Implications of distributed crustal deformation for exhumation in a portion of a transpressional plate boundary, Western Transverse Ranges, Southern California

Spatial and temporal patterns of exhumation are inextricably linked to patterns of crustal deformation because crustal deformation drives rock uplift. A new interpretation of a segment of the Pacific-North America transpressional plate boundary in southern California is analyzed in the context of crustal shortening, rock uplift, and exhumation. Deformation is partitioned between two structural anticlinoria formed above thrust faults that root into a mid-crustal d! ecollement. The southern anticlinorium began growing after 5Ma and is characterized by almost no topographic expression, rock uplift of B3 km, and exhumation of o1.2 km. Deposition in the Los Angeles basin on the south generally kept pace with growth of this anticlinorium. In contrast, the northern anticlinorium is younger, has a significant topographic expression, rock uplift of 2.5–4.0 km, and exhumation of B1.5– 2 km. On-going surface uplift above the northern anticlinorium is suggested by the mismatch between the magnitude of rock uplift relative to the exhumation. These data emphasize that the distribution of deformation between faults in the upper and middle crust, crustal root formation in the lower crust, and flexural subsidence are primary controls of patterns of exhumation, which together dictate net surface uplift in active orogenic belts. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.