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Constraints from magnetotelluric measurements on magmatic processes and upper mantle structure in the vicinity of Lassen Volcanic Center, northern California
Stephen K. Park and Linda C. Ostos, Department of Earth Sciences, University of California Riverside, 2258 Geology, Riverside, California 92521, USA. Published online 4 Apr. 2013; http://dx.doi.org/10.1130/GES00799.1. Themed issue: Geodynamics and Consequences of Lithospheric Removal in the Sierra Nevada, California.
A geophysical survey in northern California provides new images of magma source regions beneath Lassen Volcanic Center and volcanically active areas to the east. While geologists can predict the processes that form magma beneath volcanoes including depths and temperatures, they cannot deduce the geometries of the source regions. Magma is electrically conductive, and a geophysical technique called magnetotellurics can be used to create images of the distribution of electrically conductive bodies down to depths of 200 km or more. Based on how conductive are these bodies, the percentages of magma and/or fluids can be estimated. This study by Stephen K. Park and Linda C. Ostos, spanning Lassen Volcanic Center in northern California, shows a highly conductive body at a depth of 100 km and approximately 50 km east of the peak. This body is too conductive to be magmatic, and we instead suggest that it results from dewatering of the subducting Gorda plate. Zones of enhanced conductivity found in the upper mantle above the body provide conduits to active volcanic centers in the L
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