Ten-million years of activity within the Eastern California Shear Zone from U-Pb dating of fault-zone opal

Earth and Planetary Science Letters
By: , and 

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Abstract

Reconstructions of long-term fault activity are essential for understanding both the mechanisms controlling fault behavior and accurate earthquake hazard assessments. Increasing evidence for temporal variations in strain accumulation suggests non-uniform strain rates over a range of historic to geologic timescales. The paucity of long-term records of fault activity has limited our ability to resolve these variations. We present a method for constraining long-term fault activity based on U-Pb dating of fault-related opal from secondary fault segments within the Eastern California Shear Zone (ECSZ). The presence of sheared and breccia-cemented opaline silica within well-exposed faults at near-surface conditions suggest that opal formation is associated with high-magnitude earthquakes capable of surface rupture (>6 M). Temporal constraints from sheared syntectonic opal (n=74) on related secondary faults from this study provide new insights on the timing of fault initiation, reactivation, and longevity. The oldest dates obtained indicate that ECSZ activity commenced at or before 10 Ma. Multiple deformation events dated within a single structure on episodically deposited and sheared opal (up to six generations), demonstrate that fault reactivation occurred over 105 year timescales (0.7-0.1 Ma). Relative probabilities of dated deformation events can be used to evaluate changes in fault activity in the past 2.5 Ma (n=60). This analysis indicates enhanced fault activity starting at 2 Ma and peaking around 1 Ma, possibly due to fault-interactions and distribution of deformation between the ECSZ and the San Andreas Fault.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ten-million years of activity within the Eastern California Shear Zone from U-Pb dating of fault-zone opal
Series title Earth and Planetary Science Letters
DOI 10.1016/j.epsl.2019.05.047
Volume 521
Year Published 2019
Language English
Publisher Elsevier
Contributing office(s) Geology and Geophysics Science Center, Geology, Minerals, Energy, and Geophysics Science Center
Description 9 p.
First page 37
Last page 45
Country United States
State California
Other Geospatial Mojave Desert