Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Araçuaí Orogen, Brazil.
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2016
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The Capelinha Formation (Macaúbas Group) consists of a lower quartzitic unit with metamafic intercalations and an upper metapelitic sequence. It occurs in a complex tectono-metamorphic sector of the Araçuaí orogen, where post-collisional collapse-related structures superimposed collisional structures. The garnet-bearing assemblages started crystallization in the collisional deformation stage that formed the main regional foliation around 570 Ma. Garnet porphyroblasts display a well-developed growth zonation of Fe-Mg-Ca-Mn and show, from core to rim, increasing almandine and pyrope contents in contrast with decreasing grossular and spessartine contents. Mineral relations and microstructures provide criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation ex¬change and net transfer reactions. The P-T values calculated from cores to rims of gar¬nets, aligned along clockwise trends, resulted in increasing temperatures (from 500 ºC up to 620 ºC) under decompression conditions (from 8.0 kbar to 4.5 kbar). The Th-U-Pb dating of homogeneous monazites by electron microprobe revealed a recrystalliza¬tion period at around 490 – 480 Ma. These ages can be related to the tectono-thermal event associated with the gravitational collapse, constraining the youngest time limit for metamorphic processes in the Araçuaí orogen.
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Capelinha formation, Garnet metapelites, Geothermo barometry, Electron microprobe Th U Pb dating
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QUEIROGA, G. N. et al. Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Araçuaí Orogen, Brazil. REM. Revista Escola de Minas, v. 69, p. 33-44, 2016. Disponível em: <http://www.scielo.br/pdf/rem/v69n1/0370-4467-rem-69-01-0033.pdf>. Acesso em: 11 jul. 2016.