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

当大陆碰撞时，就像今天的亚洲和印度，大陆地壳可以被带到100-150公里的深度。 在某些地壳岩石中发现的金刚石和柯石英等矿物，证明了超高压岩石曾被深埋，然后又被挖掘出地表。 这种折返发生的时间框架对于理解与大陆碰撞有关的构造过程发生的速度是很重要的。 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（即温度压力计）与用于获得岩石年龄的矿物（即地质年代计）不是同一种矿物。 有待检验的假设是，这两种矿物中稀土元素的收支可用于找到岩石年龄与矿物何时在一定深度生长之间的联系，以便追踪这些岩石在剥露过程中返回地表的路径。 碰撞造山带中大陆超高压火山岩的折返是一个重要的过程，它影响着我们对板块构造的认识，地壳物质再循环进入地幔，俯冲带岩浆作用和一般的碰撞过程。 了解地质年代学和变质演化之间的关系是目前一个非常活跃的研究领域，这是由最近的进展，允许在原位化学分析的微分析技术。 该项目将侧重于格陵兰东北部的一个极好的例子，那里的折返期足够长-大约5 500万年-以解决稀土元素沿着压力-温度路径的交换问题，其结果将很容易转移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.