Abstract
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 Unpublished PhD dissertation, State University of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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