Exhumation of the North American Cordillera revealed by multi-dating of Upper Jurassic–Upper Cretaceous foreland basin deposits

Abstract

New low-temperature thermochronology and geochronology data from Upper Jurassic-Upper Cretaceous strata from the North American Cordilleran foreland basin in Utah, Colorado, Wyoming, and South Dakota document rapid exhumation rates of the adjacent Cordilleran orogenic belt to the west. Both zircon (U-Th-[Sm])/He (zircon He) and apatite fi ssion track (AFT) thermochronology were applied to proximal and distal synorogenic deposits in order to identify a thermochronometer suitable to record source exhumation during the North America Cordilleran orogeny. AFT lag times from Upper Jurassic-Upper Cretaceous deposits are 0-5 m.y. and indicate a relatively steadystate to slightly increasing exhumation rate between 118 Ma and 66 Ma. These lag-time measurements are consistent with active shortening and rapid exhumation rates of ~0.9->1 km/m.y. of the North American Cordillera throughout the Cretaceous.Double dating of the detrital AFT samples was performed on apatites with young AFT cooling ages, in order to test whether or not the young cooling ages represent a signal related to exhumation rather than volcanic activity. Maximum depositional ages using detrital zircon U-Pb geochronology match existing ages on basin stratigraphy. This study indicates that AFT is the most effective thermochronometer to resolve source exhumation from Lower to Upper Cretaceous foreland stratigraphy in the central Cor dilleran foreland, and indicates that source material was exhumed from 4 to 5 km depths but was never buried more than a few kilometers (<4 km) since Cretaceous time. Zircon He dates indicate that the orogenic hinter land could not have been exhumed from depths >8-9 km. Double dating of apatites (with AFT and U-Pb) shows that volcanic contamination is a signifi cant issue that can, however, be addressed by double dating.

Detrital Zircon Geochronology of Upper Cretaceous to Paleocene Sandstones From South‐Central Wyoming: Evidence for Middle Campanian Laramide Deformation

“…This same increase in the Yavapai‐Mazatzal zircon population—with the interpretation of early initiation of Laramide deformation—is also observed in surrounding areas. Compiled U‐Pb detrital zircon data from the Bighorn Basin, the Green River Basin, the Rock Springs uplift, and the Piceance Basin (Laskowski et al, ; Leary et al, ; May et al, , ; Painter et al, ) all show formations with greater than 25% Yavapai‐Mazatzal zircon populations (highlighted; Figure ). The significant increase of Yavapai‐Mazatzal‐age grains begins as early as early Campanian in the Chimney Rock Tongue of the Rock Springs Formation on the Rock Springs uplift and the Mancos Shale in the Piceance Basin, and middle Campanian in the Bighorn Basin, Great Divide Basin, and Hanna Basin (Figure ).…”

“…Recycling of the Sevier foreland basin strata represents another potential source. These strata were exhumed as the result of eastward migration of the deformation front (Laskowski et al, ; Lawton, ; Lawton & Bradford, ; Painter et al, ). Data compiled from the Bighorn Basin ( n = 2,118) show a dominant age group associated with the active magmatic arc to the west and a minor contribution from the 1800–1600 Ma age group (Figure ).…”

New insights into the stratigraphic and structural evolution of the middle Jurassic S. Neuquén Basin from Detrital Zircon (U‐Th)/(He‐Pb) and Apatite (U‐Th)/He ages

“…Furthermore, (U-Th)/(He-Pb) double dating can be used to determine both (1) first-cycle volcanic zircon contributions (DZ U-Pb=ZHe age) and (2) depositional lag time. Depositional lag time is defined as the difference between the youngest nonvolcanic ZHe age and depositional age, which is commonly used to elucidate the syn-depositional hinterland thermal and tectonic evolution, including the timing and magnitude of cooling in the uncovering source regions (e.g., Filleaudeau, Mouthereau, & Pik, 2012;Painter, Carrapa, DeCelles, Gehrels, & Thomson, 2014;Rahl et al, 2003;Reiners, Ehlers, & Zeitler, 2005b;Reiners et al, 2005a;Saylor, Stockli, Horton, Nie, & Mora, 2012).…”

Detrital zircon microtextures and U‐PB geochronology of Upper Jurassic to Paleocene strata in the distal North American Cordillera foreland basin

“…Blatt [] wrote that “The most important problem in the interpretation of the micropetrology of sandstones is the evaluation of the abundance of detritus of first‐cycle as opposed to polycyclic origin.” Even with the advent of multiple new provenance techniques since that time, most studies today are still hampered by this fundamental limitation. Much previous work has suggested that sediment recycling in the NA Cordilleran foreland basin is extensive [ Dickinson and Gehrels , , , ; Leier and Gehrels , ; Laskowski et al ., ; Painter et al ., ; Bush et al ., ]. However, detrital zircon U‐Pb dating is ubiquitous among these studies, and a major difficulty associated with detrital zircons is that they are very robust and can remain intact for several sedimentary cycles.…”