Apatite fission-track thermochronology of southern Rocky Mountain-Rio Grande rift-Western High Plains Province
Shari A. Kelley and Charles E. Chapin


Apatite fissio- track (AFT) thermochronology has been a useful tool in evaluating the tectonic; and topographic evolution of the Southern Rocky Mountains, Rio Grande rift, and western High Plains provinces. AFT data from the Front Range and Wet Mountains document that little differential uplift has occurred in the late Cenozoic between the Southern Rocky Mountains and the High Plains in Colorado, except at the southern end of the Wet Mountains. AFT results support a model whereby the central portion of the Front Range was uplifted vertically and the eastern and western flanks of the range were thrust laterally during early Laramide compression. Only about 1 km of denudation occurred in the central Front Range during early Laramide deformation, while 2.5 m of material was removed during late Laramide deformation and the development of Rocky Mountain erosion surface. AFT ages from the east flank of the Rio Grande rift in the northern Sangre de Cristo Mountains of Colorado and the Sandia Mountains of New Mexico, as well as AFT data how the east side of the southern Sangre de Cristo Mountains and the High Plains of New Mexico, record early Oligocene to middle Miocene cooling. This cooling event is likely related to epeirogenic denudation of at bast 2 km of Mesozoic to early Cenozoic sedimentary, rocks during early extension on the Rio Grande rift. Widespread Oligocene volcanism in the rift and along the Southern Rocky Mountain-High Plains boundary may have regionally elevated the heat flow . An east-to-west increase in AFT age in the Sangre de Cristo Mountains between Las Vegas and Santa Fe, New Mexico (12-34 Ma along the Rincon Range-High Plains boundary: 44-74 Ma in the Santa Fe Range), when coupled with other geologic evidence, is used to unravel the complicated tectonic history of this area. Laramide deformation elevated the Santa Fe Range and the site of the Española Basin relative to the Rincon Range, where lateral thrusting dominated. Sediments shed from the Santa Fe area accumulated in areas now occupied by the eastern Rincon Range and on the High Plains. During the early phase or rill development, the highland to the west,  including the Santa Fe Range to the west of the Picuris-Pecos fault, collapsed to form the Española Basin, allowing preservation of Laraide AFT ages in the Santa Fe Range. Epeirogenic uplift and erosion that was triggered by early rift extension occurred along  the Hlight Plains margin, stripping away the accumulated early Cenozoic sediments, Paleozoic to Mesozoic sedimentary rocks, and in some areas, Oligocene volcanic rockes. Denudation in the eastern Rincon Range waz enhanced in some places by the development of minor down-to-the west normal faults sod associated footwall uplift within the Sangre de Cristo Mountains. Much of the current elevation of th Santa Fe and Rincon Ranges is acommodated by faults activated during the late phase it extension within the range rather than along faults on the margins of the southern Sangre de Cristo Mountains.


  1. Kelley, Shari A.; Chapin, Charles E., 1995, Apatite fission-track thermochronology of southern Rocky Mountain-Rio Grande rift-Western High Plains Province, in: Geology of the Santa Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 87-96.

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