Northern Appalachian Transect: Southeastern Quebec, Canada Through Western Maine, U.S.A.; Quebec City, Canada to Portland, Maine, July 20-26, 1989

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Northern Appalachian Transect:
Southeastern Quebec, Canada
through Western Maine, U.S.A.
Quebec City, Canada to Portland, Maine
July 20-26, 1989
Field Trip Guidebook T358
Leaders:
Robert H. Moench and Pierre St.-Julien
Associate Leaders:
Gary M. Boone Eugene L. Boudette Wallace A. Bothner
Richard Goldsmith ArthurM. Hussey, II John D. Unger
American Geophysical Union, Washington, D'.C.
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN: 0-87590-559-5
Printed in the United States of America
COVER View from Eustis Ridge southeasterly to Bigelow Mountain, Maine
Leaders
Robert H. Moench and Pierre St. Julien
U. S. Geological Survey, Denver, Colorado, USA and
Universite Laval, Ste-Foy, Quebec, Canada
Associate Leaders
Gary M. Boone
Department of Geology, Syracuse University, Syracuse, NY
and Maine Geological Survey, Augusta, ME
Eugene L. Boudette,
State Geologist,
New Hampshire Geological Survey,
Durham, NH
Wallace A. Bothner
Department of Earth Sciences
University of New Hampshire
Durham, NH
Richard Goldsmith
U. S. Geological Survey
Reston, VA
Arthur M. Hussey, II
Department of Geology, Bowdoin College, Brunswick, ME
and Maine Geological Survey, Augusta, ME
John D. Unger
U. S. Geological Survey
Reston, VA
IGC FIELD TRIP '1'358:
NORTHERN APPALACHIAN TRANSECT:
SOUTHEASTERN QUEBEC, CANADA, THROUGH WESTERN MAINE, USA
INTRODUCTION TO THE EXCURSION
Robert H. Moench
U.S. Geological Survey, Denver, Colorado
This excursion crosses the entire exposed of moderate displacement, these rocks were
width of the northern Appalachian orogen, unaffected by Paleozoic deformations.
from Quebec City, Canada, south to Portland, Abruptly to the southeast is the
Maine, a distance of 230 mi (370 km). autochthonous foreland thrust belt, only a
Because of the great distance and the great few kilometers wide in the Quebec City area,
complexity of the geology, we decided to in which Middle Ordovician flysch and
focus on specific areas of outstanding "wildflysch" deposits are deformed by
interest, rather than attempt to show all northwest-verging thrust faults and
that can be seen in the time available. overturned folds. The thrust belt is
Emphasized throughout are the primary sharply bounded on the southeast by Logan's
lithologic features that characterize the line, generally regarded as the main frontal
principal lithotectonic belts shown on thrust fault, or fault zone, of the northern
Figure 1, which also shows the outlines of Appalachians.
the detailed maps for six of the seven days South of Logan's line is the external
of the excursion. No guide article and (northwestern) domain of the Quebec
detailed map has been prepared for day 3, Appalachians, for brevity named the external
which is open for several options in Quebec nappes on Figure 1. This belt, 25 to 50 km
Province near the Maine border. wide in Quebec, is composed of several
The transect covers a region for which northwest-transported, older-over-younger
new comprehensive geologic maps are now allochthonous sheets of predominantly
available (St-Julien and Slivitsky, 1987; clastic Cambrian to Middle Ordovician
Osberg and others, eds., 1985; Moench and deposits that accumulated in deep water far
Pankiwskyj, 1988). A brief discussion of to the southeast, on the continental slope
relevant geophysical features, resulting in of ancient North America. According to St
large part from a cooperative United Julien's model, the nappes formed by gravity
States - Canadian deep seismic reflection sliding induced by abrupt Middle Ordovician
profile in the area of this transect, uplift of the continental slope and
follows. Geologic mapping on which the subsidence of the platform. The external
Maine portion of this guide is based was nappe belt is bounded on the southeast by
done by the Maine and United States the Richardson fault, which is regarded as a
Geological Surveys. basal thrust of the stack of "hard-rock"
thrust sheets that comprise the internal
nappe belt.
