The petrology and petrogenesis of the Bay of Islands Ophiolite Suite, Western Newfoundland
The Bay of Islands Complex, situated on the west coast of Newfoundland, forms the upper slice assemblage of a number of allochthonous slices that were emplaced on platformal carbonate rocks of the ancient North American continental margin during the lower Middle Ordovician. The Complex consists of a...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
1976
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| Online Access: | https://research.library.mun.ca/6793/ https://research.library.mun.ca/6793/1/JohnMalpas.pdf https://research.library.mun.ca/6793/3/JohnMalpas.pdf |
| Summary: | The Bay of Islands Complex, situated on the west coast of Newfoundland, forms the upper slice assemblage of a number of allochthonous slices that were emplaced on platformal carbonate rocks of the ancient North American continental margin during the lower Middle Ordovician. The Complex consists of a complete ophiolite sequence disposed in four main massifs and believed to represent obducted portions of oceanic lithosphere. During early stages of displacement from the oceanic environment, a basal dynamothermal aureole was developed and remains part of the Complex. Temperatures of metamorphism in this aureole suggest that the ophiolitic rocks were just formed and still hot when displaced. This, together with other evidence, suggests their production in a marginal basin or in the environs of a ridge, subduction zone, transform triple point. -- Petrological, mineralogical and chemical data show that the Complex may be divided into a lower series of ultramafic tectonites representing mantle material, and a higher series of cumulate and extrusive rocks capped by clastic sediments which may be correlated with oceanic crust. -- Examination of the tectonite series reveals a lower spinel lherzolite member overlain by harzburgites. Both rock types are cut by numerous deformed and undeformed olivine-pyroxene veins. These veins represent early crystallisation products from a picritic tholeiite magma derived at 18 kb and 1100°C by ~ 23% partial melting of a spinel lherzolite to leave a harzburgite residuum. The remainder of the magma crystallised as different cumulate and extrusive rocks under crustal conditions. -- The petrogenetic model derived from the mineralogy and chemistry implies a rising diapiric body beneath an accreting centre and allows for the production of tholeiitic, transitional and mildly alkaline basalts from a similar parent. The nature of the basalt erupted depends upon rate of upwelling and rate of crysallisation within the diapir. Prolonged fractionation at pressures of 8-18 kb may explain the derivation ... |
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