An alternative interpretation of strike-slip shear sense in the Brevard fault zone

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6112862

Bobyarchick, A R ^[1]

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1. Univ. of North Carolina, Charlotte, NC (United States). Dept. of Geography and Earth Sciences

In many localities, the Brevard fault zone (BFZ) contains shear bands that indicate dextral strike-slip shear sense if the prevailing mylonite foliation in the shear zone is interpreted to be the finite simple shear plane. Apparent stretching lineations are often sub-horizontal, supporting the interpretation of strike-slip motion. The juxtaposition of such shear indicators with other local and regional structures related to contraction across the fault zone has led to kinematic histories for the Alleghanian evolution of the BFZ that incorporate finite and superposed periods of reverse and strike-slip movement. Because the Appalachian orogen is primarily a contractional mountain belt, simple assumption of a phase of strike-slip movement in the BFZ leads to several contradictions. Among these are the listric seismic structure of the fault zone, the lack of demonstrable displacement indicators, an inadequate explanation for the kinematic transition from contraction to shear, lineation-parallel fold axes of non-sheath folds, and the presence in specific segments of the BFZ where the dextral strike-slip shear bands are inconclusive. Deformation by sub-simple shearing is an important factor in interpreting shear sense from shear bands and stretching lineations. The shear bands most likely require contraction at a moderate angle to the mylonite foliation. Dextral asymmetry implies oblique convergence across the BFZ, with the Piedmont directed westward. Sub-horizontal lineation, if assumed to be active rather than passive, may be the maximum axis of the oblate ellipsoid that results from sub-simple shearing, and not necessarily a specific direction of tectonic transport. Based on observation made along the eastern margin of the Grandfather Mountain window in NC, a continuum model for the Alleghanian evolution of the BFZ includes early oblique dextral convergence leading to partial or total detachment between the Blue Ridge and Piedmont near the apex of dextral shear.

• OSTI ID: 6112862
• Report Number(s): CONF-9304188--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:4
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
APPALACHIAN MOUNTAINS
DEVELOPED COUNTRIES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
MOUNTAINS
NORTH AMERICA
NORTH CAROLINA
SHEAR
SLIP
TECTONICS
USA