Dynamics and tectono-metamorphic framework of ultra-high temperature orogenic systems

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Ultrahigh-temperature (UHT) crustal metamorphism on the regional-scale (>50,000 km2) occurs when the decay of radiogenic isotopes produces crustal heat to temperatures >900 °C in long-lived (40-100 million-year), thickened mountain belts (orogens) such as beneath modern-day Tibetan Plateau. However, mantle heat transfer into the crust, through magmatic underplating, intrusion, or delamination processes, may be common, significant, and underappreciated in regional UHT terranes worldwide. Resolving the relative contributions of mantle and crustal heat sources in continental crust will impact our understanding of middle- to lower-crust evolution and their thermal, physical and chemical changes in orogenic systems. The Taltson Orogen, Northwest Territories, Canada, is a regional-scale UHT orogen that reached UHT and subsequently cooled in <30 million-years, requiring a significant component of mantle heat transfer in addition to crustal-derived radiogenic heat production. My research program aims to evaluate and quantify the amount of mantle-derived heat input into the Taltson Orogen crust, by using a structural, metamorphic, geochronological numerical and petrologic approach. This research will target the Taltson Orogen guided by three objectives: 1) determine the largest possible contribution of mantle-derived heat sources, 2) establish a modern structural and tectono-metamorphic framework, and 3) evaluate evidence for mantle-derived heat input. Studies will involve field observations and targeted sampling followed by collection of micro-analytical chemical, isotopic, age and structural data. Methods will include whole rock geochemistry, petrologic modelling and detailed pressure-temperature-time-deformation path construction, in situ age (U-Pb zircon, monazite, titanite, rutile; Lu-Hf garnet; Ar-Ar & Rb-Sr mica) and trace-element analyses, and kinematic and rheologic analyses of shear zones. Quantifying mantle-derived versus crustal-derived heat sources will facilitate testing the hypothesis that mantle heat contributions play an important role in regional-scale UHT terranes. In turn, this research stands to significantly improve our understanding of the evolution of the thermal, structural, and rheologic dynamics of UHT orogenic systems. This work will also help resolve a long standing controversy on whether the Taltson Orogen formed by thickening of a continental back-arc or by thickening in a Tibetan plateau like setting. Furthermore, this work will allow us to examine the Taltson Orogen's currently debated role in the amalgamation of the supercontinent Nuna and evaluate its far-field tectonic effects, including its control on the distribution of mineral deposits, throughout the Canadian Shield.