Structural studies of the Gander and Davidsville groups in the Carmanville-Ladle Cove areas, Newfoundland

Uzuakpunwa, Anene Benedict (1973) Structural studies of the Gander and Davidsville groups in the Carmanville-Ladle Cove areas, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The study area lies in the northeastern margin of the Central Mobile Belt of Newfoundland Appalachians. It is underlain by the lower Palaeozoic rocks of the Gander and Davidsville groups, and an older gneissic complex considered a basement to the Gander Group. -- The gneissic basement consists mostly of psammitic banded gneisses and interbedded micaceous quartzites which were unconformably overlain by the Gander group. The latter includes psammitic and semi-pelitic schists, minor conglomerates, greywackes and basic lava flows that acquired a pre-Middle Ordovician composite fabric and a greenschlst to amphibolite facies grade of metamorphism. The Group is separated from the overlying less deformed and metamorphosed sequence of mafic agglomerates, grey slates, interlayered siltstones, minor conglomerates, greywackes and black slates of the Middle Ordovician Davidsville Group by either a melange, ultramafic belt, or a fault. -- Intrusion of the pre-Middle Ordovician garnetiferous muscovite-biotite granites post-dated the development of the composite gneissic banding in the gneissic basement, and predated the first deformation of the Gander Group. A post Middle Ordovician (pre-Devonlan?) quartz diorite intruded the Gander Group, Davidsville Group and the melange. Evidence suggests that the quartz diorite intruded the Davidsville Group before the latter was penetratively deformed. -- The ultramafic rooks of the Gander Group are composed dominantly of pyroxenite, minor chromite bearing serpentinites and talc-carbonate schists which were marginally metamorphosed, and have the same composite fabric as the enveloping metasedimentary rocks. They do not appear to be genetically related to the serpentinized dunite breccia, mafic pillow lavas and hornblende gabbros which were incorporated as blocks in the nearby melange belt separating the Gander and Davidsville Groups. The melange is considered tectonic, having been formed during the upthrusting of the Davidsville Group (onto the Gander Group) as a folded nappe. -- Four main phases of deformation (each producing a fabric) are recognized in the Gander Group, and two other phases (one penetrative), which may or may not be related to those of the Gander Group, are recognized in the Davidsville Group. Evidence suggests that the third deformation of the Gander Group pre-dated the first deformation of the Davidsville Group. The main schistosity in the Gander Group is a second fabric, which has formed by transposition of an earlier one. Tight to isoclinal folds, boudins and interference patterns were produced during the second and third deformations of the Group. A major southwesterly plunging synform, and numerous minor folds were generated during the first deformation of the Davidsville Group. Kink bands and a series of faults offset the regional foliations and are believed to be developed after the main episodes of folding. -- The climax of metamorphlsm in the Gander Group, occurred during the second phase of deformation, producing muscovite-biotite schists, actinolite schists, and amphibolites. A later thermal metamorphic event affected rocks of the Gander and Davidsville Groups.

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