Geologic Framework of Thermal Springs, Black Canyon, Nevada and Arizona

摘要

Thermal springs in Black Canyon of the Colorado River, downstream of Hoover Dam, are important recreational, ecological, and scenic features of the Lake Mead National Recreation Area. This report presents the geologic framework results from a U.S. Geological Survey study of the geohydrology and geochemistry of the springs. The study was conducted in cooperation with the National Park Service. Exposures in Black Canyon are mostly of Miocene volcanic rocks, underlain by crystalline basement composed of Miocene plutonic rocks or Proterozoic metamorphic rocks. The rocks are variably tilted and highly faulted. Results of kinematic analysis of fault data collected along tributaries to the Colorado River indicate two episodes of deformation, consistent with earlier studies. The earlier episode formed during east-northeast directed extension, and the later during east-southeast directed extension. At the northern end of the study area, pre-existing fault blocks that formed during the first episode were rotated counterclockwise, probably during the later episode.