2007 GSA Denver Annual Meeting (2831 October 2007)
Paper No. 83-27
Presentation Time: 8:00 AM-12:00 PM


ANDERSON, R. Ernest, U.S. Geological Survey, PO Box 347 120 Rio Del Loma, Kernville, CA 93238, anderson_ernie@yahoo.com and BERGER, Byron, U.S. Geol Survey, Federal Center MS964, Denver, CO 80225-0046

The Waterman Hills detachment fault (WHDF) north of Barstow is reported as formed during passage of a rolling hinge, but kinematics are conflicting; N-directed upper-plate brittle strain in the Mud Hills and NE-directed lower-plate ductile strain in the Waterman Hills/Mitchell Range. In the Waterman Hills, the last slip events on the WHDF, determined from foliated gouge and the reorientation of directly subjacent L-tectonites, were S-directed, approximately antipolar to brittle strain in the Mud Hills to the north. We interpret the N-S shear strain on the WHDF to be associated with flexing of the detachment around E-W axes. The flexing and detachment shear are the youngest Miocene deformation and followed major fluid-flow across the fault, cataclasis, and vertical collapse. The flexing also post-dates main-phase extension (pre 18 Ma?) and bears no obvious spatial or genetic association with regional post-18-Ma strike-slip faulting. It records N-S shortening kinematiclly consistent with other major Miocene shortening strains including 1) the horizontal contractional component of widespread constrictional L tectonites formed in a lower-plate Miocene pluton, 2) strong folding around northeast axes of L and LS mylonites and ultramylonites in the pluton at scales ranging from sub-meter to hundreds of meters, 3) kilometer-scale steep-axis bending of previously steeply tilted early Miocene upper-plate volcanic and sedimentary rocks, and 4) development of the post-18 Ma east-west Barstow syncline 7 km to the north. Collectively, the assemblage of shortening strains, oriented either normal to the NE-trending axis of regional extension or approximately N-S, spans the full range of age and depth of known Miocene deformation in the central Mojave metamorphic core complex. These relations invite consideration of a tectonic model that is a) three dimensional, b) fundamentally constrictional in both the ductile and brittle realms and c) not driven by plane-strain extension as in the rolling hinge model. Also, the restricted extent (12x35 km), extension-normal long-axis shape, and 3-D aspect of high strain in the core complex are more consistent with a localized tectonic blister than a sub-horizontal crustal shear zone coupled to high-strain areas located 200 km to the east and west as favored in published reports.

2007 GSA Denver Annual Meeting (2831 October 2007)
General Information for this Meeting
Session No. 83--Booth# 67
Structural Geology and Tectonics (Posters)
Colorado Convention Center: Exhibit Hall E/F
8:00 AM-12:00 PM, Monday, 29 October 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 227

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