TY - JOUR
T1 - Orogens of Big Sky Country
T2 - Reconstructing the Deep-Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA
AU - Ronemus, Chance B.
AU - Orme, Devon A.
AU - Guenthner, William R.
AU - Cox, Stephen E.
AU - Kussmaul, Christopher A.L.
N1 - Funding Information:
We would like to thank David Mogk for contributing his expertise on the geology of the Beartooth Mountains and Andrew Laskowski for sharing his regional expertise during drafting of this manuscript. This work additionally benefitted from conversations with Caden Howlett, Stuart Parker, Alyssa Abbey, and Kendra Murray. We would also like to thank Sidney Hemming and the staff of the Argon Geochronology for the Earth Sciences Laboratory at Columbia University (New York, NY, USA) for assistance with the generation and interpretation of biotite 40Ar/39Ar data. We thank the Arizona LaserChron Center (Tucson, AZ, USA) for assistance with the generation of zircon U-Pb data, the CU TRaIL laboratory (Boulder, CO, USA) for assistance with generation of apatite (U-Th-Sm)/He data, and Linda Angeloni at the UIUC Helium Analysis Laboratory (Urbana, IL, USA) for assistance with generation of zircon (U-Th)/He data. Funding for this research was provided by Montana State University and the Tobacco Root Geological Society. WRG acknowledges NSF-EAR Grant 1735788 for laboratory support. We would like to thank Emily Finzel, Kalin McDannell, and an anonymous reviewer for their reviews of this manuscript, which greatly improved its quality.
Funding Information:
We would like to thank David Mogk for contributing his expertise on the geology of the Beartooth Mountains and Andrew Laskowski for sharing his regional expertise during drafting of this manuscript. This work additionally benefitted from conversations with Caden Howlett, Stuart Parker, Alyssa Abbey, and Kendra Murray. We would also like to thank Sidney Hemming and the staff of the Argon Geochronology for the Earth Sciences Laboratory at Columbia University (New York, NY, USA) for assistance with the generation and interpretation of biotite Ar/Ar data. We thank the Arizona LaserChron Center (Tucson, AZ, USA) for assistance with the generation of zircon U‐Pb data, the CU TRaIL laboratory (Boulder, CO, USA) for assistance with generation of apatite (U‐Th‐Sm)/He data, and Linda Angeloni at the UIUC Helium Analysis Laboratory (Urbana, IL, USA) for assistance with generation of zircon (U‐Th)/He data. Funding for this research was provided by Montana State University and the Tobacco Root Geological Society. WRG acknowledges NSF‐EAR Grant 1735788 for laboratory support. We would like to thank Emily Finzel, Kalin McDannell, and an anonymous reviewer for their reviews of this manuscript, which greatly improved its quality. 40 39
Publisher Copyright:
© 2022. American Geophysical Union. All Rights Reserved.
PY - 2023/1
Y1 - 2023/1
N2 - 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.
AB - 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.
KW - Laramide
KW - North American Cordillera
KW - deep-time
KW - geochronology
KW - thermal history modeling
KW - thermochronology
UR - http://www.scopus.com/inward/record.url?scp=85147092657&partnerID=8YFLogxK
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U2 - 10.1029/2022TC007541
DO - 10.1029/2022TC007541
M3 - Article
AN - SCOPUS:85147092657
SN - 0278-7407
VL - 42
JO - Tectonics
JF - Tectonics
IS - 1
M1 - e2022TC007541
ER -