area, petrographically characterized by sillimanite-biotite-garnet gneisses (Picanço et al. 1998).

The rocks of the Cachoeira Sequence are considered as supracrustal remains of volcano-sedimentary sequences, preserved from the intense Neoproterozoicmigmatization and anatexis (Silva 1981, Dantas et al. 1987). In the area calci-silicatic rocks, dolomitic marbles, schists, quartzites and metabasic rocks were also mapped, besides gneisses and kinzigitic gneisses (Dantas et al. 1987, Gimenez Filho et al. 1987).

In a regional context, the Registro Domain (São Paulo State), is correlated with the Curitiba Domain(Paraná State), defined by Siga Jr. et al. (1993), as discussed by Basei et al. (1999) and Passarelli et al. (2004).

PETROGRAPHIC-STRUCTURAL CHARACTERIZATION

The southeasternmost portion of the Juréia Massif, with an area of approximately 47 km², is composed of mylonitic paragneisses affected by the Serrinha Shear Zone (SSZ).

The contacts of the Juréia paragneisses with the gneissic-migmatitic rocks are normally hidden, due to the intense tropical weathering and the vast Tertiary and Quaternary sedimentary cover.

However, as suggested by some authors (Dantas et al. 1987, Gimenez Filho et al. 1987), a gradual contactcan be locally suggested between these rocks.In thecentral part of the Registro Domain, Serrinha region, near Pocinho Hill (Figure 2) a gradual passage is observed between the paragneissic rocks and the cordierite-garnet-biotite granodiorites to tonalites with migmatitic features, which are not granodiorites/tonalites in the igneoussense, but probably deformed leucossomes. Two different paragneisses, seemingly: those blasto-mylonitic, developed under s.l. amphibolite-facies conditions, from the Juréia area, without signs of a former high-grade protholith, whilst those from Serrinha Region are possibly the reworked (mylonitized, sheared) equivalents of the high-grade, cordierite-garnet-biotite tonalitic gneisses. This can be seen even from the differences between biotite from the two sets of rocks.

The SSZ, defined by Passarelli et al. (2000), occurs between Registro and Iguape Domains, presenting mylonitic granitic rocks imbricated with mylonitic metasedimentary rocks.

The mylonitic foliation presents a general E-Wstrike and is associated with a predominantly dextral movement with a conspicuous pure shear component. The coaxial component is observed in the SSZ central portion by means of dextral and sinistral kinematic indicators and symmetric porphyroclasts.

The SSZ presents a conspicuous, 1 km - thick, N35W - trending, SE-dipping ramification, (Figure 2) where sinistral movement is observed associated with a NW thrust component.

The easternmost sector of SSZ affects the Juréia gneissic rocks, with the mylonitic foliation characterized by strong stretching of the quartz-feldspathic portions. The mylonitic foliation (Sm) is folded towards NW and NEE, dipping moderately to sub-horizontally to NE and NW, and the main strike is N54W/30NE (Figure 3),with a gently plunging mineral stretch lineation (Lm). In this east sector, the SSZ is characterized by a dextral lateral ramp.

The paragneisses are bluish-gray and their banding is characterized by cm-sized quartzo-feldspathic stripes intercalated with the predominant biotite-rich porphyroclastic bands. The mylonitic foliation is characterized by stretched porphyroclasts (feldspars and garnet) in a finely-foliated matrix, characterized by strong orientation of biotite crystals.

The mylonitic foliation presents moderate to low dips (Figure 4), and the relationship between mylonitic foliation, mineral stretching and kinematic indication suggests a predominantly eastward distensive transport.

Mafic minerals, such as biotite and muscovite,predominate in the paragneisses. The development ofquartzo-feldspathic remobilizations is common. These rocks are garnet-rich and porphyroblasts/porphyroclasts may reach 3 ×3 cm (Figure 5).

The occurrence of very flat, stretched and boudinated remobilizations (Figure 6) is not rare in planes sub-parallel to the XZ section, suggesting the influence of deformation with prevailing pure shear component.

