Neoarchean and Rhyacian TTG-Sanukitoid suites in the southern S?o Francisco Paleocontinent,Brazil:Evidence for diachronous change towards modern tectonics

作者：Henrique Bruno,Vitalino Elizeu,Monica Heilbron,Claudio de Morisson Valeriano,Rob Strachan,Mike Fowler,Samuel Bersan,Hugo Moreira,Ivo Dussin,Luiz Guilherme do Eirado Silva,Miguel Tupinamba,Julio Almeida,Carla Neto,Craig Storey

摘要：The southern portion of the Sao Francisco Palaeocontinent in Brazil is denoted by Archean nuclei and Paleoproterozoic magmatic arcs that were amalgamated during Siderian to Orosirian orogenic processes(ca.2.4-2.1 Ga).New isotopic U-Pb in zircon and Sm-Nd whole rock combined with major and trace element composition analyses constrain the crystallization history of the Neoarchean Piedade block(at ca.2.6 Ga)and the Paleoproterozoic Mantiqueira Complex(ca.2.1-1.9 Ga).These therefore display quite different magmatic histories prior to their amalgamation at ca.2.05 Ga.Sm-Nd and Rb-Sr isotopes imply a mixed mantle-crustal origin for the samples in both units.A complete Palaeoproterozoic orogenic cycle,from subduction to collision and collapse,is recorded in the Piedade Block and the Mantiqueira Complex.Rhyacian to Orosirian subduction processes(ca.2.2-2.1 Ga)led to the generation of coeval(ca.2.16 Ga)TTG suites and sanukitoids,followed by late(2.10-2.02 Ga)high-K granitoids that mark the collisional stage.The collisional accretion of the Mantiqueira Complex against the Piedade Block at 2.08-2.04 Ga is also recorded by granulite facies metamorphism in the latter terrane,along the Ponte Nova suture zone.The collisional stage was closely followed by the emplacement of within-plate tholeiites at ca.2.04 Ga and by alkaline rocks(syenites and enriched basic rocks)at ca.1.98 Ga,marking the transition to an extensional tectonic regime.The discovery of two episodes of TTG and sanukitoid magmatism,one during the Neoarchean in the Piedade Complex and another during the Rhyacian in the Mantiqueira Complex,indicates that the onset of subduction-related melting of metasomatized mantle was not restricted to Neoarchean times,as generally believed,but persisted much later into the Paleoproterozoic.

发文机构：Universidade Do Estado Do Rio de Janeiro University of Portsmouth Universit€at Salzburg Universidade Federal de Ouro Preto Laboratorio de Geocronologia e Isotopos Radiog^enicos

关键词：GeodynamicsHighBa–SrgranitoidsDiachronousTTG-SanukitoidtransitionPaleoproterozoicMantiqueiracomplex

分类号： P58[天文地球—岩石学]