Chemale Hartmann and Da Silva Brasiliano Cycle Southern
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Communs geol. Surv. Namibia, 10 (1995), 153-168 Stratigraphy and tectonism of the Brasiliano Cycle in southern Brazil F. Chemale Jr.1, L.A. Hartmann1 and L.C. da Silva2 1Departamento de Geologia, 1G-UFRGS, 90570-970 Porto Alegre, Brazil. 2Departamento de Geologia, Brazilian Geological Survey (CPRM), Porto Alegre, Brazil Juvenile crustal accretion in the Brasiliano Cycle occurred in the São Gabriel Block of southern Brazil, whereas the Dom Feliciano Belt along the Atlantic coast corresponds mainly to Brasiliano granites, gneisses and migmatites mostly derived from a Palaeoprot- erozoic to Archaean crust. These geotectonic units are separated by a volcano-sedimentary rift-related sequence of probable Mesopro- terozoic age, strongly reworked during the Neoproterozoic. The basement rocks are represented by Palaeoproterozoic granulites and the Uruguayan granite-greenstone belts that define an important geotectonic cycle in southern Brazil, the Trans-Amazonian Cycle. However, the Brasiliano Cycle was most significant in the region, defined by two main tectonic events, the São Gabriel (750-700 Ma) and Dom Feliciano (around 600 Ma) events. W- and NW-verging thrust-related tectonics and later strike-slip deformation are recog- nised in the region. Granitic and effusive magmatism is abundant as a late manifestation of the Brasiliano Cycle in southern Brazil, along with the generation of foreland sedimentary basins. Introduction Geological setting The Archaean to Early Palaeozoic of southern Brazil The study area covers part of the Mantiqueira Province is covered by younger Phanerozoic sequences. These (Fig. 1) which consists of Archaean to Late Palaeozoic units have been strongly affected by the Brasiliano Cy- units formed during at least four main orogenic cycles, cle (1000 to 470 Ma) resulting in a complex tectonic namely the Jequié (3330-2600 Ma), Trans-Amazonian arrangement, juxtaposing Palaeoproterozoic units to (2600-1800 Ma), Uruçuano (1800 to 1000 Ma) and Bra- Brasiliano terranes. siliano (1000-450 Ma) (Almeida and Hasui, 1984). The The Brasiliano Cycle in the region includes a com- Mantiqueira Province, a NE-SW-trending geotectonic plex tectonic stratigraphic arrangement of granite- unit, has been strongly affected by Brasiliano tectonics. migmatitic-gneissic terranes, volcano-sedimentary su- This has resulted in multiple granitic intrusions and re- pracrustal metamorphic rocks and late- to post-tectonic working of Archaean to Mesoproterozoic granite-gneiss volcano-sedimentary sequences. The latter represent terranes as well as some Mesoproterozoic greenschist to the final stages of the Brasiliano Cycle, during which amphibolite supracrustal sequences. This Province can the assembly of West Gondwana occurred. The Man- be divided into northern, central and southern sectors, tiqueira Province (Fig. 1) is one of the main Brasiliano only the last being discussed in this paper. The southern geotectonic units, and is the location of the study area segment of Mantiqueira Province is situated, running within Brazil (Almeida et al., 1977). from south to north, in Uruguay and the Rio Grande Several authors have applied plate tectonic models to do Sul (RS) and Santa Catarina (SC) states of Brazil, this part of Brazil using regional geological data, and comprising the following units (Fig. 2): by correlating the Brasiliano/pan-African belts such as a) Palaeoproterozic granite-greenstone terrane and the Ribeira, Dom Feliciano, Damara and Gariep Belts the Ismael Cortinas mafic dyke swarm which corre- in southern Brazil and southern Africa respectively sponds to Palaeoproterozoic units in Uruguay, called (Porada, 1979, 1989; Basei, 1985; Brito Neves and the Florida Block by Frãgoso-Cesar (1991). Cordani, 1990; Frãgoso-Cesar, 1991; Fernandes et al., b) Palaeoproterozoic high-grade terranes, the Santa 1992). Nevertheless, several questions still remain un- Catarina Granulite Complex (SCGC on Fig. 2b) and answered. The study area does not display complete se- Santa Maria Chico Granulite Complex (SMCGC on quences and in spite of extensive geological mapping, Fig. 2b). Both are somewhat affected by the Brasiliano little reliable isotope data used in the above mentioned Cycle, resulting in strike-slip tectonic reactivation, in- papers are available to formulate a consistent tectonic trusion of granites and deposition of late- to post-tec- model. tonic volcano-sedimentary sequences (e.g. Itajaí Basin The main purpose of this paper is to present the and Taquerembó volcanic rocks). stratigraphy of different geological terranes affected c) The Tijucas belt is made up of greenschist to am- by the Brasiliano Cycle in southern Brazil (Fig. 2) and phibolite facies supracrustal rocks with some exposures sketch the main tectonic features, with support of field of Palaeoproterozoic gneissic rocks. U/Pb zircon data geology, geochemistry and available geochronological from metavolcanic rocks give a minimum age of 1400 results. We also propose a lithospheric model to explain Ma (Orlandi Filho et al., 1990) for the Formation of the data. these rocks. However, the belt was deformed during the Dom Feliciano Event (see below). 