From subduction to sand: Quantifying the balance between tectonic and surface processes during early continental collision and UHP rock exhumation

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Many of the Earth's great mountain ranges, such as the Alps and the Himalaya, result from the collision between two continents. As mountains get pushed up by tectonic forces, they also get worn away by surface erosion. The uplift of topography causes long-term regional and global climate change, and conversely, changes in climate have also been linked to changes in the rate of tectonic processes. This project will define and quantify the competition between growth and erosion during the early stages of mountain uplift by exploiting a combination of state-of the art advances in numerical modelling and analytical techniques. During the early stages of continental collision, unusual (and diagnostic) rock types form under very high pressure conditions. Certain minerals in these rocks preserve details of the pressures and temperatures experienced during the journey from initial formation deep in the mantle, through their subsequent transport to the Earth's surface, their erosion, and their final deposition as sand grains in a sedimentary rock. The minerals retain distinctive chemical signatures which allows them to be distinguished from those formed in other rock types, even when eroded and turned into sand. Sand grains retain information about not only the original rock type, but also about details of the formation and transport history of the original rock. Unlocking this information will therefore yield insight into earlier stages of mountain belt growth history than is currently preserved in the bedrock record. However the methods needed to decipher these details are currently insufficiently precise to provide useful insight into changes in rates of tectonic or erosive processes, or constraints for the models. This project will therefore also develop and exploit innovative techniques for obtaining high-precision data from these high pressure rocks and their eroded remains. These data will enable the competing forces which act to shape a mountain belt during the early stages of formation to be quantified and allow the numerical models to be robustly tested. The unique contribution of this proposal lies in the combination of geodynamic numerical modelling with studies based on observational data and hence exploiting the synergy between these two, normally disparate, fields.