Contributions of crystallography, mineralogy, and petrology to the geology of the Lucerne pluton

American Mineralogist, Volume 65, pages 4l I-437, 1980

Contributions of crystallography, mineralogy, and petrology to thegeology of the Lucerne pluton, Hancock County, Maine'

Devro R. WoNEs

U.S. Geological Survey andDepartment of Geological Sciences

Virginia Polytechnic Institute and State UniversityBlacksburg, Virginia 24061

Abstract

Mineralogical studies of the Lucerne pluton, Hancock County, Maine, have established thepre-intrusive geology and the intrusive nature of the pluton, contributed to the interpretationof gravity and magnetic anomalies, explained geomorphic features surrounding the pluton,and identified post-plutonic faulting. The pluton is a biotite granite, rich in alkali feldspar,containing both seriate and porphyritic facies. Post-intrusive faulting, followed by erosion,has exposed two levels ofthe pluton. The northern, or higher, level has a slightly greater Fe/(Fe + Mg) but is lower in total Fe + Mg. Five percent of the alkali feldspars in both facies aremantled by Anrn plagioclase. The alkali feldspars are microcline perthites of Abto.*Or6o."ocomposition.

Biotite, which varies in Ti and Al contents, was the primary major phase to crystallize fromthe magma, closely followed by the apparently simultaneous crystallization of plagioclase,qvattz, and alkali feldspar. Most of the magmatic crystallization took place at l-2 kilobarstotal pressure at temperatures between 650' and 700oC. Boron may have been a signifcantconstituent. The source region for the magma may have been a previously metamorphosedgraywacke containing quartz, plagioclase, alkali feldspar, and biotite.

Introduction

Minerals make up a large part of the inorganicnatural substances found within the earth. If we ex-clude liquids and natural glasses, then almost allrocks are made up of minerals. The properties of therocks are dependent upon the configurations of theminerals that they contain. I would like to share withyou some of the contributions that mineralogy hasmade to rry understanding of the Lucerne pluton incentral Maine.

Mineralogy impinges on geological studies inmany ways. The most fundamental is the recognitionand classification of rocks. The development of agiven stratigraphy, the recognition of separate ig-neous events, and the description of structural ele-ments within an area are all dependent on the recog-nition of minerals, their morphology, and theirorientation.

I Presidential Address, Mineralogical Society of America.

Delivered at the 60th Annual Meeting of the Society, No-

vernber 6, 1979.

0003-o04x/80/0505-041 1$02.00 4l I

Although my title includes crystallography, I willuse that discipline within the Mineralogical Society'striad of interests as fundamental to the mineralogicalobservations that I will be sharing with you. Withoutcrystallography we would not understand the basis ofthe optical measurements made in thin sections, themorphology and polymorphism of feldspars and alu-mino-silicates, or theflnodynamic models of mineralsolid solutions, or recognize the ductile deformationof quartz. Crystallography is fundamental to all thephenomena discussed in this article.

The Lucerne pluton (Fig. l) is located near (but,unfortunately, not on) the Maine seacoast, just eastof the Penobscot River. Six hundred seventy-two km2in area, it is one of the ten largest plutons in NewEngland and is located in a region of geological com-plexity. I chose it for study as a pluton that had notbeen mapped, had sufficient outcrop to make modaland chemical studies feasible, and was large enoughto represent a significant intrusive event in its ownright. The project also has uncovered new regionalrelationships. The chemical and modal data of the

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Lucerne pluton are similar to those of neighboringplutons, but the Lucerne is distinct in its texture andmineralogy.

Geologic setting

The geology of coastal Maine can best be de-scribed as a collection of fault-bounded blocks, eachof which has a unique stratigraphy. The multiple de-formations and high grades of metamorphism thatcharacterize these rocks have obliterated much of thestratigraphic and paleontological evidence for theages of the rocks of this area. Stewart and Wones(1974) and Wones and Stewart (1976) suggested thatthere are three or four major crustal blocks in the

area; Osberg (1974,1978) has suggested two or three.The Lucerne pluton intrudes all but the most north-western of these blocks, from which it is separated bythe Norumbega fault zone (Fig. 2).

