Abstract: Anatomy of a Hinterland Thrust Fault in the Sevier Orogenic Belt: An Example From the Pequop Mountains, NE Nevada

Phyllis A. Camilleri

A major factor in the unpredictability of subsurface structures and hydrocarbon traps in the hinterland of the Sevier thrust belt is the complexity of overprinted contractional and extensional structures. Moreover, although geometries of normal faults have been well documented, the geometries of thrust faults remains enigmatic because of the pervasive extensional overprint. Detailed mapping has revealed that the Pequop Mountains expose the most complete, well-preserved cross section through a thrust fault (Independence thrust) in northern Nevada and thus provides a rare, detailed glimpse of the geometry of a hinterland thrust.

The Independence thrust was exhumed, but not reactivated, by a normal fault. The exposed part of the Independence thrust cuts through nearly the entire Paleozoic section. The thrust defines an overall mid-to-upper crustal ramp with no apparent flats in the Paleozoic section. The thrust cuts lower Cambrian-lower Ordovician footwall strata at a low to moderate angle, upper Ordovician to middle Devonian strata at a high angle, and upper Devonian to Mississippian strata at a moderate angle. The sense-of-slip on the Independence thrust is top-to-the-southeast and the maximum amount of stratigraphic separation is approximately ~3 km. An unknown, but probably significant, amount of shortening along the Independence thrust was accommodated by internal deformation of its hanging wall. Hanging all strata are deformed by map-scale northwest vergent back folds and thrusts. Data from the Pequop Mountains illustrate that normal faults do not necessarily reactivate thrust faults and suggest that duplicated Paleozoic sections and thrust-related folds may be preserved in the subsurface. These contractional features may be a viable exploration target in the Sevier hinterland in northern Nevada.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada