Maine Geological Survey Neotectonics of Maine 1989

Geology of Southwestern Coastal Maine

Arthur M. Hussey II Department of Geology Bowdoin College Brunswick, Maine 04011

ABSTRACT

Southwestern Maine is underlain by 6 distinct sequences of metasedimentary and metavolcanic rocks ranging in age from Late Precambrian or Cambrian to Early Silurian. These sequences include 1) the Merrimack Group of Late Precambrian • Early Ordovician age; 2) the Casco Bay Group of Late Precambrian • Early Ordovician age; 3) the Falmouth - Brunswick sequence of Precambrian · Early Ordovician age; 4) the Kearsarge • Central Maine sequence of Early Silurian age in southwestern Maine, but ranging to Early Devonian age in the central part of the Kearsarge. Central Maine synclinorium; 5) the Cross River Formation of probable Ordovician age; and 6) the Rye Formation of Late Precambrian . Ordovician age. Rocks in the Boothbay area originally mapped as part of the Bucksport Formation are now correlated with, and mapped as part of the lithically similar Sebascodegan Formation of the Casco Bay Group (originally the Sebascodegan member of the Cushing Formation). The boundaries separating sequences 2 from 4, 2 from 3, and 2 from 5 are interpreted to be westward-dipping thrusts, and the notion of a synclinorially folded thrust originally proposed for the base of the Casco Bay Group must be abandoned. The boundary between the Rye Formation (6) and the Merrimack Group (1) is a zone of ultramylonite representing either a strike slip fault with dominantly right-lateral movement or a pseudo-wrench part ofan east-dipping thrust. The west-dipping thrusts are probably related to the Acadian orogeny of Early Devonian age. Intrusive igneous activity spans a time from Middle Ordovician to Cretaceous. Intermediate to basic plutons were intruded into the Merrimack Group in New Hampshire in middle to late Ordovician time. Large granitic plutons were intruded from Early Devonian time, immediately following Acadian deformation, to mid Car­ boniferous time. Anorogenic felsic alkalic intrusion began with the emplacement of members of the Agamenticus Complex in Late Permian time and continued on into the Cretaceous. Dike swarms, probably related to the onset of tensional rifting leading to the the formation of the Atlantic Ocean, were emplaced in Late Triassic to Early Jurassic time, and basic plutonism and associated volcanism occurred during the Cretaceous. The Cape Elizabeth, Flying Point, and Nonesuch River faults are high angle faults which represent the extension of the Norumbega fault system into southwestern Maine. These faults underwent movement from mid-Devonian to as late as Jurassic time. Principal movement on these faults occurred after Acadian metamorphism but prior to emplacement of the Carboniferous plutons. Other high angle faults are interpreted to be normal faults, most of which are apparently down-dropped to the northwest. Movement on these may correlate with time of Juro- Triassic rifting. In southwestern Maine none of these faults are major boundaries between sequences. They merely offset major thrusts which are the true boundaries. Major recumbent and upright folding and metamorphism of the Casco Bay, Falmouth · Brunswick, and Kearsarge Central Maine sequences are interpreted to be the result of the Acadian orogeny in Early Devonian time. The Merrimack Group was multiply deformed prior to the intrusion of the 473 ± 34 Ma Exeter pluton in southeastern New Hampshire during an orogenic episode prior to the time of the Taconic orogeny in western New England. Hercynian deformation and metamorphism is restricted to variably wide zones concentric to the Mississippian age Sebago and Lyman plutons.

25 A. M. Hussey II

INTRODUCTION

The purpose of this paper in a volume on neotectonics and and solved once and for all. What we likely are doing is seismicity of Coastal Maine is to provide an overview of the impressing upon the unsuspecting reader our pet biases which geological setting of southwestern Maine. The area included in too often are subsequently cited in derivative literature as fact. this review extends from Kittery on the south to Pemaquid Point In order to avoid this, the words "possibly," "probably," "may," on the east, and inland to Lewiston and Sanford (Figure 1). This and other phrases or symbols indicating uncertainty will be used area is underlain by metamorphic rocks of Late Precambrian to frequently and without apology in this discussion. Such is the Early Devonian age which have been intruded by plutonic rocks state of the art. ranging from Middle Ordovician to Mesozoic in age. Six dis­ tinct stratigraphic sequences comprise the metamorphic rocks of the study area. They are l) the Merrimack Group consisting of PREVIOUS WORK Late Precambrian - Early Ordovician easterly derived calcareous flysch; 2) the Casco Bay Group composed of felsic and mafic Katz ( 1917) conducted the first significant detailed mapping volcanic rocks, and pelitic, psammitic, and calcareous in the greater Casco Bay area, and is responsible for naming and metasedimentary rocks of Late Precambrian - Ordovician age; describing the formations of the Casco Bay Group. Fisher 3) the Falmouth - Brunswick sequence consisting of mafic and ( 1941 ) carried out original detailed and reconnaissance mapping felsic metavolcanic rocks and volcanigenic metasedimetary of the Lower Androscoggin Valley area, correlating the rocks of rocks of Late Precambrian age and originally correlated with the the Lewiston area with the fossiliferous sequence described by Cushing Formation; 4) the Kearsarge - Central Maine sequence Perkins and Smith (1925) in the Waterville area. He was the first of metamorphosed calcareous flysch, pelite, and ribbon lime­ to recognize a Silurian age for at least part of the highly metamor­ stone of Siluro-Devonian age; 5) the Cross River formation, phosed and migmatized sequence of the Lewiston area, pre­ migmatized very sulfidic and graphitic gneiss of probable Or­ viously regarded as Precambrian in age on the basis of degree of dovician age, and 6) the Rye Formation, migmatized and bias­ metamorphism (Keith, 1933). tom y loni ti zed metasediments and amphibolite of Late Precambrian - Ordovician age. This study is based on investigations by Pankiwskyj (1978a) STRATIGRAPHY and Creasy ( 1979) in the Poland quadrangle, Newberg ( 1981a,b, 1985) in the Gardiner, Vassalboro, Wiscasset and Palermo areas; Casco Bay Group Gilman ( 1977, 1978) in the Kezar Falls and Newfield quad­ rangles, Eusden ( 1984) in the Berwick quadrangle, and the writer Formations of the Casco Bay Group include, in decreasing in the Lewiston quadrangle (Hussey, 1981 a), in the greater Casco order of age, the Cushing Formation, Sebascodegan Formation, Bay - Boothbay area (Hussey, 197 la,b; 198lb,c,d, 1986, and Cape Elizabeth Formation, Spring Point Formation, Diamond work in progress), and in Southern York County (Hussey, 1962). Island Formation, Scarboro Formation, Spurwink Metalimes­ Figure 2, modified after the 1985 Bedrock Geologic Map of tone, Jewell Formation, and Macworth Formation. Lithologies Maine (Osberg et al., 1985) shows the geology as it is interpreted of these units are summarized below. Further details are given from mapping done through the 1985 field season. Several in Hussey ( 1985). problems of stratigraphic and structural interpretation exist, and The Cushing Formation is a complex and variable sequence the interpretation presented may be subject to extensive revision of quartzo-feldspathic gneisses, feldspathic sillimanite gneiss, when further detailed mapping is completed in this and adjacent amphibolite, rusty-weathering sulfidic schist, coticule, marble, areas. and well-bedded generally sulfidic manganiferous metachert. In the discussion that follows, formally defined and recog­ Rock units west of the Flying Point fault (Fig. 3) previously nized stratigraphic units will be indicated by capitalization of the assigned to the Cushing Formation appear to form a separate first letter of the lithology or stratigraphic rank (e.g., Macworth stratigraphic sequence that cannot be readily correlated on Formation, Spurwink Metalimestone). Names of stratigraphic lithologic grounds with the Cushing Formation east of the Flying units used informally pending a formal definition in accepted Point fault. These two sequences may be independent of each publications will be indicated by lower case letter for the lithol­ other, possibly having been deposited in separate lithotectonic ogy or stratigraphic rank (e.g., Cross River formation, Wilson belts. The writer (Hussey, in press) refers to the sequence west Cove member). All areal names have been cleared and reserved of the Flying Point fault informally as the Falmouth - Brunswick for future formal use. sequence and this useage is followed here. Seldom can we as field geologists formulate unequivocal The Cushing Formation crops out in anticlinal belts and answers to the problems of interpreting the complex, multi­ fault slivers southeast of the Flying Point Fault, and includes the variate systems we deal with. I feel we do a disservice in making Peaks Island, Wilson Cove, Bethel Point, Merepoint, and Yar­ positive statements that make complex problems seem simple mouth Island members (Hussey, 1985). Metavolcanic and

26 Geology of southwestern coastal Maine

...... · ......

\ Point Boothbay Harbor '-Georgetown Island Ph ippsburg ' smoll Point

r-::-:1 Keorsorge-Central Maine ~ Seq uence

~~:-; Penobscot /Benner Hill / ", Sequences

~ Cross River Forma tion

~ Cosco Boy Group

lo-::ol Falmouth- Brunswick ~ Sequence

~ Merrimack Group

• Rye For ma t ion

0---- -====----=25 ===----====::i50 Miles 0----===:::"2'i0iim--c::= =::i40 Kilometers

Figure I. Location of the discussion area, showing the principal lithotectonic sequences of southwestern Maine.

27 A. M. Hussey II

< w a: < > Cg 0 " "' 0

~ I Sl J

69' 30" + 43• 45"

N~ I

0 10 20 Miles ---==---=---=====-----=----=~===:J

°-=-=•-=-===--•'c'==----==::::030 Kilometers

Figure 2. Generalized geologic map of southwestern coastal Maine (modified after Osberg et al., 1985), and schematic cross sec­ tion of the Brunswick - Boothbay Harbor area approximately along the line A-A'.

