ABSTRACT
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, J.F., 1980. 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. Unpublished PhD dissertation,
State University of New York at Albany. 620pp.(2 vol.), +xxii; 1 folded
plate (map)
University at Albany Science Library call number: SCIENCE MIC
Film QE 40 Z899 1980 C37
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