Philippe Agard, UPMC Paris, will deliver the ESE Departmental Seminar on 25 February.
Join us online on Thursday 25 February by clicking “Livestream” on the seminar page at 12pm.
The Alps preserve abundant oceanic blueschists and eclogites that exemplify the selective preservation of fragments of relatively short-lived, small, slow-spreading North Atlantic-type ocean basins (here the ~400-700 km wide Alpine Tethys), whose subducting slabs reach down to the Mantle Transition Zone. Whereas none of the subducted fragments were returned during the first half of the subduction history, those exhumed afterwards experienced conditions typical of mature subduction zones worldwide. Sedimentary-dominated units were underplated intermittently, mostly at ~30-40 km depth, while mafic/ultramafic-dominated units subducted to ~80 km (In the W. Alps), whose protoliths had formed close to the continent, were offscraped from the slab only a few Ma before continental subduction. Spatiotemporal contrasts in burial and preservation of the fragments reveal how along-strike segmentation of the continental margin affects ocean subduction dynamics.
Philippe Agard is Professor at Sorbonne Université in Paris and fellow of Academia Europaea and Institut Universitaire de France. He received his doctoral degree from the Ecole Normale Superieure and UPMC. His field-based approach (e.g., in the Alps, Iran, Oman, China) combines metamorphic petrology and tectonics to investigate regional-scale geodynamics and processes like subduction, obduction or strain (de)localisation. His present interests include unravelling the former structure and rheology of the subduction plate interface, notably in the Alps, understanding the initiation of deep viscous coupling in subduction zones or upper plate dynamics and ophiolite emplacement in Iran.