2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 7
Presentation Time: 3:50 PM

Insights on Lithospheric Delamination from the Sierra Nevada Earthscope Project (SNEP)

ZANDT, George, Department of Geosciences, University of Arizona, Tucson, AZ 85721, GILBERT, Hersh, Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, JONES, Craig, Dept. of Geological Sciences, University of Colorado, CB 399, Boulder, CO 80309 and OWENS, Thomas J., Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, gzandt@email.arizona.edu

Interdisciplinary studies in the southern Sierra Nevada of eastern California have documented ongoing removal (delamination) of the dense residual root from beneath the southern Sierra Nevada batholith. However, many questions remain concerning the timing, spatial extent, mechanism, and consequences of this still poorly understood lithospheric foundering process. The Sierra Nevada Earthscope Project (SNEP) is a scientific experiment designed to investigate these questions with a 2-phase (2 year) seismic deployment of 46 broadband Flex-Array stations embedded in the existing stations of the USArray Transportable Array in the region. In the two phases, approximately 80 sites have been occupied with ~25 km spacing from the northern edge of Kings Canyon north to Honey Lake and from the edge of the Central Valley into the Great Basin.

In this presentation, we will focus on the most recent seismic results that image the 3D lithospheric structure beneath the central and northern Sierra Nevada. Crustal thickness, reflectivity (layering), Moho “brightness”, and mantle wavespeeds vary dramatically across and along the length of the Sierra Nevada, but these changes are not simply correlated with present day topography or surface geology. We will explore the hypothesis that the removal process is intermittently progressing northward beneath the region, changing the crust and upper mantle, and partially controlling the volcanic and uplift history of the range. Data from the recently completed phase 2 deployment, to nearly the northern limit of the exposed Sierra Nevada batholith, will be used to constrain the northern extent of the affected region and investigate the character of the batholith where root removal may not have yet occurred or is in an embryonic stage.