Paper No. 7
Presentation Time: 9:00 AM-6:00 PM
RAMP-FLAT DETACHMENT EXTENSIONAL FAULTING ON THE TULE SPRINGS DETACHMENT?
TEMPLETON, John A., Lamont-Doherty Earth Observatory, 61 Route 9W, PO Box 1000, Palisades, NY 10964-8000, ANDERS, Mark H., Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964 and ADLER, Alex D., Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, johnt@ldeo.columbia.edu
This contributes to the ongoing debate about the nature of low-angle structures and the architecture of crustal extension. The Tule Springs detachment (TSD) is one of the earliest cited examples of a rooted detachment fault that initiated and slipped at an extremely low angle, as well as being the type example for a low-angle normal fault with ramp-flat geometry (Axen, 1993). The TSD is the central of three low-angle structures between the Beaver Dam Mountains and the Meadow Valley Mountains, which together are ascribed 54 ± 10 km of extension (Axen et al, 1990). Yet even as the ramp-flat detachment model has been widely applied, new interpretations have emerged that question whether the TSD, and related detachments, really accommodate significant crustal extension or are instead rootless upper crustal structures that accommodate only limited, local deformation, thus calling for revised models of regional extensional geometry and magnitude (Walker et al, 2007; Diehl and Anderson, 2010).
The primary evidence for extensional reactivation of the Tule Springs thrust is twofold: (1) that all normal faults in the upper plate can be shown to truncate downdip at the detachment surface, and (2) that tilting of footwall strata toward detachment updip in the southwest part of the range is due to footwall unloading and uplift concurrent with slip along the detachment ramp. New field mapping of the detachment surface and related rocks shows that while upper plate deformation is extensive, few faults can be conclusively shown to truncate at or merge into the detachment surface. Furthermore, flexural unloading as the cause of tilted footwall strata requires an unreasonably low elastic thickness and does not account for the tilted footwall strata on the northern edge of the range. Taken together these tilted strata delineate a range-scale footwall syncline that is not easily related to detachment faulting or flexural uplift. Lastly, the TSD outcrops around the edges of the range, but is interpreted to shallowly underlie the entire range (Axen, 1993). Spatial analysis of the fault surface reveals inconsistencies between this interpretation and the absence of any exposure of the TSD in the central parts of the range.