The stratigraphy of each fault-bounded block ispresented in northwest-southeast cross sections (Fig.2 and 3). The most southeasterly block, the Ellsworthblock, contains the Ellsworth Schist, a polydeformedquartzo-feldspathic chlorite-rich schist. Southwest ofthe area studied, the Ellsworth Schist is uncon-formably overlain by the Castine Volcanics, a Silu-rian-Devonian unit containing conglomerate, schists,agglomerates, pyroclastic deposits, and lava flows(Osberg, 1974; Stewart and

'Wones, 1974). To the

Fig. L Location ofthe Lucerne pluton.

WONES: LUCERNE PLUTON 413

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GEOLOGY OFT H E L U C E R N E P L U T O N

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northeast, in New Brunswick, the Ellsworth block a thrust fautt. This fault zone displaces the South

projects into a terrane that contains the Green Head Penobscot pluton by 24 km. The Turtle Head fault

Formation of Precambrian age (Stewart, 1974; per- zone is intruded by the Lucerne Pluton, and there is

sonal communication). no evidence of displacement along this zone after the

The Ellsworth block is bounded on the north by intrusion.the Turtle Head fault zone (Stewafi, lg74). Stewart Northwest of the Turtle Head fault zone lies the

and I interpret this zone as a right-lateral strike-slip Penobscot block. This block is named for the Pe-

fault, although Osberg (1978) has suggested that it is nobscot Formation, a graphitic, sulfide schist made

4t4 WONES: LUCERNE PLUTON

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Fig. 3. Cross sections through the Lucerne pluton. Locations ofcfoss sections are indicated in Fig. 2. Symbols for formations as inFig.2.

up of thin (0.5-5 cm) beds of siltstone intercalatedwith pelitic beds of variable (0.5-50 cm) thickness.The Wallamatogus pluton, made up of muscovite-biotife granite, intrudes the Penobscot Formation,and is confined to this block. Similar granitic rockshave been found in the Belfast region (Bickel, 1976;Stewart, 1974) to the southwest, and in the pleasantMountain region to the northeast. Dikes of mon-zonite and gabbro also have been observed in thePenobscot block.

West of Penobscot Bay, Bickel (1976) has mappedthe western contact of the Penobscot Formation (andthe Penobscot block) as a fault. The rocks west of thisboundary are complexly folded and poly-metamorphosed. The oldest of these units is the pass-agassawakeag Gneiss. Osberg (1978) has suggestedthat this fault continues to the northeast as the con-tact between the Penobscot Formation to the south-east and the Vassalboro Formation to the northwest.Wones (1976) has suggested that this contact is anunconformity between the Vassalboro Formationand the Penobscot Formation. Ludman (197g) hasdemonstrated that the analogous contact near the St.Croix River is a reverse fault, but Ruitenberg andLudman (1977) have suggested that the Waweig For-mation in New Brunswick is coeval with the Vassal-boro (Flume Ridge) Formation and unconformablyoverlies the Cookson (Penobscot?) Formation.

Clearly the Penobscot Formation lies in fault contactagainst the Passagassawakeag block, but whether thisfaulting precedes or follows the deposition of theVassalboro Formation is uncertain.

The Passagassawakeag Gneiss is not found north-west of the Norumbega fault zone. This fault zonetruncates the Lucerne pluton (Wones and Thomp-son, 1979; Wones and Stewart, 1976) and displaysright lateral offset of unknown total amount.

The Vassalboro Formation, a calcareous pelitecontaining larrinar beds of silty and shaly material,contains beds of sulfide-bearing pelite, l0 to 100 cmthick. The Vaqsalboro Formation is assumed to beSilurian or Early Devonian (Osberg, 1968) and isprobably equivalent to the Kellyland (Larrabee et al.,1965), Buiksport (Trefethen, 1950), and FlumeRidge (Ruitenberg and Ludman, 1977) Formations.The Vassalboro Formation lies on both sides of theNorumbega fault zone. This implies that the Norum-bega fault zone may not be a large feature, exceptthat rocks similar to the Vassalboro are known fromLong Island Sound in the south to the St. John Riverin New Brunswick. Unfortunately, at present there isno rigorous estinate of the motion associated withthis fault zone.

