Dating metamorphic processes in the deep continental crust: petrochronology of key UHT and HP units from orogens in Brazil

Abstract

The integration of metamorphic timescales with pressure-temperature (P-T) information derived from rocks formed in the deep continental crust can provide important insights on the understanding of the evolution of plate tectonics in Earth as a response to the secular cooling and rheological changes over time. The petrochronology approach links time (i.e., ages and duration) with P-T data based on the combination of textural, chemical and isotopic information. This way, the petrochronology approach has been widely used, especially in Phanerozoic orogenic belts, to determine the rate and duration of metamorphic processes to a better comprehension of the formation and evolution of the continental crust. The timing of metamorphic processes is usually constrained by in-situ dating methods (i.e., laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and Ion microprobe). However, the chronological resolution of the in-situ dating techniques is not sufficient to distinguish protracted and short-lived events in Neoproterozoic orogens due to the large uncertainties (~1-2%). This proposal aims to apply an integrated approach using both in-situ (LA-ICP-MS) and high-precision (chemical abrasion-thermal ionization-mass spectrometry - CA-ID-TIMS) U-Pb geochronology techniques. This combined approach will be tested in Neoproterozoic high-grade metamorphic rocks from the Brasília and Araçuaí orogens (SE, Brazil) formed in different metamorphic regimes (i.e., UHT and HP), to determine more precise and reliable metamorphic timescales of the Neoproterozoic deep continental crust to better understand the secular changes in the styles of plate tectonics. (AU)