Tectonic Evolution of the Death Valley Region

Abstract

Progress in understanding the evolution of continents hinges on seamlessly applying techniques of modern structural geology to the largest possible regions of the crust. In most areas, meaningful practice of regional structural geology is limited by a lack of correspondence between highly strained crust and well-defined regional strain markers, that is, large-scale geologic features whose initial geometry can be reasonably inferred, and their kinematic evolution constrained, through structural, stratigraphic, isotopic, paleomagnetic, and geodetic study. A ~100,000-km^2 segment of the U.S. Cordilleran orogen, encompassing the celebrated landscapes of Death Valley National Park and five nearby parks that are among the most visited in the U.S., was severely deformed in late Cenozoic time. In addition to spectacular geologic exposures, the region harbors a rare endowment of regional structural markers, developed before and during late Cenozoic deformation. The markers are defined by isopachs and facies boundaries in the west-thickening Neoproterozoic-Paleozoic Cordilleran miogeocline, by pre-Cenozoic thrust faults that disrupt the miogeoclinal wedge, and by proximal Tertiary terrigenous detrital strata and their source regions. The region is still tectonically active, providing an opportunity to compare deformation patterns of the last decade, constrained by geodetic studies, with late Cenozoic deformation patterns spanning 15-20 m.y. These scientific assets have attracted the attention of significant numbers of structural geologists over the last three decades, and distinguished the region as the birthplace of, and testing ground for, an impressive number of fundamental tectonic ideas. Oroclinal bending of mountain ranges, continental transform faulting and "pull-apart" basins, low-angle normal faulting, the influence of plate motions on intracontinental deformation, the "rolling hinge" model of progressive extensional deformation, the fluid crustal layer or "crustal asthenosphere" concept, and Pratt isostatic compensation of mountain ranges were all originally discovered or have their best known expressions in the region. This remarkable history of geologic investigation and innovation continues unabated as growing numbers of scientists recognize it as a unique place on Earth to ponder the nature and origin of large-scale continental deformation.