SOME NORTH AMERICAN EXAMPLES OF THE GEOLOGIC IMPACT OF SEISMIC MODELS OF LITHOSPHERIC STRUCTURE

We have summarized several seismic experiments in terms of how the resulting models impact geologic studies. One final step in our investigations of the High Lava Plains of eastern Oregon was the development of a 3-D tomographic model of the upper crust of the Harney basin region. This area was chosen because it might contain three calderas that are the sources of major ash flows in the region, and two probable calderas were identified. Another example comes from the DEEP PROBE and CD-ROM seismic refraction experiments shared a common shotpoint in central Wyoming. Together, these profiles plus seismic tomography and reflection images reveal the lithospheric structure across a major suture (Cheyenne belt) between the Archean Wyoming craton and Proterozoic terranes to the south. This result is consistent with a variety of geological data and provides a framework for additional geological studies. Finally, the Arkansas sector of the Ouachita orogenic belt was imaged by a COCORP reflection profile and a crustal refraction experiment. The results reveal that a large crustal block to the south collided with Laurentia but did not completely deform the Cambrian rifted margin of Laurentia. The implications of this model are far reaching, especially for the source of the accompanying massive intraplate deformation (Ancestral Rocky Mountains) in the interior of southern Laurentia. In the related Southern Oklahoma aulacogen, a seismic refraction/wide-angle reflection model across it shows that the crust was massively magmatically modified during Cambrian rifting and massively inverted in the Pennsylvanian. The source of the driving force for this deformation is still a point of contention.