Cheyenne belt

Yavapai province to the south. It runs through the southeastern quadrant of the state of Wyoming, United States. It was formed during the Paleoproterozoic Medicine Bow orogeny between 1.78 and 1.74 billion years ago when island arcs collided with the Wyoming craton.^[1] This is an example of a convergent boundary

Ma) to the south. ^[2]

tholeiitic basalt with a minimum age of 2000 Ma, and this is taken as the time at which the Wyoming craton was rifted from a larger craton to produce the passive margin. The Yavapai province south of the belt contains no Archean crust, and it is intruded by granitoid rock with radiometric dates between 1780 and 1630 Ma. This province is interpreted as eugeoclinal rock (rock formed in an island arc). Additional granitoid intrusions that are 1400 Ma in age are interpreted as intrusions that took place after the Yavapai province was sutured to the Wyoming province.^[2]

subduction zone.^[2] The question of which plate was the subducting plate is still a matter of research.^[4] Research during the 1980s suggested that the overriding plate was the Yavapai arc, based on the presence of calc-akaline intrusions (typical of volcanism in an overriding plate) in the Yavapai province. Further evidence is provided by the higher degree of metamorphism of rock on the Yavapai side of the decollement versus the Wyoming side, indicating that rock was brought upwards from greater depth along the decollement.^[2] However, more recent research calls this into question, suggesting either plate might have been the subducting plate but favoring subduction of the Yavapai plate beneath the Wyoming plate. This model is supported by isotopic evidence and by radiometric dates suggesting arc volcanism had ceased in the Yavapai island arc 20 million years before it accreted to the Wyoming plate.^[4]