Great Falls Tectonic Zone

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Location of the Great Falls Tectonic Zone.

The Great Falls Tectonic Zone is a major intracontinental

Great Falls of the Missouri River, a major geologic feature of the area. The central and western portions of the zone are believed to be about 1.1 to 3.3 billion years old.[7] The central part of the zone lacks Archean rock, however, leading at least one group of scientists to speculate that it was formed very late in the Paleoproterozoic Era.[7]

The Great Falls tectonic zone has been periodically active since the Proterozoic, and possibly as late as the Holocene.[6] Little of the zone is visible due to Phanerozoic cover, the exception being the Little Belt Mountains.[2] However, it is believed that the tectonic zone controlled the geologic development of nearby basins and subbasins.[8]

The Great Falls tectonic zone was first identified in 1985.[4] Geologists originally believed the zone was part of the Wyoming craton, but now conclude that it is distinct from it.[2] There is continuing controversy over whether the region is a shear zone or suture,[1][9] and the role the zone played in the formation of the North American continent.[2] At one time, both the Great Falls Tectonic Zone and the Vulcan structure were both considered sutures, but debate remains open on the point.[2] At least one group of geologists has concluded the zone represents the closure of an ocean basin.[2] The zone lacks gravity anomalies or electromagnetic signatures which would allow scientists to conclude that it was generated by subduction.[4] There is significant evidence that the zone has been periodically remineralized since Precambrian times.[10] Square Butte, Shaw Butte, Crown Butte and the other structures of the Adel Mountains Volcanic Field lie astride the tectonic zone near the city of Great Falls.[11]

See also

References

  1. ^ a b Boerner, D.E.; Craven, J.A.; Kurtz, R.D.; Ross, G.M.; and Jones, F.W. "The Great Falls Tectonic Zone: Suture or Intracontinental Shear Zone?" Canadian Journal of Earth Sciences. 35:2 (1998).
  2. ^ a b c d e f Mueller, Paul A.; Heatherington, Ann L.; Kelly, Dawn M.; Wooden, Joseph L.; and Mogk, David W. "Paleoproterozoic Crust Within the Great Falls Tectonic Zone: Implications for the Assembly of Southern Laurentia." Geology. 30:2 (February 2002).
  3. ^ O'Neill, J. Michael and Lo, David A. "Character and Regional Significance of Great Falls Tectonic Zone, East-Central Idaho and West-Central Montana." AAPG Bulletin. 69 (1985).
  4. ^
    ISBN 0-8137-2377-9
  5. ISBN 0-19-516589-6
  6. ^ a b O'Neill, J. Michael and Lopez, David A. "Character and Regional Significance of the Great Falls Tectonic Zone, East-Central Idaho and West-Central Montana." American Association of Petroleum Geologists Bulletin. 69:3 (1985).
  7. ^ a b Gifford, Jennifer N.; Foster, David A.; Mueller, Paul A.; Mogk, D.W.; Kamenov, George D.; and Probst, Kelly. Plutonic Imaging: A View into the Lower Crust and Upper Mantle of the Great Falls Tectonic Zone. 2008 Joint GSA, SSSA-ASA-CSSA, and GCAGS Annual Meeting. October 7, 2008.
  8. ^ O'Neill, J.M., editor. Metallogeny of Mesoproterozoic Sedimentary Rocks in Idaho and Montana—Studies by the Mineral Resources Program, 2004–2007. U.S. Geological Survey Open-File Report 2007–1280. Washington, D.C.: U.S. Geological Survey, 2007.
  9. ISBN 0-8137-2433-3
  10. ^ Foster, F. and Childs, J.F. "An Overview of Significant Gold Lode Systems in Montana, and Their Regional Geologic Setting." Explorations in Mining Geology. 2 (1993); Hoy, T. "The Purcell Supergroup in Southeastern British Columbia: Sedimentation, Tectonics and Stratiform Lead-Zinc Deposits." In Precambrian Sulfide Deposits. Special Paper 25. Geological Association of Canada, 1982.
  11. ISBN 0-87842-323-0
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