153 Chemale, Hartmann and da Silva d) The Neoproterozoic to Early Palaeozoic Vila Geology of basement rocks Nova Belt is represented by tonalitic to granodioritic gneisses, greenschist to amphibolite facies volcano- Santa Catarina Granulite Complex sedimentary rocks, mafic-ultramafic units (with a close relation to the volcano-sedimentary rocks), foliated This complex is made up mostly of depleted TTG granites, formed and/or deformed by the Silo Gabriel granulitic orthogneisses, and contains small interleaved Event between 700-750 Ma (Chemale et al., 1994a). supracrustal lenses composed of banded iron Forma- e) The Neoproterozoic to Early Palaeozoic Dom tion, quartzites, calc-silicate gneisses and rare kinzin- Feliciano Belt is represented by different types of Bra- gites (Hartmann et al., 1979). Undepleted bimodal or- siliano granitic rocks and units of older cycles. This thogneisses and small bodies of basic-ultrabasic rocks belt corresponds to an association of Brasiliano flat- of tholeiitic affinity occur in restricted areas. lying migmatic gneisses and granites as well as some The regional planar fabric in these rocks consist of Archaean to Palaeoproterozoic remnants of tonalitic- NS-trending, subvertical gneissic banding, intensely trondjemitic gneisses, amphibolites, paragneisses and transposed along the southern border of the complex anorthosites. These units have been formed/deformed by strikeslip mega-shear zones oriented at N45°E (Per- during the Dom Feliciano Event with the main tecto- imbó shear zone, Fig. 3). In the interior of the complex no-metamorphic peak at 562-616 Ma (Chemale et al., there is a Neoproterozoic tectonic reactivation of NE- 1994b). SW and E-W faults. f) Late to post-tectonic plutono-volcanic-sedimenta- The main metamorphic high-grade event occurred ry sequences, the Seival and Itajaí Associations, which at 2.2 Ga during the Trans-Amazonian orogeny (Hart- are foreland manifestations of the Dom Feliciano Event mann et al., written com., 1993; Basei, 1985). Howev- in the Palaeoproterozoic Granulite Complexes and in er, these rocks formed during the late Archaean (Basei, the Vila Nova Belt. 1985; Mantovani et al., 1987). 154 Stratigraphy and tectonism of the Brasiliano Cycle, southern Brazil Santa Maria Chico Granulite Complex and 2020 Ma, Umpierre and Halpern, 1971; Cingolani et al., 1990) and low-grade volcano-sedimentary belts The Santa Maria Chico Granulite Complex occurs SW intruded by late granites. These granites yield a Rb/Sr of the lbaré Shear Zone (Fig. 4). It is made up of quartz- age of 1970 Ma (Umpierre and Halpern, 1971). feldspathic gneisses (tonalites and trondhjemites), ma- The Ismael Cortinas mafic dyke swarm occurs as fic gneisses, anorthosites, ultramafics and supracrustal several N60°-80°E-trending mafic dykes cutting the rocks metamorphosed up to amphibolite and granulite granite-greenstone terrane. K-Ar, Rb-Sr and Sm-Nd grade (Nardi and Hartmann, 1979). The regional planar radiometric results of these dykes point to a meaning- fabric is E-W, developed during the high grade meta- ful crustal stretching event at 1800 Ma (Bossi et al., morphism at 2100 Ma (Sm-Nd mineral age, Hartmann, 1993). 1987). However, these rocks were accreted during the Archaean (Tdm Sm-Nd age, Hartmann, written com., Stratigraphy and Tectonism of the Brasiliano Belts 1993). in Southern Brazil The Complex is intruded by Brasiliano (younger than 600 Ma) granites and partly covered by early Palaeozo- The authors recognise the following Brasiliano geo- ic, late to post-tectonic volcano-sedimentary rocks. The tectonic units in southern Brazil, the Vila Nova Belt, Brasiliano Granites are included in the Santo Afonso Tijucas Belt and Dom Feliciano Belts. While the Vila Suite. In the Isla de Rivera, extensive gold mineralisa- Nova Belt corresponds to one of few areas in Brazil tion occurrences are associated with Brasiliano strike- with Brasiliano accretion (Babinski et al., in prep.), the slip shear zones oriented WNW-ESE and N-S. Tijucas and Dom Feliciano Belts are pre-Brasiliano crust with strong Uruguayan granite-greenstone belt reworking during the Neoproterozoic. Especially in the DFB, where there occurs a great volume of Brasiliano The Uruguayan granite-greenstone belt comprises of granites, migmatites and gneisses that always display dioritic to granodioritic granite-gneiss complexes (2070 negative epsilon Nd