Gravity patterns and Precambrian structure in the North American Central Plains

Bouguer gravity patterns revealed in horizontal gradient images are used to locate and examine the tectonic nature of Precambrian structural boundaries buried beneath the North American Central Plains. The southern boundary of the Superior province west of the midcontinent gravity high (MGH), interpreted as a collisional suture, is relocated as much as 200 km south of previous geophysically defined positions, close to a position defined recently by using drill-hole information; east of the high, this boundary is thought to trace a 900-km arc subparallel to the MGH. The western boundary of the Superior province is regarded as a suture containing significant components of transcurrent faulting. The eastern boundary of the Wyoming province, another suture, is traced northward into the Churchill province, near the northwestern margin of a 1900 1600 Ma magmatic belt. This boundary and Proterozoic terrane to the east are transected by previously unrecognized faults hundreds of kilometres long. Gravity patterns also suggest that the North American Central Plains conductivity anomaly may not be a continuous, suture-related conductor. *Present address: Lunar and Planetary Institute, 3303 NASA Road 1, Houston, Texas 77058-4399