Collaborative Research: Probing the Thermal Evolution of the San Andreas fault at Parkfield: Thermochronology in the San Andreas Fault Observatory at Depth (SAFOD)

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Analysis of rock samples from the 4-km-deep San Andreas Fault zone Observatory at Depth (SAFOD) drillhole provides an excellent opportunity to explore a fundamental question in fault mechanics regarding the frictional strength of faults, while simulataneously extending our knowledge of the regional uplift history in the Parkfield, California, area. SAFOD will provide samples through the Salinian block and from near at least one abandoned segment of the San Andreas fault system before finally intersecting the active San Andreas fault strand(s). Building on previous analysis of Pilot Hole samples collected in 2002, deep Salinian samples, as well as samples adjacent to the abandoned and active fault segments are analyzed using low temperature thermochronometry (specifically apatite and zircon fission-track dating, (U-Th)/He dating of apatite and zircon crystals, and 39Ar-40Ar dating of K-feldspar grains). The thermochronometry and complementary modeling studies characterize the long-term thermal evolution of the region and probe the faults themselves for evidence of localized thermal perturbations. Constraining frictional heating using thermochronometry presents an independent approach that can help establish the frictional properties of the San Andreas fault.