INTEGRATED STUDIES OF LITHOSPHERIC AND CRUSTAL ARCHITECTURE IN THE ROCKY MOUNTAIN REGION

The Rocky Mountain region of the western U. S. is best known for its Cenozoic tectonism. However, the Precambrian and Paleozoic history of this region has played a major role in establishing its lithospheric and crustal architecture. This fact has been highlighted by the recent results of the Continental Dynamics of the Rocky Mountains Project (CD-ROM) project and well as in a variety of related integrated studies in the region. The GEON Cyberinfrastructure project is using the Rocky Mountain region as a test bed for its effort to facilitate studies of the 4-D evolution of the continents. The Proterozoic region (Southern Rocky Mountains) south of the Cheyenne belt is particularly interesting because its evolution since 1.8 Ga involves accretion, stabilization, and several modifications of the lithosphere that are well documented geologically. Initial formation of juvenile continental crust took place by development and assembly of magmatic arcs between 1.8 and 1.6 Ga. From 1.45 to 1.35 Ga, the crust underwent another period of differentiation leading to emplacement of A-type granites in the middle crust across southern Laurentia. Analysis of the CD-ROM seismic data show that the crustal thickness is generally 40-53 km thick along the seismic profiles and displays striking crustal thickness variations over relatively short distances. These variations have only moderate correlation with modern topography. Details of crustal structure revealed include delineation of a shear zone and a batholith complex associated with the Colorado mineral belt, and mafic intrusions in the upper crust of probable Cambrian age. Potential field databases for the region have matured recently and now a large amount of information is publicly available. These data have their own utility, but when used together with seismic data, major new insights can be realized. This has been demonstrated by recent results in the Sangre de Cristo Mountains, several Rio Grande rift basins, and the Uncomphagre uplift.