28 Geology of southwestern coastal Maine

INTRUSIVE ROCKS

Cretaceous I Ki I Basic ring complexes Triassic I Tri I Agamenticus Complex PLUTO NS Carboniferous or younger Ci I Gabbro. syenite. ultramafics I AG- Agamenticus complex

Carboniferous Cg 12-mica granite and pegmatite AD- Alfred complex I AL- Androscoggin Lake pluton Carboniferous or older Cgbd I Foliated gabhro-diorite LD- Leeds pluton I B- Biddeford pluton

Dg 1 2-rnica granite C- Cape Neddick complex Early Devonian {I H- Hedgehog Hill pluton Dgd I Foliated granodiorite L- Lyman pluton I S- Sebago batholith SO- Saco pluton High-angle post-metamorphic fault T- Tatnic complex W- Webhannet pluton Folded thrust (teeth on upper plate)

Sedimentary or intrusive con tact

STRATIFIED ROCKS

s Rindgerncre Formation of Shapleigh Group, Ssp Sangerville Fonnation; Ssp; Patch Mountain Member. Early Silurian Q] Sangerville Fonnauon {I S I Waterville. Windham Fonnations ~s Anasagunticook Member. Sangerville Fonnation

Late Ordovician to Early Silurian ~-s_o_v_~I V:i ssalboro Fomiation

(fault contact) I Ocr I Cross River Fonnation Ordovician :=::::~ I Op IPenob scot Fonnation 1 ZObg I Berwick and Gonic Fonnations ! Precambrian-Ordovician I ZOe IEliOI Fonnation 1I ZOk IKittery Fonnarion (fault contact)

ZOm I Macwonh Fonnmion c... :i ZOcbm I Jewel. Spurwink, Scarboro. Diamond 0 Island, and Spring Point Formations ~ 0 Precambrian-Ordovician ZOce ICape Elizabeth Fonnation >- co< 0 ZOse ISeba scodegan Fonnation u Vl u< ZOc IC ushing Fonnation

(fault contact)

Precambrian-Ordovician ZOtb I Falmouth-Brunswick sequence

Precambrian -Ordovician ZOr ~-----'I Ry e Fomiation

Figure 2. Continued.

29 A. M. Hussey II metasedimentary rocks above the Bethel Point member, phyllite. At garnet grade it is principally an actinolite - biotite - originally included in the Cushing as the Sebascodegan member, chlorite - plagioclase schist. Highly stretched felsic metavol­ are raised to forrnation rank (Hussey, 1988). The Cushing For­ canic fragments and blue quartz pyroclasts, very similar to those mation exhibits the most distinctive volcanic characteristics, in the Cushing Formation, are locally abundant, and suggest a including volcanic breccia, crystal tuff texture, and very pyroclastic origin for much of the formation. In a few localities, feldspathic mineralogy, in the belt extending from South the rock is much more massive greenstone, representing mafic Portland northward through Harpswell Neck. Amphibolites flows. In the Harpswell area the Spring Point Formation consists have been interpreted variously as metamorphosed basic flows of two members (Hussey, 1971 b ): a lower mafic metavolcanic and tuffs (Hussey, 1985), impure interlayered magnesian car­ member and an upper felsic metavolcanic and volcanogenic bonate and shale (Hussey, 1971 b, 1985), and as syntectonic metasedimentary member. The lower member is mostly dark premetamorphic sills (Newberg, 1981 a; Hussey, 1985). greenish gray, thin to medium layered hornblende-garnet­ The Sebascodegan Forrnation (Hussey, 1988) consists of chlorite amphibolite with zones of dark reddish gray garnet-rich feldspathic biotite granofels with interbeds of calc-silicate gneiss quartz - plagioclase- biotite granofels (essentially coticule). The and sillimanite gneiss, with significant metavolcanic breccia and upper member consists of thin to medium-bedded liqht gray crystal tuff in its western part. It is regarded as a facies of the quartz - plagioclase - biotite granofels representing original upper part of the Cushing Forrnation. Rocks originally mapped feldspathic sandstones and felsic tuff beds. Minor lithologies as the Bucksport Formation in the Boothbay Harbor area (Fig. include thin amphibolite and chlorite schist beds representing 1) are now correlated and included with the Sebascodegan mafic tuffs prior to metamorphism. Formation on the basis 1) of lithologic similarity, and 2) that they The Diamond Island Formation is a massive black quartz - are overlain by the Cape Elizabeth Forrnation. The Cushing graphite - muscovite phyllite locally with abundant pyrite, the Forrnation is now interpreted to represent a facies proximal to an weathering of which imparts a yellow and orange staining to eruptive center lying to the west, and the Sebascodegan forma­ outcrops. Contorted paper-thin quartz veins characteristically tion to be a more distal apron of reworked volcanic detritus to occur along cleavage planes. the east. The Scarboro (this is the spelling adopted by Katz, 1917; The correlation of the Sebascodegan with the Cushing raises the official spelling of the municipality is now "Scarborough") a problem for future resolution: how do we separate the outcrop and Jewell Formations are essentially identical, consisting of belt of these rocks in southwestern Maine from the supposedly rusty- and non-rusty weathering dark gray, light gray, mottled younger (Late Ordovician to possibly Early Devonian) Buck­ greenish and purplish gray, and green phyllites, the latter repre­ sport Formation of south central Maine. It is conceivable that senting basic to intermediate tuff. At appropriate metamorphic the age of the Bucksport should be reconsidered. grade garnet is abundant, and staurolite, chloritoid, and an­ The Cape Elizabeth Formation has a variable lithology dalusite are locally common. Beds 5 to 50 cm thick of micaceous depending on the grade of metamorphism. At low grade quartzite and amphibolite are present sporadically throughout (chlorite, biotite, and garnet) it is generally a thin-bedded alter­ both forrnations. The Scarboro Forrnation includes a 5 to 20 m nation of fine-grained medium gray feldspathic and micaceous thick gray metalimestone near its base. quartzite and medium dark gray phyllite, with small garnet Separating the Scarboro and Jewell Fonnations is the Spur­ porphyroblasts at garnet grade. The quartzose beds are charac­ wink Metalimestone, a 30 to 60 m thick sequence of thin-bedded teristically finely laminated, and these laminae occasionally medium gray fine-grained metalimestone with 2 to 4 cm thick show fine-scale soft-sediment slump deformation. Minor interbeds of quartzose biotite phyllite. lithologies of the Cape Elizabeth Forrnation at low grade include The Macworth Formation consists of finely-laminated thin 20-30 cm beds of hard mica-poor or -free feldspathic quartzite and weakly bedded medium brownish gray quartzose phyllite and minor calc-silicate granofels. In the chlorite zone the more and minor rusty phyllite. Calcite is present in the southern third quartzose beds contain ankerite and calcite which gives rise to of the outcrop belt of the Fonnation; actinolite is present in the the characteristic buff weathering of these beds. At staurolite northern part, especially on Cousins Island where the Macworth grade, the more quartzose beds are quartz - plagioclase - biotite Fonnation superficially resembles the Vassalboro and Berwick (- muscovite - garnet) schist, and the more micaceous beds are Fonnations. Rare interbeds with central zones of feldspathic biotite - muscovite - garnet - staurolite schist, with minor an­ granules have been observed, and thin felsic metatuff beds are dalusite. At sillimanite grade, sillimanite is locally abundant in locally present. Above the Jewell Formation on Great the schistose beds, and at K-feldspar - sillimanite grade, the Cape Chebeague Island in Casco Bay is a unit of slightly chalky­ Elizabeth Formation is extensively migmatized and injected by weathering medium brownish gray feldspathic and calcareous pegmatites which locally contain abundant sillimanite. phyllite that is tentatively correlated with the Macworth Fonna­ The Spring Point Formation is a heterogeneous sequence of tion, thus establishing it as the highest stratigraphic unit of the metavolcanics and volcanogenic metasediments. In the Scar­ Group. It is possibly transitional to the Vassalboro Fonnation, borough area at chlorite grade the formation consists of medium or it may be equivalent to the Berwick Fonnation of the Mer­ greenish gray chlorite - garnet (manganiferous) - plagioclase rimack Group.

