Mantle refertilization from 3.2 billion years ago points to an early start of plate tectonics

Gamal EL Dien, Hamed1*, Doucet, Luc-Serge1, Murphy,J. Brendan1, 2, Li,Zheng-Xiang1

1 Earth Dynamics Research Group, The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia, 2 Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Canada

* Corresponding author: E-mail address: hamed.gamaleldien@curtin.edu.au

Progressive mantle melting during the Earth’s earliest evolution led to the formation of a depleted mantle and a continental crust enriched in highly incompatible elements. Re-enrichment of Earth’s mantle can occur when continental crustal materials begin to founder into the mantle by either subduction or, to a lesser degree, by delamination processes, profoundly affecting the mantle’s trace element and volatile compositions. Deciphering when mantle re-enrichment/refertilization became a global-scale process would reveal the onset of efficient mass transfer of crust to the mantle and potentially when plate tectonic processes became operative on a global-scale. Here we document the onset of mantle re-enrichment/refertilization by comparing the abundances of petrogenetically significant isotopic values and key ratios of highly incompatible elements compared to lithophile elements in Archean to Early-Proterozoic mantle-derived melts (i.e., basalts and komatiites). Basalts and komatiites both record a rapid-change in mantle chemistry around 3.2 billion years ago (Ga) signifying a fundamental change in Earth geodynamics. This rapid-change is recorded in Nd isotopes and in key trace element ratios that reflect a fundamental shift in the balance between fluid-mobile and incompatible elements (i.e., Ba/La, Ba/Nb, U/Nb, Pb/Nd and Pb/Ce) in basaltic and komatiitic rocks. These geochemical proxies display a significant increase in magnitude and variability after ~3.2 Ga. We hypothesize that rapid increases in mantle heterogeneity indicate the recycling of supracrustal materials back into Earth’s mantle via subduction. Our new observations thus point to a ≥3.2 Ga onset of global subduction processes via plate tectonics.


Biography

I am a Ph.D. student working at Earth Dynamics Research Group, Curtin University in three major projects: (1) Geochemical records linking mantle plumes, supercontinent cycles and plate tectonics, (2) Crustal growth of the Arabian-Nubian Shield and Neoproterozoic mantle dynamics, and (3) Subduction zone geochemical cycle

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