DAY 1
The transect begins at Quebec City, at DAY2
the thrust-faulted northwestern margin of
the Appalachian orogen. The first day, led The second day of the excursion, also led
by Pierre St-Julien, starts on the platform by St-Julien, covers the distance between
northwest of the orogen, where billion-year Quebec City and Thetford Mines, Quebec, and
old Grenville gneiss of the Canadian Shield crosses the external and internal nappes,
is unconformably overlain by a horizontal and the Baie Verte Brompton line (B-B
Middle Ordovician sequence of transgressive line). The focus of the day is on the B-B
sandstone and conglomerate, shelf-facies line, regarded as the suture zone along
carbonate rocks, and shale and flysch-like which fragments of oceanic crust and
deposits. Except for several normal faults associated melange were obducted onto the
T358: 1
FIGURE 1 LITHOTECTONIC MAP FOR TRIP
72'"
T-358, NORTHERN APPALACHIAN TRANSECT
EXPLANAT ION
I D
Cambrian to Lower Devonian metasedimentary
and metavolcanic rocks
Mesozoic alkalic plutons and volcanic rocks (M, Mont
Megantid;includes Pennsylvanian(?) pluton (A)
north of Lewiston, ME
Carboniferous peraluminous granite
(SB, Sebago batholith)
Devonian peraluminous granite and calc-alkalic rocks
(MB, Mooselookmeguntic batholith),
and gabbroic rocks
Middle(?)to Late Ordovician and Early Silurian
trondhjemitic, calc-alkalic, and alkalic plutons;
• includes Middle Ordovician tonalite and sheeted
gabbro-diabase, in northern NH (TG)
Cambrian and Early Ordovician(?)ophiolite complexes
~
Baie Verte - Brompton and Hurricane Mountain
ophiolite - melange zones
I}I
Middle and Upper Proterozoic rocks of Chain Lakes
massif (CLM)and Coastal lithotectonic block
----
Normal, transcurrent(?), and unclassified faults
~ Thrust and thrust(?)faults
,...-r--'t--<" Premetamorphic slides
Seismic reflection line
Compiled by W.A. Bothner and R.H. Moench from Williams (978),
Moench and others 0984. and unpub. mapping), Osberg and others, eds.
(985), Lyons and others (986), and St. Julien and Slivitsky 0987>'
INDEX MAP
75° 70°
CANADA 0 ' ,/1./',~
QUE.Btc \:
l,
oM0NTR AL..},) ME:
'~-----I----{\
: : I
~ VT) \
'1 :
I NH' P RTLAND
USA I ---,-I---J
}---~---.J
o 25 50 KM NY Ir:----M--An- BOSTON
!wi ..... """ I CT I
..
40°
ancient continental margin when Iapetus productive sources of asbestos fiber. Stops
closed during the Middle Ordovician Taconian also are planned in sedimentary breccia of
orogeny. The Ordovician(?) Thetford Mines the Cambrian or Lower Ordovician St-Daniel
ophiolite, to be visited in detail, is the Formation, the melange unit that lies
best exposed and most complete ophiolitic conformably above the Quebec ophiolites; and
complex of the B-B line in the Quebec in the Lower Cambrian Caldwell Formation of
Appalachians, and one of Canada's most the internal nappes structurally below the
T358: 2
ophiolites. The internal nappes and thrust orogen after the Middle Ordovician Taconian
sheets apparently involve Precambrian orogeny and before the Early to Middle
basement as well as the overlying Cambrian Devonian Acadian orogeny.
