Introduction to: The Rocky Mountain region—An evolving lithosphere: Tectonics, geochemistry, and geophysics

Abstract

The Rocky Mountains are the eastern, high elevation portion of the continental-scale Cordilleran mountain chain that extends along the western portion of the North American continent. This wide zone records the complex tectonics associated with a series of Mesozoic to Recent additions to and modifications of the continent. This volume focuses on the southern Rocky Mountain region, the area that extends from southern Wyoming, across the Colorado Rockies, to meld with the region dominated by the Rio Grande rift and Colorado Plateau. These various physiographic domains share a common tectonic heritage as a region that was uplifted from near sea level in the late Cretaceous, underwent regional uplift, compressive deformation, and lithospheric modification at appreciable distance from the western margin of the North American plate during the 70–45 Ma Laramide orogeny, then underwent a complex series of magmatic modification events, localized lithospheric extension, and late Cenozoic denudation and incision. The result is the high elevation and topographically rugged western U.S. orogenic plateau shown in Plate 1. There has been strong scientific interest in the region of the Southern Rocky Mountains for over a century, but our knowledge of the deep lithospheric structure of the region has been improved greatly by a series of seismic experiments that began in the mid 1990s. New insights have been provided by seismic data that were acquired by a combination of earthquake and natural source recording efforts; such as the Deep Probe experiment (Henstock et al., 2001; Gorman et al., 2002), Rocky Mountain Front experiment (Sheehan et al., 1995), and CD-ROM experiment (Dueker et al., 2001; Karlstrom and the CD-ROM Working Group, 2002). Previous work on the geologic evolution of this region has been extensive and includes recent summaries related to the CD-ROM experiment (Karlstrom, 1998; 1999). This volume provides a synthesis and integration of geological and geophysical results of the CD-ROM (Continental Dynamics of the Rocky Mountains) collaborative investigation. This effort has involved more than 22 investigators at 14 institutions and 21 graduate students. After an initial workshop in 1995, CD-ROM was funded from 1997 to 2002 by the Continental Dynamics Program of the National Science Foundation, with supplemental funding from the Deutsche Forschungsgemeinschaft. The experiment was designed as a fully interdisciplinary series of coordinated geologic and geophysical studies to understand the tectonic evolution of the lithosphere of the southern Rocky Mountain region. As described in the papers in this volume, the overall project produced a seismic refraction line from Wyoming to New Mexico (Plates 1 and 2), geologic studies of shear zones and Laramide structures, xenolith studies, and teleseismic and reflections lines across key tectonic boundaries within the longer transect, including the Cheyenne belt and Jemez lineament. The southern Rocky Mountain region is one of the best places in the world to study continental evolution because this region preserves a unique record of the assembly, stabilization, maturation, and early stages of disassembly of a continent. The core of North America is underlain by high velocity (old, cold) lithosphere (blue in Plate 2) whereas many areas Book Title Book Series Copyright 2004 by the American Geophysical Union 10.1029/Series#LettersChapter#