Exhumation Associated with Continental Strike-Slip Fault Systems

Multiple constraints on divergent strike-slip deformation along the eastern margin of the Sierran microplate, SE California
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Published:January 01, 2007
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CiteCitation
Jonathan C. Lewis, Robert J. Twiss, Christopher J. Pluhar, Francis C. Monastero, 2007. "Multiple constraints on divergent strike-slip deformation along the eastern margin of the Sierran microplate, SE California", Exhumation Associated with Continental Strike-Slip Fault Systems, Sarah M. Roeske, Alison B. Till, David A. Foster, James C. Sample
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We have examined the deformation associated with a right-releasing stepover along the dextral Walker Lane belt where it traverses Wild Horse Mesa in eastern California. We use a micropolar inversion of both seismic focal mechanism and fault-slickenline data and compare the results to the micropolar deformation parameters inferred from paleomagnetically determined block rotations and GPS velocities. The focal mechanisms, fault-slickenlines, and GPS velocities all show horizontal shear with a consistent ENE–WSW to E–W maximum extension-rate axis (d 1). A subset of data shows crustal thinning with a similarly oriented d 1. We interpret these results as a reflection of divergent strike-slip (i.e., transtensional) boundary conditions in a negative flower structure developed in the right-releasing stepover. The fault-slickenline data also show a crustal thickening solution that we attribute to the local accommodation of block rotations. Paleomagnetic data demonstrate clockwise-looking-down rotations of 12.0° ± 2.6° (68% confidence limits) in ca. 3 Ma volcanic rocks, relative to the same rocks outside the stepover. Assuming rotations took 2–3 m.y. gives average microspins (block rotation rates) of 4.0° ± 0.9°/m.y. to 6.0° ± 1.3°/m.y. GPS velocities define a current macrospin (half the continuum rotation rate) of 3.9° ± 0.6°/m.y. to 6.1° ± 1.5°/m.y. These spin components are consistent with expectations for transtension. Our calculations of relative vorticity W from the GPS and paleomagnetic data are generally consistent with values obtained from the inversion of the fault-slickenline data, but the uncertainties in the data do not permit a definitive test of these results.
- California
- Coso Range
- crustal thinning
- deformation
- earthquakes
- faults
- focal mechanism
- Global Positioning System
- Inyo County California
- lineation
- microplates
- neotectonics
- paleomagnetism
- plate tectonics
- preferred orientation
- rotation
- seismicity
- seismotectonics
- Sierra Nevada
- slickensides
- Southern California
- stereographic projection
- strain
- strike-slip faults
- structural analysis
- style
- tectonics
- transtension
- United States
- Wild Horse Mesa