Detrital zircon provenance record of middle Cenozoic landscape evolution in the southern Rockies, USA

Abstract

The high-elevation, high-relief landscape of the southern Rocky Mountains (Rockies), USA, reflects interactions between tectonics, paleoclimate, and surface processes. The southern Rockies experienced several episodes of uplift, extension, and major climate changes during the Cenozoic, but the landscape and river drainage evolution remain poorly constrained. Here we apply detrital zircon UPb geochronology to Eocene-Miocene strata in south-central Colorado to constrain the depositional ages and sediment provenance. A total of 1284 concordant UPb ages were determined and are grouped into 75–11 Ma, 1500–1300 Ma, and 1800–1500 Ma populations. Intense late Eocene-Oligocene regional volcanism provided abundant air fall zircons into the latest Eocene-Oligocene sedimentary systems where maximum depositional ages can be used to closely proximate depositional ages and improve the chronostratigraphy. The new data are integrated with interpretation of sedimentary environments, and the detrital zircon signatures of potential source terranes and age-equivalent strata in other nearby basins to interpret landscape and paleodrainage evolution. Specifically, the new provenance data show that (1) after the main phase of the Laramide deformation, the Wet Mountains, but not the Sangre de Cristo Range, was the dominant local topographic feature, and a southward-flowing river connected the Wet Mountain Valley with the Huerfano and Raton Basins to the south; (2) during the Eocene-early Oligocene, aggradation of the Wet Mountain Valley and the Huerfano Basin formed a low-relief surface, and subsequent river erosion changed the drainage pattern eastward and likely formed the modern lower Arkansas River valley; and (3) during the Miocene, dissection of the low-relief surface by the opening of the Rio Grande Rift formed the upper Arkansas River valley, and the upper valley was connected with the lower valley to establish the modern drainage pattern of the Arkansas River in the southern Rockies.