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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 PDF

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

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

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About The ProductPublished by the American Geophysical Union as part of the Field Trip Guidebooks Series. This excursion crosses the entire exposed width of the northern Appalachian orogen, from Quebec City, Canada, south to Portland, Maine, a distance of 230 mi (370 km). Because of the great distan
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