30 Geology of southwestern coastal Maine

Falmouth - Brunswick Sequence lithologies include biotite - quartz - plagioclase - muscovite - sillimanite schist, rusty-weathering biotite - quartz - graphite - The Falmouth - Brunswick sequence crops out in a belt muscovite schist, and impure marble. The principal lithology is between the Vassalboro Formation of the Kearsarge - Central very similar to that of the Berwick, Bucksport and Sebascodegan Maine sequence and the Flying Point fault extending from Formations. Falmouth toward the northeast beyond the map area. The se­ The Waterville Formation consists of thin-bedded biotite - quence consists of four formations, Nehumkeag Pond, Mount sillimanite - muscovite - garnet schi st, and minor calc-silicate Ararat, Torrey Hill and Richmond Comer, originally correlated granofels. In the middle of the formation is a thin metalimestone as members of the Cushing Formation, but now interpreted to member consisting of ribbony-bedded fine-grained marble with form a separate sequence. The Nehumkeag Pond formation, as thin interbeds of quartz-biotite schist, and at the base is a discon­ defined by Newberg (1981), consists of buff to slightly rusty­ tinuous thin unit of rusty-weathering quartz - muscovite - weathering fine-grained quartz - K-feldspar - plagioclase - graphite schist. Included as part of the Waterville Formation is biotite - muscovite gneiss. Minor mappable lithologies include the lithically similar and correlative Anasagunticook Member of impure marble and associated rusty weathering mica schist. The the Sangerville Formation. Mount Ararat formation consists primarily of light gray quartz - The Windham Formation, mapped only south of the Sebago plagioclase - biotite gneiss and granofels with subordinate am­ pluton, is lithically similar to the Waterville Formation with phibolite and biotite - hornblende - plagioclase granofels in beds which it is correlated. The principal lithology of the formation ranging from 1 cm up to mappable lenses 200 m thick. Minor is thin to medium-bedded muscovite - biotite - garnet - quartz - associated lithologies include rusty mica schist and homblende­ plagioclase schist with staurolite, sillimanite, or kyanite rich calc-silicate gneiss. The Torrey Hill formation consists of (Thompson and Guidotti, 1986) at the appropriate grade. This non- to poorly-bedded very sulfidic and rusty-weathering quartz is the only formation in the study area in which kyanite is part - muscovite - biotite - graphite - sillimanite schist with minor of the paragenesis. Interbedded with the schist are thin beds of sulfidic micaceous quartzite interbeds. The Richmond Comer micaceous quartzite. Toward the middle of the Windham For­ formation is a heterogeneous assemblage of mostly mation is a metalimestone member identical to that present in metasedimentary rocks including l) quartz - plagioclase - biotite the Waterville Formation. A thin discontinuous zone of fine­ - garnet granulose schist (the dominant lithology), 2) am­ grained purplish-gray quartz - plagioclase - biotite schist similar phibolite with thin calc-silicate laminae, 3) pink coticule, and 4) to the biotite granulite of the Vassalboro Formation occurs be­ rusty mica schist. The Falmouth - Brunswick sequence is no tween the pelite and metalimestone. longer correlated with the Cushing Formation on the basis I) that The Sangerville Formation is traced on the southeast limb there is no correlation of lithic sequence from one side of the of the Currier Hill syncline of the Skowhegan area (Ludman, Flying Point fault (part of the Norumbega fault system) to the 1977) across the Livermore quadrangle to the northeast corner other, 2) that the Cushing sequence east of the Flying Point fault of the Lewiston 15 ' quadrangle by Pankiwskyj et al. (1976). As lacks the thin alternations of amphibolite and felsic granofels here mapped (Figure 2), the Sangerville Formation includes typical of the Mount Ararat formation. parts of the Sabbatus, Taylor Pond, and Androscoggin Forma­ tions of Fisher ( 1941 ), the Turner Formation of Warner and Formations of the Kearsarge - Central Maine Sequence Pankiwskyj (1965), and the Patch Mountain Formation of Guidotti ( 1965). The Sangerville Formation consists of a non­ Late Ordovician to Early Silurian formations in the study to slightly rusty-weathering association of variably bedded to area comprising a cover to the pre-Silurian Falmouth - massive metamorphosed pelite and quartz wacke that, in most Brunswick sequence are the Vassalboro, Waterville, Windham, areas, is very extensively migmatized. The dominant lithology and Sangerville Formations. These formations are the lower part is quartz - plagioclase - biotite granofels and schist. Sillimanite of a conformable sedimentary sequence ranging to Early is common in the schist. In the area just north and east of Devonian age in the center of the Kearsarge - Central Maine Sabattus the formation is least migmatized and consists of thin synclinorium to the northwest of the study area. These forma­ to medium-bedded alternations of fine-grained medium gray tions are not considered part of the Merrimack Group as pre­ quartz - plagioclase - biotite granofels and medium brownish­ viously suggested by Billings ( 1956). As discussed below, the gray biotite - muscovite - sillimanite - garnet - quartz schist. Merrimack is now regarded as a separate and older sequence of Graded bedding is common here. These rocks are distinguished metasediments of pre-Silurian age (Gaudette et al., 1984). The from the Waterville Formation by the relatively thicker granofels lower part of the Rindgemere Formation of the Shapleigh Group, relative to pelite. They are very similar to the Mayflower Hill correlated with the Sangerville Formation, is included in this Formation of Osberg, ( 1968), and with the lower part of the discussion. Rindgemere Formation (Hussey, 1985) with which they are The Vassalboro Formation is a thick sequence of variably correlated. bedded medium gray quartz - plagioclase - biotite (-hornblende) The Patch Mountain Formation of Guidotti ( 1965) is now granofels and calc-silicate granofels. Minor interbedded ranked as a member of the Sangerville Formation. It consists of

31 A. M. Hussey /I

well-bedded alternations of light gray calc-silicate granofels, matite with rafts of biotite granofels and occasionally am­ dark gray quartz - plagioclase - biotite (-hornblende) granofels, phibolite. These rafts represent broken beds of lithologies resis­ and fine-grained granoblastic marble with abundant calc-silicate tent to migmatization and mobilization. The Bucksport-type minerals. In places the member consists of massive marble, and rocks, now correlated with the Sebascodegan member of the locally, thick beds of quartz - plagioclase - biotite granofels. In Cushing Formation, structurally overlie the Cross River Forma­ the area just northeast of Sabbatus where the Sangerville is tion and the contact is inferred to be a folded thrust fault. essentially unmigmatized, the Patch Mountain Member consists of thin, ribbony-bedded metalimestone very similar to the ribbon Rye Formation limestone members of both the Waterville and Windham Forma­ tions. The principal lithology of the Rye Formation on Gerrish Island, Kittery, is an association of fine-grained, mylonitized Merrimack Group dark chocolate-brown metapelite with muscovite, biotite, garnet, quartz, plagioclase, fibrolitic sillimanite, relict staurolite, and The Merrimack Group consists of the Kittery, Eliot, and occasionally relict andalusite; and mylonitized fine-grained I to Berwick Formations of southwestern Maine and adjacent New 2 cm alternations of chocolate-brown quartz - biotite - Hampshire. The group is limited in outcrop to an area southeast plagioclase gneiss and medium greenish-gray quartz - of the Nonesuch River fault, and southwest of the Casco Bay plagioclase - hornblende - biotite gneiss. Partially crushed and Group outcrop belt. rolled porphyroclasts of plagioclase and microcline up to 4 cm The Kittery Formation typically consists of a variably thin in diameter are locally abundant giving the rocks a characteristic to thick-bedded association of calcareous and feldspathic blastomylonitic fabric. Within this association are thin units of quartzite and dark gray chlorite/biotite phyllite. Graded bed­ marble, sulfidic black graphitic schist, and amphibolite. Locally ding, cross-bedding, flame structures and many other primary the main lithic association has been reduced to ultramylonite sedimentary structures are well preserved, and Rickerich ( 1983) with pseudotachylite stringers through deep-seated ductile fault­ interprets the environment of deposition of the formation to have ing (Hussey, 1980; Swanson, 1988). On Gerrish Island the rocks been that of a deep-sea turbidite fan. From a statistical analysis other than the pseudotachylite have been heavily migmatized of the orientation of small-scale cross bedding foresets, Rickerich and injected by sills of blastomylonitic granite, granodiorite and determined a general east to west sediment transport for the granite pegmatite ranging up to several meters in thickness. It turbidites of the Kittery Formation. is the regularity of these feldspathic layers that lead earlier The Eliot Formation is inferred to lie conformably above the investigators, including the writer, to interpret this sequence on Kittery Formation. It consists of thin-bedded alternations of Gerrish Island as metavolcanic. Close examination reveals that medium gray buff-weathering calcareous and ankeritic quartz­ these felsic layers occasionally cross-cut relict bedding at very mica phyUite, and dark gray phyllite. In New Hampshire, Freed­ low angles, and must be injected, not interbedded, material. man ( 1950) mapped an upper member, the Calef Member, Other than the amphibolite that may have been basaltic ash beds consisting of mostly dark graphitic phyllite. A similar lithology before metamorphism, there are no volcanics in the Rye Forma­ is present along the Mousam River (Fig. 2). tion. The Berwick Formation characteristically is an interbedded association of quartz - plagioclase - biotite - amphibole granofels and calc-silicate granofels. Cale-silicate minerals include STRATIGRAPHIC RELATIONS, AGE, AND zoisite, diopside, hornblende or actinolite, and grossularite (the CORRELA TIONS latter essentially restricted to compositionally zoned concre­ tions). Bedding thickness varies considerably, some parts of the Casco Bay Group and Falmouth - Brunswick Sequence formation being essentially massive biotite granofels. Although contacts with the underlying Eliot are not exposed, there is no The writer now regards the Casco Bay Group to be of Late indication of structural discordance between the two, and the Precambrian(?) to early Ordovician(?) age rather than Devonian contact is inferred to be conformable (Hussey, 1985). as earlier stated (Hussey, 1968). The principal basis for this reassignment is the Rb/Sr whole-rock dating (Table I) reported Cross River Formation by Brookins and Hussey (1978). Brookins and Hussey ( 1978) interpreted these ages to reflect The Cross River Formation (Hussey, 1985) is restricted in time of formation of the different units. However many workers outcrop to the cores of two doubly-plunging antiformal windows interpret such ages to reflect total or, as in this case, partial in the Boothbay area. The upper part of the formation is a resetting during a metamorphic event. Assuming that the latest non-rusty variably-bedded quartz - plagioclase - biotite - garnet metamorphism of this sequence occurred as the result of the granofels. The lower part is moderately to extremely rusty­ Acadian orogeny in Early Devonian time, these Cambro-Or­ weathering sillimanite- and graphite-bearing nebulitic mig- dovician ages suggest deposition and vulcanism sometime prior

