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)....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.展开更多
The generation of the continental crust is widely accepted to have taken place predominantly in the Archean,when TTG magmatism associated with greenstone-belt supracrustal succession development was typically followed...The generation of the continental crust is widely accepted to have taken place predominantly in the Archean,when TTG magmatism associated with greenstone-belt supracrustal succession development was typically followed by emplacement of high-K granites before crustal stabilization.This study focuses on the Campos Gerais complex(CGC),which is an Archean granite-greenstone belt lithological association in a tectonic window located in the southwesternmost portion of the São Francisco craton(SFC).The CGC is an important segment of Paleo-to Mesoarchean continental crust to be integrated into paleogeographic reconstructions prior to the transition into the Paleoproterozoic.This investigation reports field relationships,28 major and trace element compositions,U–Pb(zircon)geochronological results,and Hf and Sm–Nd isotope data for orthogneiss and amphibolite samples.The results indicate that the CGC records a complex Archean crustal evolution,where voluminous 2.97 Ga TTG tonalites and trondhjemites(ε_(Nd)(t)=-4.7;T_(DM)=3.24 Ga)were followed by 2.89 Ga sanukitoid tonalite production(ε_(Nd)(t)=-1.9;T_(DM)=3.02 Ga),broadly coeval with the development of the Fortaleza de Minas and Pitangui greenstone-belts.These events are interpreted to represent the initial stage of an important subduction-accretion tectonic cycle,which ended with the emplacement of 2.82–2.81 Ga high-K leucogranites and migmatization of the TTG-sanukitoid crust,with hybrid and two-mica,peraluminous compositions(ε_(Nd)(t)=-8.0 to-8.6;T_(DM)=3.57–3.34 Ga).The presence of inherited zircons with207Pb/206Pb ages of 3.08 Ga,3.29 Ga,3.55 Ga and 3.62 Ga indicates that the Mesoarchean tectonic processes involved reworking of Meso-to Eo-archean crust.Renewed TTG magmatism took place at ca.2.77 Ga represented by juvenile tonalite stocks(ε_(Nd)(t)=+1.0 to-1.5;T_(DM)=2.80–2.88 Ga)which intrude the TTG-greenstone belt association.Crustal stabilization was attained by 2.67 Ga,allowing for the emplacement of within-plate tholeiitic amphibolites(ε_(Nd)(t)=-3.1;T_(DM)=2.87 Ga).The CGC shows important tectonic diachronism with respect to other Archean terrains in the southern São Francisco craton,including an independent Meso-to Neoarchean crustal evolution.展开更多
基金FAPERJ,CNPQ,CAPES and FINEP funding agenciesjoint projects with CPRM and Petrobras。
文摘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.
基金support from the PRONAGEO mapping program of the CPRM(Brazilian Geological Service)funding to CMV and MH respectively。
文摘The generation of the continental crust is widely accepted to have taken place predominantly in the Archean,when TTG magmatism associated with greenstone-belt supracrustal succession development was typically followed by emplacement of high-K granites before crustal stabilization.This study focuses on the Campos Gerais complex(CGC),which is an Archean granite-greenstone belt lithological association in a tectonic window located in the southwesternmost portion of the São Francisco craton(SFC).The CGC is an important segment of Paleo-to Mesoarchean continental crust to be integrated into paleogeographic reconstructions prior to the transition into the Paleoproterozoic.This investigation reports field relationships,28 major and trace element compositions,U–Pb(zircon)geochronological results,and Hf and Sm–Nd isotope data for orthogneiss and amphibolite samples.The results indicate that the CGC records a complex Archean crustal evolution,where voluminous 2.97 Ga TTG tonalites and trondhjemites(ε_(Nd)(t)=-4.7;T_(DM)=3.24 Ga)were followed by 2.89 Ga sanukitoid tonalite production(ε_(Nd)(t)=-1.9;T_(DM)=3.02 Ga),broadly coeval with the development of the Fortaleza de Minas and Pitangui greenstone-belts.These events are interpreted to represent the initial stage of an important subduction-accretion tectonic cycle,which ended with the emplacement of 2.82–2.81 Ga high-K leucogranites and migmatization of the TTG-sanukitoid crust,with hybrid and two-mica,peraluminous compositions(ε_(Nd)(t)=-8.0 to-8.6;T_(DM)=3.57–3.34 Ga).The presence of inherited zircons with207Pb/206Pb ages of 3.08 Ga,3.29 Ga,3.55 Ga and 3.62 Ga indicates that the Mesoarchean tectonic processes involved reworking of Meso-to Eo-archean crust.Renewed TTG magmatism took place at ca.2.77 Ga represented by juvenile tonalite stocks(ε_(Nd)(t)=+1.0 to-1.5;T_(DM)=2.80–2.88 Ga)which intrude the TTG-greenstone belt association.Crustal stabilization was attained by 2.67 Ga,allowing for the emplacement of within-plate tholeiitic amphibolites(ε_(Nd)(t)=-3.1;T_(DM)=2.87 Ga).The CGC shows important tectonic diachronism with respect to other Archean terrains in the southern São Francisco craton,including an independent Meso-to Neoarchean crustal evolution.