The number of blocks is dependent on the magni-tude of the Norumbega fault zone. Stewart and I splitthe Passagassawakeag and Vassalboro Blocks at theNorumbgga fault zone. Osberg (1978) treats them asa single block.

The Lucerne pluton intrudes a group of fault-bounded blocks ofdisparate stratigraphies ofearly tomiddle Paleozoic age. The faults bounding theseblocks were active in Paleozoic time and have beendescribed as strike-slip faults, thrust faults, and re-verse faults. The northern portion of the Lucernepluton has been removed by faulting, and has notbeen located as of this writing. The rocks of theBottle Lake Quartz Monzonite (Bottle Lake Complexof Ayuso, 1979) to the NE have been carefully exam-ined by myself, Douglas Tietbohl, and RobertAyuso, but we have not found granitic rocks petro-graphically similar to the Lucerne pluton NW of theNorumbega fault zone.

The definition of these formations, their contacts,their deformational histories, and their metamorph-ism has been accomplished through the use of miner-alogy. To be sure, the hand-specimen observationsdo not require sophisticated equipment for this pur-pose, but years of mineralogical investigations giveus a high degree of confidence in our definitions offormations and interpretations of their history.

WONES: LUCERNE PLUTON 4t5

Geology of the Lucerne pluton

The intrusive nature of the Lucerne pluton can beobserved in a variety of locations (Wones, 1974,1976) (Fig. 2). In North Penobscot, Maine, an apo-physis of the pluton, 100 m wide, exploits a pre-existing fault zone between the Penobscot Formationand the South Penobscot pluton. Rotated xenolithsof both the Penobscot Formation and the South Pen-obscot pluton can be found within the apophysis ofthe Lucerne pluton. Dikes of the Luceme can befound within both country rocks within a few metersof the contact. The dikes are coarse-grained; singlecrystals of alkali feldspar are found across the entirewidth of the small (2-4 cm) dikes.

Large dikes of the granite of the Lucerne plutoncan be found in the hybrid zone of the PenobscotFormation southeast of the town of Orland. Thesedikes are approximately 2 to 4 m wide and intrude azone of Penobscot schist previously intruded by dior-ite, gabbro, monzonite, and muscovite-granite dikes.

The western boundary of the Lucerne against theVassalboro is relatively straight where the pluton in-trudes the Vassalboro Formation. The intrusive na-ture of the contact can be seen one half mile north ofDedham, on Route lA NE of Dedham ElementarySchool. on the summit of a small hill NW of HatcasePond, on Blackcap Mountain, and SW of ParksPond. At Parks Pond the Lucerne pluton intrudes theParks Pond Monzonite and inclusions of the mon-zonite can be seen within the granite (Cavalero,1965). Along the entire western boundary, dikes ofthe Lucerne are uncommon and only extend a fewmeters from the contact. Large rotated inclusions ofVassalboro Formation several meters across havebeen observed within the pluton but only within afew meters of the contact.

The NW boundary of the Lucerne pluton is theNorumbega fault zone. A roof pendant has beenidentified in the region of Morrison Ponds, and inthis region the pluton narrows to 2 km. The coarsetexture persists up to all the contacts, including theroof pendant, and the fault zone. Near Great Pond,the Lucerne pluton has undergone extreme cataclasisand is brecciated and mylonitized within a few me-ters of the fault zone (Fig. 4f).

The eastern contact is not as well exposed as thewestern contact. However, just west of the UnionRiver and north of Route 9, familiarly known as "theAirlins," both intrusive and mylonitic contacts canbe seen between the Lucerne pluton and the Vassal-boro Formation. The mylonites presumably repre-

sent small faults, but they do not appear to persist re-gionally. They are interpreted as extensions of a tracewithin the Norumbega fault zone that becomes betterdeveloped to the NE in the region of Sabao Moun-tain in the Nicatous Lake quadrangle.

Contacts of the Lucerne pluton with the PenobscotFormation are well developed on the shores of BeechHill Pond and Green Lake. Here the contact isabrupt, there are relatively few inclusions, and raredikes of the Lucerne Pluton are found within thePenobscot Formation.