32 Geology of southwestern coastal Maine

TABLE L RB/SR WHOLE-ROCK AGES FOR FALMOUTH­ the metavolcanic phases of the Massabesic Gneiss in New BRUNSWICK AND CASCO BAY SEQUENCES, AND PEGMATITES, Hampshire (Bothner et al., 1984), the Monson Gneiss in the PORTLAND - ORRS ISLAND AND RICHMOND AREAS. Pelham Dome in Massachusetts (Robinson et al., 1986), core gneisses and Ammonoosuc volcanic cover in the Oliverian Cushing Fonnation 481 ±40Ma* Spring Point Fonnation 539 ± 50 Ma* domes of western New Hampshire (Naylor, 1968), and pre­ Cape Elizabeth Fonnation 485 ±40 Ma* Silurian bimodal volcanics of the Miramichi anticlinorium in Scarboro Fonnation 509 ±45 Ma* western New Brunswick (Fyffe, 1982). These correlations sug­ Mount Ararat Fm., gest a Late Precambrian - Ordovician age for the Falmouth - Fal.-Bruns. seq. 494 ±25 Ma*** Foliated pegmatite 385 Ma** Brunswick sequence. Non-foliated pegmatite 375 Ma** Merrimack Group (ages after Brookins and Hussey, 1978 [*],Brookins, personal communication [**].and Gaudette et al., 1983 [***]). The Kittery Formation is in contact with the Rye Formation along a 30 to 50 m wide zone of unmetamorphosed ultramylonite (Hussey, 1980), representing a deep ductile fault zone which to the Ordovician. If not reset by Acadian metamorphism they Swanson ( 1988) interprets to have significant right-lateral strike then indicate formation in Early Ordovician time. slip movement. The contact between the Merrimack Group and The Cape Elizabeth Formation traces into the Hogback the Kearsarge - Central Maine Sequence is the Nonesuch River Schist of Perkins and Smith ( 1925) in the Palermo area of Central fault. The Berwick Formation is correlated with the Paxton and Maine, and is probably equivalent to the high grade sillimanite­ Oakdale Formations of Massachusetts, and with the Southbridge bearing migmatites of the Passagassawaukeag Gneiss of Bickel and Hebron Formations of southern Nassachusetts and Connec­ ( 1976) in the Belfast area. It is lithically similar to gray schists ticut (Barash and Pease, 198 J ). Peck ( 1976) tentatively corre­ and gneisses of Ordovician age described by Osberg and Guidot­ lates the Kittery Formation with quartzose units of the ti (1974) in the Rockland area. Low grade Cape Elizabeth Merrimack Group in the Clinton area of Massachusetts just west Formation in the Saco area is lithically identical to the Eliot of the Clinton-Newbury fault. Formation of the Merrimack Group which is regarded to be Late On a lithic basis the Berwick Formation is identical to the Precambrian - Early Ordovician in age. The principal constraint Vassalboro and Bucksport Formations, and the Sebascodegan on the age of the Eliot and other formations of the Merrimack member of the Cushing Formation. Osberg ( 1980) regards the Group is the 473 ± 37 Ma whole-rock age of the Exeter Pluton Vassalboro Formation to be of Late Ordovician to Early Silurian which intrudes the Kittery and Eliot Formations of the Group in age and hence it has been held that the Merrimack Group may southeastern New Hampshire (Gaudette et al., 1984). In view of also be of Late Ordovician to Early Silurian age. However, the these possible correlations, the age of the Cape Elizabeth For­ weight of accumulating radiometric ages of some of the plutons mation cannot be established more precisely than Late that cut the group (Exeter, and Newburyport) suggest a pre-Or­ Precambrian - Early Ordovician. dovician age for the group (Gaudette, et al., 1984; Zartman and The Cushing Formation and the upper units of the Casco Naylor, 1984). This seemingly would rule out a correlation of Bay Group (Spring Point through Jewell Formations) are un­ the Berwick and Vassalboro Formations, and reinforce the inter­ known beyond their outcrop belt. Because of the general con­ pretation that these are separate terranes unrelated in time and formability of the Cape Elizabeth Formation to these formations, space. Inasmuch as the strength of this notion of non-correlation the Cushing Formation below and the Spring Point through rests with the single radiometric age reported for each of the Jewell Formations above, the age of these formations cannot be above two plutons, it would be prudent to reserve final judge­ stated more precisely than Late Precambrian - Early Ordovician. ment of correlation or non-correlation until additional age deter­ The greater radiometric age reported by Brookins and Hussey minations are made by other methods. ( 1978) for the Scarboro and Spring Point Formations probably reflects analytical uncertainty, inasmuch as primary structures Cross River and Sebascodegan Formations clearly establish the stratigraphic sequence of these formations (Hussey, 1985). The Cross River Formation correlates either with the The Macworth Formation, based on its lithic similarity, may Penobscot Formation east of the Sennebec Lake fault (Bickel 's correlate with either the Berwick or Vassalboro Formations. Its [1976] St. George fault), or with the rusty schist of the Benner age may thus be anywhere from Late Precambrian to Late Hill sequence of Osberg and Guidotti (1974), also east of the Ordovician. Sennebec Lake fault. Fossils in the Benner Hill sequence indi­ The Falmouth - Brunswick sequence is interpreted to be a cate an Ordovician age for that sequence (Boucot et al., 1972; pre-Silurian basement terrane to the adjacent part of the Siluro­ Neuman, 1973). The Penobscot Formation is correlated with the Devonian Kearsarge-Central Maine sequence. The Mount Cookson Formation of eastern Maine (Osberg et al., 1985). Ararat Formation is lithically similar to, and may correlate with, Fossils in the Cookson indicate an early Ordovician age for the

33 A. M. Hussey II youngest part of that sequence. If the Cross River correlates with plutonic recumbent and upright folding activity of the Mer­ the Penobscot Formation its age would then be Cambrian to rimack Group discussed below. Future work must resolve this Early Ordovician. If it corelates with the Benner Hill sequence problem. its age would be Ordovician but probably not Cambrian. As indicated above, the Bucksport - like rocks in the Booth­ INTRUSIVE ROCKS bay Harbor area are now included as part of the Sebascodegan Formation which is interpreted to be a facies of the upper part of Intrusive rocks occupy approximately one third of the study the Cushing Formation and not with the type Bucksport Forma­ area, collectively representing an intrusive history spanning the tion to the north of the study area. The age of these rocks is thus time from the Early Devonian to the Cretaceous. probably Late Precambrian - Early Ordovician. The principal plutons of the area are the Sebago batholith, and the Lyman, Webhannet, Biddeford, Saco, Leeds, Lake Kearsarge - Central Maine Sequence Androscoggin, and Hedgehog Hill plutons; and the Agamen­ ticus, Cape Neddick, Alfred, and Tatnic complexes. In addition, The Kearsarge - Central Maine sequence including the many minor plutons, mostly composed of two-mica granite, Rindgemere Formation of the Shapleigh Group is in fault contact occur throughout the area, principally in the outcrop belt of the with the Merrimack and Casco Bay Groups. The Nonesuch Cape Elizabeth Formation between Bath and Georgetown. River fault separates the Shapleigh Group from the Merrimack The Biddeford pluton is composed of medium-grained non­ Group southwest of the Lyman pluton, and it juxtaposes the Cape foliated light gray biotite granite. The Webhannet pluton con­ Elizabeth Formation of the Casco Bay Group against the Vassal­ sists of three intrusive phases, foliated subporphyritic boro Formation of the Kearsarge - Central Maine sequence granodiorite, gray weakly foliated granite, and non-foliated pink northeast of the Saco pluton. The Vassalboro Formation is biotite-muscovite granite (youngest). The Lyman, Leeds, and separated from the Cape Elizabeth and Macworth Formations in minor unnamed plutons are composed of weakly foliated biotite­ the Portland area by the Flying Point fault. North of Portland the muscovite granite, locally with accessory garnet. The Sebago Falmouth - Brunswick sequence is separated from the Vassal­ batholith is composed of massive to moderately foliated biotite­ boro Formation by the Hackmatack Pond fault (Fig. 2), a west­ muscovite granite. Creasy (1979) maps and describes two dipping thrust fault. Osberg et al. ( 1985) regard the contacts phases of the batholith, an outer phase which consists of 2-mica between units of the Kearsarge - Central Maine sequence to be granite of great textural heterogeneity, and containing numerous conformable. xenoliths, and an inner phase much more homogeneous in tex­ The Sangerville Formation is correlated with the Mayflower ture and almost devoid of metasedimentary inclusions. Foliated Hill Formation of the Waterville area, the Rangeley Formation granodiorite forms the arcuate Hedgehog Hill pluton just east of of north central Maine, and lower parts of the Rindgemere Lewiston. Formation of southwestern Maine (Hussey, 1985). Graptolites Pegmatites of simple mineralogy (quartz, microcline, al bite, in the Mayflower Hill Formation (Osberg, 1968), and a shelly biotite, muscovite, garnet, and schorl) are common throughout fauna in the Rangeley Formation (Moench and Boudette, 1970) the study area in the sillimanite and sillimanite - K-feldspar both support a Late Llandovery age for these formations, hence zones of regional metamorphism, occurring as elongate pods and also the lower part of the Rindgemere and the Sangerville lenses, irregular stringers, and evenly-walled dikes. The ir­ Formations. Osberg (1980) correlates the Waterville Formation regular and concordant pegmatites tend to be foliated, and the with the Greenvale Cove Formation of north central Maine and thinner ones of these, folded. Pegmatite dikes are generally he assigns an early Silurian age for it on the basis of its position massive, unfolded, and unfoliated. Brookins (pers. comm., stratigraphically below the Sangerville, and poorly preserved I 978) reports a Middle-Devonian age for both foliated and graptolites. The Vassalboro Formation is correlated with the unfoliated pegmatites in the Falmouth - Yarmouth area (Table I). Quimby Formation of north central Maine, and is assigned an The Saco pluton is composed of strongly Iineated and weak­ age of Late Ordovician to Early Silurian. This correlation of the ly foliated diorite. Similardiorite, cut by and therefore older than Vassalboro Formation with the Quimby Formation introduces the Sebago batholith, forms a small stock at the south end of the one major problem in stratigraphic interpretation and synthesis Westbrook tongue of the batholith. The original igneous in southern Maine. As presently mapped, the Vassalboro Forma­ mineralogy of these bodies has been changed almost completely tion traces out on strike northeast into the Flume Ridge Forma­ either by regional metamorphism or deuteric alteration. tion which Ludman ( 1980) regards to be of Siluro-Devonian age. Gabbro, ultramafic rocks and syenite form an intrusive The Vassalboro is lithically identical to the Bucksport Formation complex 7 km in diameter centered around Lake Androscoggin with which it is correlated (Osberg et al., 1985). It is also in Wayne. All phases are relatively younger than the 2-mica lithically identical to the Berwick Formation, a correlation granite of the Leeds pluton and pegmatites. Noritic gabbro, originally made by the writer (Hussey, 1968) but seriously monzodiorite, and porphyritic granodiorite form the Alfred com­ questioned now in the light of Ordovician radiometric ages for plex in the town of Alfred. Noritic gabbro, quartz diorite, and the Newburyport and Exeter plutons and the extensive pre- olivine gabbro with included blocks of volcanic agglomerate

