Evidence for paleoseismic slip on a continental low-angle normal fault: Tectonic pseudotachylyte from the West Salton detachment fault, CA, USA

Document Type

Article

Journal/Book Title/Conference

Earth and Planetary Science Letters

Volume

387

Issue

1

Publication Date

2014

First Page

170

Last Page

183

Abstract

Highlights • Evidence for repeated ancient seismicity along a continental low-angle normal fault. • Thick (>1.0 m) accumulations of tectonic pseudotachylyte. • Pseudotachylyte formed in the shallow-crust with little fluid involvement. • Seismic slip occurs during low-angle normal fault evolution. The potential of continental low-angle normal faults (LANF) to nucleate large (>6.0 Mw) earthquakes at low-angles remains unclear despite much focused research. We document evidence for ancient seismicity along a continental LANF (detachment fault) that formed and slipped at low-angles and produced tectonic pseudotachylyte. These thick and laterally persistent pseudotachylyte accumulations along the West Salton detachment fault (WSDF), Salton Trough, USA, preserve convincing evidence for a frictional melt origin including: spherulitic microlites, ductile-flow structures, preservation of high temperature phases as clasts, and injection veins. Cumulative thickness of pseudotachylyte along the fault ranges from 0.1 to 1.5 m, and pseudotachylyte–cataclasite in the fault core and damage zone are exposed along ∼2.6 km length of the fault. Reworked fragments of pseudotachylyte in cataclasites, and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles. The limited exposure (

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