Geology of Vermont
Structural Evolution of the Worcester Mountain Range, North-Central
by Marjorie Gale and Jonathan Kim
A poster presented at Geologic Association of Canada/MAC Meeting, May
Click on individual images to enlarge or by Fig. # in box below.
1 - Location; Fig. 2 - Lithotectonic
Belts; Fig. 3 - (pdf) Regional
Bedrock Map; Fig. 4 - Shaded Relief;
Fig. 5 - Geology on Relief; Fig.
6 - Morrisville Quad (Springston et al., 1998);
Fig. 7 - Southern Worcesters; Fig.
8 & 9 - Cross-section A-A and B-B'; Fig. 10 - Representative
Structures: Row 1, Row
2, Row 3, Row
4; Fig. 11 - Equal Area Nets; Fig.
12 - Correlation with Quebec; Fig.
13 - Correlative Geology in Quebec.
The Worcester Mountain Range (WMR), located in the Rowe-Hawley Belt
and east of the Baie Verte - Brompton Line, is composed of Pre-Silurian
greenschist to amphibolite facies metasedimentary and meta-igneous
rocks of the Hazens Notch, Ottauquechee, and Stowe formations. The
rocks were deformed and metamorphosed during the Taconian and Acadian
orogenies. The WMR is a fault-bounded, asymmetric, doubly-plunging
anticlinorial window formed by superposition of four major deformational
phases. Garnet-kyanite schist and amphibolite comprise the core
of the WMR, whereas finer-grained chlorite-muscovite phyllites and
schists compose the flanks and are in fault contact with albitic
schists and mafic rocks of the Green Mountain slice. This presentation
focuses on the 3-dimensional geometry generated by superposition
of the ductile structural events.
earliest deformation (D1) produced a penetrative schistosity parallel
to compositional layering and a stack of east-dipping lithotectonic
packages emplaced above the Prospect Rock Fault. The second deformational
fabric (S2) is axial planar to isoclinal F2 folds and forms a
composite S2/S1 fabric. The tectonic contact between amphibolites
of the WMR core and the structurally underlying Hazens Notch schists
is deformed by moderately-steeply north plunging F2 folds. S2/D2
kinematics are equivocal. Although most lithotectonic contacts
predate S2, S2 is commonly the dominant fabric in the core schists
of the WMR.
Acadian F3 folds are tight, shallowly plunging
asymmetric folds with an axial planar spaced cleavage. S3 forms
a composite anastamosing fabric with S2. D3 is responsible for
the arching of the WM and the Green Mt. Anticlinorium. Garnet-kyanite
schists of the WMR core plunge southward below Stowe Fm. phyllites
at the southern closure of the antiform. The WMR antiform is truncated
on the both sides by D3/reactivated D2 faults.
The fourth deformational phase (D4) affecting
the WMR resulted in an irregular warping of the F3 antiformal
axis by large-scale open folds that are visible along their ~30
km. length. S4 develops irregularly as a crenulation cleavage
axial planar to F4 folds. F4 folds clearly deflect S3 to the east.
The architecture of the WMR reflects the
juxtaposition of lithotectonic units during Taconian ductile thrusting
followed by several phases of subordinate folding and faulting
continuing through the Acadian Orogeny. The WMR terminates to
the north via north-plunging F2 folds and to the south via south-plunging
F3 folds. Acadian anticlinorial windows exposing coarse-grained
garnet schists in the Becancour Dome and Carrineault Antiform
in S. Quebec may be along-strike analogues for the WMR.