ABSTRACT
Table Mountain is the northernmost massif in the Bay of Islands
Ophiolite. It represents a continuous, approximately 7 kilometer
thick, section of residual harzburgite tectonites capped by a
nearly flat-lying assemblage of deformed and undeformed cumulate
rocks. The notable mesoscopic structural features of the massif
include a zone of penetrative deformation extending upsection from
the tectonized harzburgites approximately 500 meters into the
dunites and basal cumulates. The orientation of the foliation and
associated lineations as well as the inferred shear sense within
the zone is consistent with that affecting the harzburgites.
Highly deformed dunite lenses which range in thickness up to 300
meters and up to 5 kilometers in lateral extent lie beneath the
plagioclase-bearing cumulates. They have a gradational contact
with the harzburgites. Throughout the harzburgite section
compositional layering, defined by variations in enstatite
concentration, is parallel or nearly parallel to the S1
foliation., The layering may either have limited lateral extent
(associated with transposed intrusives) or it occurs in clusters
of layers traceable as a group for several kilometers. The
inclination of both the foliation and the layering relative to the
essentially flat-lying contact between the cumulate and residual
suites becomes progressively more shallow at deeper levels within
the harzburgite. Petrographic examination of the massif indicates
the presence of clinopyroxene and altered plagioclase (now
hydrogarnet and sericite) in the upper 50 to 200 meters of
harzburgite adjacent to the dunite lenses. Trace amounts of
subhedral clinopyroxene occur throughout the harzburgite,
typically associated with polycrystalline enstatite clots.
Petrofabric analyses of olivine fabrics of samples from the
harzburgite section indicate that the [100] maxima strengthen with
increasing depth from the cumulate carapace. Fabric asymmetries
relative to the trace of the foliation and spinel lineation
indicate a dominantly sinistral shear sense. This concurs with the
consistently oriented fold vergence data. A model of a spreading
ridge system, modified after Dewey and Kidd (1977) and Casey
(1980), is adapted to explain the "herringbone" relationship
between the compositional layering of the undeformed cumulates and
that of the S1 foliation. This foliation is here proposed to dip
away from the parental ridge axis.
Blake, R.W., 1982. The Structural Geology of the Tectonized
Ultramafic Suite of the Table Mountain Massif, Bay of Islands
Complex, Newfoundland. Unpublished MSc. thesis, State University
of New York at Albany. 188 pp., +xii; 2 folded plates (maps)
University at Albany Science Library call number: SCIENCE
Oversize (*) QE 40 Z899 1982 B54
MS thesis scanned text pdf - 28.5MB
Plate 1 - Geological
map
of Table Mountain massif, Bay of Islands Ophiolite Complex,
Newfoundland
(uncoloured geological outcrop map; scale
~1:15,840)
Plate 2 - Structural
cross-section
of the north face of Table Mountain
(uncoloured section; scale ~1:15,840)
Return to MS Theses completed in the Geological Sciences Program, University at Albany