South of Route lA the Ellsworth Schist appears tobe deformed by the Lucerne pluton. Drag folds inthe schist are interpreted to show that the LucernePluton moved north relative to the Ellsworth Schist.At the SE corner of the Lucerne pluton, contacts (ofthe Lucerne pluton) with both the Blue Hill plutonand the Ellsworth Schist are well exposed at the townline between Surry and Blue Hill. There the contactzone is marked by disseminated arsenopyrite withinthe older units. The Lucerne pluton is clearlyyounger than the Blue Hill pluton, and is a distinctlyseparate pluton.

The southern contacts are not well exposed, al-though mapping by D. B. Stewart in the Blue Hillquadrangle (Stewart and Wones, 1974) has closelyconstrained the contact west of Toddy Pond. This isthe only region in which the granite of the Lucernepluton becomes porphyritic near the contact. A sig-nificant characteristic of the Lucerne pluton is that itremains coarse-textured and seriate throughout thebody, except for a central core facies that is only ex-posed in the northern third of the pluton.

A small fault extends across the Lucerne plutonfrom Dedham Elementary School on the west side ofthe pluton to North Mariaville on the eastern side ofthe body. Both contacts are offset by right-lateral dis-placement of about 300 m. A zone of mylonitic rockhas been followed more or less continuously (outcroppermitting) between these two offsets. This fault maybe equivalent to the Sunnyside fault described byBickel (1976) in the Belfast Quandrangle.

North of the fault, the core of the pluton is occu-pied by a porphyritic facies of the granite. Quartz,plagioclase, alkali feldspar, and biotite all occur asmedium to coarse (biotite excluded) phenocrystswithin a fine- to medium-grained matrix of the sameminerals. Miarolitic cavities of about 3 mm diameteroccur within the groundmass, and contain termi-nated feldspar crystals. The contacts of the porphy-ritic facies with the seriate facies are gradational.Near Springy Pond Mountain the contact is marked

lltONES: LUCERNE PLUTON

Fig' 4' Representative slabs of the Lucerne pluton: (A) EL 417 , seriate facies near eastern margin, south of Sunnyside fault; (B) ORC65, seriate facies near core ofpluton, south ofthe Sunnyside fault; (C) GPC 604, seriate facies north ofthe Sunnyside fault; (D) GpC603' porphyritic facies north of the Sunnyside fault; (E) GPC 607, mylonitized seriate facies north of Sunnyside fault; (F) brecciatedseriate facies adjacent to Norumbega fault Zone, north of Great pond.

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by sprays of tourmaline several cm across, but atother localities the boundary is simply marked by agradual coarsening of the groundmass over tens ofmeters towards the outer perimeter of the pluton.

The fabric of the pluton is massive. There is notendency for the minerals to be oriented either as lin-eations or foliations, except in the west-central por-tion of the southern part of the body (see foliationsymbols in Fig. 2). In this region the pluton has beendeformed by subsolidus deformation. Ductile defor-

mation of quartz and biotite and brittle deformationof the feldspars can be observed in thin sections ofthe rocks of this zone (Fig. 5a-c) which is marked bya pervasive deformation rather than by mylonites.This feature occurs entirely within the interior of thepluton and does not appear to offset any ofthe con-tacts, although the contacts near Moose Stream at thesouth end of the western contact are not well ex-posed. Ductile deformation of quartz and brittle be-havior of the feldspars suggests that this deformation

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418 IIONES: LUCERNE PLUTON

was subsolidus and took place at about 500.C (Tullisand Yund, 1977). Kink-banding of altered biotitescoupled with deformation of secondary sphene sug_gests that the deformation took place after the sub-solidus alteration.

North of the Sunnyside fault numerous mylonitesare found with the pluton (Fig. ae). These usuallytrend N60E or N20W. They do not seem to line upinto continuous zones, nor do they dominate singlioutcrops. Their overall density has not been deter_mined. I interpret these features as the termination ofone of the fault traces of the Norumbega fault zone.There is no major offset of the contacts of the Lu-cerne pluton in this region, yet the small mylonitesstrike NE into a fault contact between the granite ofCranberry Lakes and the Vassalboro Formation.