34 Geology ofsouthwestern coastal Maine

form the Tatnic complex in South Berwick, North Berwick, and rimack Group, and Kearsarge - Central Maine Sequence have Wells. In York Beach cone sheets and funnel intrusions of each been affected by two major deformations, plus several gabbro, anorthositic gabbro, and cortlandtitic gabbro comprise minor episodes. In the following discussion, however, the desig­ the Cape Neddick complex. nations F1, F2, etc. for one of the sequences neither implies nor The Agamenticus complex is a roughly circular post-tec­ denies any correlation with similar designations for another tonic plutonic ring complex composed of four intrusive phases, sequence. alkaline syenite, alkaline quartz syenite, alkaline granite, and The deformational history of the Casco Bay Group is most biotite granite (in the presumed order of injection}. Reflective clearly illustrated in the Small Point area of Phippsburg, and the of the alkaline composition of the magmas from which these shoreline exposures in Cape Elizabeth. In the Small Point area, plutons formed are such minerals as hastingsite, ferrohastingsite, F1 structures are mesoscopic-scale recumbent isoclines of un­ riebeckite, arfvedsonite, aegirine-augite, aegirine, and enig­ known facing direction and regional vergence. On Small Point, matite. fracture cleavage which is axial-planar to the recumbent folds Basic dikes, including basalt, diabase, camptonite, and has been tightly and recumbently folded. Because of the limited monchiquite, are present throughout the area in greatly varying occurrence and small scale of these structures, they have not abundances. They range in thickness from less than a centimeter been designated as F2 in the folding sequence of the Casco Bay to greater than 30 m. They are undeformed and unmetamor­ Group as a whole. F2 structures, instead, include small-scale phosed but frequently show markedly contrasting degrees of mesoscopic upright to slightly overturned asymmetric folds deuteric alteration. These dikes cut all metasedimentary units, which are congruent with macroscopic folds defined by the map pegmatites, and granitic plutons, and are younger than all other pattern of lithic units in the area. These mesoscopic structures intrusive phases except the Cape Neddick, Tatnic and Alfred generally have a folded muscovite schistosity (which may have complexes. The dikes form a swarm, locally accounting for20% been axial-planar to F1 isoclines), but locally biotite has been of the outcrop area in a relatively narrow belt that extends from recrystallized to form a schistosity parallel to axial planes of F2. southwest of the study area into the vicinity of Kennebunkport. In the Harpswell area to the west, major folds as defined by map The swarm either dies out or trends out to sea just south of the pattern (Hussey, 197lb) correlate with F2 thus establishing this mouth of the Saco River, Biddeford. Another minor swarm is as a major folding event in that area. However, in the Portland located in a crudely east-west trending belt through the city of Lewiston. These dikes individually have a general ENE trend. Table II lists radiometric ages for plutons in the study area. In the study area, biotite and biotite-muscovite granites TABLE II. RADIOMETRIC AGES OF PLUTONS lN SOlITH- (Webhannet, Biddeford, Lyman, Waldoboro,and Sebago WESTERN MAINE AND ADJACENT AREAS. plutons) yield either Devonian or Carboniferous ages. The Web­ hannet pluton gives an early Devonian age indicating intrusion Radiometric Relative Pluton Method Age (Ma) Age Source and cooling just after the peak of Acadian deformation (Gaudette et al., 1982). The Sebago, Biddeford, Lyman, and Saco Plutons Exeter pluton Rb/Sr 473 ± 37 M. Ord. (I) Ne wburyport pluton Zirc 450 ± 15 L. Ord. (2) all give Carboniferous ages which correlate with ages obtained Webhannet pluton Zirc 403 ± 13 E. Dev. (3) by Lux and Guidotti ( 1985) for metamorphic rocks north of the Webhannet pluton Rb/Sr 390±20 E. Dev. (3) Sebago batholith. The 307 Ma age for the Saco pluton is Waldoboro pluton Rb/Sr 367± 4 L. Dev. (4) perplexing in view of the strongly deformed and metamorphosed Biddeford pluton Rb/Sr 344± 12 E. Miss. (3) Sebago batholith Zirc 324± 3 L. Miss. (5) character of the pluton. Although the Nonesuch River fault cuts Lyman pluton Rb/Sr 322± 12 L. Miss. (3) centrally through the pluton, the foliation, lineation, and Saco pluton Rb/Sr 307 ± 20 M. Penn. (3) metamorphic alteration are not restricted to the fault zone, but Agamenticus complex K/Ar 228 ± 5 L. Trias. (6) Basic dikes are pervasive throughout. This led the writer to regard the Saco dolerite K/Ar 200± 9 Juras. (7) pluton as a syn-Acadian intrusive older than the granite plutons dolerite K/Ar 19 1± 10 Juras. (7) of southwestern Maine. The anomalously young age of the Saco dolerite K/Ar 184± 8 Juras. (7) pluton may possibly represent resetting of the origional syn­ camptonite K/Ar 124± 6 Crct. (7) Tatnic complex, gabbro K/Ar 122± 2 Crct. (6) Acadian age by thermal effects of the intrusion of the Lyman Alfred complex, gabbro K/Ar 120± 2 Cret. (6) pluton. Cape Neddick complex. gabbro K/Ar 116 ± 2 Cret. (6)

STRUCTURE Sources: ( l ) Gaudenect al. ( 1984) (2) Zartman and Naylor ( 1984) Folds (3) Gaudene ct al. ( 1982) (4) Knight and Gaudcnc (1987) (5) Aleinikoff et al. ( 1985) All of the stratified rocks of the southwestern Maine area (6) Foland and Faul ( 1977) have been multiply deformed. The Casco Bay Group, Mer- (7) McHone and Trygstad ( 1982)

35 A. M. Hussey II

- Cape Elizabeth area (Hussey, 1971 b, 1982) bedding and schis­ northwest trend (seen only to the west of the discussion area), tosi ty are locally flatlying or gently and openly folded, and thus, probably related to the intrusion of the Sebago batholith. locally, F1 folds have not been significantly developed. In the In the Boothbay area, minor recumbent F1 folds are indi­ Orrs Island area, F3 and F4 are minor crenulations of earlier cated by the distribution of a thin amphibolite unit within the lineation and schistosity, and Fs are steeply dipping kink bands Cape Elizabeth Formation of that area. F1 folds which control with consistent left-lateral kinking sense. the major map distribution of the formations are upright to In the Cape Elizabeth area, the Cape Elizabeth Formation slightly overturned folds, with which most of the observed tight preserves F1 parasitic mesoscopic east-facing and -verging to nearly isoclinal mesoscopic-scale folds are associated. These recumbent isoclines, and mesoscopic upright to slightly over­ F1 folds correlate with the F1 folds of the Bath - Brunswick - turned folds correlated with F2. The latter deform both upward Portland area. and downward-facing bedding sequences suggesting the presence of both upright and inverted limbs of F1 recumbent folds. Faults The Merrimack Group is deformed by three major fold sequences, best seen along the Ogunquit-York shoreline ex­ The major faults of the study area are shown in Figures 2 posures of the Kittery Formation in the southern part of the and 3. The names of the post-metamorphic faults are given in discussion area (Hussey et al., 1984). Ft folds are south to Figure 3. southeast-facing, northwest-verging isoclines probably parasitic Thrust Faults. The contact between the Vassalboro Forma­ to much larger recumbent folds. F1 folds are upright to slightly tion and Falmouth - Brunswick sequence from Falmouth overturned open to tight folds with frequent plunge reversals. F3 northward is the Hackmatack Pond fault of Pankiwskyj (1978b). folds are relatively open, overturned, generally dextral fold sets It is interpreted to be a westward-dipping thrust fault on the basis with well-developed strain-slip cleavage parallel to F3 axial of the USGS Quebec - Western Maine Seismic Reflection Profile planes. Major F1 folds determine the distribution of the Kittery to the northeast of the study area (Stewart et al., 1986). In the and Eliot Formations in southwestern Maine. Macroscopic F1 study area, this fault has been strongly folded (probably during fold hinges have not yet been mapped in the Merrimack Group. the event that produced F3 folds during migmatization). This In the Kearsarge - Central Maine Sequence northeast of the folding has resulted in a southeasterly dip of bedding, foliation, Sebago Lake Batholith, F1 folds are large-scale east-facing, and schistosity nearthe Portland-Brunswick segment of the fault west-verging recumbent isoclines (Osberg et al., 1985). These (Fig. 2). A second west-dipping reflector east of this appears to are refolded by large-scale upright to moderately overturned F1 coincide with the Beech Pond fault of Newberg ( 1985) which folds which are largely responsible for the map pattern. F3 folds the writer interprets to be a thrust fault contact between the are small mesoscopic- to macroscopic-scale reclined to strongly Falmouth - Brunswick sequence and the Cape Elizabeth Forma­ overturned isoclines with north- to northwest-trending axial tion. The contact between the Sebascodegan member of the planes. These folds deform bedding, axial planes, axial-plane Cushing Formation of the Boothbay Harbor area and Cross River cleavage of F1, migmatite stringers, and thin concordant peg­ Formation is interpreted to be a third major thrust along which matite lenses. They are restricted to the northeast margins of the rocks of the Casco Bay sequence have overridden the Penobscot Sebago batholith, and the Lyman pluton (Hussey et al., 1986). or Benner Hill sequences. This fault is indicated by a well­ The zone of F3 folds northeast of the Sebago batholith are what defined west-dipping reflector on the seismic line suggesting that the writer referred to as the "Lewiston Fold Domain" (Hussey, in that area, the fault is unaffected by F1 folds. However, in the 1981 a). These folds are probably related to migmatization as­ Boothbay area this fault is clearly folded, and is exposed in two sociated with the injection of the Sebago batholith, and to force­ doubly-plunging antiforms. The boundary between the Sebas­ ful intrusion of the Lyman pluton. codegan Formation and the Benner Hill and Penobscot sequen­ Southeast of the Sebago batholith and structurally below it, ces to the east is an easterly dipping thrust originally named the metasediments show very little development of folds correlative St. George Fault by Bickel ( 1976). However, because this name with F3 and migmatite until the outcrop belt of the Rindgemere is preempted for a major fault in coastal New Brunswick, this Formation is encountered at the west edge of the discussion area. fault is here renamed the Sennebec Lake fault after Sennebec In the Rindgemere Formation, particularly in the Kezar Falls Lake which lies along the fault trace. This fault is clearly area (Gilman, 1977), migmatization becomes very extensive, indicated on the USGS seismic reflection line (Stewart et al., and deformation is chaotic, seldom with distinction of the dif­ 1986). ferent fold sequences seen northeast of the Sebago batholith. In It is clear from the foregoing discussion that the earlier the area southeast of Sanford, Eusden et al. (1987) describe a interpretation of the Casco Bay Group as klippe bounded by major northwest-facing, southeast verging recumbent F1 fold, single synclinorially folded thrust fault (Hussey, 1985, Osberg the Blue Hills Nappe, which has been refolded by overturned et al., 1985) must be abandoned. southeast-verging F1 folds which largely control the map pattern. The contact between the Vassalboro and Rindgemere For­ F3 is a major deflection of F1 fold axes from a northeast to a mations southwest of Sebago Lake is inferred to be a folded

