RECONSTRUCTING THE BASIN AND RANGE PROVINCE: THE EVOLUTION OF AN EXTENSIONAL OROGEN IN TIME AND SPACE

The Basin and Range province of western North America is a classic example of large magnitude diffuse deformation. More is known about timing, amount, and spatial variations of extension within the Basin and Range province than in any other comparable region. Even though selected portions of the Basin and Range are rich in kinematic data, the kinematic history of the province as a whole is still not well understood. For example, many existing reconstructions of portions of the Basin and Range are internally consistent however combining adjacent reconstructions often leads to large overlaps or gaps where the two different areas meet.

The detailed kinematic history of the Basin and Range was obtained by compiling kinematic data (amount, timing and direction of displacement) along three transects through the northern (40° N) central (36°−37° N) and southern (34° N) portions of the province. Extension 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 sequential restorations highlight 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 Eastern California Shear Zone is possible and supported by available data. They also highlight new problems in our understanding of the evolution of extension, particularly with regard to strain compatible deformation east and west of the Sierra Nevada/Great Valley block.

Results include 1) 250 ±50km of extension oriented N78°W in both the northern (50% extension) and central (200% extension) parts of the province. 2) A significant portion of pacific plate shear jumped into the continent at ~8Ma and has migrated westward with time. 3) Timing of extension north and south of the Garlock fault is either incompatible with a smooth NNW trending continental edge as suggested by marine data or implies a triangular window of significant >50 km extension (24−16 Ma) followed by compression (14−0 Ma) in the Coast Range/ Great Valley region.