Granitoids of the Wesleyville area in northeastern Newfoundland : a study of their evolution and geological setting

Jayasinghe, Nimal Ranjith (1979) Granitoids of the Wesleyville area in northeastern Newfoundland : a study of their evolution and geological setting. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (23MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Granitic rocks occupy more than three quarters of the Wesleyvllle area. They consist of eight granitoids, namely, the Wareham Quartz Monzonite and the Cape Freels, Lockers Bay, Deadman's Bay, Newport, North Pond, Business Cove and Big Round Pond granites. The first five of these intrusions are megacrystic - characterized by > 2 cm long microcline crystals set in a finer grained "matrix". The North Pond and the Business Cove granites are garnetiferous, two-mica granites. The Big Round Pond pluton is a medium-grained biotite granite. Radiometric ages, field relationships and structural evidence indicate that the granitoids have been emplaced in the Silurian to Carboniferous times. -- The country rocks of the granitoids are represented by two gneissic units: the Square Pond Gneiss and the Hare Bay Gneiss. The Square Pond Gneiss consists of psammitic to semi-pelitic gneiss, schist and metasediment with an eastward prograding metamorphism from greenschist to amphibolite facies. The Hare Bay Gneiss consists mostly of migmatite in the amphibolite facies. The contact between the two gneiss terrains is marked by a "migmatite front". -- The gneisses have been deformed at least twice before the migmatization. The peak metamorphism and the migmatization have occurred during a third deformation event, the latter part of which has also included the emplacement of the Wareham, North Pond and the Business Cove plutons. A fourth deformation event has produced two major, north-northeast-trending sinistral shear zones in the area. The western one cuts through the North Pond, Wareham and the Lockers Bay plutons. The easterly shear zone has deformed the western margin of the Cape Freels Granite and the adjacent Hare Bay Gneiss. Age relationships between these shear zones and the Dover Fault are not known. The Deadman's Bay Granite post-dates the shear zone and pre-dates a suite of north-south trending alkalic basalt dikes. The dikes are truncated by the Newport and the Big Round Pond granites. -- Geoehemical work indicates that the North Pond Granite could have been derived by the fractionation of feldspars and biotite from a Wareham Quartz Monzonite-tvpe magma. The initial ⁸⁷Sr/⁸⁶Sr ratios and the chemistry of the megacrystic granitoids and the Big Round Pond Granite suggest that they could have been produced by the partial melting of greywacke. -- None of the plate-tectonic models so far proposed adequately explain the development of the Gander Zone. No new plate-tectonic model has been proposed in the present study but it adds a few more constraints to future plate-models dealing with the Gander Zone in Newfoundland.

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