36 Geology ofsouthwestern coastal Maine

thrust on the basis of differences in relative ages of the sequences accretion. Splays related to the Flying Point fault can be seen in on either side of the contact. shoreline exposures on the west side of Flying Point in Freeport. High-Angle Post-Metamorphic Faults. The writer has Here rocks of the Cushing Formation have been brecciated, and mapped northeast-trending post-metamorphic faults extending the foliation contorted and cut by numerous slickensided sur­ through the Greater Casco Bay area (Hussey, 1971 a,b; faces. Slickensides are generally steep, indicating that the latest 1981 b,c,d). Three of these, the Flying Point, Cape Elizabeth, movement was nearly dip slip. and Nonesuch River faults (Fig. 3) are correlated with the Evidence for the South Portland fault is the omission of units Norumbega fault of Stewart and Wones (1974). These faults of the Casco Bay Group from South Portland to Great Chebeague appear to involve a moderate amount (up to 30 km) of left-lateral Island. This is probably a normal fault down-dropped on the slip and minor dip slip (Hussey, 1985). A fourth fault, the Back northwest side. The amount of slip probably does not exceed a River fault (Fig. 3) with apparent left-lateral slip of approximate­ few hundred meters. ly 1.5 km may be an independent fault or it may be part of the The Cape Elizabeth fault has been traced by Hussey Norumbega system. Other post-metamorphic faults are inter­ (197la,b) and Newberg (1981) from the Old Orchard Beach area preted to be nonnal faults, commonly downdropped to the to and beyond Dresden. Pankiwskyj (1978b) has traced this fault northwest. to the northeast into the Norumbega fault of Stewart and Wones The Nonesuch River fault has been traced southwestward (1974), and it may merge with the Flying Point fault north of the into New Hampshire (Hussey and Newberg, 1978) where it joins discussion area. The Cape Elizabeth Fault is well-exposed in a with the Campbell Hill fault of Lyons et al. (1982). Evidence one-kilometer wide zone along the shoreline of Ram Island Farm defining the Nonesuch River fault is as follows: in Cape Elizabeth. Here exposures of the Cape Elizabeth For­ 1) Juxtaposition of the Vassalboro and Cape Elizabeth mation show numerous variably-oriented high-angle faults that Formations in the Saco-Portland area. are locally filled with breccia or gouge. The zone includes a 2) The marked topographic lineament fonned by the Non­ low-angle, west-dipping thrust fault of unknown but potentially esuch River, the Presumpscot River northeast of Westbrook, and significant throw. The major break of the Cape Elizabeth fault the short northeast course of the Saco River in the outcrop belt at Ram Island Fann is occupied by a 5 to I 0 m-thick vein of of the Saco pluton. milky quartz traceable approximately 2 km to the northeast, and 3) Truncation of metamorphic isograds in the Cape along which different members of the Cushing Formation are Elizabeth Fonnation, resulting in the juxtaposition of staurolite­ juxtaposed against the Cape Elizabeth Formation. In the area of grade Vassalboro Formation against chlorite to garnet-grade Harpswell Neck, Harpswell, the offset of the Cape Elizabeth­ Cape Elizabeth. Cushing contact, and the sillimanite-andalusite metamorphic 4) Structural contortion and quartz veining (locally drusy) isograd suggest possible left-lateral slip movement of 4 to 5 km, in the Nonesuch River bed south of Gorham. but this may also be significantly less if there is a major com­ Although positive evidence for the continuation of the fault ponent of dip-slip and if the overall dips of the formational northeast of Yarmouth is lacking, it may possibly extend north­ contacts and the isograd are gentle. east to join the Pleasant Pond fault of Newberg ( 198 la). The Back River fault follows Back River south of Wiscasset. The Flying Point fault is traced from its junction with the It is indicated by I ) the Back River lineament, 2) offset of a Nonesuch River fault south of Gorham, through Brunswick to granite orthogneiss and a thin amphibolite unit in the Cape the Richmond area from whence it may extend well beyond the Elizabeth Fonnation, and 3) strong retrograding of biotite to discussion area to join with the main break of the Norumbega chlorite close to the Back River lineament. Left-lateral strike fault to the northeast. In the Portland area this fault juxtaposes slip motion of 1.5 km is suggested by the pattern of offset of the non-migmatized greenschist facies to low amphibolite facies amphibolite and orthogneiss. Macworth and Cape Elizabeth Formations on the southeast The Phippsburg fault has been mapped between Small Point against pegmatite-injected, migmatized upper amphibolite and Phippsburg. Althouqh net movement along the fault must facies Falmouth - Brunswick sequence and Vassalboro Fonna­ be very minor, the lineament it forms is very conspicuous. The tion on the northwest. Rocks of the Casco Bay Group of similar epicenter of the April 1979 earthquake is nearly on strike with grade and degree of migrnatization southeast of the fault are this lineament. In addition, exposures of the Cape Elizabeth found only northeast of Merrymeeting Bay between Bowdoin­ Formation along State Highway 127 just east of Bath show ham and Bath. If movement were strictly horizontal along this extensive slickensiding on strike with the lineament (J. Rand, fault, this would suggest a displacement in excess of 50 km pers. comm.). assuming that all sequences were metamorphosed at the same The Cousins Island fault is inferred to form the eastern time, during the Acadian orogeny. Net movement might be contact of the Macworth Formation. This is postulated on the considerably less if l) net movement includes a significant basis that Casco Bay Group metapelites are at higher metamor­ component of dip slip, and 2) metamorphic isograd surfaces and phic grade to the east than the rocks of the Macworth Formation, migmatite fronts are very gently dipping, or if different terranes and that the Macworth Formation truncates regional metamor­ were independently metamorphosed at different times prior to phic isograds of these metapelites.

37 A. M. Hussey II

Hussey (l981a) and Newberg (1981a) map a high-angle The distribution of epicenters shows little relationship to fault extending along the linear lowland just west of Oak Hill in major faults, except for an apparent cluster of older events the Sabattus - Litchfield area. This fault, here named the Max­ between the Nonesuch River and Flying Point faults. More well Swamp fault, is indicated by both the topographic lineament recent events form linear arrays of epicenters, generally norther­ and by the omission of the Waterville Formation between the ly-treading, in the Lewiston area and just east of Sebago Lake. Sangerville and Vassalboro Formations just east of Sabattus. The Sebago Lake cluster is located within the limits of the In the Hebron area of the Poland Quadrangle Creasy (1979) Sebago batholith. The cluster near Lewiston extends from the maps a northeast-trending normal fault which he names the Ben edge of the Leeds pluton southward through the complexly Barrows fault. The fault is documented on the basis of offset of folded belt of the Sangerville Formation, almost to the Sebago lithic contacts, and silicified and sheared zones within the pluton. These two belts do not coincide with any mapped faults. granites of the Sebago batholith. He interprets the Ben Barrows It is noteworthy that recent events are concentrated mostly in fault to be a post-metamorphic normal fault downdropped to the the area northwest of a line extending from Waterville to the northwest and having a dip-slip movement of 1-2 km. southern end of Sebago Lake. Relatively few recent events are Twelve kilometers northwest of the Ben Barrows fault, found southeast of that line. The area northwest of that line Guidotti ( 1965) defined the Moll Ockett fault. It has a trend approximately coincides with the area of Central Maine Gravity parallel to the Ben Barrows fault and is recognized on the basis gradient (Kane and Bromery, 1966). of l) a sharp topographic break; 2) sharp lithic and stratigraphic contrasts on either side of the fault; 3) contrasting structural styles and patterns; 4) presence ofbreccia at several places along METAMORPHISM the fault trace; and strong retrograde metamorphism. Guidotti regards the fault as a normal fault dipping 60 to 80 degrees to the The stratified rocks of the discussion area have been northwest and down-dropped to the northwest. metamorphosed to a low-pressure-intermediate (Buchan type) Several minor unnamed faults are shown in Fig. 2. Many facies series from lower greenschist facies to upper amphibolite of these are silicified zones for which offset cannot be facies. Pelitic rocks are characterized at intermediate grade by demonstrated. Many minor northwest trending faults in the the presence of andalusite, cordierite, and staurolite, the latter Harpswell area are parallel to left-lateral kink bands (Fs) and overlapping the stability field of sillimanite. The presence of may represent situations where deformation has exceeded the kyanite in the Gorham-Gray area suggests a higher pressure limits of kinking and passed into minor left-lateral strike-slip metamorphism there. Thomson and Guidotti (1986) postulate faults. Several intraformational bed-parallel gouge zones, brec­ that the metamorphism that produced the kyanite occurred below cia zones, slickensided surfaces, and silicified zones have been the base of the sheetlike Sebago batholith. Subsequent regional observed in the discussion area, particularly along coastal ex­ tilting and differential erosion has exposed these deeper levels. posures, but are too small to be represented on Figure 2. Of Peli tic rocks of the Small Point area, now at andalusite and notable mention is the concentration of faults along the shore at sillimanite grades of metamorphism, preserve 2 to 4 cm long the southwest end of Harpswell Neck. Here faults of unknown pseudomorphs of muscovite after chiastolite, suggesting an ear­ throw and regional extent are indicated by intraformational lier intermediate-grade metamorphic event. bed-parallel breccia, a silicified and pyritized zone up to 10 m Retrograde metamorphism has variably affected the entire wide, and several northwest trending faults related to kinking. area, and is generally expressed in the partial to complete Throughout the study area, minor indentations in the chloritization of biotite and sometimes garnet. Chloritization is shoreline often can be shown to be related to minor brittle particularly strong in the vicinity of high-angle post-metamor­ faulting where gouge or loosely cemented breccia has been phic faults, suggesting a genetic relationship between faulting removed by wave action. and retrograding.

