Zircon fission track dating humphreys

Numerous thermochronological studies have been applied to the southwestern part of the Colorado Plateau (e.g., Dumitru et al., 1994; Kelley et al., 2001; Flowers et al., 2008), and some data exist for the central parts (Stockli et al., 2002; Hoffman et al., 2011; Murray et al., 2016). (2014) presented a few ages and models related to the highly debated origin of the Unaweep Canyon, which cuts across the Uncompahgre Plateau.

Less attention has been devoted to the northeastern part of the plateau, including the Uncompahgre Plateau. In this paper we present new thermochronological data that help constrain the timing and magnitude of the Uncompahgre Plateau uplift.

This late Eocene to Oligocene magmatism caused thermal resetting of most of the AFT (except top basement) and AHe ages from the Uncompahgre Plateau, even though samples were collected as much as 60 km away from the intrusion.

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It extends from the San Juan Mountains in southern Colorado in a northwestward direction until it plunges beneath the Uinta Basin in northeastern Utah (Figs. The Uncompahgre Plateau is separated from the Paradox Basin on the southwest by steeply dipping reverse faults, and the overlying Mesozoic sediments have been flexed into faulted monoclines.

Strata are nearly vertical along these structures, draped parallel to the steep fault planes that are interpreted as reverse faults at depth (e.g., Trudgill, 2011).

However, some distinctive monoclines are present within the northeastern part of the plateau in the Colorado National Monument (CNM).

These eroded monocline structures are exposed along the Monument, Fruita, and Redlands fault systems and are the results of high-angle faults within the Precambrian basement, most likely developed during Laramide contraction (Lohman, 1965; Jamison and Stearns, 1982; Jamison, 1989).

Thermal history modeling of top basement samples reveals Late Cretaceous heating to temperatures of at least 90 °C, implying sedimentary burial to ∼3 km, followed by cooling throughout the latest Cretaceous to Eocene.

However, AHe ages (38–31 Ma) indicate minor reheating to 40–80 °C for these samples in the late Eocene to Oligocene.Zircons from the La Sal Mountains laccolith gave an Oligocene U-Pb crystallization age of 29.1 ± 0.3 Ma.AFT ages from the laccolith range from 33 to 27 Ma, confirming rapid cooling of this shallow subvolcanic intrusion.The structures are interpreted as rejuvenated segments of an older fault system that formed during the late Paleozoic to early Mesozoic Ancestral Rocky Mountain orogeny (Cater, 1966, 1970; Case, 1991).The eastern flank of the Uncompahgre Plateau is less well defined, because the northeastward-tilted plateau gently and uniformly dips beneath Quaternary deposits along the Gunnison River.How much the Laramide tectonism contributed to the overall uplift and how much should be attributed to Cenozoic epeirogenic events is still uncertain and the question of old versus young uplift with the subsequent erosional response, as well as the possible driving forces, are still debated topics (Karlstrom et al., 2012).