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.