The presence of feldspar porphyroclasts or even quartz-feldspathic remobilizations with very symmetrical shapes is quite common in the XZ section of the deformation ellipsoid (Figure 7). However, S-C type structures and rotated plagioclase porphyroclasts of the d-type (Hanmer and Passchier 1991) are observed in sections approximately parallel to XZ (Figure 8), indicating dextral movement.

The paragneisses are characterized by a quartz-biotite-muscovite-plagioclase assemblage, with traces ofgarnet and microcline, and monazite, zircon and tourmaline as accessories.

The foliation is defined by biotite and muscovite orientation and quartz and feldspar stretching. It is characterized by the strong segregation of the quartz-feldspathic bands from the biotite-rich bands. Plagioclase porphyroclasts indicate dextral movement (Figure 9, 10) and can develop pressure shadows, filled with recrystallized quartz (Figure 10).

The quartz crystals tend to segregate in polycrystalline ribbons. They are usually recrystallized or restored, forming sub-grains. The larger grains can preserve the undulose extinction.

The larger oligoclase crystals form fractured, sometimes recrystallized, sigmoidal-shaped porphyroclastswith quartz and muscovite inclusions (Figure 11). The smaller crystals of the matrix are subhedral and clean. They also appear segregated with quartz.

Biotite crystals occur in stripes. They present light yellow to dark, reddish-brown pleochroism, and are subeuhedral.

Garnet crystals also form rounded porphyroclasts and are usually fractured. They present biotite, quartz and muscovite inclusions. They can also develop pressure shadows constituted by quartz, biotite and muscovite.

GEOCHRONOLOGY AND ISOTOPIC GEOLOGY

The U-Pb TIMS (Thermo Ionization Mass Spectrometry) analyses in monazite were carried out in CPGeo (Centro de Pesquisas Geocronológicas) of the Instituto de Geociências of the Universidade de São Paulo (IGc-USP).

Monazite crystals were concentrated by standard crushing and milling, sieving, density separation on the Wilfley table, electromagnetic separation using Frantz equipment, and density separation by heavy liquids (Bromoform and Methylene Iodide). Individual crystals were measured to enable the use of the relation between density and volume in weighing, were then photographed and washed in H₂O, HCl and HNO₃ prior to dissolution.

Individual monazite crystals were dissolved in 3ml Savillex, capsules containing H₂SO₄. and HNO₃ and a mixed ²⁰⁵Pb-²³⁵U tracer solution (spike ²⁰⁵Pb) on a hot plate for 72 hours.

Lead and uranium were isolated in anionic resin columns, according to the procedures described in Basei et al. (1995), adapted from Krogh (1973, 1982) and Parrish (1987).

The measurements were performed by the multicollector mass spectrometer FINNIGAN MAT-262(Sato and Kawashita 2002). At CPGeo, the average values obtained for the NBS-981 and NBS-983 standards were respectively ²⁰⁴Pb/²⁰⁶Pb = 0.05903±0.02% and 0.000368 ±3%; ²⁰⁷Pb/²⁰⁶Pb = 0.91479±0.01% and 0.071212 ±0.05%, and ²⁰⁸Pb/²⁰⁶Pb = 2.1675 ±0.01% and 0.013617 ±0.06%, with annual variation of 1s. The fractionation correction factor used for normalization was 0.095% a.m.u. (atomic mass unit). The results were calculated using the ISOPLOT program (Ludwig 2003) and presented with the corresponding 2s deviations. The constants used are those recommended by Steiger and Jager (1977).

Total procedural blanks for this study ranged from 7 to 4 pg for Pb. Additional analytical details are presented in the Table I.

Analyzed crystals of monazite from a sample representative of the paragneisses from the Juréia Massif (sample K-96, Figure 2) were selected on the basis of their high transparency and lack of inclusions and cracks. Limpid, yellowish monazite crystals of the M (0.6) and M (0.7) magnetic fractions, weighing between 2.4 and 5.4µg, were separated and analyzed.

The analyzed M (0,6) and M (0,7) monazite magnetic fractions presented similar ages, 751±4Ma and 741±7Ma respectively. The age 751±4Ma (Figure 12) is considered the best value due to very good analytical results, with low errors and high ²⁰⁶Pb/²⁰⁴Pb ratio (Table I).

