2D and 3D modeling of the Laramide fold geometry of Derby Dome and its en echelon interchange with Dallas Dome, southern Wind River Basin, Wyoming
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The Wind River Mountains of central Wyoming formed as a basement-cored uplift during the Laramide orogeny (ca. ~75-35 Ma) and produced a series of left stepping, en echelon NW-SE trending folds, including Dallas Dome and Derby Dome, along the southwestern margin of the Wind River Basin. The orientation of the fold structures are consistent with regional NE-SW shortening during Laramide time. However, the development of the en echelon fold pattern is enigmatic. The objective of the study was to determine the stress geometries that produced Derby Dome, a Laramide fold structure adjacent to the Wind River Mountains using various techniques to: 1) model the structures in 2D and 3D using the Move� software suite, 2) evaluate changes in shortening across the structures, 3) evaluate strains associated with folding, 4) analyze the relationship of fractures to the stress regime, and 5) evaluate local strike-slip faulting. The 2D and 3D modeling in Move� yielded shortening calculations and strain geometries consistent with the regional shortening direction of 60�/240�. The fracture analysis confirmed that ~81% of fractures found on the NE limb of Derby Dome are also consistent with the regional shortening direction. Seismic reflection techniques were used to image a strike-slip fault in the Dallas-Derby dome interchange, which displays ~280 m of lateral offset and ~20 m of vertical throw. It is unclear whether the fault penetrates the basement rock and cannot be attributed to a pre-existing basement weakness without a deeper, clearer seismic profile.