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 a n aggressive diamond exploration program in the region. The presence o f this, apparently uncharacteristic, mineralization within the Protero zoic orogen was initially a puzzle. Recent seismic reflection and geoc hronology evidence however suggests that the Glennie domain of the oro gen may be cored by a microcontinental Archean block while geochemical results imply that segments of the Precambrian basement of southern S askatchewan mainly comprise Archean crust which has been reworked by t hermotectonism. 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 interpretatio n of wide-angle reflection data along a 730 km north-south profile in north-central Saskatchewan reveals a very complex structure with the c rustal 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 f easibility study with an 8-station array with individual seismographs operating for 4 to 6 months supports and extends this image of complex ity, Relative travel time differentials across a 500 km array are as l arge as 700 ms. While key features of these delay times correlate with the crustal structure, a significant portion of the variations must b e assigned to deeper levels of the lithosphere. Receiver function anal ysis 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 th ickness in the southwestern area of the province. SKS analysis at a si ngle 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 compl ex crustal and upper mantle structure.