Ordovician volcanism and mineralization in the Wild Bight group, central Newfoundland: a geological, petrological, geochemical and isotopic study

• Main Author: Swinden, H. S.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1987
• Subjects: Clear Island; Notre Dame Bay; Wild Bight; Newfoundland
• Online Access: https://research.library.mun.ca/6780/; https://research.library.mun.ca/6780/1/HaroldScottSwinden_1.pdf; https://research.library.mun.ca/6780/3/HaroldScottSwinden_1.pdf

The Wild Bight Group, part of the Newfoundland Dunnage Zone or Central Mobile Belt, is a thick (probably more than 8 km.) sequence of dominantly epiclastic (~75%) and lesser volcanic (~25%) rocks which outcrops in and to the south of central Notre Dame Bay. The base of the group is not exposed. It passes conformably upward into fossiliferous shale with a Caradocian (Middle Ordovician) graptolite fauna. On this basis, it is considered as Early to Middle Ordovician in age. -- Volcanic rocks occur throughout the stratigraphic section of the Wild Bight Group. Eleven separate volcanic sequences are identified and sampled, most of which comprise dominantly or wholly mafic pillow lava. Less commonly, massive basalt or pillow breccia and associated mafic pyroclastic rocks are the dominant lithology. Felsic volcanic rocks occur in five of these sequences and volcanogenic sulphide deposits or prospects in four of them. The entire assemblage is intruded by fine to medium grained mafic sills and, less commonly, dykes, which are interpreted on field and geochemical evidence to be subvolcanic. -- The mafic volcanic rocks exhibit a greenschist facies metamorophic assemblage of chlorite - albite - quartz - epidote ± (actinolite, sphene, magnetite and calcite). The only primary mineral remaining is clinopyroxene. Comparison of secondary mineral chemistry with ancient and modern oceanic rocks and with experimental results are consistent with metamorphism at temperatures in the range 200°C to 280°C and low water/rock ratios. The local presence of secondary amphibole is interpreted to reflect slightly higher temperatures. -- Major and trace element whole rock analyses of volcanic and subvolcanic rocks, as well as clinopyroxene mineral chemistry, reveal a complex geochemical association. Two broad paleotectonic environments can be identified using high field strength elements; volcanic rocks in the lower and middle parts of the group have a clear island arc geochemical signature (negative Ta and Nb and positive Th with respect to La ...