This age is interpreted as the timing of the main regional metamorphic event, registered in metasedimentary rocks of the eastern portion of the Registro Domain (Passarelli 2001), associated with a paragenesis of the high amphibolite facies (J.M. Azevedo Sobrinho, unpublished data), reaching temperatures high enough for the generation of monazites. An important deformation phase around 722 ±30 Ma (Rb-Sr, WR isochron, Picanço et al. 1998) is also registered in the Itatins Complex and Cachoeira Sequence rocks.

As discussed by Giles and Nutman (2002), the possibility of prograde metamorphic growth at > 450ºC and thermal resetting at > 700ºC makes the U-Pb system in monazite a useful geochronometer for amphibolite facies metamorphism.

The T_DM model age of 2293 Ma obtained for these paragneisses can represent a weighted average of the isotopic compositions of their source rocks, therefore a hybrid age.

Highly negative ÎNd(0) and ÎNd(t)_{(t=750 Ma)} values of -22.04 and -13.88 respectively and very high Sr⁸⁷/ Sr⁸⁶ initial ratio of Ri = 0.72996 were obtained, considering the time of the metamorphic event determined by U-Pb dating (monazites). These values are expected for rocks that present important crustal contribution in their formation and long crustal residence. The analytical data are presented in Tables II and ^III.

The K-Ar method was applied to mylonites of the SSZ eastern, central and western sectors (Figure 13). The minerals used were fine-grained biotite of the Juréia paragneiss (eastern sector), fine-grained biotite of the monzogranitic protomylonite (central sector), and coarse-grained muscovite of the mylonitic metasedimentary rock (western sector). The analytical results yielded reliable ages of 482±12 Ma, 493 ±9 Ma, and 575 ±16Ma, from east to west (Table IV).

The age of 575 Ma for the mylonite of the SSZ western sector was obtained in coarser-grained muscovite ( ~ 35 mesh), which must have properly retained the Ar gas in its crystalline lattice. It yielded a similar value to that obtained by the U-Pb method for monazites of thegranitic protomylonite of the SSZ central sector, with ages between 570 and 580 Ma (Passarelli et al.2003). This age, around 575 Ma, is interpreted as the main period of SSZ movement. Other results obtained for biotite crystals may reflect later movements of the shear zone, which can represent the closure of regional heating, associated with the kinematics of the involved tectonic blocks.

Additionally, despite of the analytical errors, the biotite age obtained for the central sector resulted a little older than that obtained for the eastern sector. This suggests that the eastern sector - Juréia paragneisses - would have remained heated for a longer time, that is, remained at temperatures higher than 250ºC for a period a little longer than the other SSZ sectors.

DISCUSSION

The four tectonic domains in the studied area represent the product of assembly of West Gondwana during the Neoproterozoic.

The Juréia Massif paragneisses are inserted in the Registro Domain that shows tectonic contact with adjacent Embu and Mongaguá Domains to the north andwith Iguape Domain to the south, through the Itariri-Cubatão Shear Zone System and the Serrinha Shear Zone respectively.

The geological contacts observed between the migmatitic granite-gneiss rocks and the paragneisses aregradational, and the Cachoeira Sequence rocks could represent the mesossome parts of the migmatites.The neossomatic portions would correspond to the cordierite-garnet-biotite granodiorites to cordierite-garnet-biotite tonalites, that crop out in the central part of the Registro Domain (Serrinha region). In the area between Itariri and Ana Dias, the migmatites neossome also has granodioritic to tonalitic composition, with garnet associated to plagioclase and biotite, and frequently the mesossomes are composed by biotite gneisses, biotite schists, or kinzigites (Picanço et al. 1998).

The Registro Domain correlates southwards with the Curitiba Domain (Basei et al. 1999), and the Juréia Massif paragneisses with the Cachoeira Sequence (Passarelli et al.2004). However, it must be pointed out that the studied rocks from this work are correlated to those from Cachoeira Sequence, that outcrops in the S-SE area of São Paulo state, studied by Dantas et al.(1987), Gimenez Filho et al. (1987) and Picanço et al.(1998).

