Mesoarchaean (2820 Ma) high-pressure mafic granulite at Uaua, Sao Francisco craton, Brazil, and its potential significance for the assembly of archaean supercratons
Elson P. Oliveira, Cristina Talavera, Brian F. Windley, Lei Zhao, Julia J. Semprich, Neal J. McNaughton, Wagner S. Amaral, Gabriel Sombini, Margareth Navarro, Dailto Silva
ARTIGO
Inglês
High pressure (HP) granulites of regional scale form as a result of tectonic events that lead to crustal thickening or subduction of the crust into the mantle. Most HP granulites are Phanerozoic, a few are Proterozoic, and Archaean HP granulites are even scarcer. Here we present field relationships,...
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High pressure (HP) granulites of regional scale form as a result of tectonic events that lead to crustal thickening or subduction of the crust into the mantle. Most HP granulites are Phanerozoic, a few are Proterozoic, and Archaean HP granulites are even scarcer. Here we present field relationships, mineral chemistry and zircon U-Pb ages, Hf isotope data and trace elements data for the mafic granulite and associated rocks of the Uaua terrane, Sao Francisco Craton, Brazil, as evidence for the likely existence of a thick continental crust in the Mesoarchaean/Neoarchaean transition. The HP mafic granulite occurs as lensoid bodies within shallow dipping diorite to leucodiorite gneisses. Small scale layering between mafic granulite and diorite gneiss indicate these rocks are cogenetic. Garnet-clinopyroxene pairs with quartz, zircon, ilmenite, plagioclase, and clinopyroxene inclusions in garnet characterize the HP assemblage. Garnet porphyroblasts also show opx-cpx-plag symplectite coronas, which coupled with hornblende and plagioclase define PT conditions to lower grade granulite and amphibolite facies. Microprobe data combined with phase equilibria modelling (pseudosections) indicate 16-18 kbar and 930-960 degrees C for the peak HP assemblage, and 6.2-7.0 kbar and 660-760 degrees C for lower pressure granulite to amphibolite facies symplectite coronas. Metamorphic zircon rims in equilibrium with garnet have SHRIMP ages of 2819 +/- 14, and igneous zircon cores of 3127 +/- 14 Ma. The cores of zircon in associated gneiss samples have U-Pb ages between 3090 +/- 13 Ma (LA-ICP-MS) and 3125 +/- 15 Ma (SHRIMP) with age cluster at 3120 +/- 6 Ma. epsilon(Hf(t)) values on igneous zircon of the HP mafic granulite are slightly positive whereas metamorphic zircon rims are negative. The associated diorite gneiss invariably yielded negative zircon epsilon(Hf(t)) values. Trondhjemite sheets intrusive in the mafic granulite are ca. 20 m.y. younger (2794 +/- 13 Ma) than the host granulite. We interpret the igneous protoliths of the mafic granulite and leucodiorite gneiss as a single igneous complex emplaced in the continental crust, later deformed and metamorphosed by contraction and crustal thickening during collision of blocks/cratons to form Earth's first supercratons by the end of the Mesoarchaean
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ
305658/2015-8; 312509/2014-6
FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP
2014/50353-0; 2012/15824-6
Fechado
Mesoarchaean (2820 Ma) high-pressure mafic granulite at Uaua, Sao Francisco craton, Brazil, and its potential significance for the assembly of archaean supercratons
Elson P. Oliveira, Cristina Talavera, Brian F. Windley, Lei Zhao, Julia J. Semprich, Neal J. McNaughton, Wagner S. Amaral, Gabriel Sombini, Margareth Navarro, Dailto Silva
Mesoarchaean (2820 Ma) high-pressure mafic granulite at Uaua, Sao Francisco craton, Brazil, and its potential significance for the assembly of archaean supercratons
Elson P. Oliveira, Cristina Talavera, Brian F. Windley, Lei Zhao, Julia J. Semprich, Neal J. McNaughton, Wagner S. Amaral, Gabriel Sombini, Margareth Navarro, Dailto Silva
Fontes
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Precambrian research Vol. 331 (Sept., 2019), n. art. 105366 |