| The notion of detachment faulting—low-angle normal faulting of regional extent—has become a staple of geometric and kinematic models in extended areas, and has spawned a variety of mechanical models that attempt to reconcile the phenomenon with classical failure theory. Part I of this study critically examines popular elastic models that attempt to attribute low-angle normal faults to reorientation of the tectonic stress field. While such models do indeed rotate principal stresses into an orientation consistent with low-angle normal faulting, the resulting stress magnitudes are insufficient to produce low-angle normal-sense slip, and suggest that stress release on high-angle normal faults will occur before low-angle normal faults have developed.; Part II of the study focuses on geometrical and kinematic models of detachment faulting, specifically on one celebrated example: The Sevier Desert basin in west-central Utah, commonly viewed as the result of nearly 40 km of Tertiary slip on a vast extensional detachment. New field mapping, structural analysis, sedimentological study, and seismic-reflection interpretation in the Canyon Range, on the eastern margins of the Sevier Desert basin, demonstrate that the low-angle contact between Tertiary and pre-Mesozoic rocks in these mountains, commonly interpreted as the “breakaway zone” of the Sevier Desert detachment, is likely depositional, and that data from the area are fully consistent with the older interpretation of the range as a simple horst bounded on both sides by high-angle normal faults. A comprehensive re-evaluation of the full suite of seismic and well data from the Sevier Desert basin places new constraints on the timing and kinematics of detachment faulting in this area—and also raises questions about the viability of the detachment model itself. An alternative, non-detachment model, combining late-stage thrust loading, regional subsidence, and high-angle normal faulting, may explain subsurface observations in the Sevier Desert basin. Such a model, if correct, implies dramatically lower total extensional strain in the northern Great Basin than is commonly assumed. |
