Inter-wedging nature of the Cheyenne belt: Archean-Proterozoic suture defined by seismic reflection data
New seismic reflection data from the CD-ROM project (Continental Dynamics of the Rocky Mountains) show that the Archean-Proterozoic suture in Wyoming, the Cheyenne belt, consists of a crustal-scale, conjugate thrust wedge, where Archean and Proterozoic crust were thrust into each other. Moderately S-dipping reflections extend to depths of 15-18 km and surface at the mapped shear zones of the Cheyenne belt; these terminate close to a north-dipping reflection that extends to about 24 km depth and converges at the surface at the Farwell-Lester Mountain (FLM) area with several strong, south-dipping reflections. The FLM zone is marked by dismembered ophiolites suggestive of an ocean basin and may represent a back-arc basin subsequently closed by continued south-dipping subduction, resulting in a cryptic suture. Arcuate criss-crossing reflections in Archean basement to the north of the Cheyenne belt are related to folding, inferred conjugate thrusting and an antiformal duplex stack. This stack formed during Paleoproterozoic suturing in supracrustal rocks comprising at least the upper 24 km of the crust. Our analysis of wide-angle seismic data does not reveal a 7 km/s lower crustal layer that could be interpreted as underplate in southern Wyoming or northern Colorado. A suture, marked by complex interwedging of crustal blocks, was probably steepened by continued convergence to the south.