Exhumation is a process by which rocks deeply buried or crystallized at depth are brought to the surface in response to erosion of overriding material or tectonic processes. The Aleutian is an ideal location to study the dynamics of exhumation and arc systems in general because (1) it displays an extensive exposure of plutonic rocks and (2) it lacks back-arc spreading or intra-arc rifting, simplifying its exhumation history. In this project, we will obtain a regional data set of exhumation timing, rates, and trends from samples spanning >1400 km of the Central Aleutian arc. To provide a broader context of the Aleutian arc exhumation history, we are studying plutonic rocks (predominantly composed of diorites and granodiorites, which are rocks that are primarily made of plagioclase, amphibole, and quartz). This will allow us to test the various hypotheses for exhumation mechanisms that have been proposed in the literature but have not been directly tested. We will obtain emplacement depths (pressures) by using the Al-in-hornblende geobarometer. Petrographic analyses will be used to constrain the mineral assemblage of samples and microprobe analyses will be employed to obtain mineral compositions. Geobarometry calculations will be used to quantitatively estimate the depth of pluton emplacement. This study will provide insights into arc system dynamics and may help constrain whether magmatic, tectonic, and/or climatic forces drive plutonic exhumation.

Clumped isotopes are a powerful geochemical proxy within paleoclimatology, enabling further advancements in reconstructions of temperatures. Past studies have shown that the abundance of doubly substituted isotopologues participating within homogeneous carbonate exchange reactions is temperature dependent. Through these substitutions, ‘clumping’ is observed when two heavy isotopes bond with each other—for this study, the clumping of 13C and 18O in carbonates. The vibrational properties of the bonds within the 13C18O(16O)2 ^2- isotopologue influence zero-point energies of molecules and give rise to a temperature dependence. This can be utilized in calcium carbonate, CaCO3, which is a common mineral found in the shells of marine organisms, allowing temperature to be reconstructed using their fossilized remains from sediments. This project seeks to investigate the change in temperature of waters from off the coast of Antarctica from throughout the early Cenozoic using paleothermometry. This will be done by analyzing an existing isotopic dataset derived from bivalve mollusk samples at Seymour Island, on the Antarctic Peninsula. Currently, the dataset ranges in age from about 34 Ma to 66.8 Ma, covering three major paleoclimatic events that experienced large shifts in ocean temperature. Reconstructed temperatures will be compared to past studies that have recorded these trends to determine whether records produced from clumped isotopes are dependable. In the future, this study looks to expand beyond sea surface temperatures and investigate deep sea temperatures using benthic foraminifera.

Two-thirds of Earth’s surface is covered by oceanic crust, which is formed when lava erupts at mid-ocean ridges where tectonic plates spread apart, creating the planet’s largest volcanic chain. Our understanding of this process is largely informed by data from satellites or ship-mounted sonars, which can only resolve features that are about 30-100 m in size. Here, we present data collected using underwater robot Sentry just 70 m above the seafloor at the East Pacific Rise, a volcanically active fast-spreading mid-ocean ridge segment in the eastern Pacific Ocean. This segment last erupted in 2005, covering an area roughly the size of Manhattan, and we expect it to erupt again within the next few years. Tectonic plate separation is partially accommodated by tectonic strain due to faulting. Faults dam lava flows during eruptions, controlling the shape of the seafloor and the formation of the upper layers of oceanic crust. Analyzing faults near mid-ocean ridges provides insight into how tectonic plate separation occurs, and the factors that control the formation of new oceanic crust. Faults near the ridge axis have a horizontal offset of less than 10 m, which is impossible to measure from the previously existing seafloor data. Data collected by Sentry provides meter-scale mapping of the seafloor, producing a more detailed view of the seafloor than ever before. This allows us to make quantitative fault measurements, which are necessary for studying tectonic plate separation and oceanic crust formation at mid-ocean ridges.