Extensional and colisional magmatic records in the Apiai Terrane, south-southeastern Brazil: integration of geochronological U-Pb zircon ages

The aim of this work is the presentation of a synthesis of available geochronological data for the basement inliers and metavolcano-sedimentary sequences which occur in the southern part of the Apiai Terrane, south-southeastern Brazil. These data, especially those obtained during the last decade, have made substantial modifi cations to the tectonic scenario of south-southeastern Brazil with the recognition of the presence of extensional basins (continental rifts) with magmatism and sedimentation at the late Paleoproterozoic (1790 - 1750 Ma) and of the Mesoproterozoic (1600 - 1450 Ma). These processes started at the late Paleoproterozoic in the Betara, Perau and Apiai Mirim Nuclei, and the basins became wider during the Mesoproterozoic with the deposition of the Betara, Perau, Votuverava and gua Clara metavolcano-sedimentary sequences. A different pattern is found for the Itaicoca Sequence which occupies the northern part of the Apiai Terrain. Here two rock associations of different ages are found. The fi rst is a metamorphosed carbonate platform association with subalkaline, tholeiitic metabasic rocks with minimum deposition ages at the end of the Mesoproterozoic or beginning of the Neoproterozoic (Itaiacoca Sequence; 1030 - 900 Ma), while the second mainly contains metapsammites and metavolcanic rocks including ultrapotassic trachytes deposited during the Cryogenian-Ediacaran transition between 645 and 628 Ma (Abapa Sequence). It is then proposed that the present scenario of the Apiai Terrane be representative of the distinct tectono-sedimentary histories, refl ecting a polycyclic evolution. In the Mesoproterozoic, stable conditions prevailed, with the deposition of the majority of the sequences (Lajeado, gua Clara, Betara, Perau, Votuverava) in a passive margin context, succeded by a Tonian extensional phase (deposition of the Itaiacoca Sequence). In the Ediacaran the region was transformed into an unstable active margin, with the predominance of magmatic arcs (Tres Corregos, Cunhaporanga and Agudos Grandes) and restricted sedimentation (Abapa, Antinha and Iporanga Sequences).