continental slope and rise deposits. Also On the northwest side of the Connecticut
involved in the nappes are ultramafic Valley Gaspe belt is a rather thin
sheets, as the Pennington sheet described in sequence of Upper Silurian conglomerate,
St-Julien's contribution, considered to have sandstone and limestone (Lac Lambton
been cut from the basal peridotite layer of Formation), not unlike the Lac Aylmer,
the ophiolite complexes. succeeded to the southeast by Silurian or
Devonian calcareous shale and slate (Ayers
Cliff Formation). The Ayers Cliff is
DAY 3 overlain by a great thickness of Lower
Devonian gray slate and graded siltstone and
No guide article has been prepared for graywacke (Compton Formation). Lower
day 3, between Thetford Mines and the Lac Devonian (Emsian) plant fossils, confirmed
Megantic area. This day will be open for at La Patrie, Quebec by Francis Huber (oral
several available options in the St-Victor commun., 1988), have been recovered from the
synclinorium and the Connecticut Valley Compton. Rocks of this belt, like those of
Gaspe and Frontenac belts (Fig. 1), the St-Victor synclinorium, are deformed by
described below. Also of interest is the upright folds and steeply dipping slaty
Cretaceous alkalic stock at Mont Megantic. cleavage, but with many local complications.
The day ends at Lac Megantic, Quebec, just The Frontenac belt is stratigraphically
north of the Victoria River fault, or Monroe complex and lacks known fossils. It is not
fault south of the international border, surprising that opinions concerning the age
which marks the southeast side of the and origin of these rocks, based on mapping
Connecticut Valley Gaspe belt for a on both sides of the international border,
distance of at least 450 km in Quebec and differ now as they have for the past half
New England. The following discussion is century. Whereas St-Julien and Slivitsky
provided in lieu of a field guide. (1987) assign tentative Ordovician to
The southeast side of the B-B line is Cambrian ages and an oceanic origin to most
marked by a major thrust fault, southeast of of the rocks of the Frontenac belt, Moench
which is the St-Victor synclinorium (Fig. believes, also tentatively, that all of the
1). The synclinorium, structurally belt is part of the so-called Piermont
characterized by northeast-trending upright allochthon, defined in western New Hampshire
folds and steeply dipping cleavage, contains (Moench and others, 1987), and proposed by
graptolite-bearing strata of the Middle him to extend as much as 300 km across
Ordovician Magog Group, composed of euxinic southeastern into northwestern Maine
shale, chert, tuffaceous sandstone, flysch, (Moench, in press). According to his model,
and felsic tuff. Small synclinal bodies of the allochthon contains an extensional basin
Magog also occur northwest of the fault, sequence of Upper Ordovician, Silurian, and
where they lie unconformably above the St Early Devonian sedimentary and bimodal
Daniel melange of the B-B line. Tuffs of volcanic and intrusive rocks that originated
the Magog are thought to be related to near the Silurian tectonic hinge (Fig. 1),
volcanics of the Ascot Formation, which is and was thrust to its present position
exposed along the southeast side of the during the Acadian orogeny. The main
synclinorium. The Ascot, though undated, is justification for considering these rocks to
thought to represent an eruptive center of a be allochthonous is the sharp juxtaposition
magmatic island arc that was active during of a thick, continuously deposited Silurian
Early to Middle Ordovician plate convergence basin sequence within the allochthon against
and closure of Iapetus. an autochthonous terrane that contains far
Also along the southeast side of the St thinner near-shore Silurian deposits.
Victor synclinorium is a faulted synclinal Most of the rocks of the Frontenac belt
belt of Upper Silurian conglomerate, were mapped originally as the Frontenac
sandstone, and limestone comprising the Lac Formation. They are separable into: 1) an
Aylmer Formation, which lies unconformably extensive sequence of tuffaceous turbidites
above the Magog Group and is faulted aga~nst with pillow basalt and mafic dike swarms; 2)
the Ascot volcanics. The Lac Aylmer and all a strongly bimodal subaqueous volcanic pile,
of the rocks of the Connecticut Valley locally with vent-facies mafic agglomerate
Gaspe belt, southeast of the Guadeloupe and fragmental rhyolite; and 3) a complexly
fault (Fig. 1), represent a vast Silurian stratified, possibly melange-like assemblage
and Early Devonian cover sequence that was of euxinic shale, epiclastic volcanics,
spread across almost the full width of the sheeted diabase-gabbro and hypabyssal
T358: 3
felsite, and small bodies of serpentinite. the Hurricane Mountain belt, in the same
Unit 1 lies conformably above unit 2 (and pattern as the Baie Verte-Brompton line.
