Aspectos tectônicos das intrusões dos granitos do cerne, passa três e Rio Abaixo, sudeste do Pré-cambriano Paranaense. Estudo baseado em datações 39Ar-40Ar em Micas

Abstract

The Cerne, Passa Três and Rio Abaixo granitic stocks are NE-SW-striking elliptic bodies intrusive in the metavolcano-sedimentary sequences of the southeastern portion of the Ribeira Belt (Paraná State, Brazil). These stocks are mainly biotite syenogranite, monzogranite and quartz-syenite with porphyritic textures containing microcline megacrystals. They are usually isotropic, but may also contain magmatic flow foliation and deformation restricted to the contact with the host rocks. These granites present petrological, geochemistries and geocchronological similarities, with many A-type characteristics, but they are enriched in Ba Sr and Zr. 40Ar-39Ar analyses of the Cerne Granite biotites indicate an integrated age of 557 ± 2 Ma, which is quite close to the lower Concordia intercept age interpreted as the crystallization age of about 563 Ma obtained by TIMS analysis of zircon from the Cerne and Rio Abaixo intrusions by Cury (2003). The 40Ar-39Ar determinations in the host muscovite schists from the vicinity of the Cerne granite are older (800-1200 Ma) than crystallization ages, indicating that the temperatures of the granite intrusion and of the regional metamorphic event that took place during the Brasiliano Cycle (c.a. 600 Ma) were not high enough to erase the isotopic record from these muscovites (T < 300ºC). These granitic stocks represent a late-orogenic magmatism (~560 Ma) in the context of the deformations phases registered in the Apiaí Domain, being different and subsequent to the event of Três Córregos - Cunhaporanga magmatic arc (c.a. 630-590 Ma). Their emplacement was closely associated with transcurrent shear zones and the development of the major antiforms and synforms during the Upper Proterozoic/Cambrian, associated with the final adjustments of the agglutination of the Gondwana Supercontinent.