Mineralogical characterization of protolith and fault rocks from the SAFOD Main Hole

Authors

John G. Solum, U.S. Geological Survey
Stephen H. Hickman, U.S. Geological Survey
David A. Lockner, U.S. Geological Survey
Diane E. Moore, U.S. Geological SurveyFollow
Ben A. van der Pluijm, University of Michigan - Ann Arbor
James P. Evans, Utah State University

Date of this Version

2006

Comments

Published in GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L21314, doi:10.1029/2006GL027285, 2006

Abstract

Washed cuttings provide a continuous record of the rocks encountered during drilling of the main hole of the San Andreas Fault Observatory at Depth (SAFOD). Both protolith and fault rocks exhibit a wide variety of mineral assemblages that reflect variations in some combination of lithology, P-T conditions, deformation mechanisms, and fluid composition and abundance. Regions of distinct neomineralization bounded by faults may record alteration associated with fluid reservoirs confined by faults. In addition, both smectites occurring as mixed-layer phases and serpentine minerals are found in association with active strands of the San Andreas Fault that were intersected during drilling, although their rheological influence is not yet fully known. Faults containing these mineralogical phases are prime candidates for continuous coring during Phase 3 of SAFOD drilling in the summer of 2007.