Wyoming Craton
The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the initial core of the continental crust of North America.
The Wyoming Craton was
Local preservation of 3.6–3.0 Ga
The Wyoming, Superior and Hearne-Ray cratons were once sections of separate continents, but today they are all welded together. The collisions of these cratons began before ca. 1.77
Younger metamorphic dates (1.81–1.71 Ga) also typify the eastern and northern Wyoming province peripheries in the western Dakotas and southeastern Montana. The final assembly of the eastern Wyoming Craton as part of the continent Laurentia began during the ca. 1.78–1.74 Ga interval of island-arc accretion along the southern margin of the growing craton.[3]
Geologic summary
The Precambrian basement of Wyoming consists mainly of three major geologic terranes, the Archean Wyoming Craton or Province, the Paleoproterozoic Trans-Hudson orogen, and the Paleoproterozoic Colorado orogeny. The Colorado orogen collided with the Wyoming Craton at 1.78–1.75 Ga. Collision of the Colorado orogen and the Trans-Hudson orogen with the Archean craton produced strong structural overprinting along the southern and eastern margins of the Wyoming craton.
The Wyoming Craton consists mainly of two gross rock units—granitoid
Wyoming province subdivisions
The present-day lithospheric architecture of the Wyoming Province is the result of cumulative processes of crustal growth, tectonic modification, and lithospheric contrasts that have apparently persisted for billions of years.
The Wyoming
An analysis by Kevin Chamberlain et al. (2003), on the basis of differences in late Archean histories, subdivides the Wyoming Province into five subprovinces: three in the Archean core, (1) the Montana metasedimentary province, (2) the Bighorn subprovince, and (3) the Sweetwater subprovince, and two Archean terrains that may have originated elsewhere (that is, allochthonous to the 3.0 Ga craton), (4) the Sierra Madre – Medicine Bow block, and (5) the Black Hills – Hartville block. Based on imaging by the "Deep Probe" analysis, a thick lower crustal layer corresponds geographically with the Bighorn subprovince and may be an underplate associated with ca. 2.70 Ga mafic magmatism. The Sweetwater subprovince is characterized by an east–west-tending tectonic grain that was established by three or more roughly contemporaneous late Archean, pulses of basin development, shortening, and arc magmatism. This tectonic grain, including the 2.62 Ga Oregon Trail structure, controlled the locations and orientations of Proterozoic rifting and uplifts related to the Laramide orogeny. If there has been any net crustal growth of the Wyoming Province since 3.0 Ga, it has involved a combination of mafic underplating and arc magmatism.[2]
Accretion events
During the Paleoproterozoic, island-arc terrane associated with the Colorado orogeny accreted to the Wyoming Craton along the Cheyenne belt, a 500-km-wide belt of Proterozoic rocks named for Cheyenne, Wyoming. As a result of the collision, older, Archean rocks of the Wyoming province were intensely deformed and metamorphosed for at least 75 km inboard from the suture, which is marked today by the Laramie Mountains. Along the east margin of the craton, collision with the Paleoproterozoic Trans-Hudson orogen intensely deformed Archean cratonic rocks in the Hartville uplift.
Mesoproterozoic (~1.4 Ga) anorthosite and syenites of the Laramie Anorthosite Complex and granite (ilmenite-bearing Sherman Granite) intrude into rocks of the Colorado orogen in the Laramie and adjacent Medicine Bow Mountains. Both the anorthosite and granite transect the Cheyenne belt in the Laramide Mountains, and intrude crystalline rocks of the Wyoming province. These intrusions comprise the northernmost segment of a wide belt of 1.4 Ga granitic intrusions that occur throughout the Colorado orogen.[4]
Long after its assembly, the Wyoming Craton owes its spectacular mountainous terranes mainly to a regional episode of compressional deformation during the Laramide orogeny (ca.60 Ma). The basement blocks composed of Precambrian rocks were uplifted locally to high levels in the crust during the deformation, and subsequent erosion has molded the uplifted rocks into the rugged present-day topography. Vertical displacement of the basement surface was as much as 30,000 ft. (9250 m). By contrast, in western Wyoming thrust faulting, associated with the Sevier orogeny of approximately the same age, was thin-skinned, and the lack of disruption of magnetic anomalies in the region indicates that the basement rocks were little disturbed and not significantly uplifted during the thrusting. Even younger high-angle faulting of Pliocene–Pleistocene age has formed the Teton Range. Vertical relief on the east face of the mountains is about 25,000 ft. (7800 m).[4]
See also
- North American Craton
- Cheyenne belt
- Colorado orogeny
- Grouse Creek block located west of the craton
- Superior Craton
References
- ^
Foster, David A., Paul A. Mueller, David W. Mogk, Joseph L. Wooden and James J. Vogi (2006). "Proterozoic Evolution of the Western Margin of the Wyoming Craton: Implications for the Tectonic and Magmatic Evolution of the Northern Rocky Mountains". Can. J. Earth Sci. 43 (10): 1601–1619. doi:10.1139/E06-052.)
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Chamberlain, Kevin R., Carol D. Frost, and B. Ronald Frost (2003). "Early Archean to Mesoproterozoic evolution of the Wyoming Province: Archean origins to modern lithospheric architecture". Canadian Journal of Earth Sciences. 40 (10): 1357–1374. doi:10.1139/e03-054.)
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: CS1 maint: multiple names: authors list (link - ^
Dahl, Peter S., Daniel K. Holm, Edward T. Gardner, Fritz A. Hubacher, and Kenneth A. Foland (1999). "New constraints on the timing of Early Proterozoic tectonism in the Black Hills (South Dakota), with implications for docking of the Wyoming province with Laurentia". Geological Society of America Bulletin. 111 (9): 1335–1349. doi:10.1130/0016-7606(1999)111<1335:NCOTTO>2.3.CO;2.)
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: CS1 maint: multiple names: authors list (link - ^ a b c Sims, P. K., C. A. Finn, and V. L. Rystrom (2001). "Preliminary Precambrian Basement Map Showing Geologic-Geophysical Domains, Wyoming". United States Geological Survey: USGS Open-File Report 01-199.
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(help)CS1 maint: multiple names: authors list (link) - doi:10.1139/E06-075.