ABSTRACT
The Betts Cove ophiolite complex lies within the Dunnage Zone island
arc terrain of central Newfoundland. It forms the base of the lower
Ordovician
Snooks Arm Group, which consists of mafic igneous rocks of the
ophiolite
and a thick sequence of volcanic and volcaniclastic rocks which
conformably
overlies it. The Snooks Arm Group is unconformably overlain by
sub-aerial
sediments and volcanics of the presumed Silurian Cape St. John Group.
The base o£ the ophiolite complex consists predominantly of
ultramafic
rocks. These are interlayered on a variety of scales, and show
mesoscopic
igneous structures which suggest that they were produced by magma
chamber
processes. They consist largely of olivine, orthopyroxene, and
clinopyroxene,
with minor plagioclase and chromite. These phases are generally quite
altered,
but original igneous textures are well-preserved in most samples.
A thin sequence of interlayered ultramafic and gabbroic rocks overlies
these layered ultramafic rocks. This sequence is similar to the
underlying
one, but contains a significantly greater proportion of gabbroic rocks.
Most of the mesoscopic features of these interlayered rocks are similar
to those of the layered ultramafic rocks. In some places interlayered
rocks
pass upward into a thin zone of homogeneous gabbro, which is largely
devoid
of compositional variation, igneous layering, and other mesoscopic
features.
This gabbro consists primarily of variably altered plagioclase,
clinopyroxene,
orthopyroxene and rare olivine.
A sheeted diabase dike complex overlies the plutonic portion of the
ophiolite. In some places the contact between the dikes and the
plutonic
rocks is quite sharp, while in others dikes related to the sheeted
complex
extend downward as far as the upper portion of the layered ultramafic
sequence.
The sheeted complex consists almost entirely of altered diabase and
picritic
diabase dikes, with rare screens of gabbroic and ultramafic plutonic
lithologies.
The ophiolite is capped by altered, basic volcanic rocks, occurring
as pillows, massive flows, and volcanic breccia. Dikes of the sheeted
complex
extend upward into these volcanics in places.
Many of the original petrologic and structural characteristics of the
Betts Cove ophiolite have been obscured by deformation and
metamorphism,
which occurred at the same time as or soon after the formation of the
ophiolite.
Despite this, detailed mapping has shown that the ophiolite consists of
a conformable sequence of igneous rocks similar to those seen in other
ophiolite complexes. It differs somewhat from many ophiolites, however,
in that the thickness of its gabbroic sequence is quite small. Field
relationships,
augmented by geochemical and petrologic data, suggest that the
ophiolite
complex was produced from a picritic primitive melt by igneous
processes
occurring within and adjacent to a high-level, sill-like magma chamber,
Structural relationships observed within the complex provide some
constraints
for the size and geometry of this chamber.
Regional relationships and geochemical data suggest that the Betts
Cove ophiolite was formed during Early Ordovician time as a marginal or
rear-arc basin above an east-dipping subduction zone.
Idleman, B.D., 1981. Geology of the Plutonic and Hypabyssal Rocks of
the Betts Cove Ophiolite Complex, Newfoundland.
Unpublished MSc. thesis, State University of New York at Albany. 139
pp., +xii; 3 folded plates (maps)
University at Albany Science Library call number: SCIENCE
Oversize
(*) QE 40 Z899 1981 I37
MS thesis (scanned
text
pdf - 21 MB)
Plate 1 - Generalized
geology
of the Betts Cove Ophiolite Complex, Newfoundland
(uncoloured geological map; scale ~1:15,720)
Plate 2 - Geology
of
the Kitty Pond area, Betts Cove Ophiolite Complex, Newfoundland
(uncoloured geological map; scale ~1:4,630) 1.8MB
Plate 3 - Outcrop
Geology
of the Kitty Pond area, Betts Cove Ophiolite Complex,
Newfoundland
(uncoloured geological map; scale ~1:4,630)
Return to MS Theses completed in the Geological Sciences Program, University at Albany