Pliocene–Pleistocene strata that record axial-fluvial sedimentation of the ancestral Rio Grande fluvial system crop out in New Mexico and southern Colorado, and they preserve the history of drainage evolution and late-stage exhumation of the Rio Grande rift. Presented here are new U-Pb detrital zircon data (N = 8 samples; n = 2382 analyses) from the Camp Rice andPalomas formations collected at two to three stratigraphic intervals in the Socorro, Hatch-Rincon, Jornada del Muerto, and Mesilla basins. U-Pb ages were then integrated with similar, previous studies from age-equivalent strata that are exposed in southern Colorado and northern New Mexico to develop sedimentary mixing models for the entire Rio Grande rift corridor in this region.
New U-Pb detrital zircon data from the central and southern portion of the Rio Grande fluvial system record peak ages at 34, 167, 519, 1442, and 1686 Ma, suggesting that the ancestral Rio Grande was receiving detritus from late Cenozoic volcanic fields (e.g., San Juan and Mogollon Datil volcanic fields), recycled Mesozoic stratigraphy (Mesozoic eolianites), and Proterozoic basement provinces (e.g., A-Type granitoids and the Mazatzal and Yavapai provinces). Although peak ages across the southern Rio Grande rift are similar across all basins and stratigraphic horizons in this study, there are distinct spatial and temporal, up-section changes in provenance recorded across the southern Rio Grande fluvial system in central and southern New Mexico. Basal strata (~5.0–4.5 Ma) record the largest contributions of detritus derived from the San Juan and Mogollon Datil volcanic fields (34–29 Ma) and lesser occurrences of recycled Cordilleran arc zircons derived from recycled Mesozoic stratigraphy from the Colorado Plateau. The late Pliocene phase (3.1–2.6 Ma) marks similar contributions of detritus derived from late Cenozoic volcanic fields and marks the emergence of peaks that overlap with recycled Cordilleran arc sources (217–82 Ma). Pleistocene (2.0–1.6 Ma) stratigraphic horizons show a relative decrease of zircons that overlap in age with the San Juan and Mogollon Datil volcanic field sources and an increase in contributions of recycled Cordilleran arc zircons (223–92 Ma). Isolated, secondary Cambrian peak ages occur at the 2.0 Ma stratigraphic horizon in the Mesilla basin and 3.1 Ma stratigraphic horizon in the Socorro basin and overlap in age with Cambrian intrusions that have been reported from parts of New Mexico and southern Colorado (519–516 Ma). All stratigraphic horizons record contributions derived from Precambrian basement sources that were being exhumed during Oligocene–Miocene rifting.
Mixing models were determined from the Rio Grande rift corridor in southern Colorado and throughout New Mexico and used with detrital zProvenance data andircon provenance trends to better understand the timing and nature of drainage development. Inputs for mixing models required grouping source areas into three primary provinces that included detritus from (1) late Cenozoic volcanic fields primarily associated with the San Juan and Mogollon Datil volcanic fields (2) recycled Mesozoic strata (reflecting previously determined Mesozoic eolianite provenance signatures); and (3) recycled Paleozoic and Precambrian basement that crop out along the Rio Grande rift flanks.
The earliest phase of drainage development (~5.0–4.5 Ma) in northern New Mexico was characterized by elevated detrital contributions from recycled Mesozoic stratigraphy likely derived from the Colorado Plateau, whereas basins in central and southern New Mexico were receiving detritus largely from rift flanks (i.e., Paleozoic and Precambrian sources) and late Cenozoic volcanic-field sources. The late Pliocene (3.1–2.6 Ma) phase of drainage development in northern New Mexico was marked by a relative decrease in detrital contributions from recycled Mesozoic strata. The model shows nearly equal detrital contributions from recycled Mesozoic strata, rift flank, and volcanic field sources at the 3.1–2.6 Ma stratigraphic horizon in central and southern New Mexico. The Pleistocene (2.0–1.6 Ma) phase of drainage development records a shift in provenance in the southern rift basins and models suggest decreased contributions from late Cenozoic volcanic field and rift flank sources, and increased contributions from recycled Mesozoic stratigraphy.
Provenance data and mixing trends that demonstrate increased detrital contributions from recycled Mesozoic strata of the Colorado Plateau support a model of headward erosion of the Rio Puerco into the Jemez Lineament and southwestern margin of the Colorado Plateau during the Plio–Pleistocene. Headward erosion and possibly minor exhumation along the western margin of the rift resulted in increased detrital contributions from the oldest and deepest parts of caldera sources between the Pliocene and late Pliocene. These same caldera source areas were less of a source for the system by the Pleistocene
|Advisor:||Hampton, Brian A.|
|Commitee:||Amato, Jeffrey M., Burgette , Reed J., Dugas, Daniel P.|
|School:||New Mexico State University|
|School Location:||United States -- New Mexico|
|Source:||MAI 82/7(E), Masters Abstracts International|
|Keywords:||Ancestral Rio Grande, Camp Rice and Palomas formations, Detrital zircon geochronology, New Mexico, Rio Grande Rift|
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