Petrochronology of high‐pressure granulite facies rocks from Southern Brasília Orogen, SE Brazil: Combining quantitative compositional mapping, single‐element thermometry and geochronology

Abstract

We use a combination of several in situ techniques to assess the P‐T‐t path of high‐pressure granulites from the Passos Nappe in the Southern Brasília Orogen (SE Brazil). Quantitative element mapping and single‐element thermometers (Zr‐in‐rutile and Ti‐in‐quartz) are coupled with P‐T pseudosections and monazite and rutile dating. Compositional and temperature maps, based on cathodoluminescence mapping and in situ analyses of Ti‐in‐quartz, are presented as a novel approach to evaluate crystallization temperature. The studied rocks have a pelitic protolith and record a peak pressure assemblage of garnet + kyanite + rutile + K‐feldspar + quartz + melt ± plagioclase that formed at ~830°C and 1.2 GPa. Retrograde conditions of ~560°C and 0.6 GPa are determined based on the grossular content of garnet and the crystallization of biotite and ilmenite. Metamorphic peak conditions occurred ca. 635 Ma, according to monazite dating, with a younger date of ca. 615 Ma associated with later kyanite crystallization. Rutile ages of ca. 590 Ma are linked to the late retrograde stage (at ~600°C). Results show that the distribution of Ti‐in‐quartz is heterogeneous, decreasing in abundance towards the rim of crystals, though the higher temperatures constrained with Ti‐in‐quartz thermometry are broadly consistent with peak conditions. The peak pressure conditions are consistent with continental collision setting in the Southern Brasília Orogen and were followed by an early cooling/decompression stage and then by a slow cooling during exhumation and transport to shallower crustal levels.

Ti‐in‐zircon and Ti‐in‐quartz thermometry using electron probe microanalysis: A promising approach in retrieving thermal conditions of granulite facies metamorphism and felsic magmatism in the Sandmata Complex, Aravalli Craton (NW India)

“…These concentrations are equivalent to the temperatures of ~700°C for the Ti‐in‐zircon thermometry (Ferry & Watson, 2007) and ~ 420°C for the Ti‐in‐quartz thermometry (at 5 kbar; Thomas et al, 2010). Recent studies have shown that the results of Ti‐in‐zircon (e.g., 550–1070°C; Fu et al, 2008; Watson et al, 2006; Yuguchi et al, 2016) and Ti‐in‐quartz (e.g., 300–1000°C; Ashley & Law, 2015; Fumes et al, 2021; Kendrick & Indares, 2018; Spear & Wark, 2009; Storm & Spear, 2009; Wark & Watson, 2006) thermometers were successfully applied to evaluate crystallization conditions of most igneous rocks and equilibrium conditions of medium‐ to high‐grade metamorphic rocks. The calculated temperature conditions in this study indicate that the Ti‐in quartz protocol can be used to evaluate the recrystallization of quartz down to greenschist facies conditions.…”

“…Batanova et al, 2018) and are helpful in achieving low detection limits (<6 ppm), even under extreme analytical conditions (e.g., 20–25 kV accelerating voltage, 200–900 nA beam current, 180–960 s counting time; Batanova et al, 2018; Donovan et al, 2011). Several authors have applied these improved strategies to measure trace element concentrations from monazite (Deshmukh et al, 2017; Hrushikesh et al, 2020 and the references therein; Jercinovic & Williams, 2005; Jercinovic et al, 2012; Prabhakar, 2013), quartz (Donovan et al, 2011; Fumes et al, 2021; Kendrick & Indares, 2018; Rusk et al, 2006; Wark & Watson, 2006) and olivine (Batanova et al, 2015; Batanova et al, 2018; Shaikh et al, 2017; Sobolev et al, 2005; Sobolev et al, 2007; Sobolev et al, 2009). In this study, we have adopted some of these advancements in acquiring statistically improved Ti analysis using EPMA.…”

Geotermometria Dos Metapelitos Das Unidades Intermediárias Da Nappe De Passos (Mg)

“…As unidades da NP compreendem uma sequência plataformal depositada na margem oeste do Cráton São Francisco (Zanardo, 1992;Simões, 1995). Essa sequência apresenta gradiente metamórfico invertido onde, em direção ao topo, ocorrem as rochas de mais alto grau, como granulitos de alta pressão e eclogito retrogradado (Simões, 1995;Luvizotto, 2003;Luvizotto et al, 2011Luvizotto et al, , 20122014;Santos et al, 2021;Fumes et al, 2022;Simões et al, 2022).…”

Repeated Caledonian burial and ultrafast cooling and exhumation of high‐pressure granulite facies rocks from the Blåhø Nappe on the island of Fjørtoft, Western Gneiss Region, Norway

“…Such rates can be constrained by combining geothermobarometric and geochronological methods (e.g. Fumes et al, 2022; Morita et al, 2022; Tajčmanová et al, 2006; Zou et al, 2021). Simulation of cation diffusion in garnet is another method that can provide key constraints on the timescales of metamorphic processes (e.g.…”