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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 sutured together with the Superior and Hearne-Rae cratons in the mountain-building episode that created the Trans-Hudson Suture Zone to form the core of North America (Laurentia). It was incorporated into southwest Laurentia approximately 1.86 billion years ago.〔 〕 Local preservation of 3.6–3.0 Ga gneisses and widespread isotopic evidence for crust of this age incorporated into younger plutons indicates that the Wyoming Craton originated as a 100,000 km2 middle Archean craton that was modified by late Archean volcanic magmatism and plate movements and Proterozoic extension and rifting.〔 〕 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 Ga, with post-tectonic magmatism at ca. 1.715 Ga (the Harney Peak granite). This tectonic-magmatic interval is 50–60 million years younger than that reported for the Hearne-Superior collision of the Trans-Hudson orogeny in Canada. 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.〔 〕 ==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 plutons (2.8–2.55 Ga) and gneiss and migmatite—together with subordinate (<10 percent) supracrustal metavolcanic-metasedimentary rocks. The granitoid rocks are mainly potassic granite and were derived principally from reworked older (3.1–2.8 Ga) gneiss. Magnetic contrast between the granitoid rocks and gneiss provides a means to map these gross rock units in covered areas. The overall structural pattern of the Archean units shown by magnetic data is crudely semi-circular and open to the north. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wyoming Craton」の詳細全文を読む スポンサード リンク
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