Age of the Lucerne pluton

The Turtle Head fault zone displaces the CastineVolcanics (Stewart, 1974), a sequence of rocks clearlyof late Silurian and Early Devonian age. The Lu-cerne pluton cuts the Turtle Head fault zone, and thismust be younger than Early Devonian. The Lucernepluton is cut by the Norumbega fault zone, whichalso deforms Pennsylvanian sedinents in NewBrunswick (Wones and Stewart, 1976).

Brookins (1976; personal communication) hasbeen working on the ages of the plutonic rocks of thePenobscot Bay region. He has determined a prelimi-nary age for the Lucerne pluton of 375=25 milliolyears. This is in agreement with a K-Ar age of 365m.y. by Faul er al. (1963) for the Lucerne pluton. R.E. Zartman (personal communication) has deter-mined a single zircon PblPb age of 380-F4 miilionyears. The Lucerne pluton is Middle Devonian inage.

Texture and fabric ofthe Lucerne plutonThe Lucerne pluton is made up of granite contain-

ing quartz, alkali feldspar, plagioclase, and biotite.The texture is seriate. This term is used all too littleby petrographers, and I would like to urge perogra-phers to seriously consider it in future descriptions oftheir rocks. Equigranular and porphyritic have longbeen popular terms, but not so seriate. If one exam-ines textures of the Lucerne pluton (Fig. 4a-e), it isclear that quartz, plagioclase, and alkali feldspar alloccur in a variety of grain sizes, ranging from a fewmm to several cm. Alkali feldspars are always coars-est, in maximum size, followed by quartz, plagio-clase, and biotite in that order. The biotite is nevercoarser than 5 mm and often occurs as grains less

than a millimeter in diameter. Table I lists averagegrain sizes for the minerals within the three facies ofthe pluton.

The porphyritic core in the northern third of thepluton contains phenocrysts as coarse as several cmin length within a fine- to medium-grained ground-mass. The mineralogies of the phenocryst and thegroundmass are essentially identical. Although themain body of porphyritic material is found in thenorthern core of the pluton, scattered pods of por-phyritic material a meter or less in diameter havebeen observed throughout the entire pluton. Theseporphyritic zones are never well developed near thecontacts ofthe body except near the SW contact nearthe western shore of Toddy Pond. The total numberof porphyritic pods observed is about two dozen. andthey are concentrated toward the central axis of thepluton.

I have divided the pluton into three facies: seriatefacies south of the Sunnyside fault; seriate faciesnorth of the Sunnyside fault; and porphyritic faciesnorth of the fault.

Inclusions are very rare except that rotated blocksof country rocks are common within a meter of thecontact.

Table l. Average range ofgrain sizes ofessential mincrals in rocksofthe Lucerne pluton

Maximum Mlnimum Z K_feldsparLong Dimension Long Dimension nant led ty

( c n ) ( c m ) p l a g i o c l a s e

Seriate granit ic rocks south of Sunnyside FaulE( 1 3 5 s a n p l e s )

0 . 9 8 r 0 . 0 3 ( s . d ) 0 2 0 ! O . t 2

K - f e l d s p a r 2 . 9 6 0 . 9 0 O . 3 t 0 . 2 6

P l a g i o c l a s e 1 . 3 9 O . 5 j 0 . 2 0 0 . 3 0

E i o E i t e 0 . 1 9 0 . 0 9 o . t o 0 . 0 3

0 . 0 5 I 0 . 0 3

S e r i a t e g r a n i t i c r o c k s n o r t h o f S u n n y s i d e l . a u l t( 8 7 s a m p l e s )

Q u a r t z 1 . 1 0 0 . 3 5 O . 2 4 0 . 1 3

K - f e l d s p a r 2 . 6 3 1 . 0 3 O . 3 2 0 . 2 9 0 , 0 7 0 , 0 8

P f a g i o c f a s e 1 , 3 4 0 . 5 9 0 . 2 2 0 , 1 3

B i o t i t e 0 . I 9 0 . 0 9 O . O 9 0 . 0 5

P h e n o c r y s ! s o f p o r p h y - i t i c g r a n i E i c r o c k s n o r t h o f S u n n y s i d e F a u ] t( 2 7 s a m p l e s )

