Geology of the Strait of Belle Isle area, northwestern insular Newfoundland, southern Labrador and adjacent Quebec

Abstract

The Strait of Belle Isle area comprises three principal geological terranes and each is described separately. Precambrian terrane. The oldest rocks in the area are widespread leucocratic to melanocratic biotite-quartz-felspar gneiss including some quartz-rich gneiss, pelitic gneiss, amphibolite, and minor calcareous gneiss of Helikian or earlier age. The gneiss was intruded by plutons of the anorthositic suite, commencing with metagabbro throughout the area and continuing with mangerite and hornblende granite north of the Strait of Belle Isle. Small bodies of foliated granite were probably emplaced early in this sequence. Regional folding along northeast-trending axes accompanied by amphibolite to granulite facies metamorphism probably occurred after intrusion of the metagabbro and before emplacement of the hornblende granite. Later, more hydrous megacrystic to massive granitic plutons were emplaced diapirically, mostly within the gneiss of the northern Long Range. Phyllonite, up to 300 m thick, was formed by outward thrusting along the northeast margin of the megacrystic pluton at Canada Bay. Gneiss and megacrystic granite along the east margin of the area were folded along northeast-trending axes and subjected to greenschist fad es metamorphism during or soon after emplacement of the megacrystic plutons. Small bodies of fine grained, massive to foliated, mostly leucocratic rocks of probable cataclastic origin are present near the east coast of the Long Range. The protolith of these bodies is of the same age as the Grenville basement, but cataclasis is of late Grenville or later age or both. Normal faulting followed by reverse faulting is evident on Belle Isle and similar faults are present along the margin of the Long Range Grenville inlier. A zone of greenschist facies metamorphism of Ordovician age crosses the Precambrian rocks along the east margin of the area and may extend to the southern end of the Grenville inlier. Lower Paleozoic autochthonous strata. Hadrynian, Cambrian, and Ordovician autochthonous strata of the Strait of Belle Isle area are part of an easterly thickening wedge of strata extending to the southwest and underlying much of the northern Gulf of St. Lawrence. The strata were deposited on a shelf that gave way easterly to a shelf edge and then to a turbiditic fades which formed along the former continental slope and rise. The oldest strata comprise quartzite, conglomerate, siltstone, and minor basalt of the Bateau Formation on Belle Isle. Tholeiitic diabase dykes of the Long Range dyke swarm of latest Hadrynian age intrude the Bateau Formation and are feeders to tholeiitic basalt flows of the overlying Lighthouse Cove Formation. These flows are interlayered with basal arkosic sandstone, conglomerate and siltstone of the succeeding Bradore Formation. In all, these strata are as much as 700 m thick. A regolith is widely evident on the basement complex beneath the Bradore beds. The Cambrian to Middle Ordovician is represented by up to 1500 m of shallow water marine carbonates and some shale and quartz sandstone derived from the Precambrian rocks to the northwest as the proto- Atlantic ocean waters gradually transgressed to the northwest. Lower Ordovician carbonate of the St. George Group consists of about 600 m of calcitic dolomite and dolomitic limestone, which exhibits subtle lateral changes from one rock type to the other. Fossils are not abundant and include graptolites, trilobites, and gastropods. Carbonate in the top of the group contains zinc occurrences. Following the Lower Ordovician deposition, the entire continental shelf was uplifted and exposed to subaerial erosion. After perhaps 5 million years, the shelf again subsided and 500 m of marine limestone of the Table Head Group was then deposited in a Middle Ordovician epicontinental sea upon a karst surface. Water on the shelf then deepened, and detritus for the first time came from the east when the Hare Bay Allochthon was being moved westward on to the shelf. The resulting black shale and minor greywacke of the Goose Tickle Formation, as much as 500 m thick, were ·deposited gradationally upon the carbonate. Hare Bay Allochthon. The Allochthon consists of a variety of sedimentary and volcanic and plutonic rocks including greywacke, polymictic conglomerate, quartz-pebble conglomerate, siltstone, shale, mafic pillow lava, peridotite, harzburgite, dunite, gabbro, and diorite. These rocks make up six contrasting rock assemblages which are separated by thrust faults. The lower structural slices consist of sedimentary rocks and the highest structural slice consists of an ophiolite suite. Melange zones commonly separate the thrust slices. One of these zones contains large exotic blocks. The commonest blocks are serpentinized peridotite, mafic volcanic rocks, amphibolite, foliated gabbro, greywacke, diorite, hornblendite and hornblende-biotite schist. These are contained in a matrix of black and green shale. Most rock types of the blocks may be matched directly to rocks in nearby structural slices. The rocks of the Hare Bay Allochthon originated in the east, in the region near what is now Notre Dame Bay, and record a part of the development and destruction of the ancient continental margin of eastern North America.

Depth related brachiopod faunas from the lower Cambrian Forteau Formation of southern Labrador and western Newfoundland, Canada

“…Crossbedded, skeletal and intraclastic dolostone associated with metre-scale archeocyathid mounds occur locally in southern Labrador and the drill hole at Savage Cove; only scattered archeocyathans occur with other skeletal debris in grainstone at MSM and East Castor Pond (ECP). In southern Labrador and near the Highlands of St. John, the member is fully or partially dolomitized (Cumming in Bostock et al, 1983;Knight, 1991;this study). Small, dolomitized archeocyathid mounds mark the basal contact and abundant quartz sand is intermixed in the dolostone just east of Fox Cove.…”

“…Legend is applicable to all stratigraphic figures (8)(9). Dunbar, 1934 figure 8; Cumming in Bostock et al, 1983;Knight, unpublished data). Although incomplete in Labrador, the 56 to 70 m succession is still divisible into the three members (See figure 2 in James and Kobluk, 1978;Figure 3, this paper).…”

“…This succession has long been considered to preserve a third order sequence of onlap and offlap of the FIGURE 2. Geology map of the south coast of Labrador showing localities in the Forteau Formation, Labrador Group that were studied and yielded a rich brachiopod fauna (map based on Bostock et al, 1983 andGower, 2010). LLQ -L'Anse-au-Loup quarry, DCQ -Diablo Cove quarry 6 margin during the late early to early middle Cambrian when the proto-shelf was interpreted to be an eastward deepening ramp (James et al, 1989).…”

The Double Mer Formation and the Lake Melville rift system, eastern Labrador

“…1) Stukas and Reynolds 1974). Dikes similar to those in the Long Range have been interpreted as feeders for the Lighthouse Cove Formation on Belle Isle, which has a minimum age of 540 Ma (Bostock et al 1983).…”

Late Neoproterozoic Avalonian and related peri-Gondwanan rocks of the Newfoundland Appalachians

“…1). The opposing margins of that oceanLaurentian in the west (present coordinates), Gondwanan in the east-are characterized by faunally distinctive lower Paleozoic cover sequences resting on Proterozoic basements of fundamentally different age and character (Hutchinson, 1962;Bostock et al, 1983;James et al, 1989;Williams, 1979;Williams et al, 1992). In the Newfoundland Appalachians, those Neoproterozoic rocks of peri-Gondwanan orogenic affinity are traditionally viewed to lie east of the central mobile belt (cf., Williams et al, 1970) restricted to the lithotectonically distinct Avalon Zone (Williams, 1979;.…”