TIME OF DEFORMATION AND METAMORPHISM SEISMICITY Deformation resulting in Ft and F2 folds of the Kearsarge Figure 3 shows the locations of earthquake epicenters be­ Central Maine Sequence is clearly the result of the Acadian tween the years 1776 and 1986 (after Chiburis, 1981 ; and orogeny of Early Devonian time. These folds affect rocks of Johnston and Foley, 1987). Older epicenters are indicated by Late Ordovician and early Silurian age which are, in a broader open circles. Younger epicenters, shown by the black-filled regional basis, part of a conformable sequence of strata ranging circles, are those for which Richter values are given, and for up to early Devonian age (Osberg et al., 1985). F3 folds of this which epicenters have been determined instrumentally. Loca­ sequence are restricted to the areas on the northeast margins of tions of older epicenters are those determined by felt effects, the Carboniferous age Lyman and Sebago plutons (Hussey, mostly reported in newspaper accounts, and are subject to con­ 1986). On the east side of the Lyman pluton the F3 folds are siderable error in location. mjnor folds with biotite schistosity and axial planes parallel to

38 Geology of southwestern coastal Maine

70°00' I •

1 I • 0 1 44°30 • • 44°30 • Oe r 1 • 0 0 •• ~I 0 • II • 0• 0 • • ~, LLJ - :;; ~ ~

1 44°00 r- 1 I I 0 ....Cl) I 0 I I I

I 0

1. Mol I Ockett Foult • 2. Ben Barrows Fault 3. Maxwell Swam p Fault 4 . Nonesuch River Fault 5. Flying Point Fault 6 . South Portland Fault 0 • 7 . Cape El izabeth Fault 8 . Phippsburg Fault 9. Bock River Fault I • 10. Cousins Island Fault I \ • • Oillll•C= ::::Jl••IE5= :::J••c:::::::J30 Mi les 0-==--==-- 20 ==::J40 Kilometers

A town locat ions e recent epicenters; instrumentally determined 0 older epicenters; general location

Figure 3. Locations of earthquake epicenters ( 1776- 1986) and post-metamorphic faults in southwestern coastal Maine. Earthquake data from Chiburis (1981) and Johnston and Foley ( 1987).

39 A. M. Hussey II the contacts with the pluton. The schistosity which is nearly at Similarly the post-metamorphic Cape Elizabeth fault appears to right angles to the axial planes of F2 folds dies out within a follow a topographic lineament in the Biddeford p1uton, but kilometer of the pluton. Clearly, the F3 folds here are related to again, the Biddeford-Berwick contact is not offset appreciably. the forceful intrusion of the Lyman pluton. Similarly, the larger­ Major motion for this fault must then have predated Car­ scale northwest to north trending F3 folds northeast of the Sebago boniferous time. Other faults in the study area that involve batholith are interpreted to be structural effects related to the normal movement with downdropping to the northwest are the emplacement of that pluton. F3 folds in both localities thus are Ben Barrows and Moll Ockett faults. This normal faulting of Carboniferous age and only locally developed around the postdates the Carboniferous Sebago pluton and speculatively is upper contacts of the plutons and their country rock. correlated with Late Triassic rifting in other parts of the Ap­ The time ofF1 and F2 deformation of the Merrimack Group palachians. was pre-Middle Ordovician if the radiometric age of the Exeter pluton is correct. According to Gaudette et al. (1984) the Exeter pluton postectonically intrudes the Kittery and Eliot Formations ACKNOWLEDGMENTS and has resulted in a contact metamorphism that overprints an earlier low-grade regional metamorphism. The time ofF3 defor­ I am deeply indebted to the former State Geologists of the mation is unknown. Maine Geological Survey, John Rand and Robert Doyle, and the The deformation of the Casco Bay Group may have oc­ present State Geologist, Walter Anderson, under whose curred during a pre-Silurian event, or at the same time as the guidance, encouragement, and financial support my field work Kearsarge - Central Maine Sequence, during the Acadian has been accomplished over the past 30 years. I gratefully orogeny in Early Devonian time. The answer to this question in acknowledge the critical comments and suggestions made by part may lie in the association of a metamorphic event with the many colleagues on field trips and in conferences, especially development of F2 folds as described below. Philip Osberg, Charles Guidotti, Gary Boone, Allan Ludman, Metamorphism of the Kearsarge - Central Maine sequence Donald Newberg, David Stewart, Wallace Bothner, the late is a result of the Acadian orogeny except 1) the high-grade zone David Wones, James Skehan, Olcott Gates, Peter Gromet, and northeast of the Sebago batholith for which Lux and Guidotti Norman Hatch. I thank Olcott Gates and Wallace Bothner for ( 1985) report a Carboniferous age of metamorphism, 2) the their valued critical comments on an earlier draft of this paper. Gray/Gorham area southwest of the Sebago batholith, which Thomson and Guidotti (1986) interpret to be related to emplace­ ment of the Sebago batholith, and 3) the zone of reoriented biotite schistosity on the east side of the Lyman pluton. These three REFERENCES CITED areas are essentially zones of metamorphism and migmatization spatially related to the contact areas of the Carboniferous Aleinikoff, J. N., Moench, R. C., and Lyons, J.B., 1985, Carboniferous U/Pb age plutons. of the Sebago batholith, southwestern Maine: Metamorphic and tectonic There appears to be no metamorphic discontinuity in the implications: Geo!. Soc. Am. Bull., v. %, p. 990-996. metamorphism of the Kearsarge - Central Maine Sequence, and Barosh, P., and Pease, M. H., Jr., 1981, Correlation of the Oakdale and Paxton the Casco Bay Group (except across the post-metamorphic Non­ Formations with their equivalents from eastern Connecticut to southern Maine: Geol. Soc. Am., Abstracts with Programs, v. 13, n. 3, p. 122. esuch River Fault). This suggests that the present prograde Bickel, C. E., 1976, Stratigraphy of the Belfast quadrangle, Maine: Geol. Soc. mineral assemblage developed during the Acadian orogeny. A Am., Mem. 148, p. 97- 108. well-developed biotite schistosity is associated with the F2 folds Billings, M. P., 1956, The Geology of New Hampshire, Pt. 2, Bedrock Geology of the Cape Elizabeth Formation suggesting that the folds of New Hampshire: New Hampshire State Planning and Development Commission, Concord, N.H., 203 p. developed during the Acadian orogeny also. The earlier Bothner, W. A., Boude1te, E. L., Fagan, T . J., Gaudette, H. E., Laird, J., and metamorphism particularly as indicated by muscovite pseudo­ Olszewski, W. J., Jr., 1984, Geologic framework of the Massabesic morphs in the Small Point area may be related to an early phase Anticlinorium and the Merrimack Trough, southeastern New Hampshire, of metamorphism in the Acadian orogeny or to an earlier in Hanson, L. S., ed., Geology of the Coastal Lowlands, Boston, Mass., to Kennebunk, Maine: Guidebook, New England Intercollegiate orogeny. Geological Conference, Salem State College, Salem, Mass., 1984, p. Major thrust faults and folded thrusts formed during the 186-206. Acadian orogeny. The post-metamorphic Nonesuch River fault Boucot, A. J., Brookins, D. G., Forbes, W., and Guidotti, C. V., 1972, Staurolite­ underwent principal movement, maybe strike slip, prior to zone Caradoc (Middle-Late Ordovician) age Old World province brachiopods from Penobscot Bay, Maine: Geol. Soc. Am. Bull., v. 83, emplacement of the Lyman and Saco plutons whose contacts p. 1953-1960. with their country rock have not been appreciably offset. Reac­ Brookins, D. G., and Hussey, A. M., II, 1978, Rb-Sr ages for the Casco Bay tivation of the fault after emplacement of the plutons is suggested Group and other rocks from the Portland - Orrs Island area, Maine: Geol. by the topographic lineaments within the plutons (Hussey and Soc. Am., Abstracts with Programs, v. 10, n. 2, p. 34. Chiburis, E. F., 1981, Seismicity, recurrence rates, and regionalization of the Newberg, 1978). This later movement, probably normal, was northeastern United States and adjacent southeastern Canada: Dept. not of sufficient magnitude to offset the contacts significantly. Geology and Geophysics, Weston Observatory, Boston College, 76 p.

