Catastrophic emplacement and depositional processes during large asteroid impacts: lithofacies analysis and applied volcanology, Manicouagan (Canada)

When asteroids or comets collide with Earth they cause catastrophic shock, vaporisation, melting, fragmentation and ejection, significantly modifying the crust and devastating environments and biota. Such 'hypervelocity collisions' are a fundamental process of planetary evolution and arguably the greatest natural hazard. Significant advances in shock metamorphism, petrology and modelling have been made, but several geological aspects of what happens remain poorly understood. We need to better understand the processes of molten ejecta emplacement in order to account for the wider effects. A principle source of information lies in Earth's geological record, but accessible, well-preserved large impact craters filled with clastic and melted products are rare.

This project will help decipher the fragmentation and emplacement processes of crater-fill material in very large impact craters on Earth, focussing on Manicouagan (Canada) and Chicxulub (Mexico). Both impacted continental crust, one on land the other at sea, and both have been drilled. The investigation will document, analyse and interpret the crater fills to shed new light on the physical processes of their formation. The student will draw upon state-of-the-art geological and physical volcanological techniques and understanding about how hot magma is fragmented, emplaced, and then deposited and agglutinated back together to form thick rock bodies that subsequently cool, and variously devitrify and crystallise. An objective is to develop a new facies scheme for large impact crater fills in order to help reconstruct the events by which they form.