perhaps 3), and probably also grades The Hurricane Mountain is conformably
laterally into units 2 and 3. The volcanics overlain by a flysch-like sequence called
are host to important polymetallic massive the Dead River Formation, of Late Cambrian
sulfide deposits of the Clinton River area, and Early Ordovician age. Although it is
about 20 km south of the city of Lac tempting to correlate the Boil Mountain,Jim
Megantic, and to the southwest in Maine. Pond, and Hurricane with the ophiolite and
The southeast side of the Frontenac belt melange of the B-B line, seen on day 2,
is underlain by gray slate, much like that ~oudette and Boone believe that obduction of
of the Lower Devonian Compton Formation. the Boil Mountain Complex onto the Chain
The Early Devonian age of this belt is Lakes massif occurred during the earliest
confirmed south of the international border, Ordovician Penobscottian orogeny, well
where the same gray slate is interbedded before presumed Middle Ordovician Taconian
with felsic tuff that has yielded an Early obduction of the rocks of the B-B line.
Devonian U-Pb zircon age of 413+-4 Ma Boudette, Boone, and Goldsmith interpret the
(Aleinikoff and Moench, 1985). To the Chain Lakes massif as the outcrop area of a
northeast in northern Maine, moreover, distinctive Middle Proterozoic (1.5-1.6 Ga)
Marvinnev (1986) has shown that this same basement terrane, caught between billion
gray slate lies gradationally above the year-old Grenville gneisses of Ancient North
Frontenac Formation (unit 1, listed America, and probable Late Proterozoic
above). At least the upper part of the basement of the Gander terrane to the
Frontenac, therefore, can be considered to southeast. Geophysical support for this
be no older than Late Silurian. The lower interpretation is summarized in the
part of the Frontenac and conformably following contribution by Bothner and
underlying rocks of the Clinton Formation Unger. Readers are cautioned that the
and melange of Chesham are not closely Boundary Mountains terrane is distinct from
dated, but U-Pb zircon data from fragmental the Boundary Mountains anticlinorium, which
metarhyolite in rocks equivalent to the is a younger structural feature.
Clinton in Maine (lower part of unit 2, After several stops in the Boil Mountain
above) indicate an age that is no older than to Dead River sequence, day 4 ends at Lower
430 Ma (J.N. Aleinikoff, oral commun., Silurian orthoquartzite and quartz
August, 1988). A younger felsic metatuff in conglomerate assigned to the Clough
the same unit has been dated at 418+-4 Ma Quartzite. The Clough was deposited
(Lyons and others, 1983; reported as a dike northwest of the Silurian tectonic hinge
but later confirmed as volcanic; data (Fig. 1), near the northwestern shore of the
recalculated by Aleinikoff). ancestral basin of the Kearsarge - central
Maine belt. The enormously thick basin
sequence, deposited without break from
Middle Ordovician to Early Devonian time, is
DAY 4
the focus of dayS.
On day 4 the excursion travels from Lac
Megantic to Rangeley, Maine (Fig. 1). South
DAY 5
of the international border, Gene Baudette,
Gary Boone, and Richard Goldsmith will lead
On the fifth day, the excursion, led by
the excursion through the complex rock
Moench, begins at Rangeley and ends at Weld,
assemblages of the Boundary Mountains anti
Maine, and crosses the entire Middle
clinorium, described in their contribution.
Ordovician to Lower Devonian sequence
The first stops in Maine are in Middle exposed in the northwestern part of the
Proterozoic diamictite of the Chain Lakes Kearsarge central Maine belt or
massif, proposed by Baudette and Boone to synclinorium. A new map for this area has
have originated by meteorite impact. recently become available (Moench and
Structurally above the southern side of the Pankiwskyj, 1988). The sequence to be
massif is a south-younging sequence that visited is estimated to be about 10 km
includes the Cambrian ophiolitic Boil thick, and is divided into several
Mountain Complex and Jim Pond Formation, formations described in Moench's
succeeded by sedimentary melange known as contribution, which also cites the fossil
the Hurricane Mountain Formation, which localities that serve to date the rocks at
contains probable Cambrian primitive sponges least within broad limits. Most of the
found by Harwood (1973). On Figure 1, the rocks are turbidite assemblages. Although
Jim Pond and Hurricane Mountain are shown as some have volcanic sources, actual flows and
T358: 4
tuffs occur only near the Middle to Upper assemblage of rocks that comprise part of
Ordovician base of the sequence. In the coastal lithotectonic block. The
addition to several extensive premetamorphic
coastal block, which can be regarded as part
faults or slides (Fig. 1), interpreted by of a composite Avalonian terrane, is the
Moench to represent the soles of giant focus of day 7.
