Metamorphic architecture of orogenic belts

地球大陆地壳的大部分由变质岩组成，这些变质岩是在古代和现代山带深处由板块碰撞产生的热量和压力形成的。因此，对变质岩的研究有助于我们了解大陆和山带是如何在地质时期演变的。变质作用不能直接观察到，但在板块碰撞过程中对地壳和地幔的加热和变形的计算机模拟可以用来间接研究变质过程。在拟议的研究中，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，当山带变大变热时，脆弱的下地壳会从山带中心向外流动，形成一个地下“通道”，该通道可以通过系统两侧的侵蚀暴露出来。计算机模型预测的变质作用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，一个巨大的山脉（格伦维尔造山带）占据了加拿大地盾的东南边缘。这些岩石中韧性流动的类型可以用整个系统中地壳强度变化的模型来解释。在过去的25年里，变质资料(例如：大陆岩石中的微金刚石表明，大陆地壳可以在板块碰撞中俯冲；然而，目前还不清楚这些被俯冲的岩石是如何回到地球表面的。我们的计算机模型显示，浮力和俯冲地壳的减弱共同作用可以导致地壳迅速从俯冲带中喷出，其结果与一些自然例子的观察结果相吻合。这项工作将扩展到研究挪威以前俯冲的地壳岩石，在那里这种类型的变质作用首次被描述。这个项目将有助于更好地了解山带是如何形成和破坏的，从而了解加拿大地盾的古老山脉是如何生长然后消失的。

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.