ESS Department - November 9th, 2023 For several years, my research on plate tectonics has focused on how incipient divergent plate boundaries (i.e. continental rifts) initiate via a system of short segments that exploit inherited mechanical weaknesses in the continental lithosphere. In recent times, I have been fascinated by how these segments establish themselves (i.e. localize), and how they progressively grow laterally and accommodate the thinning of the lithosphere (i.e. propagate), all of which ultimately lead to continental break-up and creation of new oceanic crust. In my seminar talk, I will present exciting new results from the research efforts of my group at Columbia University, revealing the critical roles of brittle damage and fluid-driven weakening on rift localization, propagation, linkage, and coalescence along the East African Rift System.
ESS Department - November 2nd, 2023 Most of Earth’s heat-producing elements are in the continental crust, particularly the upper crust. Thus, defining the upper crust composition is crucial for understanding the distribution of these elements that are responsible for powering mantle convection and plate tectonics. In order to constrain the composition of the upper continental crust and provide uncertainties on that composition, we analyzed the fine-grained matrix of more than 100 samples of glacial diamictites. These samples span both space and time, with depositional ages ranging from 2.9 Ga to 300 Ma. Systematic changes in the composition of the diamicrites document the rise of atmospheric oxygen and a change in bulk composition of subaerial crust from mafic-dominated in the Archean, t o a more felsic composition from the Neoproterozoic onwards. This fundamental change in composition likely reflects the emergence of plate tectonics in the Late Archean.