Geology and 40Ar/39Ar geochronology of the Coastal Complex near Trout River and Lark Harbour, western Newfoundland
Bruce D. Idleman 1990
A Dissertation submitted to the State University of New York at Albany in partial fulfillment of the requirements for the degree of Doctor of Philosophy
College of Science and Mathematics, Department of Geological Sciences
Advisor: W.S.F. Kidd

The Coastal Complex is an assemblage of variably deformed and metamorphosed ophiolitic rocks exposed along the western side of the Bay of Islands ophiolite in western Newfoundland. The complex consists of several isolated massifs that lie above and in thrust contact with sedimentary rocks of the Humber Arm Supergroup. Mapping of the massifs south of Trout River and northwest of Lark Harbour has shown them to be tightly folded on a regional scale. The folds are upright, north to northeast trending, and doubly plunging over distances of several kilometers. They affect both the basal thrust and the overlying ophiolitic rocks. The oldest rocks in the two massifs are gabbros and peridotites, some of which contain an early penetrative foliation and an associated stretching lineation (D1) formed under upper amphibolite to granulite-facies metamorphic conditions. They are intruded by large tabular bodies of trondhjemite that postdate the D1 fabrics in the mafic and ultramafic rocks. Final cooling of the plutonic terrain below about 500ºC occurred by 490 Ma, as revealed by 40Ar/39Ar ages obtained from magmatic hornblende. The plutonic rocks are cut in places by gently dipping ductile shear zones (D2) several hundred meters wide and 5 kilometers or more in preserved length. The shear zones rocks are mafic and rare ultramafic mylonites formed under greenschist to upper amphibolite-facies metamorphic conditions. They are constrained by 40Ar/39Ar dating of metamorphic hornblende to have formed between 460 and 475 Ma, synchronous with the obduction of the western Newfoundland ophiolites. Numerous dikes and other hypabyssal intrusive bodies of diabase and microgabbro were emplaced into the complex during this event. Some of these bodies were strongly affected by the D2 deformation, while others are undeformed and crosscut the shear zone fabrics. The complex is capped by a bimodal suite of volcanic rocks, which nonconformably overlie the plutonic and metamorphic units and postdate the development of the D2 shear zones. Field relationships and geochronological data from the two field areas suggest that the Coastal Complex represents an imbricate stack of ophiolitic thrust slices assembled along the leading edge of the Bay of Islands ophiolite during its obduction.

Idleman, B.D., 1990. Geology and 40Ar/39Ar geochronology of the Coastal Complex near Trout River and Lark Harbour, western Newfoundland. Unpublished PhD dissertation, State University of New York at Albany. 542pp., +xx; 3 folded plates (maps)
University at Albany Science Library call number:  SCIENCE MIC Film QE 40 Z899 1990 I34
Copies of this PhD dissertation can be ordered from Proquest UMI

        Front matter (title, table of contents, abstract, acknowledgements) - 0.6MB pdf file
        Photo pages in dissertation (colour photos with captions): - 39.4MB pdf file

        Plate 1 - Geologic map of the Coastal Complex, Trout River - Chimney Cove area, Newfoundland, Canada
                    (uncoloured geologic outcrop map; scale ~1:15,840) 6.9MB pdf file
        Plate 2 - Geologic map of the Coastal Complex, Lark Harbour area, Newfoundland, Canada
                    (uncoloured geologic outcrop map; scale ~1:15,840) 1.7MB pdf file
        Plate 3 - Cross-sections through the Coastal Complex, Trout river and Lark Harbour areas, Newfoundland, Canada
                    (uncoloured geologic sections; scale ~1:15,840) 0.7MB pdf file

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