slumps, rocks of this belt are deformed by
northeast-trending, tight upright folds and
axial surface schistosity formed during the DAY 7
first stage of Early Devonian Acadian
compression. As the ambient regional The seventh and final day of the
metamorphic grade increases southward (from excursion, led by Hussey, begins near
greenschist facies near Rangeley), evidence Brunswick, Maine and ends at Cape Elizabeth,
of multiple deformation becomes more south of Portland. Most of the stops are in
obvious. The regional sillimanite isograd, spectacular wave-washed outcrops of coastal
shown on Figure 1 of Moench's contribution, Maine. The day will be devoted to strongly
is considered to represent the approximate metamorphosed, multiply folded sequences of
transition from upper crust on the the coastal block whose ages are only poorly
northeast, characterized by steep-walled constrained between Late Precambrian and
Devonian plutons with distinctive Early Ordovician. Although rocks of the
metamorphic aureoles, to middle crust on the area can be considered as part of a
southwest, characterized by subhorizontal composite Avalon terrane, the stops listed
granitic sheets with metamorphic aureoles in Hussey's contribution emphasize the
that blende into the ambient grade of the metamorphosed products of a volcanic center
country rocks. Whereas the products of high and related sedimentary fill representative
grade metamorphism and associated superposed of a basin (back-arc?) that lay between the
deformation in the vicinity of Weld and Kearsarge central Maine belt to the
farther north are related to the Devonian northwest, and more typical Avalonian
plutons of western Maine (Fig. 1), similar platform rocks to the southeast.
features surrounding the thin, sheetlike
Sebago batholith to the south (Fig. 1),
dated at 325+-3 Ma (Aleinikoff and others, REFERENCES CITED
1985), are clearly Carboniferous in age (Lux
and Guidotti, 1985). Aleinikoff, J.N., and Moench, R.H.,
Metavolcanic stratigraphy in northern New
England--U-Pb zircon geochronology,
DAY6 Geological Society of America Abstracts
with Programs, 17, no. 1, p. 1, 1985.
The sixth day begins with an ascent of Aleinikoff, J.N., Moench, R.H., and Lyons,
Bald Mountain, near Weld village, Maine, for J.B., Carboniferous U-Pb age of the Sebago
spectacular exposures of complexly deformed, batholith, southwestern Maine, Geological
staurolite zone, Lower Devonian turbidites Society of America Bulletin, 96, pp. 990
near the axial zone of the Kearsarge 996, 1985.
central Maine belt. Then, following a stop Harwood, D.S., Bedrock geology of the
at the type locality of the Lower Devonian Cupsuptic and Arnold Pond quadrangles,
Hildreths Formation (dark-gray metagraywacke west-central Maine, U.S. Geological Survey
and calc-silicate rocks), the excursion Bulletin 1346, 90 pp, 1973.
travels to the southeast for stops in
Lux, D.R., and Guidotti, C.V, Evidence for
Silurian calcareous flysch described in
extensive Hercynian metamorphisn in
Hussey's contribution, near Waterville,
western Maine, Geology, 13, pp. 696-700,
Maine, on the southeast side of the
1985.
Kearsarge - central Maine belt.
Lyons, J.B., Zartman, R.E., and Aleinikoff,
Seismic profiling to the northeast of the
J.N., U-Pb ages of zircons from the
route of the excursion suggests that the
Ordovician Highlandcroft Plutonic Suite
Kearsarge - central Maine belt is floored at
and Silurian intrusives, Geological
a depth of 10-12 km and is separated from
Society of America Abstracts with
high-rank gneisses to the southeast in part
Pr0grams, 15, no• 3, p. 187, 1983•
by a major northwest-dipping fault zone,
lrvinney, R.G., Tectonic implications of
and in part by the subvertical Norumbega
stratigraphy, structure, and metamorphism
fault zone.
in the Penobscot Lake region,northweste-rn
After crossing the Norumbega fault zone,
Maine, Ph.D Dissertation, Syracuse
which is poorly exposed, day 6 ends at
University, Syracuse, New York, 261 pp.,
Brunswick, Maine, and in a totally different
1986.
