Structural Analysis of the Mount Wright Map-Area, Southernmost Labrador Trough, Quebec, Canada
The Mount Wright map-area, covering approximately 7,200 km 2 of the Canadian Precambrian Shield, is situated at the southern end of the Labrador trough and lies across the Grenville metamorphic front. Subhorizontally interbanded charnockitic, granulite-facies Archean rocks, which are now restricted to the smaller northern part of the region and form a part of the Superior province, were deformed at least twice during the Kenoran orogeny (2,390 to 2,590 m.y. B.P.). The Archean rocks subsequently formed the basement on which lower Proterozoic (Aphebian) rocks of the Kaniapiskau Supergroup of the Labrador trough were deposited. South of the Grenville front, the supracrustal sequence and the Archean basement were later polyphase deformed and metamorphosed, mainly at the amphibolite-facies level, during the Hudsonian orogeny (1,640 to 1,830 m.y. B.P.) and the Grenville orogeny (1,150 to 850 m.y. B.P.). A study of the several tectonic episodes that affected this part of the Grenville province has been greatly enhanced by the occurrence of a thin but widespread group of ironstone, quartzite, and marble formations (the Gagnon Group) that provides excellent lithostratigraphic marker bands near the base of the lower Proterozoic succession. Analysis of the interference patterns within the Gagnon Group reveals the effects of at least three major phases of folding, the earliest of which postdated an initial period of metamorphism and migmatization. Isolated areas of granulite-facies rocks, occurring south of the front, probably represent zones of partially recrystallized Archean basement. Although it has been shown that, north of the Grenville front, the eastern part of the Labrador trough was strongly involved in the Hudsonian orogeny, it is difficult to assess the effects of this event in the Mount Wright map-area. We present a structural sequence in which the earliest folding of the lower Proterozoic supracrustal rocks is tentatively assigned to the Hudsonian orogeny.