Hematite accommodated shallow, transient Pleistocene slow slip in the exhumed southern San Andreas fault system, California, USA

Author:

DiMonte Alexandra A.1,Ault Alexis K.1,Hirth Greg2,Bradbury Kelly K.1

Affiliation:

1. 1Department of Geosciences, Utah State University, Logan, Utah 84322, USA

2. 2Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island 02912, USA

Abstract

Abstract Slow slip is part of the earthquake cycle, but the processes controlling this phenomenon in space and time are poorly constrained. Hematite, common in continental fault zones, exhibits unique textures and (U-Th)/He thermochronometry data patterns reflecting different slip rates. We investigated networks of small hematite-coated slip surfaces in basement fault damage of exhumed strike-slip faults that connect to the southern San Andreas fault in a flower structure in the Mecca Hills, California, USA. Scanning electron microscopy shows these millimeter-thick surfaces exhibit basal hematite injection veins and layered veinlets comprising nanoscale, high-aspect-ratio hematite plates akin to phyllosilicates. Combined microstructural and hematite (U-Th)/He data (n = 64 new, 24 published individual analyses) record hematite mineralization events ca. 0.8 Ma to 0.4 Ma at <1.5 km depth. We suggest these hematite faults formed via fluid overpressure, and then hematite localized repeated subseismic slip, creating zones of shallow off-fault damage as far as 4 km orthogonal to the trace of the southern San Andreas fault. Distributed hematite slip surfaces develop by, and then accommodate, transient slow slip, potentially dampening or distributing earthquake energy in shallow continental faults.

Publisher

Geological Society of America

Subject

Geology

Reference35 articles.

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