Thermobarometry and electron-microprobe Th-U-Pb monazite dating in garnet metapelites from the Capelinha Formation, Araçuaí Orogen, Brazil.

• Autor(a) principal: Queiroga, Gláucia Nascimento
• Data de Publicação: 2016
• Outros Autores: Schulz, Bernhard, Martins, Maximiliano de Souza, Castro, Marco Paulo de, Soares, Antônio Carlos Pedrosa, Evangelista, Hanna Jordt, Silva, Ana Lúcia da
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFOP
• Texto Completo: http://www.repositorio.ufop.br/handle/123456789/6721; http://dx.doi.org/10.1590/0370-44672015690066
• topic: Capelinha formation; Garnet metapelites; Geothermo barometry; Electron microprobe Th U Pb dating

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.