MAGNITUDE OF RIGHT-LATERAL OFFSET OF SOUTHERN DEATH VALLEY FAULT ZONE FROM MIOCENE VOLCANIC ASSEMBLAGES

Initial results from field studies of a volcanic section in the Ibex Hills, Southern Death Valley suggest possible correlations with middle Miocene volcanic rocks in the Wingate Wash area, suggesting as much as 20-40 km of right lateral offset along the southern Death Valley fault. The amount of strike-slip movement in the southern Death Valley region is controversial with estimates ranging from no more than 8 km (Wright and Troxel, 1967, GSAB) to 80 km (Stewart, 1967, GSAB). In this study we use Miocene volcanic and sedimentary rocks in southern Death Valley as an offset marker to clarify the total amount of slip. The volcanic assemblage in the Ibex Hills has a number of similarities with the assemblage in Wingate Wash described by Luckow et al. (2005, ES Reviews) including: 1) a section of basaltic pyroclastics in the lower part of the section, with interbedded lahar deposits; and 2) a thick (5-20m) white tuff unit that is similar to a tuff unit in the middle Miocene section in the Owlshead Mountains. Geochronology done by Luckow et al. in Wingate Wash and the Owlshead Mountains has the region divided into two basic periods: an early interval (~14-13.4 Ma) , and a later phase (~13-12.5 Ma). One date from the volcanic sequence in Ibex Pass has been reported (Calzia, 2000, GSA Guidebook) suggesting that rocks of this section are a time equivalent to the Wingate Wash section. However, Topping (1993, GSAB) suggested this section contains the ~10Ma Rhodes tuff, and although possible, the most conspicuous tuffs in the Ibex Hills section are almost certainly older, middle Miocene rocks. Geochronological and geochemical studies in progress should clarify this age relationship and potential correlation to test our hypothesis.