Seminar – James Dottin

Isotopic evidence for multiple recycled sulfur reservoirs in the Mangaia mantle plume

Abstract
Earth’s mantle is geochemically characterized with long-lived radiogenic isotopes of Sr, Nd, and Pb that define four geochemical endmember reservoirs (DMM, EM I, EM II, and HIMU). HIMU (High μ= ²³⁸U/²⁰⁴Pb) is a reservoir that is thought to form from the recycling of altered oceanic crust that was carbonated and mixed with the peridotitic mantle. Mangaia, an island in the Cook-Austral suite, is the type locality in the Pacific Ocean for HIMU that also exhibits evidence for recycled anomalous sulfur of Archean origin. In this seminar, I will discuss a project in which I (and Co-authors) revisit Mangaia with high precision analyses of sulfide inclusions in olivine and pyroxene minerals separates and test for the prevalence Archean sulfur in the HIMU mantle source feeding Mangaia. We aim to constrain the nature of HIMU and use sulfur isotope compositions of Mangaia basalts to provide insight into the mixing of multiple melt sources. From the data we are able to highlight (1) a newly identified recycled endmember composition at Mangaia that is likely younger than the source linked to a reservoir that hosts Archean-related sulfur and (2) isotopic disequilibrium among mineral separates from the same sample that suggests mixing of sulfur from two sources that were captured at different stages of crystallization.