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Understanding the Lithosphere

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The lithosphere is the cold, mechanically strong outer layer of the Earth, making up its tectonic plates. It controls surface topography, natural hazards and the development of natural resources. Yet, its composition, evolution and many of the mechanisms of how it controls what happens at the surface remain unclear. Britain and Ireland offer intriguing new evidence on the processes. Recent seismic tomography shows pronounced, previously unknown variations in the lithospheric thickness across the islands. These variations show a remarkable match to the distribution of seismicity and offer a solution to a long-standing puzzle: why Ireland is nearly aseismic and Britain has substantial seismicity, although mostly in its western part. Tomography shows that Ireland has a thick, cold and, by inference, mechanically strong lithosphere—and features few earthquakes. Western Britain, by contrast, has thin, warm and mechanically weak lithosphere, and it hosts numerous low to moderate magnitude events. Lithospheric thinning in the circum-Irish Sea area also shows a remarkable match with the distribution of the Paleogene uplift and magmatism, which occurred in the course of the North Atlantic Igneous Province (NAIP) emplacement. Across NAIP and in other Large Igneous Provinces (LIPs), thin-lithosphere channels—pre-existing and evolving in the course of the LIP emplacement—appear to determine the enigmatic distributions of the volcanism, often scattered over thousands of kilometers. The composition and evolution of the lithosphere are in question, in particular, beneath cratons, the Archean cores of continents whose very definition has been debated. Computational-petrology modeling and inversion can integrate quantitatively different geophysical and geological measurements and facilitate the multi-disciplinary research effort that is required.

This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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