In addition, a more detailed study is necessary to furnish new insights into the correlation of these rocks with to those originally defined by Silva et al.(1981) also as Cachoeira Sequence, in Paraná State (NNE of Antonina city). In this area, this sequence is predominantly composed by metaultramafic and metapsamitic to metapelitic rocks in the amphibolite to granulite metamorphic facies. Hence, as the Cachoeira Sequence is not a continuously exposed unit, detailed field relations are necessary to confirm or reject the continuity of both units.

The migmatitic granite-gneiss rocks present a poorly preserved Paleoproterozoic record between 1.9 and 2.2Ga (zircon U-Pb ages), and underwent strong reworking in the Neoproterozoic. The Neoproterozoic influence can also be observed in the structure of these rocks, with a gneissic banding developed usually sub-parallel to the mylonitic foliations the Cubatão and ItaririShear Systems.

T_DM ages for the migmatitic granite-gneiss rocks of the Registro Domain, and Atuba Complex (Curitiba Domain) fall between 2.8 and 2.7Ga, locally 2.4 Ga (Gneisses of Timirim Hill - Registro Domain - Passarelli et al. 2004, and Mandirituba Gneisses, Atuba Complex - Siga Jr. et al. 1995), while a T_DM model age of 2.3 Ga for the Juréia gneisses is considered a hybrid age, due to the paraderived material. However, TDM ages around 1.5 Ga are found in a kinzigitic gneiss of Itariri (Picanço et al. 1998), assumed as Cachoeira Sequence outcropped between migmatitic granite-gneiss rocks and granulitic rocks of Itatins Suite, the latter with T_DM ages around 2.5Ga (Picanço et al. 1998).

The age of deposition of the Juréia paragneiss protoliths is still uncertain. On the other hand, monazite U-Pb ages around 750 Ma imprinted in these rocks representa conspicuous deformation phase that reachedthe high amphibolite facies, similarly to what is observed in rocks of the Itatins Complex and the Cachoeira Sequence.

However, the age around 750 Ma, obtained by Rb-Sr on schists of the Embu Complex (Vieira and Tassinari 1988) is associated with the main metamorphic phase of the Embu Complex that achieved high grade ( in situ migmatization) and medium grade (sillimanite zone) (Fernandes et al 1990). In addition, U-Pb monazite ages of 790 Ma obtained in gneissic rocks by Vlach (2001) is interpreted as the main metamorphic event in this domain and indicates a phase associated to a convergent tectonic process. In the São Lourenço da Serra area (São Paulo State), mylonitic orthogneisses, with migmatitic features, presented Rb-Sr (WR) isochron ages of 770 Ma and shrimp ages in zircons of 2000, 800 e 600 Ma, interpreted as inherited, magmatic and metamorphic zircons respectively (Cordani et al. 2000).

In addition, the granite-gneissic rocks of Serra dos Lopes, south of Taxaquara Shear Zone, near Piedade town (São Paulo State) presented an U-Pb zircon age of 788 ±2 Ma (Leite 2003), interpreted as the better age forthe magmatic crystallization of these orthogneisses, considered as host rocks of the sin-orogenic AgudosGrandes Batholith.

For the existent data, the record of the Cryogenian Period in the adjacent Embu and Registro Domains isevident as an important metamorphic and magmaticevent.Evidences of this early thermal-metamorphicevent, within the Brasiliano Cycle, have still not been found in Registro Domain more to the south (Curitiba Domain).

ACKNOWLEDGMENTS

This study was supported by grants (CRP and MASB respectively, 03/13246-6 and 04/07837-4) from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP). The authors thank Estação Ecológica da Juréia-Itatins (EEJI) for permission to field work in the restricted area of the Juréia Massif. Special thanks are due to the anonymous reviewers.

Manuscript received on April 4, 2006; accepted for publication on August 21, 2006; contributed by MIGUEL A.S. BASEI

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*

Member Academia Brasileira de Ciências

Publication Dates

• Publication in this collection
  27 Aug 2007
• Date of issue
  Sept 2007

History

• Accepted
  21 Aug 2006
• Received
  04 Apr 2006