Earth and Planetary Sciences ETDs

Charles Hoots

Publication Date

5-1-2016

Abstract

Lithospheric attachment to the high-velocity Isabella anomaly (IA) in central California was tested by mapping the lateral extent of interruption of the lithosphere-asthenosphere boundary (LAB). The study area spans the location of two plausible origins for the anomaly, the Monterey microplate (Wang et al., 2013) and Sierra Nevada batholith (Ducea & Saleeby, 1998). Results include 918 binned receiver functions that were made using multi-channel spectral deconvolution and an array-based spectral source estimation on the event data from an 18- month deployment of a high density array from the coast to the Sierra Nevada crossing the lateral location of the Isabella anomaly. Common conversion point (CCP) scattered wave imaging shows a strong negative velocity gradient (NVG) west of the San Andreas Fault (SAF) and a gap in a NVG horizon east of the SAF. This is interpreted as prominent arrivals at the base of a partially subducted microplate that become undetectable as the plate dips too steeply east of the SAF for reliable recovery of Sp converted phases. The gap in consistent NVG arrivals would indicate a local disruption of the LAB along the lateral extent of the anomaly. Although the LAB disruption cannot constrain the tectonic origin of the Isabella anomaly, it does indicate the anomaly is adjacent or attached to North American lithosphere. S-to-P (Sp) conversions west of the SAF are consistent with a sharp LAB contrast, but whether the mantle section of the lithosphere is composed of Monterey microplate mantle or North America forearc mantle is unknown. Imaging also shows a weak east-dipping NVG in the eastern half of the Great Valley. This suggests a continental LAB at the western edge of the Sierra Nevada foothills down to 100km depth. Sharp changes in Sp arrivals near and shallower than the Moho are consistent with a previously imaged west dipping sub-crustal shear zone extending down to about 30 km depth beneath the Great Valley. The Moho detected 45 km below the Sierra Nevada foothills shows that at least locally there is not a Moho hole as suggested by prior studies and any interruption of the Moho at this latitude is constrained farther to the west beneath the Great Valley. The results and interpretations in this study are in agreement with prior studies (Wang et al., 2013; Pikser et al., 2012) that suggest the IA is a steeply dipping continuation of the partially subducted Monterey microplate.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Roy, Mousumi

Second Committee Member

Worthington, Lindsay Lowe

Language

English

Keywords

LAB, Lithosphere, Asthenosphere, Receiver Functions, Sp, CCP, Common Conversion Point, Isabella, California

Document Type

Thesis

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