Geologia USP. Série Científica (Dec 2011)
Extensional and Colisional Magmatic Records in the Apiaí Terrane, South-Southeastern Brazil: Integration of Geochronological U-Pb Zircon Ages
Abstract
The aim of this work is the presentation of a synthesis of available geochronological data for the basement inliers andmetavolcano-sedimentary sequences which occur in the southern part of the Apiaí Terrane, south-southeastern Brazil.These data, especially those obtained during the last decade, have made substantial modifi cations to the tectonic scenarioof south-southeastern Brazil with the recognition of the presence of extensional basins (continental rifts) with magmatismand sedimentation at the late Paleoproterozoic (1790 - 1750 Ma) and of the Mesoproterozoic (1600 - 1450 Ma). Theseprocesses started at the late Paleoproterozoic in the Betara, Perau and Apiai Mirim Nuclei, and the basins became widerduring the Mesoproterozoic with the deposition of the Betara, Perau, Votuverava and Água Clara metavolcano-sedimentarysequences. A different pattern is found for the Itaicoca Sequence which occupies the northern part of the Apiaí Terrain.Here two rock associations of different ages are found. The fi rst is a metamorphosed carbonate platform association withsubalkaline, tholeiitic metabasic rocks with minimum deposition ages at the end of the Mesoproterozoic or beginning of theNeoproterozoic (Itaiacoca Sequence; 1030 - 900 Ma), while the second mainly contains metapsammites and metavolcanicrocks including ultrapotassic trachytes deposited during the Cryogenian-Ediacaran transition between 645 and 628 Ma(Abapã Sequence). It is then proposed that the present scenario of the Apiaí Terrane be representative of the distincttectono-sedimentary histories, refl ecting a polycyclic evolution. In the Mesoproterozoic, stable conditions prevailed, withthe deposition of the majority of the sequences (Lajeado, Água Clara, Betara, Perau, Votuverava) in a passive margincontext, succeded by a Tonian extensional phase (deposition of the Itaiacoca Sequence). In the Ediacaran the region wastransformed into an unstable active margin, with the predominance of magmatic arcs (Três Córregos, Cunhaporanga andAgudos Grandes) and restricted sedimentation (Abapã, Antinha and Iporanga Sequences).
