Structure of the Sierra Nevada from receiver functions and implications for lithospheric foundering

Receiver functions sampling the Sierra Nevada batholith and adjacent regions exhibit significant variations in the structure of the crust and upper mantle. Crustal Vp/Vs values are lower in the core of the batholith and higher in the northern Sierra Nevada, portions of the Basin and Range, and near young volcanic fields in the eastern Sierra Nevada and Owens Valley. P- to S-wave conversions from the Moho vary from high amplitude and shallow (> 25% of the direct P-arrival amplitude, 25-35 km depth) along the eastern Sierra Nevada to low amplitude and deep (< 10%, 45-55 km) beneath the western batholith. We propose that dense mafic-ultramafic residue has foundered in the east-central and southern Sierra Nevada but still resides beneath its western portion. The central and northern Sierra Nevada shows inherited, prebatholithic structure at the Moho that was not completely overprinted by emplacement of the massive end-stage batholith. Evidence for the development and/or loss of substantial residue in the northern Sierra Nevada is equivocal. The asymmetric structure of the lithosphere beneath the central Sierra, which we model using constraints from petrophysical analyses, suggests that foundering progresses from southeast to northwest. This process sharpens the seismic response of the Moho by removing its underlying lithospheric mantle and allows upwelling asthenosphere to replace the detached material. Deep crustal seismicity and recent volcanism observed to 38 degrees N appear linked to this process and correlate spatially with the change in the character of the Moho, measurements of high crustal Vp/Vs, and presence of prominent negative conversions in the crust and uppermost mantle.