A structural-metamorphic and geochemical study of the Hunt River supracrustal belt, Nain Province, Labrador

Jesseau, Conrad Wayne (1976) A structural-metamorphic and geochemical study of the Hunt River supracrustal belt, Nain Province, Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

The southern Nain Province is characterized by several northeasterly trending supracrustal belts, Archean in age, which are infolded into a complex of polygenetic quartzofeldspathic gneisses. This thesis describes a petrological, geochemical and structural-metamorphic study of one of these belts, the Hunt River Belt, a predominantly mafic supracrustal sequence. -- The Hunt River Belt consists of a series of amphibolite schists (meta-volcanics), ultramafic lenses, and minor meta-sediments. The chemistry of the meta-volcanics displays close similarities to tholeiites found in the lowermost cycles of Archean greenstone belts. The ultramafics, containing preserved igneous textures, are considered to have intruded early into a developing volcanic pile. -- The thesis area has undergone a complex history of structural and igneous development. The earliest recognized widespread event (D₁) produced a strong tectonic fabric in the Hunt River Belt, and produced banded gneisses in the quartzofeldspathic rocks through thrusting and transposition, D₂ reflects a period of pure shear deformation and overprinted the area with a pronounced planar fabric. D₃ represents a period of tectonically active crustal uplift associated with magma upwelling and gave rise to heterogeneous deformation. D₄, a period of shallow level upright open folding, closed out the periods of folding and was followed by the development of megascopic faulting and diabase dyke intrusion. -- Each of the deformational episodes was accompanied by periods of plutonic activity which led to the development of distinct gneiss types. -- Mineralogical and microstructural evidence in the amphibolite schists and the quartzofeldspathic gneisses indicates that D₁, D₂ and D₃ all occurred within the amphibolite facies of metamorphism. D₄ and subsequent faulting occurred under greenschist facies conditions.

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