ABSTRACT

The buried Shield consists of five divisions: Northern Interior Plains, Athabasca Polymetamorphic Terrain, Cree Lake-Calgary Zone, Trans-Hudson Orogen, and Superior Province. These are separated by four regional shear zones: Great Slave Lake, Virgin River, Needle Falls and Churchill-Superior Boundary Zone.

Northern Interior Plains has north-trending belts related to the 1.9 Ga Wopmay Orogen. This Aphebian basement is overlain to the west by

End_Page 158------------------------

Middle and Upper Proterozoic clastic sediments and diabase sills. Athabasca Polymetamorphic Terrain contains Archean remnants and crystalline rocks strongly reworked at 1.9 Ga. There is widespread K-metasomatism. A variety of dating methods give values from 1.8 to 2.5 Ga.

The Cree Lake-Calgary Zone resembles the Cree Lake Zone of northern Saskatchewan, with infolded Aphebian metasedimentary belts in remobilized Archean rocks. Uraniferous granites were emplaced along the Virgin River Shear Zone. Late-orogenic epizonal plutons with high U and Th form a distinctive petrographic province in southwestern Saskatchewan.

The metavolcanic and metasedimentary assemblages of the Trans-Hudson Orogen may be analogous to modern island arcs although recognition of these units in basement oil-well cores remains speculative due to the limited sampling; more is known from the approximately 1500 diamond drill cores available. Archean isotopic ages are diagnostic of the Superior Province. Its western boundary is marked by sheared low-grade rocks with a negative aeromagnetic signature.

Two Phanerozoic cratonic arches in the Western Canada Sedimentary Basin have trends that parallel basement divisions. The axis of the Peace River Arch in northern Alberta corresponds to high K-U-Th rocks in the Athabasca Polymetamorphic Terrain. The North Battleford-Sweetgrass Arch parallels and lies within the western foreland of the Trans-Hudson Orogen.

The Steen River astrobleme is an example of a small-scale Phanerozoic basement structure. It is complex, consisting of a central uplift, a rim syncline and at least one raised rim. It is 25 km in diameter and exhibits 1700 m of relief.

End_of_Record - Last_Page 159-------