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 oŁ 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