Seismic studies on the Trans-Hudson Orogen of western Canada

The discovery of diamondiferous kimberlites in the late 1980's within the central Saskatchewan segment of the Trans-Hudson Orogen prompted an aggressive diamond exploration program in the region. The presence of this, apparently uncharacteristic, mineralization within the Proterozoic orogen was initially a puzzle. Recent seismic reflection and geochronology evidence however suggests that the Glennie domain of the orogen may be cored by a microcontinental Archean block while geochemical results imply that segments of the Precambrian basement of southern Saskatchewan mainly comprise Archean crust which has been reworked by thermotectonism. We present the initial results of two seismic programs designed to elucidate the lithospheric structure associated with the economically targeted segment of the orogen, Preliminary interpretation of wide-angle reflection data along a 730 km north-south profile in north-central Saskatchewan reveals a very complex structure with the crustal thickness varying from a maximum of 50 km to a minimum of 37 km over a distance of 200 km beneath the Glennie domain. A teleseismic feasibility study with an 8-station array with individual seismographs operating for 4 to 6 months supports and extends this image of complexity, Relative travel time differentials across a 500 km array are as large as 700 ms. While key features of these delay times correlate with the crustal structure, a significant portion of the variations must be assigned to deeper levels of the lithosphere. Receiver function analysis for crustal structure is shown to be feasible in this environment where the Phanerozoic sediment thickness varies from 0 to 2.1 km and provides evidence for large variations (similar to 7 km) in crustal thickness in the southwestern area of the province. SKS analysis at a single station also adds to the evidence which shows rapid variations in anisotropy within the orogen. A teleseismic program with seventeen 3-component stations is now underway to clarify the nature of this complex crustal and upper mantle structure.