GRAVITY MODELING OF THE COLORADO MINERAL BELT

Characterizing the deep structure of long-lived,tectonically-weak zones is fundamental to understanding why these zones exist and why they remain prone to tectonic reactivation for, in the case of the Colorado Mineral Belt, over a billion years. The Colorado Mineral Belt (CMB) is a NE-trending belt of major mining centers in Colorado that coincides with a negative gravity anomaly. Determining the depth and magnitude of the anomaly may shed new light on the origin and evolution of the lower crust and upper mantle of the CMB. We have combined the data of USGS OPF-00-0042 and data of G. Randy Keller (UTEP) to create the highest resolution gravity compilation available for Colorado. We consider multiple 2-dimensional profiles of the Bouguer anomaly across the CMB and conduct forward modeling to define the 3-dimensional geometry of the anomaly. Forward modeling helps constrain whether the anomaly lies in the crust, perhaps as a granitic batholith, or in the mantle, perhaps as a basalt-depleted layer. Although model solutions are non-unique, geologic knowledge of typical density contrasts in the lithosphere help determine the most viable solutions. The resulting models shed light on the lithospheric structure linked to the CMB’s NE-trending negative anomaly, which lies within the larger N-trending negative anomaly of the southern Rocky Mountains.