Q u a r t z 1 . 0 7 0 . 3 3 O . I 2 0 . 0 6

K - f e l d s p a r 2 . 7 6 0 . 8 6 0 . 3 3 0 . 2 5 0 . 0 5 O . O 2

P l a g i o c l a s e | . I 2 O . 5 2 O . 1 4 0 . 0 8

B i o f i t e 0 . I 7 0 . 1 0 0 . 0 9 0 . 0 3

IVONES: LUCERNE PLUTON 419

Well-developed schlieren (Fig. 6) have only beenobserved near the southeastern coh(&ct on the eastshore of Lower Patten Pond. Grains of biotite definefabrics analogous to cross-bedding and funnel-shaped bedding common to clastic sediments.

Most outcrops are rough and coated with lichens.This makes routine observations of porphyritic apo-physes and schlieren diffi.cult, so these features maybe more common than I have indicated.

Aplite dikes are also uncommon and tend to occurin swarms. The most extensive occurrence is alongthe Nature Trail at the Craig Brook National FishHatchery (Wones, 1974) on the northeast shore ofAlamoosook Lake in East Orland. Along a 75-mtrail, four aplitic dikes were observed. The thickest isabout 20 cm thick. and all of them are medium-grained, rather than fine-grained. Scores ofbald out-crops, each hundreds of square meters in area, do notcontain aplitic dikes.

The only pegmatite observed was along the west-ern margin of the pluton, about 800 m north ofMoose Brook. The pegmatite, about a meter in diam-eter, was enclosed in coarse seriate granite and wasmade up of quartz, plagioclase, alkali feldspar, andtounnaline. As the bulk of the alkali feldspar in the

Lucerne pluton is 2 to 4 cm long and I to 2 cm wide,the entire pluton could be construed as a pegmatite.However, the regularity of the seriate texture fromplace to place makes such a classification highly in-appropriate.

Any smooth, weathered outcrop shows that about5 percent of the alkali feldspar megacrysts in the se-riate facies of the Lucerne are ovoidal and arerimmed by plagioclase (Table l). This viborgite or"rapakivi" texture is common among the graniticplutons of coastal Maine (Terzaghi, 1940; Stewart'1959; Abbott, 1978). Within the porphyritic facies,this texture is not obvious in outcrop, but measure-ments of stained slabs indicate that it is as commonin that facies as in the seriate facies.

Tabular zones of salmon-colored granite occur ad-jacent to quartz-filled joints in the southern third ofthe pluton. Granite within I to 2 cm of the quartzveins is salmon-colored; biotites are chloritized,plagioclase is absent, and the turbid feldspar has fewperthite lamellae. These regions of alteration arerare, and have only been observed near Craig Brookand along U.S. Route I near Upper Patten Pond'They occur in sets that strike N60E and N60W, andare nearly vertical.

Lucerne pluton. Lens cap is 55 mm in diameterFig. 6. Schlieren of biotite near the eastern margin of the

WONES: LUCERNE PLUTON

NW-trending, quartz-tourmaline veins about 2 to4 cm across have been observed at six localities.These veins do not appear to be accompanied by anyalteration of adjacent granite, but clearly transectearly textures and fabric.

Modal and analytical dataIn making a recent comparison (Wones, l9g0) be_

tween plutonic rocks of the New England region,USA, and those of the Sierra Nevada batholith(Bateman et al., 1963; Bateman and Clark, 1974), Ifound that very little systematic work has been doneon the variations of composition within plutons inNew England. Part of the object of this study was toprovide modal data for the Lucerne pluton. Samplelocations are shown in Figure 7, and the modal dataare presented in Figures 8 and 9. The data were ac_quired by counting 1000-1500 points on stained slabswhich varied in size from 100 to 500 cm2. This size isa compromise between the size required because ofthe coarse feldspar grains (ideally 1600 cmr) and myenergy in removing such large samples from theMaine woods.

