Lithospheric Foundering: Constraints from the Sierra Nevada EarthScope Project (SNEP)

Category Geophysic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Owens, Thomas۱; Gilbert, Hersh۲; Zandt, George۳; Jones, Craig۴
Holding Date 23 September 2008

The Sierra Nevada Batholith (California, USA) is interpreted in a number of studies to be currently undergoing removal of its dense residual root. Primary constraints have been from interpretation of mantle xenoliths supplemented by seismic converted wave analysis and tomography in the southern Sierra Nevada. To provide further constraints on the timing and extent of this process, the first experiment utilizing the USArray/FlexArray component of the EarthScope observatory involved deployment of over 80 broadband seismic stations along the length of the Sierra Nevada. Average station spacing was about 25km extending approximately 400km along the length of the range with an array width of approximately 150km. Stations were deployed in two phases, a southern and a northern deployment, over a two year period. SNEP data and that of surrounding USArray Transportable Array (TA) stations provide for detailed imaging of the structures associated with an active foundering event. We present an overview of seismic observations to date from this deployment. These data document lateral variations in the crust and upper mantle that suggest distinct tectonic regimes along the batholith have developed in response to lithospheric foundering.
Common-conversion-point (CCP) stacking of receiver function data document distinctive lateral variations in structure at and below the Moho. In the eastern Sierra Nevada and westernmost Basin and Range, a flat, strong Moho converted phase is observed in the receiver functions between 30 and 35km depth. This signature extents progressively westward into the range in the central/northern Sierra Nevada relative to the southernmost range. This signature suggests that foundering has taken place along the eastern portion of the batholith. A weak, gradational, Moho in the western portions of the range is interpreted to represent regions where the dense residual root still exists. The thickest crust exists in the southwestern part of the range, with some thinning of the root in the western side of the central/northern portion of the ranges.