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Abstract

A divergent (transtensional) wrench fault is one along which strike-slip deformation is accompanied by a component of extension. Faulting dominates the structural style and can initiate significant subsidence and sedimentation. The divergent wrench fault differs from other types of wrench faults by having mostly normal separation on successive profiles, negative flower structures, and a different suite of associated structures. En echelon faults, most with normal separation, commonly flank the zone, and some exhibit evidence of external rotation about vertical axes and have evidence of superimposed strike slip. Flexures associated with the wrench fault are formed predominantly by vertical components of displacement, and most are drag and forced folds parallel to and adjacent to the wrench. Hydrocarbon traps can occur in fault slices within the principal strike-slip zone, at culminations of forced folds, in the flanking tilted fault blocks, and within less common en echelon folds oblique to the zone.

Divergent wrench faults occur at active plate boundaries, in extensional and contractional continental settings, and within plates far from areas of pronounced regional deformation. Along transform margins and within wrench systems, divergent wrench styles tend to develop where major strands or segments of strands bend or splay toward the orientation of associated normal faults (e.g., elements of the San Andreas system in the Mecca Hills, California), and where major strands are regionally oblique to interplate slip lines (e.g., Dead Sea transform, Middle East). The style also develops at releasing fault oversteps and fault junctions (e.g., Ridge Basin, California), and locally where crustal blocks rotate between bounding wrench faults. In extensional settings, divergent wrench faults may form within graben doglegs and oversteps (e.g., between the Rhine and Bresse grabens, northern Europe), and they may separate regions that experienced different magnitudes of extension (e.g., Andaman Sea area). Many oceanic fracture zones have divergent wrench characteristics. The style has also been recognized in magmatic arcs (e.g., the Great Sumatran fault) and in both backarc and peripheral foreland settings (e.g., Lake Basin fault zone, Montana) near convergent plate boundaries, and in intra-plate settings (e.g., Cottage Grove fault, Illinois; Scipio-Albion trend, Michigan).

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