Long-term displacement history on the Wenchuan Fault, Longmen Shan, Eastern Tibet using Luminescence Thermochronometry

Along convergent tectonic plate boundaries, the contractional deformation of the Earth’s external layers generates topographic uplift of continents and impacts terrestrial environments in multiple ways including (1) intensified natural hazards due to seismicity and landsliding, 2) physical perturbation of atmospheric wind circulations modifying climate and, 3) increased continental erosion impacting the long-term global climate through enhanced CO2 sequestration. To understand these agents of global change, it is decisive to constrain the timing and modes of major mountain-growth episodes. In this context, dating of brittle deformation of the uppermost 10-15 km of the crust is an essential piece of information to constrain the spatio-temporal development of orogenic wedges and to advance the ongoing debate on quantifying the interactions between tectonic and climate-related surface processes in active orogens. However, this task has proved challenging because of the rarity of datable syn-kinematic mineral phases growing at temperatures < 250 °C. This hurdle has partially been overcome by using classical low-temperature thermochronology (apatite and zircon fission-track and ((U-Th)/He methods), which provides cooling rates in fault-bounded crustal blocks but only yield minimum age of fault activity and does not cover the Quaternary timescale. Optically Stimulated Luminescence (OSL) thermochronometry is a new tool, which has the potential to resolve Quaternary cooling histories of the uppermost 1-2 km of the crust, a space-time tectonic window unexplored at the moment. In this project, we will apply this cutting-edge method to strategically chosen deep-drilling cores samples from the eastern border of the Tibetan plateau (Longmen Shan, Sichuan) to quantify the timing and rates of brittle faulting at timescales > 100,000 years along fault segments that ruptured during the 2008 Mw. 7.9 Wenchuan Earthquake. The knowledge gained from this multifaceted program will be directly transferable to orogens worldwide where late stage timing and rate of brittle deformation remains poorly constrained.