Cenozoic denudation of the Wichita Mountains, Oklahoma, and southern mid-continent: apatite fission-track thermochronology constraints

Abstract

Eight new apatite fission-track (AFT) analyses of igneous rocks constrain the low-temperature thermal history of the Wichita Mountains in southwestern Oklahoma. The apparent AFT ages for Mount Scott, which range from 101±14 to 146±45 Ma, display no systematic variation as a function of elevation. AFT age ranges for the rhyolite at Bally Mountain and Mount Sheridan Gabbro are 136±36 to 160±25 Ma and 209±26 to 222±36 Ma, respectively. The mean track lengths for the Wichita Mountain samples range from 11.8 to 13.4 μm with standard deviations of 1.8–3.4 μm, and the track-length distributions are broad with relatively few tracks longer than 14 μm. The AFT age and length data are best fit by a thermal history involving heating of the basement rocks to temperatures of at least 115°C prior to Late Jurassic time, denudation and associated cooling between Late Jurassic and Albian in response to the opening of the Gulf of Mexico, burial by 0.5–1.5 km of Cretaceous sedimentary rocks, and finally cooling due to denudation starting 55–25 Ma and continuing to the present. The thermal history recorded in the AFT data from the Wichita Mountains is similar to thermal histories derived from AFT thermochronology studies along the Ouachita Trend and in the Anadarko Basin. The new data, when combined with AFT data from the Ouachita Deformation Belt, the Anadarko Basin, the eastern Sangre de Cristo Mountains in New Mexico, and the eastern margins of the Wet Mountain and Front Range in Colorado, reveal an interesting pattern of post-Cretaceous denudation in the mid-continent. The amount of Neogene denudation increases westward from about 1 km to 3 km between southwestern Oklahoma and the eastern Sangre de Cristo Mountains in east-central New Mexico, and the timing of onset of denudation decreases from 55–25 Ma in the east to 35–12 Ma toward the west. Along the Southern Rocky Mountains–High Plains boundary, the amount of denudation decreases northward from about 3 km in the eastern Sangre de Cristo Mountains to ∼1 km along the east side of the Front Range. Post-Laramide isostatic adjustment of the High Plains, the development of the Rio Grande rift, and a shift towards a drier climate with seasonal, intense thunderstorms on the High Plains may all have contributed to the observed pattern of Cenozoic denudation in the southern mid-continent.