MT SNORCLE: EM SURVEY RESULTS FROM THE MARGINS OF THE SLAVE PROVINCE

Ian Ferguson, Department of Geological Sciences, University of Manitoba

1:00 PM Tuesday 22th October 1996, Room 217 Wallace Building

The objectives of the LITHOPROBE SNORCLE (Slave and Northern Cordilleran Lithospheric Evolution) Transect are to examine the nature and evolution of the lithosphere of the Archean Slave Province, its bordering Proterozoic orogens, and younger terranes in the Northern Cordillera. Some of the questions to be addressed by the collaborative, multidisciplinary, studies on the transect include: "What kind of crust and mantle underlie the oldest rocks on earth?", "Did plate tectonics operate in the early Archean?", "Are deep structural characteristics of Proterozoic orogens fundamentally different from those of Phanerozoic orogens?" and "How were the outboard Cordilleran terranes assembled into their present distribution?". In this seminar I will examine preliminary electromagnetic survey results from Corridor 1 of the Transect which runs from Yellowknife to Nahanni Butte (Northwest Territories) and crosses the southwest Slave Province and the Proterozoic Wopmay Orogen. An additional branch, Corridor 1A, between Fort Providence and Fort Smith crosses of the Great Slave Lake Shear Zone.

A large-scale magnetotelluric (MT) survey along the 800 km Corridor 1 and 410 km Corridor 1A was conducted between August and October this year. Two types of MT soundings were made at 60 sites. Broadband measurements (0.0001 to 1000 s) completed by a contracted company (Phoenix Geophysics). provide a response suitable for defining structures from shallow depth to the lower crust. Additional long-period (LIMS) measurements (20 to >3000 s) were completed by university and GSC researchers and define a response suitable for defining structures in the mid to lower crust and in the sub- crustal lithosphere. Preliminary examination of the results reveals a strong conductivity contrast between the Precambrian rocks and overlying sediments in the west of the corridors (Fig. 1). The data also reveal a number of structures within the Precambrian rocks including a shallowing of the thickness of the lithosphere from the Slave province towards the west.
Fig. 1: Apparent resistivity along SNORCLE Corridor 1