Collaborative Research: Growth, Assembly, and Exhumation of Deep Crust, Southwestern Churchill Province, Canadian Shield

加拿大西部丘吉尔省保存了一份非凡的地质记录，记录了早期大陆地壳在生长、演化、挖掘和稳定过程中活跃的过程。特别是东阿萨巴斯卡地区暴露了一大片（1000平方公里）的岩石，这些岩石在超过20公里的深度被加热到近1000摄氏度的温度。事实上，有些岩石是在北美已知的最高压力下形成的。该地区可以划分成许多小区域，保存着独特的岩石类型和地质历史。每个单独的域都以令人印象深刻的清晰度记录了加拿大地盾构造演化的关键阶段。总之，它们提供了一个复杂的地图视图，可以描述地壳深处的一般特征。由于地壳深处通常无法进行研究，这个区域为地壳深处发生的事情提供了一个独特的视角。这项研究中的大多数岩石大约有26亿年的历史。东阿萨巴斯卡地区的实地和实验室研究记录了一个更年轻的事件（19亿年前）的影响，该事件改变了这些岩石，导致了一种假设，即该地区代表了19亿年前在地壳深处聚集的区域的地图视图，随后被隆起和暴露。因此，该地区可以在几公里波长上直接观察岩石类型、结构和非均质性，而这些岩石类型、结构和非均质性是地震成像或推断出存在于其他深层地壳未暴露的地区的。加强这一假设的关键是更好地理解各个领域的内部结构及其边界。本项目的目标是了解(1)非均质深部地壳域的组合；(2) 19亿年前变质作用的意义和成因；(3)将地球深处的熔体添加到地壳深处的作用；(4)如何挖掘出大面积的地壳深处岩石；(5)这些岩石在北美西部更广阔的背景下的形成。这种综合方法对地壳组装、稳定和挖掘过程中下地壳的特征、行为和演化提供了重要的一级约束。

The western Churchill Province of Canada preserves an extraordinary geologic record of processes active during the growth, evolution, exhumation, and stabilization of early continental crust. The East Athabasca area in particular exposes a huge tract (1000's of km2) of rocks that were heated to temperatures of nearly 1000 deg C at depths of more than 20 km. In fact some of the rocks were formed at the highest pressures ever recognized in North America. The region can be divided into a number of small domains that preserve distinct rock types and geological histories. Each of the individual domains record, with impressive clarity, key stages in the tectonic evolution of the Canadian shield. Together, they provide a map view of the complexity that may characterize the deep crust in general. Since the deep crust is generally not accessible for study this area provides a unique view of what happens deep in the earth's crust.Most of the rocks in this study are about 2.6 billion years old. Field and laboratory research in the East Athabasca area documents the effects of a much younger event (1.9 billion years ago) that has transformed these rocks leading to the hypothesis that the area represents a map view of domains assembled in the deep crust 1.9 billion years ago immediately prior to being uplifted and exposed. As such, the region may provide a direct view of the rock types, structures, and heterogeneity at several km wavelengths that are seismically imaged or inferred to exist in other areas where the deep crust is not exposed. Crucial to strengthening this hypothesis is a better understanding of the internal structure of individual domains and their boundaries. Goals of this project are to understand (1) the assembly of heterogeneous deep crustal domains; (2) the significance and cause of metamorphism 1.9 billion years ago; (3) the role of adding melts from deep within the earth to the deep crust (4) how an enormous area of deep crustal rocks can be exhumed; and (5) the setting of these rocks within the broader context of western North America. This integrated approach is placing important first-order constraints on the character, behavior, and evolution of lower crust during crustal assembly, stabilization, and exhumation.