Winter 2019 Talk: Tungsten-182 anomalies in terrestrial rocks: Evidence for core-mantle chemical interaction?

Dr. Hanika Rizo, Carleton University

Friday, March 15th, 2019 – Explore the world of extinct isotopes in terrestrial rocks

Core-mantle chemical interaction is a topic that has been hotly debated for decades. While physical (e.g. thermal) interactions across the core-mantle boundary suggest chemical exchange is also expected, it is generally assumed that the Earth’s core has been chemically isolated since its formation. This is because unequivocal geochemical evidence for this exchange has been difficult to find. The short-lived 182Hf-182W isotope system (t1/2=8.9 Ma) has always been considered to have potential to provide evidence for this process. This is because the W concentration and 182W isotopic composition of the core and the mantle can be assumed significantly different. Since W is siderophile and Hf is lithophile, core-mantle differentiation led to significant differences in the W concentration of these reservoirs. Since this differentiation occurred during the lifetime of the Hf-W system, the extinct isotope 182Hf decayed into 182W entirely in the mantle, leaving the core with an unradiogenic 182W isotopic composition. Thus, any core material “leaking” into the mantle could be detected in the 182W isotopic composition of magmas associated with deep mantle plumes. In this seminar, I will present and discuss 182W data for Hadean and Archean mantle-derived rocks that together with 182W data recently obtained in ocean island basalts, might provide the most compelling evidence to date that mantle plumes carry a core geochemical signature.

Research Interests: Hanika’s research interests are primarily focused on early earth geochemical processes. Hanika uses extinct isotopic systems, 182Hf-182W and 146Sm-142Nd, to understanding the timing and extent of metal segregation into earths core, the crystallization of earths magma ocean, and the effect of meteoritic bombardment on the silcate earth between 4.5 and 3.9 Ga.

2019 – Dr. Hanika Rizo