Partitioning of Displacement and Vertical-Axis Rotation along the Northern Walker Lane, Northwestern Nevada
P. H. Cashman, S. A. Fontalne, and R. F. Hardyman
The Walker Lane is a zone of complex faulting and dextral offsets bounded on the west by the rigid Sierra Nevada block and on the east by the Basin and Range province. It is believed to accommodate the component Pacific - North America plate motion that is not taken up by slip across the San Andreas fault system. In the central Walker Lane, dextral slip began by 28 Ma, and total slip since that time is at least 68 km.
Two structural domains at the northern end of the Walker Lane, in northwestern Nevada, are defined by sets of faults with differing orientations: The northernmost Pyramid Lake domain is characterized by northwest-striking faults with dextral slip. The next domain to the south, the Carson domain, is characterized by east-northeast-striking faults with sinistral slip. Each domain extends across the full width of the Walker Lane. Therefore, each -- domain despite its different fault geometry -- must accommodate tens of km of slip across its width. Between 30 Ma and 22 Ma, both domains (and the adjace Sierra and Basin and Range provinces) were covered by silicic ash-flow tuffs that allow us to test for vertical axis rotation of fault-bounded blocks.
We combine mapping, kinematic analysis of faults, and paleomagnetic studies on tuffs from fault-bounded blocks to compare the style of deformation in the two domains. We use three-dimensional boundary element modelling as an independent predictor of rotation of fault-bounded blocks when the bounding faults are in different initial orientations. The numerical modelling will allow us to place quantitative constraints on an estimation of the regional strain field, by using the sense and magnitude of vertical-axis rotation.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California