Orogens of Big Sky Country: Reconstructing the Deep-Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

Chance B. Ronemus, Devon A. Orme, William R. Guenthner, Stephen E. Cox, Christopher A.L. Kussmaul

Research output: Contribution to journalArticlepeer-review

Abstract

Archean rocks exposed in the Beartooth Mountains, Montana and Wyoming, have experienced a complex >2.5 Gyr thermal history related to the long-term geodynamic evolution of Laurentia. We constrain this history using “deep-time” thermochronology, reporting zircon U-Pb, biotite 40Ar/39Ar, and zircon and apatite [U-Th(-Sm)]/He results from three transects across the basement-core of the range. Our central transect yielded a zircon U-Pb concordia age of 2,805.6 ± 6.4 Ma. Biotite 40Ar/39Ar plateau ages from western samples are ≤1,775 ± 27 Ma, while those from samples further east are ≥2,263 ± 76 Ma. Zircon (U-Th)/He dates span 686.4 ± 11.9 to 13.5 ± 0.3 Ma and show a negative relationship with effective uranium—a proxy for radiation damage. Apatite (U-Th)/He dates are 109.2 ± 23.9 to 43.6 ± 1.9 Ma and correlate with sample elevation. Multi-chronometer Bayesian time-temperature inversions suggest: (a) Cooling between ∼1.90 and ∼1.80 Ga, likely related to Big Sky orogeny thermal effects; (b) Reheating between ∼1.80 Ga and ∼1.35 Ga consistent with Mesoproterozoic burial; (c) Cooling to ≤100°C between Mesoproterozoic and early Paleozoic time, likely reflecting continental erosion; (d) Variable Paleozoic–Jurassic cooling, possibly related to Paleozoic tectonism and/or low eustatic sea level; (e) Rapid Cretaceous–Paleocene cooling, preceding accepted proxies for flat-slab subduction; (f) Eocene–Miocene reheating consistent with reburial by Cenozoic volcanics and/or sediments; (g) Post-20 Ma cooling consistent with Neogene development of topographic relief. Our results emphasize the utility of multi-chronometer thermochronology in recovering complex, non-monotonic multi-billion-year thermal histories.

Original languageEnglish (US)
Article numbere2022TC007541
Number of pages34
JournalTectonics
Volume42
Issue number1
DOIs
StatePublished - Jan 2023

Keywords

  • Laramide
  • North American Cordillera
  • deep-time
  • geochronology
  • thermal history modeling
  • thermochronology

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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