The evolution of the Baie Verte Lineament,
Burlington Peninsula, Newfoundland
William S. F. Kidd
University of Cambridge, 1974. Supervisor: John F. Dewey
Summary
An area measuring about 5 km by 30 km, of the
relatively well-exposed central part of the Baie Verte
Lineament, has been mapped in detail. Two major rock divisions
are recognised by their differing structural and metamorphic
histories. A terrain of psammitic, semipelitic and mafic
schists borders the western side of the Lineament. These rocks
(part of the Fleur de Lys Supergroup) are in upper greenschist
to epidote-amphibolite metamorphic facies, and are affected by
a polyphase deformation sequence. They are intruded by
post-kinematic granite and tonalite. A large, generally
unfoliated, granodiorite (Burlington Granodiorite) borders the
eastern side of the Lineament. Outside the map area, it is
seen to be either a pre- or early syn-kinematic intrusion into
Fleur de Lys schists. The Baie Verte Lineament consists, in
the mapped area, of two adjacent narrow-parallel belts; to the
west the Baie Verte Group of uncertain (?Arenigian) age, and
to the east the early Devonian Mic Mac Lake Group. Large
lensoid “alpine-type” (ophiolitic) ultramafic bodies are
situated along the tectonic contact between the Fleur de Lys
schists and the Baie Verte Group. A narrow discontinuous strip
containing bodies of ophiolitic gabbro with parallel diabase
dykes is found at the western side of the Baie Verte Group
adjoining the tectonic contact. The internal structures and
textures of the ophiolitic rocks are described. The Baie Verte
Group consists mainly of mafic pillow lava and mafic
volcaniclastic sediments, subvertical to moderately
west-dipping, and facing east, for which a stratigraphy is
defined. At or near the base, a conglomerate, resting on
ophiolite gabbro megabreccia, contains clasts mainly referable
to the mafic parts of an ophiolite complex, with some clasts
identical to the Burlington Granodiorite, and rare clasts
referable to previously deformed silicic volcanics and related
sediments of the Fleur de Lys Supergroup found to the east of
the map area. Redeposited carbonate rocks are very
occasionally found near this horizon. The Mic Mac Lake Group
rests with spectacular unconformity, including a significant
amount of palaeotopographic relief, on the Burlington
Granodiorite. It also contains a similar erosion surface
within the subaerial sequence of silicic volcanics, mafic and
trachyte lava flows, and mostly conglomeratic sediments. A
stratigraphy is defined for the Mic Mac Lake Group. The
sequence dips west at moderate angles and, with the
significant exception of a narrow strip at the western side,
faces west. The Baie Verte and Mic Mac Lake Groups share a
single steep cleavage and low greenschist facies metamorphic
grade. An autochthonous contact between Baie Verte Group and
east-facing Mic Mac Lake Group in the southern part of the
area indicates that the Mic Mac Lake Group is in a
highly-disrupted syncline, and is unconformable on the Baie
Verte Group. To the north an attenuated Mic Mac Lake Group is
overthrust by the Baie Verte Group, and must eventually be cut
out to the north of the map area where the Baie Verte Group
directly overthrusts Burlington Granodiorite. It is shown that
the deformation of the Baie Verte and Mic Mac Lake Groups, and
the tectonic emplacement of the ophiolitic ultramafic bodies
into their present position, was wholly later than all the
regional polyphase deformation and metamorphism of the Fleur
de Lys Supergroup, and that this later deformation is almost
wholly localised in the belt of less complexely deformed rock.
Joint
mapping with J.M. Bird and J.F. Dewey at the northeast end of
the
Baie Verte Lineament demonstrated the presence of all members
of a
full ophiolite suite, overlain by mafic volcaniclastic
sediments and
a thick pile of pillow lava. The internal
igneous-relationships of
the ophiolite complex are described. These rocks are disposed
in
three thrust sheets (two being inverted), which are overthrust
eastward above previously deformed and metamorphosed Fleur de
Lys
schists. One
model has been proposed that coherently interprets the
Palaeozoic
evolution of the central and western Newfoundland Appalachians
in
terms of present-day continental margin/island arc
sedimentation,
magmatism, and tectonics. The results of this mapping are
interpreted
within the framework of this model. The Fleur de Lys schists
and
Burlington Granodiorite represent rifted continental margin
sediments, and a volcanic arc built on and intruding them
prior to
polyphase deformation and metamorphism. The Baie Verte Group
is
interpreted as the remains of the oceanic crust and mantle
floor and
mafic volcanic fill of one of several small marginal
(inter-arc)
basins that developed in the northwestern Newfoundland area in
lower
Ordovician times. It is interpreted to be in the place where
the
basin formed relative to the eastern and western Fleur de Lys
blocks
that border it. The Mic Mac Lake Group is a proximal section
to an
early Devonian calc-alkaline cordilleran caldera complex which
may
have been related either to subduction or to continental
collision
processes. It was laid down over an eroded surface of
Burlington
Granodiorite and over little to undeformed mafic rocks filling
the
Baie Verte marginal basin. Both were then deformed during the
Acadian
continental collision orogeny by contraction of the Baie Verte
basin,
with medium to high angle eastward overthrusting.