Foundering lithosphere imaged with magnetotelluric data beneath Yosemite National Park, California

Abstract

A magnetotelluric profile consisting of 14 sites and spanning 240 km from the San Joaquin Valley to the Nevada border was installed across the central Sierra Nevada, through Yosemite National Park, in an effort to constrain the northward extent of lithospheric removal beneath the range. Broadband and long-period instruments from the EMSOC (Electromagnetic Studies of the Continents) consortium were used to record data with periods ranging from 0.01 to 20,000 s, allowing the conductivity structure beneath the Sierra to be imaged to a depth of 120 km. Two-dimensional models reveal that the batholith's resistive root extends to a depth of just 30 km beneath the eastern Sierra and 45 km beneath the western Sierra. The batholith is separated by a thin conductive zone that coincides with the Moho from a resistive mantle structure at a depth of ~55 km. We propose that this resistive structure is residual root. Deeper, a broad conductive feature dipping eastward at depths of 65-100 km below the range is upwelling asthenosphere containing <1% melt that originates from the extensional tectonic regime of the Basin and Range to the east. © 2012 Geological Society of America.