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.
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
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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 -