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Atmospheric science
George Mason University
Events

23 Oct (GEOL) Val Finlayson, Tectonics, Mantle Processes

Oct 23, 2025, 4:30 - 5:30 PM

Speaker: Val Finlayson, University of Maryland, College Park

Title: Tungsten-182 and Chemical Geodynamics: A case study from the Easter-Salas y Gomez Plume

Time: Thu, 23 Oct, 4:30pm

Location: Exploratory 1309 and via Zoom (for link, email lhinnov@gmu.edu)

Host: Linda Hinnov

ABSTRACT: Recent developments in high-precision 182W/184W analyses have revealed the existence of small variations in the W isotopic composition of some high 3He/4He ocean island basalts, resulting from the decay of the short-lived 182Hf nuclide during early-Earth history. In addition to a correlation with helium isotopes, W isotopic variations display a correlation with anomalous high field strength fractionations in the host mantle source, all distinct features of the so-called “FOZO” (FOcal ZOne) component. As FOZO is implicated in the source mantle of most plumes, the characterization of 182W/184W along hotspot tracks may act in part as a geochemical tracer of the distinct FOZO component, and of mantle dynamics in a manner not previously possible with the “traditional” isotopic tools.

The Easter-Salas y Gomez hotspot track represents one example of mantle plume that has been active for at least 35 Myr. Currently, the plume is interacting with the East Pacific Rise (EPR). Previous work along the younger portion of the track has revealed a dynamic history of variable mantle source and melt production, favoring a model of a HIMU-like or FOZO-like (or, alternatively, both) plume mixing with depleted mantle (DMM) melts closer to the EPR. The isotopic variability captured in this part of the track also corresponds with an increase in melt degree closer to the ridge. This range of melt degrees and compositions provides a natural laboratory to better explore dynamics controlling the expression of isotopic anomalies such as 182W/184W deficits or elevated 3He/4He in plume source mantle.

New data from subaerial Rapa Nui (Easter Island) lavas, as well as a suite of submarine lavas dredged from nearby seamounts, reveal variable 182W/184W and 3He/4He in the hotspot track. Herein, I explore the systematics of these isotope systems compared to Sr-Nd-Pb and bulk compositional data of the lavas, as available, to understand the expression and origin of ancient isotopic signals in modern mantle melts. Extended to other plumes globally, this may have implications for the early history and long-term preservation of Earth's mantle.

 

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