INTEGRATED STUDIES OF UPPER CRUSTAL STRUCTURE IN THE SOUTHERN ROCKY MOUNTAIN REGION

The lithosphere of the Southern Rocky Mountains has been repeatedly modified since its formation in the Proterozoic. We have employed a very integrated approach aided by new developments in cyberinfrastructure to investigate the structure and evolution of the Southern Rocky Mountain region. Remote sensing, gravity, drilling, aeromagnetic, geologic, and seismic data were employed in our study. Our regional studies have shown that, in most cases, the most recognizable geological and geophysical signatures lie in the upper crust, so it was the focus of this investigation. Here, we present some of our studies of Phanerozoic features in southern Colorado and northern New Mexico that take advantage of new databases of geophysical, geological, and drilling data. One feature of interest was the Uncompahgre uplift that lies astride the Colorado-Utah border and is mostly buried. It separates the Paradox basin to the south from the Piceance basin to the north and is part of the Ancestral Rocky Mountains orogenic belt. A particular feature of interest was the large gravity anomaly associated with the Uncompahgre uplift that was determined to be due to a mafic body beneath the uplift. Also of interest were the San Juan volcanic field that is a mid-Tertiary feature, the San Luis Valley that is associated with the Rio Grande rift, and the Laramide Sangre de Cristo Mountains. Crustal-scale cross-sections of these features were constructed using modeling of gravity anomalies as the platform for integration. The results required the existence of a mafic body under the Uncompahgre uplift, a large batholith beneath the San Juan volcanic field, a complex basin structure beneath the San Luis Valley, and thin thrust sheets of Precambrian basement in large portions of the Sangre de Cristo Mountains. The larger scale tectonic context of these features was investigated by filtered gravity and magnetic maps of the region that were produced to enhance the various structural trends and features in the region. One conclusion of this effort is that the Uncompahgre uplift is most likely a northwestern extension of the Southern Oklahoma aulacogen.