Ligia Maria de Almeida Leite Ribeiro

The Betara region was located at nothwest of the Curitiba City between the Campo Largo and Rio Branco do Sul municipal districts. This region includes granite-gnaissic rocks, proto to milonitics (Betara Nucleous) and metavolcanossedimentary sequences with low to intermediate metamorphic grade (Betara Formation). These terrains occur at the southern portion of the Ribeira Belt, surrounded by metavolcanossedimentary sequences of the Votuverava Formation. The main objective of this work was realize geologic-geochronologic studies (U-Pb zircon) of metabasic rocks associated with the metavolcanossedimentary sequences (Betara Formation), as well the metabasic rocks associated with the proto milonitic to milonitic granite-gnaissic terrains (Betara Nucleous). At the center-southern portion of the Betara Region, was recognized granodioritic rocks, proto to milonitic formed during the Paleoproterozoic (~2200 Ma) with archean inheritances (zircon nucleous ~2800 Ma). Archean values (~3200Ma) where obtained with Sm-Nd (TDM) method. This values where indicative for the mantle carries away ages for the crustal protolites of these rocks. These terrains are limited at the south by the Lancinha Shear Zone, who separates the Apiaí Domain (north) from the Atuba Complex (south). In this tectonic context, the proto to milonitc ganodioritic terrains represents peaces from the basement and possibly can be related to the Paranapanema Cratonic Region. This correlations are not a simple work and the geologic propers with the geologic patterns was to close to that observed for the Setuva Nucleous (Siga Júnior et al., 2006 no prelo) and for the Atuba Complex ( Siga Júnior et al., 1995 e Sato et al., 2003). In tectonic contact with the granodioritic terrains occurs some sienogranitic rocks proto to milonitics associated with metabasic rocks (magma mixing and/or magma mingling). The U-Pb zircon values obtained to the sienogranitic rocks was related to the Upper Paleoproterozoic (1780-1750 Ma; Kaulfuss, 2001 e Cury et al., 2003), very close to the ages obtained for the metabasic rocks (U-Pb zircon at 1789+-22 Ma). The occurrence of the sienogranitic rocks associated with metabasic rocks; with anorogenic characteristics may imply extensional systems and represents an important frame on this region, related to the Estatherian Tafrogenetic Event. Increases the possibilities to occur some sedimentation associated to this anorogenic magmatism, related to rift type basins developed during this period. Ages from this interval (1800 - 1600 Ma) occurs at the Apiaí Belt for the sienogranites proto to milonitics from the Tigre Nucleous at the south of the Passa Tres granitic body and at the nothwesthern portion of the granitic bathollite Três Córregos (Kaulfuss, 2001; Cury et al., 2003 e Prazeres Filho, 2005). In the South American Continent was recognized at a great part of this center west portion (Borborema Province, Espinhaço System, São João Del Rei Group, Tocantins Province and Ribeira Belt) according with Brito Neves et al. (1995). This tafrogenetic record was relatively synchronic, but variate in magnitude and extension and at most part of the time was related to crustal rifts with alkaline to sub alkaline magmatism associated with siliciclastic sedimentation. Might represent important scars associated with the breakage of some large continental masses agglutinated during the Paleoproterozoic (Atlantica Suercontinent, Rogers, 1996) or as same during the Paleo-Mesoproterozoic (Columbia Supercontinet; Rogers and Santos, 2002; Zhao et al., 2004). The geologic studies of the metavolcanossedimentary sequences (Betara Formation) in tectonic contact with sienogranitic-granodioritic terrains (Betara Nucleous) admit to recognize three major units: Metapsamitic sequence (lower), recognized mainly by quartzites, a marble, calciossilicatic and marly sequence (intermediary) and a metapelitic sequence (upper) where predominate phyllites associated with metabasic rocks. The geochronological data obtained from the U-Pb (zircon) method refers to metabasic rock bodies (dikes or sills) who occurs in conformity and intercalated with the upper pelitic sequence. The geochemical studies of this bodies indicates this ortho derived nature and a subalkaline chemical characteristics who suggests a distensive ambient. The ages obtained in a range between 1500-1450 Ma can be interpreted like minimal ages to deposition for the Betara Formation. Values at this same range (1450-1500 Ma) were obtained recently to the Votuverava, Perau and Água Clara Formations. The Mesoproterozoic represents an important frame related to deposition of the great part of the metavolcanossedimentary sequences of the southern Ribeira Belt. The geologic-geochronologic patterns, with the structural patterns observed to the Betara Region suggests whom the placement of this terraines at the upper crustal levels occurs at the Neoproterozoic, function of a shear-controlled tectonics.

"Estudo geológico-geocronológico dos terrenos granito-gnáissicos e sequências metavulcanossedimentares da Região do Betara (PR)" / "Geologic-geochronologic study from the granite-gnaissic terranes and metavolcanossedimentary sequences from Betara Region (PR)"

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