Abstract

A major early Proterozoic orogen (Central Plains) more than 1000 km long and at least 500 km wide has been delineated in the subsurface of Nebraska, Kansas, and Missouri as a result of a new compilation of Precambrian basement drill data in the northern midcontinent. The orogen is composed of metamorphic and granitoid rocks in the ringe 1.63–1.80 Ga, and it is interpreted on the basis of isotopic ages, rock types, and structure—as reflected by magnetic and gravity anomalies—as being the eastward extension of the early Proterozoic foldbelt exposed in basement uplifts in Colorado and southeastern Wyoming. It truncates the southern margin of the Superior Archean craton and its marginal early Proterozoic orogens, the Penokean (1.83–1.90 Ga) and the Trans-Hudson (1.85–1.95 Ga). The pattern of intersecting Proterozoic mobile belts marginal to Archean cratons is comparable to that in other continents, such as Western Australia and southern Africa.

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