New Constraints on History of Deformation and Associated Fluid Flow in the Rocky Mountain Front Range and Denver–Julesburg Basin Through Geochemical Analyses of Calcite Fracture Fills

Formation of the Sevier foreland basin combined with deformation related to the basement-cored arches of the Laramide orogeny have generated an extensive and complex fracture network in the Front Range region of Colorado and adjacent Denver–Julesburg Basin. Some fractures host calcite cement, recording the history of deformation and fluid flow. This project aims to develop an improved understanding of this region’s coupled, large-scale, structural development and fluid flow history using outcrops and Wattenberg field drill core samples. We integrate petrography, laser ablation ICP-MS U-Pb geochronology, fluid inclusion microthermometry, strontium, carbon, and oxygen isotope analysis to evaluate the timing of fractures and temperature, composition, and source of fluids. Structurally distinct features (e.g., fractures, faults, and stylolites) can be dated to determine timing of basin development, diagenesis, and uplift.

Multiple types of fracture fills are identified, including early contorted fractures, fractures associated with vertical stylolites, fault breccias, joints, and synkinematic crack-seal-slip fracture fills. Initial U–Pb dating indicates a possible event at 110 Ma, consistent with layer-parallel shortening during Sevier orogeny deformation, and a younger event at about 60 Ma, consistent with fluid flow associated with the Laramide Orogeny. We postulate carbon and oxygen isotopic data will be consistent with meteoric water, and strontium isotopes will indicate interaction with radiogenic host rocks. These new results demonstrate a link between tectonics, fracturing, and fluid migration that increases understanding of drivers and history of deformation and fluid migration. Results can be applied to tectonic studies, oil and gas reservoir rocks, and geothermal exploration.