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

Abstract

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 welldeveloped 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 exchange and net transfer reactions. The P-T values calculated from cores to rims of garnets, 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 recrystallization 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.

Metamorphic record of collision and collapse in the Ediacaran‐Cambrian Araçuaí orogen, SE‐Brazil: Insights from P–T pseudosections and monazite dating

“…Ages of the fourth group fall in the interval 516–488 Ma and have been found in many sectors of the Araçuaí orogen, recording the final stage of the post‐collisonal magmatism and fluid percolation, followed by cooling and stabilization of the whole system (De Campos et al., , ; Gradim et al., ; Melo et al., ; Munhá, Cordani, Tassinari, & Palácios, ; Pedrosa‐Soares, De Campo et al., ; Queiroga et al., ; Richter et al., ; Silva et al., , ).…”

“…Ages of the fourth group fall in the interval 516-488 Ma and have been found in many sectors of the Arac ßua ı orogen, recording the final stage of the post-collisonal magmatism and fluid percolation, followed by cooling and stabilization of the whole system (De Campos et al, 2004Gradim et al, 2014;Melo et al, 2017;Munh a, Cordani, Tassinari, & Pal acios, 2005;Pedrosa-Soares, De Campo et al, 2011;Queiroga et al, 2016;Richter et al, 2016;Silva et al, 2005Silva et al, , 2011 In well-documented examples, paired metamorphic belts originated in association with: (1) a mid-crustal detachment, which allowed independent metamorphic evolution of units in the hangingwall (Buchan-type) and footwall (Barrovian-type) (Viete et al, 2010); (2) a major highangle shear zone, which divides the system into two domains, Barrovian and Buchan-type ;…”

Geologia, mineralogia, inclusões fluidas e gênese dos depósitos de titanita-epidoto de Capelinha, Minas Gerais

“…Em termos geotectônicos, tal região insere-se em um setor tectono-metamórfico complexo do Orógeno Araçuaí, designado de "Domínio Capelinha" ou "Faixa de Dobramentos Capelinha" (Queiroga et al, 2016), onde estruturas pós-colisionais relacionadas ao colapso do Figura 1. Mapa geológico da região de Capelinha (parcial e modificado de Baars et al, 1996, e Guimarães et al, 1996 mostrando as duas principais áreas de produção de titanita-epidoto: (1) Campo do Boa; (2) Fanadinho.…”

Evolução tectono-metamórfica da formação São Tomé, Grupo Rio Doce, faixa Araçuaí

“…Na região meridional do orógeno, a partir de dados geocronológicos de zircão e monazita em paragnaisses, foram reconhecidas três fases tectono-termais, sendo a primeira entre c. 620- Os estudos termobarométricos ( Tabela 3.3) e termocronológicos conduzidos em diferentes comparimentos (e.g., Melo et al, 2017b;Mondou et al, 2012;Moraes et al, 2015;Munhá et al, 2005;Novo et al, 2015;Peixoto et al, 2015;Petitgirard et al, 2009;Queiroga et al, 2016;Richter et al, 2016;Tedeschi et al, 2015)…”

“…Independente dos processos de evolução temporal, o prolongado período em que a unidade esteve submetida a condições elevadas de temperatura corrobora o padrão geral observado em diversos setores do orógeno (Melo et al, 2017b;Peixoto et al, 2017;Petitgirard et al, 2009;Queiroga et al, 2016;Richter et al, 2016).…”