The Effect of Radiogenic Heat on Mountain Buidling

Michael Berry

Document Type

Presentation

Journal/Book Title/Conference

USU Student Showcase

Publication Date

4-2014

Faculty Mentor

Anthony Lowry

Abstract

It has long been recognized that, over geologic time, some regions experience repeated episodes of mountain-building whereas others remain tectonically quiet (e.g., Wilson, 1966). Geologists have hypothesized that new episodes of tectonic deformation prefer to reactivate pre-existing earthquake faults, but that gives rise to at least two questions: 1) How did those faults develop in the first place? 2) Why does the strain potential energy needed to reactivate faults accumulate where the faults are, instead of someplace else? In a recent publication, Lowry and Gussiny (2011) found that quartz, which flows more readily than other rock types, is more abundant in the crust of regions that have experience mountain-building episodes in the recent past, including the Rocky Mountains, Basin and Range rift, and the Sierras. There are other possible contributing factors that require examination, however. Most near-surface quartz is found in granites, and granites contain relatively high amounts of heat-producing radiogenic isotopes (such as potassium, uranium, etc.) Higher heat production contributes to warmer temperatures at shallower depths in the Earth, which in turn affects the flow strength of the rock, and therefore might favor mountain-building. My project examines the contribution of radiogenic heating to mountain-building. Using seismic data gathered from EarthScope's USArray and surface heat flow measurements compiled by Southern Methodist University, I am modeling Earth temperature change with depth to test the question of how much rock lithology variations affect the geotherm (via a combination of effects on radiogenic heat production and thermal conductivity). Geotherms that best match seismic measurements of upper mantle temperature to surface heat flow are consistent with laboratory measurements of rock thermal conductivity properties, and radiogenic heat production does affect temperature as well. I will use the results of these models to examine how/if geothermal variations are preserved over the long (~billion-year) timescales of successive mountain-building episodes.

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