Sequential Kinematic Restoration as a Tool for Deciphering Evolving Plate Boundaries: the Western North America-Pacific Plate Boundary System

Orogens are often characterized by their most well known segment or most well described section. This tendency may inadvertently suggest that changes along strike may be anomalous, unique or wrong. Combining both cross section and plane view sequential reconstructions across several portions of an orogen allows us to track the evolution of a larger region in time and space. This four-dimensional reconstruction links together along strike changes and connects, in kinematically feasible ways, diverse portions of an orogen that may initially appear incompatible. This approach was tested on the Basin and Range province of western North America. The Basin and Range has been proposed to be the diffuse eastern edge of the Pacific-North American plate boundary with up to 20% of Pacific North America motion being accommodated east of the Sierra Nevada Mountains. However, how this percentage of plate motion is transferred from the Gulf of California through the southern Basin and Range/Mojave region to the eastern California shear zone is still not well understood. We obtained a permissible, kinematic history of the Basin and Range by compiling kinematic data (amount, timing and direction of displacement) along three transects through the northern (40\deg N) central (37\deg N) and southern (34\deg N) portions of the province. Extension and strike-slip deformation in all areas was sequentially restored using the kinematic data in an ArcGIS program over 2 m.y. to 6 m.y. time intervals. The process of sequential restoration highlighted misalignments, overlaps or large gaps in each incremental step, particularly in the areas between data transects. In areas where no information is available we use regions where the kinematics are known to constrain adjacent areas where the kinematics are not defined. The new sequential reconstructions show that compatible slip along the entire N-S extent of the inland shear zone from Baja to the northern Walker Lane is possible and supported by available data and that this inland shear zone had migrated westward with time. The reconstructions also highlight new problems particularly with regard to strain compatible extension east and west of the Sierra Nevada/Great Valley block.