We are very pleased to welcome Dr George Cooper to give a HotStuff seminar, entitled Crystal-scale isotope constraints on crustal melt evolution: current understanding, methods and future plans.

Abstract: 

The journey arc magmas take from the mantle, through the crust, to the surface during volcanic eruptions, is complex. Lavas produced at subduction zones represent the integration of both source heterogeneity and an array of crustal processes, such as: differentiation; mixing; homogenisation; assimilation of crust and/or sediments. Therefore, unravelling the relative contribution of the sub-arc mantle source versus these crustal processes is difficult when using the amalgamated end products in isolation. Despite this, geochemical studies typically still focus on the whole-rock or phenocryst record of the erupted volcanic products.

Recent work on plutonic xenoliths from the Lesser Antilles subduction zone has revealed a disconnect between the phenocryst record of shallow storage and the record from the volumetrically larger, and deeper plumbing system. Plutonic xenoliths, representing different parts of the whole trans-crustal plumbing system, have the potential to record processes from the deep to shallow crust, revealing the true chemical diversity of arc crust. Dr Cooper plans to trace the chemical and isotopic evolution of subduction zone melts as they pass through the crust by using crystal scale isotopes (CSI) in plutonic xenoliths.

In this talk, Dr Cooper will discuss: past petrological and geochemical results from Lesser Antilles plutonic xenoliths; methods and plans to apply CSI in plutonic xenoliths from the Lesser Antilles and Aleutian subduction zones; results of the first coupled Pb-Nd isotope analysis of cumulus plagioclase from the fast-spreading Hess Deep (East Pacific Rise) oceanic crust to assess the isotopic heterogeneity of the depleted upper mantle.