A New Integrated Analysis of Crustal Structure across the Proterozoic Cheyenne Belt Suture

We conducted an integrated analysis of the controlled-source and passive seismic datasets from the Continental Dynamics of the Rocky Mountains (CD-ROM) 1999 seismic experiment in the Rocky Mountains, and determined the crustal structure using four different receiver function methods. The resulting migrated image and crustal thickness determinations confirm and refine prior crustal structure measurements based on the CD-ROM and Deep Probe datasets. We employed receiver function migration and common conversion point (CCP) stacking, and the combined interpretation of all the results shows: 1) northward crustal thickening in central Wyoming, and 2) the presence of a strong lower-crustal reflector in the area beneath the Wyoming province and 3) its termination north of the Cheyenne belt at 42° latitude. This result provides a seismic tie between the CD-ROM and Deep Probe seismic experiments and produces a continuous N-S transect extending from New Mexico into Alberta, Canada. This new tie is particularly important because it occurs close to a major tectonic boundary (Cheyenne belt) between an Archean craton and a Proterozoic terrane.

We created a new two-dimensional P-wave velocity and interface model of the area based on the controlled-source dataset, and in addition we were able to establish an independent S-wave velocity model, and hence to determine the Poisson's and Vp/Vs ratios. By integrating all prior results, we constructed a well-constrained structural model and tectonic interpretation, which shows the structural framework of the transition from the Wyoming craton to the north, across the Cheyenne belt suture zone to the Proterozoic terranes to the south. The interpretation that crustal-scale crocodile structures are present provides an explanation for the south dip of the Cheyenne belt in the upper crust and the north-dipping slab in the mantle. The very distinct crustal structures north and south of the suture zone are clearly shown in our model.