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AGU: Journal of Geophysical Research, Solid Earth

 

Index Terms

  • Structural Geology: Fractures and faults
  • Structural Geology: Microstructures
  • Structural Geology: Mesoscopic fabrics
  • Tectonophysics: Continental tectonics—extensional
  • Geomagnetism and Paleomagnetism: Magnetic fabrics and anisotropy
Abstract
Cited By (6)
 

Abstract

Magnetic and clast fabrics as measurements of grain-scale processes within the Death Valley shallow crustal detachment faults

Nicholas W. Hayman

Division of Earth and Ocean Science, Duke University, Durham, North Carolina, USA

B. A. Housen

Geology Department, Western Washington University, Bellingham, Washington, USA

T. T. Cladouhos

WebPE, Inc., Edmonds, Washington, USA

K. Livi

Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland, USA

The rock product of shallow-crustal faulting includes fine-grained breccia and clay-rich gouge. Many gouges and breccias have a fabric produced by distributed deformation. The orientation of fabric elements provides constraints on the kinematics of fault slip and is the structural record of intrafault strain not accommodated by planar and penetrative surfaces. However, it can be difficult to quantify the deformational fabric of fault rocks, especially the preferred orientations of fine-grained minerals, or to uniquely determine the relationship between fabric geometry and finite strain. Here, we present the results of a fabric study of gouge and breccia sampled from low-angle normal (detachment) faults in the Black Mountains, Death Valley, CA. We measured a preferred orientation of the long axes of the clasts inherited from the crystalline footwall of the fault and compared the shape preferred orientation to the anisotropy of magnetic susceptibility of the fault rocks. The two measurements of fabric exhibit systematic similarities and differences in orientation and anisotropy that are compatible with the large-scale kinematics of fault slip. The dominant carriers of the magnetic susceptibility are micron- and sub-micron scale iron oxides and clay minerals. Therefore even the finest grains in the fault rock were sensitive to the distributed deformation and the micro-mechanics of particle interaction must have departed from those assumed by the passive-marker kinematic model that best explains the fabric.

Received 17 November 2003; accepted 21 April 2004; published 29 May 2004.

Citation: Hayman, N. W., B. A. Housen, T. T. Cladouhos, and K. Livi (2004), Magnetic and clast fabrics as measurements of grain-scale processes within the Death Valley shallow crustal detachment faults, J. Geophys. Res., 109, B05409, doi:10.1029/2003JB002902.

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