Gravity, Magnetic, and Geologic Constraints on the Raton Basin of Southern Colorado, USA

The overall goal of this project is to better understand geologic characteristics of the Raton Basin. The Raton Basin is a Rocky Mountain foreland basin that contains Pennsylvanian through modern sedimentary rocks. The current structure of the basin is thought to have formed during the late Cretaceous through Tertiary Laramide orogeny. During this event, the basin was folded into a syncline, and steep reverse faults formed along the western edge of the basin in which Pre-Cambrian crystalline rocks of the Sangre de Cristo Range were partially thrust over the basin itself. In the Oligocene through present, the tectonic environment of the basin has been dominated by extension and extensional magmatism related to the Rio Grande Rift. A series of small plutonic bodies and more spatially extensive magmatic dikes intruded into the basin over this time interval. A high-resolution gravity transect with approximately 70 stations was conducted across the Raton Basin near the Spanish Peaks. This transect, coupled with existing data, indicate a 20 mgal negative Bouguer gravity anomaly in the northern part of the basin and a 55-60 mgal negative anomaly in the south. Gravity models of these observations indicate that the Raton Basin is approximately 3 km thick in the north and 5 km thick in the south. Also, the basin is structurally deformed into an asymmetric synform that is tightest in the central part of the basin. High-resolution magnetic measurements were also taken to better understand the structure of the numerous dikes in the region. Magnetic susceptibility measurements were used to constrain induced magnetism of the igneous rocks. However, the total field strength of magnetic anomalies associated with the dikes indicates that normal and reversed polarity remnant magnetism is also significant.