Here are a few research themes that are driving my present and near-future research. Please contact me for more information!

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Primordial isotopic signatures in young rocks

Short-lived radiogenic isotope systems, like the 146Sm-142Nd or 182Hf-182W systems, preserve information about the early Earth. The extent to which early Earth signatures are preserved even in modern rocks is a current topic of investigation. I primarily utilize ocean island basalts (OIB) to investigate these signatures in young rocks. In the future, we will expand the available dataset for mid-ocean ridge basalts to provide ourselves a valuable comparison baseline.

 

This is a compilation of data that focuses on early Earth isotopic signatures present in the Réunion hotspot. Samples that lie outside the gray boxes, which represent terrestrial samples, preserve information about the early Earth. For many ancient rocks (warm colors), this is probably quite intuitive. For young rocks, like those from Réunion, these data show that isotopic signatures can be preserved in the deep Earth for more than 4 billion years!

 

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Core-mantle interaction

A common recent interpretion of negative W isotopic anomalies in OIB is that the core has 'leaked' into the deep mantle sources of OIB [Rizo et al., 2019 Geochem. Persp. Lett.; Mundl-Petermeier et al., 2020 GCA]. This idea challenges the historically-held notion that Earth's core-mantle boundary is impermeable, or even that we lose material from the mantle into the core over time. If the core does contribute to the silicate Earth, this fundamentally changes mass balances for siderophile elements, which are enriched in the core. I am working on developing independent tests for core-mantle interaction that complement W isotopes.

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In this figure from Brandon & Walker (2005 EPSL), an early view of core-mantle interaction at the base of mantle plumes is shown.

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Secular changes in short-lived radiogenic isotopes and the onset of plate tectonics

Neodymium is a silicate-loving element, which means that primordial Nd isotopic signatures can easily be overprinted when silicate material from the ambient mantle is assimilated into primordial mantle domains. However, this provides us a tool with which to examine the timescales on which this interaction occurred. One common explanation for why the interaction occurs is because plate tectonics returns young material from the surface into the interior, thus adding young material to primordial material. We can track the rate of change in Nd isotopic signatures and thereby constrain the timing of plate tectonics:

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This figure from Saji et al. (2018 Geochem. Persp. Lett.) shows models of tectonic recycling as they affect Nd isotopes through time. The gradual return of positive and negative Nd anomalies toward zero documents the rate of tectonic recycling through the Archean Eon (4-2.5 billion years ago). The symbols represent ancient crust that constrain the model. However, the geographic distribution of these localities is very restricted; it spans only Canada and Greenland. My group is working to expand this dataset and understand better whether the early onset of tectonic recycling was a global or local phenomenon.

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Unusual features of mantle plume systems

Volcanic hotspots are our delivery trucks for primordial isotopic signatures in modern environments. It is commonly assumed that hotspots are underlain by mantle plumes with a fixed canonical structure. However, there are certain aspects of some hotspots that differ from this classical model. For example, numerical simulations argue that the early Comoros hotspot was fueled by a mantle plume that split away from the plume feeding the Deccan Traps eruptions [Glišović & Forte, 2017 Science]. Basaltic lavas in Pakistan displaying an age-progressive relationship with the Réunion hotspot [Mahoney et al., 2002 EPSL]  may indicate that the Réunion mantle plume had a tail before it had a head. My group is developing geochemical tests for these variations on a mantle plume theme, mainly utilizing the Re-Os isotopic system.

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