A GRAVITY AND MAGNETIC ANALYSIS OF THE LITHOSPHERIC STRUCTURE OF THE SOUTHERN SIERRA NEVADA

The general crustal structure of the southern Sierra Nevada of California and the surrounding area was examined through the analysis of gravity and magnetic data. A series of Bouguer gravity, low-pass and band-pass wavelength filtered gravity and reduced to the pole total magnetic intensity maps were produced to define the general tectonic features of the study area. Two regional gravity models were constructed using broadband seismic and geological mapping as constraints to determine the general crustal structure of the region and the location of a dense upper mantle body under the Great Valley and the Sierra Nevada region. Large scale mountain ranges generally have a thicker crust underneath them with possible crustal roots but the lack of a thick crustal root underneath the Sierra Nevada reported by previous geophysical studies still needs to be resolved. This gravity analysis study provides additional information to help explain these previous findings. This study found that the crustal thickness is between 30-33 km under the Basin and Range province and 35-40 km beneath the Sierra Nevada mountains. Also these models showed the delamination of the mantle lithosphere beneath the high topography of the Sierra Nevada. In general, the gravity and magnetic analysis and gravity models were consistent with the previous seismic studies and gave an improved image of the removal of the crustal lithosphere.