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Laramide Deformation along the Southern Rocky Mountain Front: Provenance Record from the Raton and Galisteo-El Rito Basins of Colorado and New Mexico

Abstract

Large-scale partitioning of the Cretaceous Cordilleran (Sevier) foreland basin into isolated Laramide basins is addressed through analysis of the provenance record in the Paleogene Raton and Galisteo–El Rito basins of southern Colorado and northern New Mexico. These broken foreland basins, flanked by Laramide basement uplifts, recorded the retreat of the Cretaceous Western Interior Seaway and Paleogene progradation of fluvial and alluvial-fan systems. We conducted detrital zircon U–Pb geochronology on strata from the Raton and Galisteo–El Rito basins in order to constrain sediment sources and patterns of regional exhumation related to changing deformation patterns. In addition, heavy mineral analyses on Galisteo–El Rito deposits provide supplementary evidence for provenance shifts. Major grain populations derive from: (a) Mazatzal-Yavapai transitional basement (1800 to 1600 Ma) of the Sangre de Cristo range; (b) 1400 Ma granitic intrusions; (c) 1200 to 900 Ma Grenville crystalline rocks; (d) Paleozoic rocks from the Appalachian orogen (500 to 300 Ma); (e) recycled grains from Mesozoic strata; and (f) Mesozoic igneous rocks from the Cordilleran magmatic arc (<250 Ma). These basins record the partitioning of the Cretaceous foreland basin by Laramide basement uplifts, recognizable in both provenance signals and depositional styles, corresponding to eastward propagation of the Laramide deformation front and resultant advance of flexural depocenters in the North American interior. In the Raton Basin, Cordilleran, Appalachian, and Grenville peaks are only found in the Cretaceous Dakota and Vermejo formations associated with the Western Interior Seaway of the Sevier foreland. Cordilleran peaks are absent from Paleocene-Eocene samples, consistent with significant, continental drainage reorganization during Laramide deformation. In the Galisteo–El Rito basin system, we recognize a shift to dominantly Mazatzal-Yavapai basement ages in the Paleocene El Rito Formation and Oligocene Ritito Formation. The heavy mineral results show a shift to a more immature, metamorphic source composition. These new datasets bear upon reconstructions of North American paleodrainage and have important implications for potential linkages between major fluvial systems of the southern Rocky Mountains and Paleogene deepwater reservoir units in the Gulf of Mexico basin.