Metamorphic architecture of orogenic belts

地球的大部分大陆地壳是由古代和现代山脉深处的变质岩组成的，这些变质岩是在板块碰撞产生的热和压力下形成的。因此，对变质岩的研究有助于我们了解大陆和山脉带是如何在地质时期演化的。变质作用不能直接观察到，但可以利用板块碰撞过程中地壳和地幔加热和变形的计算机模拟来间接研究变质过程。在这项拟议的研究中，计算机模型的预测将与来自不同年龄的变质带的数据进行测试。结果表明，当山地带变得很大和很热时，脆弱的下地壳可以从山脉带的中心向外流动，形成一条次表层“通道”，通过对系统侧翼的侵蚀而暴露出来。计算机模型预测的变质和变形模式与喜马拉雅山脉的观测结果非常相似，类似的概念现在已经扩展到一些古老的山脉地带。在安大略省的马斯科卡-乔治亚湾地区，在很深的地方形成的变质岩表明，大约10亿年前，一条巨大的山脉(格伦维尔造山带)占据了加拿大盾的东南边缘。这些岩石中韧性流动的方式可以通过地壳强度在整个系统中变化的模型来解释。在过去的25年里，变质数据(例如，大陆岩石中的微钻石)已经证明，大陆地壳可以在板块碰撞期间被俯冲；然而，尚不清楚被俯冲的岩石如何返回地球表面。我们的计算机模型表明，俯冲地壳的浮力和减弱的组合可以导致其迅速从俯冲带排出，结果与一些自然例子的观测结果相吻合。这项工作将扩展到挪威以前俯冲的地壳岩石，这种类型的变质作用在挪威首次被描述。该项目将有助于更好地了解山脉带是如何形成和摧毁的，从而了解加拿大盾牌的古老山脉是如何生长和消失的。

Most of the Earth's continental crust consists of metamorphic rocks formed deep within ancient and modern mountain belts by the heat and pressure generated during plate collisions. Studies of metamorphic rocks therefore help us to understand how continents and mountain belts have evolved through geologic time. Metamorphism cannot be observed directly, but computer simulations of heating and deformation of the Earth's crust and mantle during plate collisions can be used to investigate metamorphic processes indirectly. In the proposed research, predictions of computer models will be tested against data from metamorphic belts of different age. Results show that when mountain belts get very large and hot, weak lower crust can flow outward from the centre of the mountain belt, forming a sub-surface 'channel' that can be exposed by erosion on the flanks of the system. Patterns of metamorphism and deformation predicted by the computer models closely resemble observations from the Himalayas, and similar concepts have now been extended to some ancient mountain belts. In the Muskoka-Georgian Bay area of Ontario, metamorphic rocks formed at great depths indicate that a vast mountain range (Grenville orogen) occupied the southeastern margin of the Canadian Shield about 1 billion years ago. The style of ductile flow in these rocks can be accounted for by models in which crustal strength varies across the system. Over the past 25 years, metamorphic data (eg. microdiamonds in continental rocks) have demonstrated that continental crust can be subducted during plate collisions; however, it is still unclear how the subducted rocks are returned to the Earth's surface. Our computer models show that a combination of buoyancy and weakening of subducted crust can lead to its rapid expulsion from the subduction zone, with results that match observations from some natural examples. This work will be extended to investigate formerly subducted crustal rocks in Norway, where this type of metamorphism was first described. This project will contribute to a better understanding of how mountain belts are created and destroyed, and thus how the ancient mountains of the Canadian Shield once grew and then vanished.