The Lajeado Group in the Ribeira Belt, southeastern Brazil, corresponds to an open-sea carbonate platform, comprised of seven overlapping siliciclastic and carbonatic formations, intruded in its upper portion by the A...The Lajeado Group in the Ribeira Belt, southeastern Brazil, corresponds to an open-sea carbonate platform, comprised of seven overlapping siliciclastic and carbonatic formations, intruded in its upper portion by the Apiai Gabbro. These rocks have a Neoproterozoic tectonometamorphic overprint related to arc magmatism and the Brasiliano collisional orogeny. Geochronological constraints are given by new U- Pb SHRIMP and LA-ICP-MS data for Lajeado Group detrital zircons and for magmatic zircons from the Apial Gabbro. The youngest detrital zircons in the Lajeado Group are 1400-1200 Ma, and constrain its maximum age of deposition to be 〈1200 Ma, whereas the 877 ~ 8 Ma age for magmatic zircons in the Apiai Gabbro give the minimum age. Detritus source areas are mainly Paleoproterozoic （2200-1800 Ma） with some Archean and Mesoproterozoic contribution （1500-1200 Ma）, with distal or tectonic stable cratonic character. The Lajeado Group should be a Stenian-Tonian carbonate platform passive margin of a continent at this time, namely the Columbia/Nuna or the Rodinia. The Apial Gabbro displays similar age to other intrusive basic rocks in the Lajeado and Itaiacoca groups and represents tholeiitic MORB-like magmatism that we relate to the initial break-up of a Mesoproterozoic continent and the formation of the Brasiliano oceans.展开更多
基金the Fundacao de AmparoàPesquisa do Estado de Sao Paulo e FAPESP,grants 01/13457-1 and 06/01327-0,for financial supportthe GeoQuEST Research Centre of the University of Wollongong for support
文摘The Lajeado Group in the Ribeira Belt, southeastern Brazil, corresponds to an open-sea carbonate platform, comprised of seven overlapping siliciclastic and carbonatic formations, intruded in its upper portion by the Apiai Gabbro. These rocks have a Neoproterozoic tectonometamorphic overprint related to arc magmatism and the Brasiliano collisional orogeny. Geochronological constraints are given by new U- Pb SHRIMP and LA-ICP-MS data for Lajeado Group detrital zircons and for magmatic zircons from the Apial Gabbro. The youngest detrital zircons in the Lajeado Group are 1400-1200 Ma, and constrain its maximum age of deposition to be 〈1200 Ma, whereas the 877 ~ 8 Ma age for magmatic zircons in the Apiai Gabbro give the minimum age. Detritus source areas are mainly Paleoproterozoic （2200-1800 Ma） with some Archean and Mesoproterozoic contribution （1500-1200 Ma）, with distal or tectonic stable cratonic character. The Lajeado Group should be a Stenian-Tonian carbonate platform passive margin of a continent at this time, namely the Columbia/Nuna or the Rodinia. The Apial Gabbro displays similar age to other intrusive basic rocks in the Lajeado and Itaiacoca groups and represents tholeiitic MORB-like magmatism that we relate to the initial break-up of a Mesoproterozoic continent and the formation of the Brasiliano oceans.
