Michael P. Cullen

Rocks of the Bass River Complex are interpreted as a multiply deformed sequence comprising four lithotectonically distinct units. The Folly River Schist and Gamble Brook Schist form the supracrustal sequence and are, respectively, heterogeneously deformed submarine meta-volcanic and meta-sedimentary sequences within which primary structures have been recognised. The Great Village River Gneiss represents circa. 900 Ma basement to the supracrustals and is composed of three distinct sequences: the Portapique River Schist, the Bass River Amphibolite, and the Great Village River Orthogneiss.

Two structural domains are identified within the Complex. Rocks of the Great Village River Gneiss define Domain A and bear local evidence of an early deformation peak (DB1) not seen in the Gamble Brook Schist and Folly River Schist of Domain S. Maximum metamorphic conditions reached sillimanite grade during this period. Both domains were deformed by the strong DB2 event which shortened the sequence by extensive tight to isoclinal folding, transposition, and possibly by translation. Granitoid rocks (circa 810 Ma??, Gaudette et al., 1983) were emplaced prior to or during this event.

Subsequently, Late Hadrynian regional folding (DB3) produced east to northeast trending, variably plunging, asymmetric folds that are overturned to the north. Locally a crenulation fabric associated with these folds has been enhanced by chlorite crystallisation. Dioritic intrusions of probable late Precambrian age post-dated the DB3 regional folding deformation and effectively date the end of pervasive tectonism in Bass River Complex rocks.

In Late Devonian and Early Carboniferous time the Complex was intruded by post- Acadian plutonic rocks and suffered right lateral displacement along the Gamble Lake Fault (DB4a) and Rockland Brook Fault (DB4b). These are the earliest phases of deformation attributed to Glooscap Fault System (King et al., 1975) displacements. Subsequently, a paleo-stress field of uncertain origin (DB4c) acted upon the rocks of the Complex producing a poorly-developed, high angle, conjugate fracture system which crosses the Rockland Brook and Gamble Lake structures but is truncated by the Londonderry Fault.

Early Carboniferous fault movement (DB5) along the Londonderry Fault emplaced the Londonderry Formation in its present location along the south margin of the Bass River Complex, locally overprinting the DB4a (Gamble Lake Fault) fabric. The final deformation to affect these rocks (DB6) involved normal slip along numerous north-trending faults which disrupt Lower Jurassic strata.

Domain A Bass River Complex rocks are correlated with circa 900 Ma gneisses of the Mount Thom Complex, 30 km to the east, and are also similar in age to gneisses in southwest New Brunswick. Relative age-equivalence of Bass River Complex Domain S rocks with the Greenhead Group of southwest New Brunswick is indicated and a similarity of Late Precambrian intrusive histories in the Bass River Complex, the Cape Breton Highlands, and southeast Newfoundland is suggested.

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Pages: 209
Supervisor: Rebecca Jamieson