T358: 5
..
Moench, R.H., The Piermont allochthon, contributions by G.M. Boone, E.L.
northern Connecticut valley area, New Boudette, Allan Ludman, W.R. Newell, and
England--Preliminary description and T.I. Vehrs, U.S. Geological Survey
resource implications, u.S. Geological Miscellaneous Investigations Map 1-1692,
Survey Bulletin, in press. scale 1:250,000, 1988.
Moench, R.H., Hafner-Douglass, Katrin, Osberg, P.H., Hussey, A.M., II, and Boone,
Jahrling, C.E., II, and Pyke, A.R., G.M., eds., Bedrock geologic map of Maine,
Metamorphic stratigraphy of the classic Maine Geological Survey, Department of
Littleton area, New Hampshire, Geological Conservation, scale 1:500,000, 1985.
Society of America Centennial Field Guide, St-Julien, Pierre, and Slivitsky, Anne,
Northeastern Section, pp. 247-256, 1987. Compilation geologique de la region de
Moench, R.H., and Pankiwskyj, K.A., Geologic l'Estrie-Beauce, Ministere de l'Energie et
map of western interior Maine; with des Ressources, Quebec, scale 1:250,000,
1987.
GEOPHYSICAL FEATURES OF THE NORTHERN APPALACHIAN TRANSECT
Wallace A. Bothner and John D.Ungerl
Department of Earth Sciences
University of New Hampshire, Durham, NH
lUnited States Geological Survey, Reston, VA
Regional geophysical studies of the and filtering. Gravity data are broadly
northern Appalachian Mountains, particularly mapped in figure 1 to show the relationships
in New England and Canada, have contributed that relate both to the seismic line in
significantly to our understanding of lithic Canada and the inferences about deep
distribution and structure at and near the structures in the U.S. projected from the
surface and of the nature of the deeper northeast, and the effects of shallower
continental crust beneath the orogen. Over intrusive bodies. Prominent aeromagnetic
the last decade deep seismic reflection linears are not shown on this map, but
profiling onshore in western central New emphasize the direct tie to mapped units at
England and in Quebec provided a first or close to the surface. Maps ')f filtered
"look" at the extent of Grenville basement gravity and magnetic data emphasize the
beneath the rocks of Iapetan heritage and of deeper features of the region and will be
the Connecticut Valley-Gaspe belt (Ando and avilable for examination during the
others, 1983; St. Julien and others, excursion (Simpson and others, 1981).
1983). Subsequent work by the U.S. The, regional Bouguer gravity field for
Geological Survey (USGS), with cooperation
the northern New England and southern Quebec
of our Canadian colleagues, extended that area is contoured at 10 Mgals (Simpson and
work to the southeast across Maine and others, 1981)• For the area of this
offshore into the Gulf of Maine (Stewart and transect the field is grossly characterized
others, 1985; Stewart and others, 1988; as an undulating northwest-dipping surface,
Hutchinson and others, 1987). Those with increasing values to the southeast. It
portions of the seismic lines crossed or
is interrupted by the northeast extension of
followed by this traverse are shown on the Appalachian gravity high and by two
Figure 1. northeast-trending steps of higher gradient
Potential field data covering the area (Kane and others, 1968; Carnese' and others,
from Quebec to Portland, ME, and offshore
across the Gulf of Maine were compiled from
both Canadian and American sources.
Additional close spaced data were collected FIGURE 1 Complete Bouguer gravity map of
at the same time as the seismic work was Quebec (PQ), Maine (ME), New Hampshire (NH),
conducted. Both gravity and aeromagnetic Vermont (VT), and adjacent areas.
data are in digital format for contouring (Facing Page)
T358: 6