--> Abstract: Termination of Laramide Arches at Orogen Margins: New fracture and Paleomagnetic Evidence for Partitioned Strike-slip Deformation in the Northern Bighorn Arch, by Karen M. Aydinian; #90181 (2013)

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Termination of Laramide Arches at Orogen Margins: New fracture and Paleomagnetic Evidence for Partitioned Strike-slip Deformation in the Northern Bighorn Arch

Karen M. Aydinian and Eric A. Erslev
University of Wyoming, Laramie, WY

How does deformation terminate at basement-involved orogen margins? Hypotheses include vertical axis rotation, partitioning of slip, and gravitational spreading. Vertical axis rotation predicts rotation of rigid bodies about a vertical axis, resulting in rotations in paleopole location. Partitioning predicts different components of motion taken up on differently oriented structures. Left-lateral motion may be taken up on discrete strikeslip faults, such as the E-striking Sage Creek Fault, while right-lateral motion is distributed more broadly in minor strike-slip faults. Gravitational collapse predicts a component of compression radial to the arch, with resulting compression being the combination of regional shortening and radial shortening. A better understanding of foreland arch formation is needed to understand fracture development in the foreland. Predicting fracture orientations and permeability at depth is critical to the development of resource plays.

Fracture analyses around the Bighorn Arch as part of the NSF/EarthScope Bighorn Project show a dominance of strike-slip minor faults (82%) and a change in shortening direction from N65E in the central Bighorns to N40E in the north. Paleomagnetic studies of Triassic Chugwater formation were conducted to test the hypothesis of vertical axis rotation. AMS and paleopole analyses for 23 locations around the northern plunge show that most locations have good correlation between primary magnetic fabrics and calculated compression directions, indicating deformation fabrics consistent with local minor fault orientations. Paleopole trends show no significant rotation from the central Bighorns to the north, ruling out vertical axis rotations as the sole cause of changes in fracture orientations and compression directions.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013