2024-2025
Asst. Prof. Ching-Yao Lai
Stanford University
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Title
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Geodynamics of early crust formation: Constraints on Earth’s long-term tectonic and thermal evolution
A unique feature of the Earth compared to the other rocky planets of our solar system is the operation of plate tectonics at the present day. However, how and when Earth developed into this present-day state is unclear. Key to deciphering Earth’s long-term tectonic evolution is the growth of the first continents, as these represent the oldest extant rock record providing our best window into the geodynamic processes of the very early Earth. Geochemical observations have been used to argue for a switch in the mode of crust formation at ~3.8-3.6 Ga, from continent formation via melting at the base of a thick, volcanically active oceanic crustal pile, to continent formation by some form of subduction. I use numerical models of early Earth mantle convection and crust formation, combined with the key geochemical observations, to provide new constraints on such a scenario. I show that continent formation by slab melting during subduction can only occur when subduction is sluggish and present a new mechanism for such subduction on the early Earth. I further show how continent formation by ocean plateau melting >~3.6 Ga is plausible, but with strict limits on the rates of volcanism in such a system that have important implications for mantle heat loss. I discuss how both sets of models together provide a possible scenario for the tectonic and thermal evolution of the early Earth.
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