Post-Laramide, Eocene epeirogeny in central Colorado—The result of a mantle drip?

Abbott, L. D., Flowers, R. M., Metcalf, J., Falkowski, S. and Niazy, F. (2022) Post-Laramide, Eocene epeirogeny in central Colorado—The result of a mantle drip? Geosphere, 18(4), pp. 1223-1246. (doi: 10.1130/ges02434.1)

Abstract

The Southern Rocky Mountains first rose during the Laramide Orogeny (ca. 75–45 Ma), but today's mountains and adjacent Great Plains owe their current height to later epeirogenic surface uplift. When and why epeirogeny affected the region are controversial. Sedimentation histories in two central Colorado basins, the South Park–High Park and Denver basins, shifted at 56–54 Ma from an orogenic to an epeirogenic pattern, suggesting central Colorado experienced epeirogeny at that time. To interrogate that hypothesis, we analyzed thermal histories for seven samples from central Colorado's Arkansas Hills and High Park using thermochronometers with closure temperatures below ~180 °C, enabling us to track sample exhumation from ~5–7 km depth. Three samples are from the Cretaceous Whitehorn pluton, and four are Precambrian granitoids. All zircon and titanite (U-Th)/He dates (ZHe and THe) and one apatite fission-track (AFT) date are similar to the 67 Ma pluton emplacement age. Whitehorn dates using the lower-temperature apatite (U-Th)/He (AHe) thermochronometer are 55–41 Ma. These data require two exhumation episodes, one ca. 67–60 Ma, the second beginning at 54–46 Ma. The pluton reached the surface by 37 Ma, based on the age of volcanic tuff filling a pluton-cutting paleovalley. The Precambrian samples do not further refine this thermal history owing to the comparatively higher He closure temperature of their more radiation-damaged apatite. Laramide crustal shortening caused 67–60 Ma exhumation. Arkansas Hills shortening ended before 67 Ma, so shortening could not have caused the exhumation event that began 54–46 Ma; thermochronology supports the Eocene epeirogeny hypothesis. Epeirogeny affected >2.0 × 104 km2, from the Sawatch Range to the Denver Basin. We attribute epeirogeny to an Eocene mantle drip that likely triggered subsequent drips, causing younger exhumation events in adjacent areas.

• Item Type: Articles
• Additional Information: National Science Foundation (NSF) grant EAR-1559306 to Flowers and Metcalf provided support for new instrumentation during the course of this study that was used to acquire data in this project. Niazy thanks the NSF-funded RESESS program, run by UNAVCO, for the opportunity to work on this project.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Falkowski, Dr Sarah
• Authors: Abbott, L. D., Flowers, R. M., Metcalf, J., Falkowski, S., and Niazy, F.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Geosphere
• Publisher: Geological Society of America
• ISSN: 1553-040X
• ISSN (Online): 1553-040X
• Copyright Holders: Copyright: © 2022 The Author(s)
• First Published: First published in Geosphere 18(4): 1223–1246
• Publisher Policy: Reproduced under a Creative Commons licence