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The Permian basin-type upthrust or tilted fault-block structures have long been an enigma to the structural geologist. These have been variously ascribed to compressive, shear, or vertical stresses. None of these stress systems will suffice as an explanation. The structures have been formed by a fourth structural style that has not been fully described.
The upthrust structures were created by thermal events that caused the earth's crust to bulge, dilate, and pull apart. The bounding faults reflect preexisting fracture systems and are not the direct result of shear failure. Vertical fractures predominate in the basement, where the crust has pulled apart along preexisting fractures. The thermal events are the result of high heat flow within the asthenosphere that causes the lithosphere to dome. Batholiths, stocks, and dikes related to this high heat-flow regime form the discrete anticlinoria. As the thermal event wanes, the dome or anticlinorium founders. Gravity takes over and movement is downward on the faults in response to the cooling cycle. Moderate extension occurs when the dome is being elevated and moderate compression follows uring the subsidence phase.
Both the first-order and second-order domal structures are present in the Permian basin. The thermal event that culminated in Late Pennsylvanian time created the Delaware-Val Verde-Marfa rift-rift-rift triple junction, and the producing anticlinoria were formed over the intracrustal intrusives.
Having a viable structural model greatly assists exploration in the Permian basin.
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