The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inl...The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inlier related to the Southern S?o Francisco Craton(SSFC),are integrated with geochronological,isotopic and geochemical data on Archean granitoids from the SSFC.The rocks are divided into three main geochemical groups with different ages:(1)TTG(3.02–2.77 Ga);(2)mediumto high-K granitoids(2.85–2.72 Ga);and(3)A-type granites(2.7–2.6 Ga).The juvenile to chondritic(Hf-Nd isotopes)TTG were divided into two sub-groups,TTG 1(low-HREE)and 2(high-HREE),derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts.The compositional diversity within the TTG is attributed to different pressures during partial melting,supported by a positive correlation of Dy/Yb and Sr/Zr,and batch melting calculations.The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs,indicating the presence of subduction processes concomitant with TTG emplacement.From~2.85 Ga to 2.70 Ga,the dominant rocks were K-rich granitoids.These are modeled as crustal melts of TTG,during regional metamorphism indicative of crustal thickening.Their compositional diversity is linked to:(i)differences in source composition;(ii)distinct melt fractions during partial melting;and(iii)different residual mineralogies reflecting varying P–T conditions.Post-collisional(~2.7–2.6 Ga)A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms,and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle.The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening,regional metamorphism and crustal melting,and post-collisional extension,similar to that seen in younger Wilson Cycles.It is compelling evidence that plate tectonics was active in this segment of Brazil from~3 Ga.展开更多
High-resolution U–Pb(ID-TIMS,baddeleyite)ages are presented for mafic dykes from selected swarms in two important Amazonian regions:the Carajás Province in the east,and the Rio Apa block in the southwest–areas
Several generations of mafic dyke swarms(2.7 to 0.8Ga),highlighted by aeromagnetic data,petrography,geochemistry,isotope geology and mostly U-Pb baddeleyite ages,crosscut the Archean and
The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated T_(Zr)<800 ℃ for most samples. Its mineralogy is dominated by quartz a...The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated T_(Zr)<800 ℃ for most samples. Its mineralogy is dominated by quartz and feldspar(77% to 95%), biotite is the only mafic mineral present(2% to 18%) and, titanite, zircon, apatite, allanite are important accessory phases. These rocks range from metaluminous to weakly peraluminous, and have large variation in major and trace elements, and high alkali contents(>6 wt.%). Zircon analyses by LA-ICP-MS and SHRIMP yielded a concordia age of 2 119±10 Ma for the porphyritic facies and an upper intercept age of 2 111±15 Ma for the equigranular facies. The whole-rock Sm-Nd T_(DM) ages vary from 2.4 to 2.8 Ga with ε_(Nd)(2.1) values between -0.7 and-5.3, indicating crustal derivation from distinct and/or heterogeneous protoliths. Field observations indicate that the Gentio metagranitoid was formed through different pulses of magma. Individual batches were subject to little or even no fractionation process after its emplacement. Although the Gentio metagranitoid crosscuts metamafic and metaultramafic rocks akin to an oceanic arc setting, this pluton is likely originated by partial melting of a more evolved quartz-feldspathic crustal igneous rock in a post-collisional environment, after the accretion of the arcs from the Mineiro belt and rocks of the Mantiqueira Complex.展开更多
基金Fundacao Carlos Chagas de AmparoàPesquisa do Estado do Rio de Janeiro(FAPERJ),for providing him a post-doctoral fellowship(E-26/202.084/2020 and 2020.03701.1).the National Council for Scientific Development(CNPq)for financial support.CNPq for his Productivity on Research grant(#311106/2020-0)。
文摘The Archean Eon was a time of geodynamic changes.Direct evidence of these transitions come from igneous/metaigneous rocks,which dominate cratonic segments worldwide.New data for granitoids from an Archean basement inlier related to the Southern S?o Francisco Craton(SSFC),are integrated with geochronological,isotopic and geochemical data on Archean granitoids from the SSFC.The rocks are divided into three main geochemical groups with different ages:(1)TTG(3.02–2.77 Ga);(2)mediumto high-K granitoids(2.85–2.72 Ga);and(3)A-type granites(2.7–2.6 Ga).The juvenile to chondritic(Hf-Nd isotopes)TTG were divided into two sub-groups,TTG 1(low-HREE)and 2(high-HREE),derived from partial melting of metamafic rocks similar to those from adjacent greenstone belts.The compositional diversity within the TTG is attributed to different pressures during partial melting,supported by a positive correlation of Dy/Yb and Sr/Zr,and batch melting calculations.The proposed TTG sources are geochemically similar to basaltic rocks from modern island-arcs,indicating the presence of subduction processes concomitant with TTG emplacement.From~2.85 Ga to 2.70 Ga,the dominant rocks were K-rich granitoids.These are modeled as crustal melts of TTG,during regional metamorphism indicative of crustal thickening.Their compositional diversity is linked to:(i)differences in source composition;(ii)distinct melt fractions during partial melting;and(iii)different residual mineralogies reflecting varying P–T conditions.Post-collisional(~2.7–2.6 Ga)A-type granites reflect rifting in that they were closely followed by extension-related dyke swarms,and they are interpreted as differentiation or partial melting products of magmas derived from subduction-modified mantle.The sequence of granitoid emplacement indicates subduction-related magmatism was followed by crustal thickening,regional metamorphism and crustal melting,and post-collisional extension,similar to that seen in younger Wilson Cycles.It is compelling evidence that plate tectonics was active in this segment of Brazil from~3 Ga.
文摘High-resolution U–Pb(ID-TIMS,baddeleyite)ages are presented for mafic dykes from selected swarms in two important Amazonian regions:the Carajás Province in the east,and the Rio Apa block in the southwest–areas
文摘Several generations of mafic dyke swarms(2.7 to 0.8Ga),highlighted by aeromagnetic data,petrography,geochemistry,isotope geology and mostly U-Pb baddeleyite ages,crosscut the Archean and
基金support of the CAPES and the Brazilian National Research Council (CNPq) for the Doctoral (No. 140411/2013-5)。
文摘The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated T_(Zr)<800 ℃ for most samples. Its mineralogy is dominated by quartz and feldspar(77% to 95%), biotite is the only mafic mineral present(2% to 18%) and, titanite, zircon, apatite, allanite are important accessory phases. These rocks range from metaluminous to weakly peraluminous, and have large variation in major and trace elements, and high alkali contents(>6 wt.%). Zircon analyses by LA-ICP-MS and SHRIMP yielded a concordia age of 2 119±10 Ma for the porphyritic facies and an upper intercept age of 2 111±15 Ma for the equigranular facies. The whole-rock Sm-Nd T_(DM) ages vary from 2.4 to 2.8 Ga with ε_(Nd)(2.1) values between -0.7 and-5.3, indicating crustal derivation from distinct and/or heterogeneous protoliths. Field observations indicate that the Gentio metagranitoid was formed through different pulses of magma. Individual batches were subject to little or even no fractionation process after its emplacement. Although the Gentio metagranitoid crosscuts metamafic and metaultramafic rocks akin to an oceanic arc setting, this pluton is likely originated by partial melting of a more evolved quartz-feldspathic crustal igneous rock in a post-collisional environment, after the accretion of the arcs from the Mineiro belt and rocks of the Mantiqueira Complex.
