Tracking Exhumation of Ultrahigh-pressure Terranes: Linking Thermobarometers and Geochronometers Through REE Chemistry

当大陆相撞时，就像亚洲和印度今天所做的那样，大陆地壳可以被带到100-150公里的深度。在一些地壳岩石中存在的钻石和柯石英矿物证明，深部的超高压岩石被埋藏得很深，然后又被挖回地球表面。这种折返发生的时间框架对于了解与大陆碰撞相关的构造过程发生的速度有多快很重要。确定时间的一个主要问题是，用于计算地球特定深度的压力和温度的矿物(即温压计)与用于获得岩石年龄的矿物(即地质计时仪)不同。要检验的假设是，这两组矿物中的稀土元素(REE)的收支平衡可以用来寻找岩石年龄与矿物在特定深度生长的时间之间的联系，以便在挖掘过程中追踪这些岩石返回地表的路径。大陆超高压地体在碰撞造山带中的折返是影响我们认识板块构造、地壳物质向地幔循环、俯冲带岩浆作用和总体碰撞过程的重要过程。了解地质计时学和变质演化之间的关系目前是一个非常活跃的研究领域，这是由于允许原位化学分析的微分析技术的最新进展。该项目将侧重于格陵兰东北部的一个极好的例子，那里的掘尸周期足够长--大约5500万年--以解决压力-温度路径上的稀土元素交换问题。结果将很容易被输送到其他变质系统和环境，最终影响造山作用的岩石学、构造和地球动力学模型。

When continents collide, as Asia and India are doing today, continental crust can be taken to depths of 100-150 km. The presence of the minerals diamond and coesite in some crustal rocks is evidence that deep, ultrahigh-pressure rocks have been buried deep and then exhumed back to Earth's surface. The time frame in which this exhumation occurs is important for understanding how fast tectonic processes associated with continental collision can take place. A major problem in determining timing is that the minerals used to calculate pressure and temperature (i.e. thermobarometers) at specific depths in the Earth are not the same minerals as the ones used to obtain the ages of the rocks (i.e. geochronometers). The hypothesis to be tested is that the budget of rare earth elements (REEs) in both sets of minerals can be used to find links between the age of the rocks and when the minerals grew at certain depths in order to track the path of these rocks back to the surface in the exhumation process. The exhumation of continental ultrahigh-pressure terranes in collisional orogens is an important process that impacts our understanding of plate tectonics through time, recycling of crustal material into the mantle, subduction zone magmatism and collisional processes in general. Understanding the relationship between geochronometers and metamorphic evolution is currently a very active field of research, which is enabled by recent advances in microanalytical techniques that allow in situ chemical analysis. This project will focus on an excellent example from North-East Greenland where the period of exhumation is long enough - approximately 55 million years - to resolve exchanges in REE along the pressure-temperature path. The results will be easily transported to other metamorphic systems and environments, ultimately influencing petrologic, tectonic and geodynamic models for orogenesis.