40 Geology of southwestern coastal Maine

Creasy. J. W., 1979, Report and preliminary geologic map of the Poland 15' Hussey, A. M., 11, 1986, Stratigraphic and structural relationships between the quadrangle, Maine: Maine Geol. Surv., Open-File Report No. 79-15, Cushing, Cape Elizabeth, Bucksport, and Cross River Formations, 18 p. Portland - Boothbay area, Maine, in Newberg, D. W., ed., Guidebook for Eusden, J. D., 1984, The bedrock geology of part of the Alton, New Hampshire, field trips, New England Intercollegiate Geological Conference, 1986, p. and Berwick, Maine, 15' quadrangles: M.S. thesis, Univ. of New 164-183. Hampshire, 114 p. Hussey, A. M., II, 1988. Lithotectonic stratigraphy, deformation, plutonism. and Eusden, J. D .. Bothner. W. A., and Hussey, A. M., II, 1987. The Kearsarge - metamorphism, Greater Casco Bay region, southwestern Maine, in Tuck­ Central Maine synclinorium of southeastern New Hampshire and south­ er, R. D .. and Marvinney, R. G., eds., Studies in Maine geology. Volume western Maine: stratigraphic and structural relations of an inverted I - Structure and Stratigraphy: Maine Geol. Surv., p. 17-34. section: Am. J. Sci., v. 287, p. 242-264. Hussey, A. M., II , and Newberg, D. W ., 1978, Major faulting in the Merrimack Fisher. L. W., 194 1, Structure and metamorphism of the Lewiston, Maine, Synclinorium between Hollis, New Hampshire, and Biddeford, Maine: region: Geol. Soc. Am. Bull., v. 52, p. 107 -159. Geol. Soc. Am., Abstracts with Programs. v. 10, n. 2, p. 48. Foland, K. A., and Faul, H., 1977, Ages of the White Mountain intrusives. New Hussey, A. M., II, Rickerich, S. F., and Bothner, W. A .. 1984, Sedimentology Hampshire, Maine, and Vermont, USA: Am. J. Sci., v. 277, p. 888-904. and multiple deformation of the Kittery Formation, southwestern Maine Freedman, J., 1950, Stratigraphy and structure of the Mount Pawtuckaway and southeastern New Hampshire, in Hanson, L. S .. ed., Geology of the quadrangle, southeastern New Hampshire: Geo!. Soc. Am. Bull., v. 61. Coastal Lowlands, Boston. Mass., to Kennebunk, Maine: Guidebook, p.449-492. New England Intercollegiate Geological Conference, Salem, Mass., p. Fyffe, L. R., 1982, Taconian and Acadian structural trends in central and northern 47-60. New Brunswick: Geol. Assoc. Canada, Sp. Paper 22, p. 117-130. Hussey, A. M., II, Bothner, W. A., and Thomson, J. A., 1986, Geological Gaudette, H. E., Kovach, A., and Hussey, A. M .. JI, 1982, Ages of some intrusive comparisons across the Norumbega Fault Zone, southwestern Maine, in rocks. southwestern Maine, USA: Canad. J. Earth Sci., v. 19, p. 1350- Newberg, D. S .. ed., Guidebook for field trips in southwestern Maine: 1357. New England Intercollegiate Geological Conference, p. 53-79 Gaudette, H. E., Olszewski, W. J., Jr., and Cheatham, M. M., 1983, Rb/Sr whole Johnston, R. A., and Foley, M. E., 1987, Earthquakes in Maine, October 1975- rock ages of gneisses from the Liberty-Orrington anticline, Maine, the December 1986: Maine Geological Survey, I :500,000-scale map. oldest (?) basement complex of the eastern margin, northern Ap­ Kane, M. F., and Bromery, R. W. 1966, Simple Bouger gravity map of Maine: palachians: Geol. Soc. Am., Abstracts with Programs, v. 15, p. 579. U.S. Geo!. Surv. Geophys. Inv. Map GP-580, scale I :500,000. Gaudette, H. E., Bothner, W. A., Laird, J .. Oslzewski. W. J., and Cheetham, M. Katz, F. J .. 19 17. Stratigraphy in southwestern Maine and southeastern New­ M., 1984, Late Precambrian/Early Paleozoic deformation and metamor­ Harnpshire: U.S. Geo!. Surv., Prof. Paper 108. p. 165-177. phism in southeastern New Hampshire -- confirmation of an exotic Keith, A., 1933, Preliminary geologic map of Maine: Maine Geological Survey. terrane: Geol. Soc. Am., Abstracts with Programs, v. 16, p. 516. Knight, D.R., and Gaudette, H. E., 1987, Rb-Sr age of the Waldoboro two-mica Gilman, R. A., 1977, Geologic map of the Kezar Falls 15' quadrangle, Maine: granite, coastal Maine: Geol. Soc. Am .. Abstracts with Programs, v. 19, Maine Geo!. Surv., Geol. Map Ser. GM-4. p. 23. Gilman, R. A., 1978, Bedrock geology of the Newfield 15' quadrangle, Maine: Ludman, A., 1977. Geologic map of the Skowhegan 15' quadrangle, Maine: Maine Geol. Surv .. Open-File Report No. 78-10, 20 p. Maine Geol. Surv., Geol. Map Series, GM-5. Guidotti, C. V .. 1965. Geology of the Bryant Pond quadrangle, Maine: Maine Ludman, A., 1980, Report of mapping progress - 1980 - Danforth, Forest, Geol. Surv .. Bull. 16, 116 p. Scraggly Lake, and Waite quadrangles, Eastern Maine: Maine Geol. Hussey, A. M.. II. 1962, The geology of southern York County, Maine: Maine Surv .. Open-File Report No. 80-13, 16 p. Geol. Surv., Bull. 14, 67 p. Lux, D. R., and Guidotti. C. V., 1985, Evidence for extensive Hercynian Hussey, A. M., II, 1968, Stratigraphy and structure of southwestern Maine, in metamorphism in western Maine: Geology. v. 13, p. 696-700. Zen, E-An e t al.. eds., Studies of Appalachian Geology, Northern and Lyons, J.B., Baudette, E. L., and Ale inikoff, J. N. , 1982, The Avalonian and Maritimes: New York, Wiley, p. 291 -301. Gander zones in central New England: Canad. Jour. Earth Sci., Spec. Hussey. A. M., II, 197 la, Geologic map of the Portland 15' quadrangle. Maine: Paper 24, p. 43-66. Maine Geol. Surv., Geol. Map Ser. GM- I. McHone, J. G., and Trygstad, J.C., 1982, Mesozoic mafic dikes of southern Hussey, A. M .. 11, 197lb, Geologic map and cross sections of the Orrs Island Maine: Geol. Soc. Maine, Bull. 2, Shorter contributions to the geology 7.5' quadrangle and adjacent area, Maine: Maine Geol. Surv., Geol. Map of Maine. p. 16-32. Ser.GM-2. Moench, R.H., and Boudette, E. L., 1970, Stratigraphy of the northwest limb of Hussey, A. M., II. 1980, The Rye Formation of Gerrish Island, Kittery. Maine: the Merrimack synclinorium in the Kennebago Lake, Rangeley. and a reinterpretation: The Maine Geologist (newsletter of the Geol. Soc. of Phillips quadrangles, western Maine, in Boone, G. M., ed., Guidebook Maine), v. 7, n. 2, p. 2-3. for fie ld trips in the Rangeley Lakes - Dead River basin region, western Hussey, A. M., 11, 1981a, Preliminary description of the geology of the Lewiston Maine: 62nd New England Intercollegiate Geological Conference, p. D 15 ' quadrangle. Maine: in Thompson, W. B .. ed., New England Seis­ 1-12. motectonic Study Activities in Maine, Fiscal Year 1980. Maine Geol. Naylor, R. S., 1968, Origin and relationships of the core rocks of the Oliverian Surv., p. 48-59. domes, in Zen, E-An, et al., eds., Studies of Appalachian Geology, Hussey, A. M .. JI , 1981b , Reconnaissance bedrock geology of the Casco Bay 15 · Northern and Maritimes: Wiley - lmerscience, New York, p. 231-240. quadrangle, Maine: Maine Geo!. Surv., Open-File Report No. 81-31. Neuman, R. B .. 1973, Staurolite-zone Caradoc (Middle-Late Ordovician) age Hussey, A. M., II, 198lc. Reconnaissance bedrock geology of a pan of the Old World province brachiopods from Penobscot Bay, Maine: Discus­ Freeport 15' quadrangle, Maine: Maine Geol. Surv., Open-File Report sion: Geol. Soc. Am. Bull., v. 84, p. 1829-1830. No. 8 1-30. Newberg, D. W. , 198la. Bedrock geology and structure of the Gardiner 15' Hussey, A. M., II, 198 Id. Bedrock geology of the Bath 15' quadrangle, Maine: quadrangle: Maine Geol. Surv., New England Seismoteetonic Studies Maine Geol. Surv .. Open-File Report No. 81-32. Activities in Maine during FY 198 1, p. 57-66. Hussey, A. M., II, 1982, The geology of the Two Lights and Crescent Beach Newberg, D. W., 1981 b, Bedrock geology and structure of parts of the Vassal­ State Parks area. Cape Elizabeth, Maine: Maine Geo!. Surv .. Bull. 26. boro and Wiscasset 15' quadrangles: Maine Geol. Surv., New England 34 p. 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41 A. M. Hussey II

Osberg, P.H., 1968, Stratigraphy, structural geology, and metamorphism in the Robinson, P., Tracy, R. J., Hollocher, K. T., Schumacher, J.C., and Berry, H. Waterville-Vassalboro area, Maine: Maine Geo!. Surv., Bull. 20, 64 p. N., IV, 1986, The central Massachusetts metamorphic high, in Robinson, Osberg, P. H., 1980, Stratigraphic and structural relations in the turbidite se­ P., and Elbert, D. C., eds., Regional Metamorphism and Metamorphic quence of south central Maine, in Roy, D. C., ed., Guidebook for field Phase Relations in Northwestern and Central New England, Guidebook, trips, New England Intercollegiate Geological Conference: Presque Isle, Trip B-5, 14th General Meeting, International Mineralogical Asso­ Maine, p. 48-60. tion,p.195-288 Osberg, P.H., and Guidotti, C. V., 1974, The geology of the Camden-Rockland Stewart, D. B., and Wones, D. R., 1974, Bedrock geology of the northern area, in Osberg, P. H., ed., Guidebook for field trips, New England Penobscot Bay area, in Osberg, P. H., ed., Guidebook for field trips, New Intercollegiate Geological Conference: Orono, Maine, p. 47-60. England Intercollegiate Geological Conference: Orono, Maine, p. 223- Osberg, P.H., Hussey, A. M., ll, and Boone, G. M., 1985, Bedrock Geologic 239. Map of Maine: Maine Geo!. Surv., 1:500,000. Stewart, D. B., Unger, J. D., Phillips, J. D., Goldsmith, R. R., Poole, W. H., Panki wskyj, K. A., I 978a, Progress report on bedrock mapping in the Poland 15' Spencer, C. P., Green, A.G., Loiselle, M. C., and St-Julien, P., 1986, The quadrangle, Maine: Maine Geol. Surv ., Open-File Report. Quebec - Western Maine seismic reflection profile: setting and first year Pankiwskyj, K. A., I 978b, Bedrock geology in the Coopers Mills-Liberty area, results: Am. Geophys. Union Geodynamics Series, v. 14, p. 189-199. Maine: Geol. Soc. Maine, Guidebook for field trip 3. Swanson, M. T., 1988, Pscudotachylyte-bearing strike-slip duplex structures in Pankiwskyj, K. A., Ludman, A., Griffin, J. R., and Berry, W. B. N., 1976, the Fort Foster Brittle Zone, S. Maine: J. Struct. Geol., v. IO, p. 813-828. Stratigraphic relations on the southeast limb of the Merrimack Thomson, J. A., and Guidotti, C. V., 1986, The occurrence of kyanite in southern Synclinorium in central and west-central Maine, in Lyons, P. C., and Maine, and its metamorphic implications: Geol. Soc. Arn., Abstracts Brownlow, A. H., eds., Studies in New England Geology: Geol. Soc. with Programs, v. 17, p. 59. Am., Mem. 146, p. 263-280. Warner, J. L., and Pankiwskyj, K. A., 1965, Geology of the Buckfield and Peck, J. H., 1976, Silurian and Devonian stratigraphy in the Clinton quadrangle, Dixfield 15' quadrangles in northwestern Maine, in Hussey, A. M., II, central Massachusetts: Geol. Soc. Am., Mem. 148, p. 241-252. ed., Guidebook for fieldtrips in southern Maine: New England Intercol­ Perkins, E. H., and Smith, E. S. C., 1925, Contributions to the geology of Maine, legiate Geological Conference, Brunswick, Maine, p. 103-118. No. I: A geological cross-section from the Kennebec River to Penobscot Zartman, R. E., and Naylor, R. S., 1984, Structural implications of some new Bay: Am. J. Sci., v. 209, p. 204-228. radiometric ages of igneous rocks in southeastern New England: Geo!. Rickerich, S. F., 1983, Sedimentology, stratigraphy, and structure of the Kittery Soc. Am. Bull., v. 95, p. 522-539 Formation in the Portsmouth, New Hampshire area: unpub. M.S. thesis, University of New Hampshire, 115 p.

42