PRECAMBRIAN STRUCTURAL CONTROL ON PHANEROZOIC FAULTING IN THE WET MOUNTAINS, COLORADO

The formation of the North American continent in the Proterozoic is an ongoing focus of research. Geologists debate the tectonic configuration of the continent at ca. 1.4 Ga, and hypotheses include a passive margin setting, a period of rifting, and a convergent margin. The Wet Mountains in southern Colorado expose an extensive suite of Proterozoic schist, gneiss, and intrusive igneous rocks. These rocks are currently part of the Colorado Front Range, and have been extensively overprinted by Phanerozoic faulting. We examine the structural configuration of the Proterozoic rocks, and compare this to the orientation of the Phanerozoic fault network. Our results indicate that the development of foliation in the Proterozoic gneiss provided a structural control on the development of the younger fault network. We hypothesize that foliation planes and fold hinges served as planes of weakness that the younger fault network exploited. We support this hypothesis with microstructural analysis of Proterozoic samples as well as stereonet data showing regional-scale structural trends.