Date of Award:

12-2025

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Committee Chair(s)

Anthony R. Lowry

Committee

Anthony R. Lowry

Committee

James P. Evans

Committee

Alexis K. Ault

Abstract

This research aims to develop advanced methods to accurately depict temperature profiles within the lithosphere, the Earth’s rigid outer layer. These temperature profiles extend from Earth’s surface to the asthenosphere, the ductile layer below the lithosphere. Constraining the poorly-known temperature distribution within the upper Earth is important for modeling the deformation of Earth’s crust over varying timescales and is essential for advancing realistic simulations of Earth dynamics. Here, I utilize enhanced global seismic data, coupled with recent advances in our understanding of mineral systems, to create several global lithospheric models in which I estimate temperature profiles from seismically observable features that represent various depth layers within the Earth. I derive temperatures from observations of oceanic plate ages, seismic velocity measurements at the depth of the Moho, and two seismic-derived representations of the lithosphere-asthenosphere boundary that I assume correspond to a fixed temperature. I analyze these temperature models to evaluate assumptions about heat transport, address gaps in seismic observations, and identify additional thermal transport processes relevant to each methodology. This comparative study enhances our overall understanding of heat transfer mechanisms within the lithosphere. Despite inconsistencies in temperature estimates from different observational constraints, I find significant correlation between predicted Moho temperatures and lithosphere-asthenosphere boundary depths across the evaluated models. The largest residuals are between models derived from seismic velocities and those representing the lithosphere-asthenosphere boundary. The seismic velocity models that assume steady-state heat transfer systematically under-predict lithosphere-asthenosphere boundary depths and those that assume half-space cooling systematically over-predict those depths. I attribute these temperature biases to unmodeled deepening of the lithosphere-asthenosphere boundary due to small-scale convective heat flow in the upper asthenosphere, as predicted by simulations of long-term deformation of the Earth’s crust, mantle, and core. Additionally, discrepancies in Moho temperatures between standard plate cooling models and seismic velocity-derived models suggest that seismic velocities consistently overestimate temperatures in the older lithosphere of ocean basins, which I attribute to neglect of the velocity effects of an additional mineral phase that should be incorporated into the mineral physics velocity-to-temperature conversion at depths less than 20 km. However, temperatures in younger oceanic lithosphere are much colder than plate cooling models predict, indicating that shallow heat transport from near-ridge hydrothermal circulation, which is neglected in plate cooling models, is important at Moho depths.

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