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Smith Lecture: Deep Crustal Structure of the Rocky Mountain Region from Seismic Observations, Xenoliths, and Local Studies of Exhumed Terranes

Kevin Mahan, University of Colorado, Boulder
Friday, January 26, 2018
3:30-4:30 PM
1528 C.C. Little Building Map
Geophysical studies, xenoliths, magmatic records, and rare exposures of once deep rocks provide different perspectives with which to investigate the structure, composition, and properties of deep continental crust. Each has its own inherent biases and/or limitations, making integrated approaches particularly valuable in furthering our understanding of lithospheric evolution. We are comparing the structural, metamorphic, geochronological, and petrophysical records from xenoliths and exhumed crustal terranes from a range of localities across the Rocky Mountain region to seismic observations from EarthScope’s USArray and other regional experiments. This presentation will focus on two aspects that offer complimentary perspectives on North American evolution. First, we use seismic results from EarthScope experiments, compilations of active source studies, and selected xenolith studies to attempt to map the distribution of high-velocity lower crust across the continental U.S. and assess its relationship to emplacement and destruction-related mechanisms such as under-and intraplating, collision, extension, heating, cooling, hydration, and delamination. One major emphasis is on the geodynamic influence of garnet-producing and -consuming reactions on the density and velocity structure of the crust. The second aspect emphasizes seismic anisotropy as an important tool for mapping crustal-scale deformation patterns at depth. One preliminary conclusion from this work is that anisotropy in the central Rocky Mountain region apparently reflects competing signals from broadly distributed Paleoproterozoic fabric domains and late-stage localized shear zones. Important points to consider are the geometric and scale biases of seismic detection methods, as well as the physical and chemical processes involved in anisotropy development during deformation.
Building: C.C. Little Building
Event Type: Lecture / Discussion
Tags: Lecture
Source: Happening @ Michigan from Earth and Environmental Sciences