Collaborative Research: High Field Strength Elements and Hf-Nd Isotope Systematics in Aleutian Lavas: Implications for Conservative Element Behavior in Subduction Zones

Washington State University, Pullman WA

Investigators

Abstract

Vervoort EAR-0230261 This is a study of high field strength element (HFSE; Ti, Ta, Nb, Zr, Hf) and Lu-Hf isotopic systematics in volcanic rocks of the Aleutian island arc. The main objective of the study is to constrain the details of HFSE and related rare-earth element behavior in subduction zones. Specifically, the study will evaluate the conditions under-which HFSE behave conservatively versus non-conservatively during subduction magma genesis. High field strength element abundances and Hf-Nd isotopes will be measured in lavas collected from along the full length of the oceanic Aleutian arc. The analytical approach will involve (1) dissolution of samples in steel-jacketed Teflon vessels; (2) spiking of samples with a mixed 94Zr, 176Lu, 180Hf, 180Ta spike; (3) separation of elements of interest with ion-exchange chemistry; and (4) analysis of samples by isotope dilution on a multi-collector ICP mass spectrometer. This study will document along-arc and cross-arc changes in Aleutian HFSE and Hf isotope geochemistry. Well-documented changes in physical conditions along the arc, in particular the inferred relative temperature of the subducting plate and mantle wedge in the eastern versus western Aleutians, and the presence or absence of subducted sediment in the mantle source beneath different parts of the arc, will provide the geologic context for interpreting the observed HFSE and Hf isotopic variation.