Mechanisms and Kinematics of a Precambrian-Cored Fold and Fault Structure: Jakey's Fork, Wyoming

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Geological Society of America Speical Papers



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The Jakeys Fork fold and fault structure is a Precambrian granite-gneiss–cored anticline in the hanging wall of the steeply west dipping Ross Lakes shear zone. The Ross Lakes shear zone juxtaposes Precambrian rocks in its hanging wall and steeply dipping to overturned Cambrian and Ordovician sedimentary rocks in its footwall. Precambrian and Cambrian Flathead Sandstone in the hanging wall of the Ross Lakes shear zone are folded in an open, kinklike fold defined by gently and steeply dipping panels of Cambrian Flathead Sandstone. Precambrian rocks in the core of the hanging-wall anticline deformed by slip on a narrow fault in the hinge zone of the fold and by randomly oriented slip on narrow, discrete faults of many orientations on either side of the hinge zone. Cambrian Flathead Sandstone was welded to the Precambrian rocks during folding, and detachment occurred in the Cambrian Gros Ventre Formation. The Ross Lakes shear zone formed by brecciation and cataclasis. Precambrian rocks in the footwall of the Ross Lakes shear zone deformed by small amounts of slip on steeply west dipping faults, which resulted in a steepening of the contact between Precambrian rocks and the overlying Cambrian Flathead Sandstone. Faults in Precambrian rocks in the footwall of the Ross Lakes shear zone bound regions of undeformed Precambrian rock with widely spaced fracture sets. Cambrian Gros Ventre and younger formations are folded into a tight, overturned footwall syncline with its steep limb parallel to the Ross Lakes shear zone.

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