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Early Earth

Early Earth Dynamics: Pt-Re-Os isotopic constraints on Hadean-Early Archean mantle evolution

 

Principal Investigator

Dr. Ambre Luguet
Steinmann-Institut
Fachbereich Geochemie
Poppelsdorfer Schloss
53115 Bonn

 

Abstract

This project aims to directly constrain the melting history and composition of the mantle of the Earth for the first 750 Ma of its history. So far, our limited knowledge hinges on isolated detrital zircons from Archean crustal rocks. They indicate crustal extraction as early as 4.4 Ga with peaks at 4.0 and 4.3 Ga but reveal conflicting models for the composition of the Hadean mantle. Both the timing and extent of these early crust formation events and the composition of the Hadean mantle have crucial implications for our understanding of the Early Earth’s chemical evolution and dynamics as well as crustal growth and thermal cooling models. Sulfides (BMS) and platinum group minerals (PGM) may hold the key to these fundamental issues, as they are robust time capsules able to preserve the melting record of their mantle source over several billion years.

I propose to perform state-of-the-art in-situ Pt-Re-Os isotopic measurements on an extensive collection of micrometric BMS and PGM from Archean cratonic peridotites and chromite deposits, and paleoplacers in Archean sedimentary basins. For the first time, < 20 μm minerals will be investigated for Pt- Re-Os. The challenging but high-resolution micro-drilling technique will be developed for in-situ sampling of the PGM and BMS with subsequent high-precision 187Os-186Os isotopic measurements by NTIMS. This highly innovative project will be the first to constrain Hadean Earth history from the perspective of the Earth’s mantle. By opening a new window towards high-precision geochemical exploration for micrometric minerals, this project will have long-term implications for the understanding of the micro to nano-scale heterogeneity of isotopic signatures in the Earth’s mantle and in extra-terrestrial materials.

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