The Growth of Earth’s Earliest Crust—Unravelling the Isotope Record
IPGP - Îlot Cuvier
Séminaires thème Origines
Washington State University
ZOOM LINK: https://cnrs.zoom.us/j/94140425975?pwd=T2EwWHZOY0trNXNsbjFxU1lxQTg0UT09 A fundamental principle of Earth’s geochemical evolution holds that continental crust is formed by extraction of melts from the mantle, leaving part of the mantle depleted in incompatible elements. Radiogenic isotopes, specifically the Sm-Nd and Lu-Hf systems, have been essential tools in revealing this evolution, although the mechanisms and volumes of mantle depletion and crustal production through time are hotly debated. Increasingly, for the Earth’s oldest rocks, the Sm-Nd and Lu-Hf records appear to be at odds: Nd isotopes indicate a prior widespread mantle depletion; Hf isotopes show a chondritic mantle with no indication of widespread development of a depleted mantle reservoir. This discrepancy has been termed the Hf-Nd paradox. In this talk, I will examine the Eo-Paleoarchean isotope records from SW Greenland and Western Australia and suggest an explanation for the Hf-Nd paradox and what this tells us about the depletion of the mantle and growth of continental crust in the early Earth.