The geology of the southern part of the North Arm Mountain Massif, Bay Of Islands Ophiolite Complex, Western Newfoundland with application to ophiolite obduction and the genesis of the plutonic portions of oceanic crust and upper mantle
Date of Award
Doctor of Philosophy (PhD)
The Bay of Islands Ophiolite Complex forms a discontinuous belt of highly allochthonous mafic and ultramafic massifs in southwestern Newfoundland. The North Arm Mountain Massif contains the only significant exposures of sedimentary rocks overlying the ophiolite and also contains the most extensive exposures of plutonic rocks in the Bay of Islands Complex. Mapping has shown that sedimentary rocks, here named the Crabb Brook Group, rest with a pronounced erosional unconformity on ophiolitic rocks. Lithologic,paleontologic, facies, structural, and tectonic relationships indicate that this Group was deposited on the back of the ophiolite allochthon as it was being obducted onto the early Paleozoic Continental Margin. These sedimentary rocks may correlate with others associated with ophiolites in the Northern Appalachians which, as yet, are of unknown age and affinity. Regional tectonic and paleogeographic relationships in Western Newfoundland allow evaluation of the obducticn process and models are developed to explain features which are common to many obducted ophiolite bodies. Many features observed in the plutonic complex of the North Arm Massif are inconsistent with models of ophiolite generation which involve small multiple magma chambers and in many cases are contrary to the notion that the majority of layered plutonic rocks were formed by differential settling and accumulation. A combination of field, structural, and petrographic relationships indicate that the bulk of the North Arm Plutonic section formed as a result of in situ nucleation and crystal growth on the bounding surfaces of a continuously evolving, chemically zoned, steady state magma chamber.
Casey, John F., "The geology of the southern part of the North Arm Mountain Massif, Bay Of Islands Ophiolite Complex, Western Newfoundland with application to ophiolite obduction and the genesis of the plutonic portions of oceanic crust and upper mantle" (1980). Geology Theses and Dissertations. 109.