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

当放射性同位素衰变产生的地壳热量在长寿命（4000 -1亿年）、变厚的山带（造山带）中（如今天的青藏高原之下）达到900°C时，就会发生区域尺度（50 - 5万平方公里）的超高温（UHT）地壳变质作用。然而，通过岩浆底镀、侵入或剥离过程，地幔向地壳的热传递可能是普遍的、重要的，但在世界范围内的区域性超高温地质体中却没有得到充分的重视。解决大陆地壳中地幔和地壳热源的相对贡献将影响我们对造山带中下地壳演化及其热、物理和化学变化的认识。加拿大西北地区的塔尔森造山带是一个区域尺度的超高温造山带，它在不到3000万年的时间里达到超高温，随后冷却，除了地壳衍生的放射性生热外，还需要地幔传热的重要组成部分。我的研究项目旨在通过使用构造、变质、地质年代数值和岩石学方法，评估和量化输入塔尔森造山带地壳的地幔热量。本研究将以塔尔森造山带为研究对象，以三个目标为指导：1)确定地幔热源的最大可能贡献；2)建立现代构造和构造变质框架；3)评估地幔热输入的证据。研究将包括实地观察和目标取样，然后收集微量分析化学、同位素、年龄和结构数据。方法将包括整个岩石地球化学、岩石学建模和详细的压力-温度-时间-变形路径构建、原位年龄（U-Pb锆石、独居石、钛矿、金红石、Lu-Hf石榴石、Ar-Ar和Rb-Sr云母）和微量元素分析，以及剪切带的运动学和流变学分析。量化地幔源与地壳源的热源将有助于验证地幔热贡献在区域尺度UHT地体中起重要作用的假设。反过来，这项研究将显著提高我们对UHT造山系统的热、结构和流变动力学演化的理解。这项工作还将有助于解决一个长期存在的争议，即塔尔森造山带是由大陆弧后增厚形成的，还是由类似青藏高原的环境增厚形成的。此外，这项工作将使我们能够检查塔尔森造山带目前在超大陆努纳合并中的争议作用，并评估其远场构造影响，包括对整个加拿大地盾的矿床分布的控制。

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.