Recent road cuts along Route I near Upper pattenPond, in the southern portion of the pluton, show lo-cal segregations of alkali feldspars (Fig. l0) on thescale of meters to tens of meters similar to those seenadjacent to the schlieren (Figure 6). My hand speci-mens do not appear to be large enough to be repre-sentative of a local area, and this leads to the scatterobserved in Figure 8. Thus, these 220 modal determi-nations probably give a satisfactory average compo-sition for the different facies of the Lucerne plutonbut are not sufficient to show regional gradients, eventhough the sample localities are I to 2 km apart. Theaverages are given in Table 2.

In preparing Figures 8 and 9, I have divided thepluton into three facies: seriate facies south of theSunnyside fault, seriate facies north of the Sunnysidefault, and the porphyritic facies. As can be seen fromTable2, the seriate granite south of the fault and thatnorth of the fault are modally distinct at the 90Voconfidsns. level, in regard to alkali feldspar andmafic mineral contents. Rocks north of the fault aresystematically lower in color index and higher in al-kali feldspar content than those south of the fault.Geophysical evidence (Sweeney, 1976) indicates ver-tical displacement along the fault, perhaps as muchas a kilometer, with the south side moved up.

A vertical composition gradient within the plutonwould be analogous to results reported for magmachambers that erupt as ash-flow tuffs (Ross and

Smith, 196l; Smith and Bailey, 1966; Hildreth, 1980),where the inverted volcanic pile is interpreted to rep-resent levels within the erupting magma chamber.Concentration of alkali feldspar toward the top andan increase in mafic mineral content toward the baseseems to be typical of these magma chambers.

The porphyritic zone is the richest in alkali feld-spar of the units and the lowest in color index.Simple fractionation of quartz, plagioclase, and biot-ite by gravity settling could explain this result, asthese minerals are denser than aftali feldspar andmight sink faster than the lower-density alkali feld-spar during the cooling of the magma that crystal-lized to form the granite.

The rocks of the Lucerne pluton (Figs. 8 and 9) areall granite (monzogranite) as defined by the IUGSclassification scheme (Streckeisen, 1973). The funda-mental variation seems to be toward the aftali feld-spar apex, and implies that the process leading to thescatter is controlled by alkali feldspar. Observationof aggregated alkali feldspar crystals (Fig. l0) sup-ports such an interpretation and indicates that alkalifeldspar was one of the early phases to crystallizefrom the melt. The presence of biotite schlieren alongthe southeast margin of the body implies that biotitealso was an early crystallizing phase.

Table 3 gives average analyses for granitic rocksfrom the three dominant facies of the Lucerne plu-ton. Samples submitted for chemical analysesweighed between 20 and 50 kg. Chemical analyseswere performed by laboratories of the U.S. Geologi-cal Survey in Reston, Virginia, using "rapid rock"methods as outlined by Shapiro (1975). crpw norma-tive calculations compare well with the averagemodal analyses. Both results demonstrate that thenorthern part ofthe pluton is enriched in I(rO and isdepleted in TiOr, Alror, and MgO as compared tothe southern part.

Geophysical data

Gravity data, obtained by Sweeney (1975, 1976),show a Bouguer anomaly of about -30 mgal over thepluton (Fig. I l). Sharp gradients that coincide withthe boundaries of the pluton imply a steep contactwith the country rocks, a relatively flat base for thepluton, and a lower density than that of the sur-rounding rocks. In Figure 3, the configuration of theLucerne pluton at depth is taken from Sweeney's(1976) interpretation of the gravity anomaly.

Alkali feldspars have a positive volume of mixing(Wright and Stewart, 1968). In the Lucerne pluton,the alkali feldspars have an average bulk composi-

ITONES: LUCERNE PLUTON 421

tion of OrroAbro and have exsolved to form micro-perthite. Thus, additional void space existing withinthe feldspars lowers the overall rock density. The tur-bid nature of the feldspars is due, in part, to thesevoids.

The porphyritic zone in the northern part of thepluton contains miarolitic cavities. Although smalland dispersed, these cavities also lower the effectivedensity of the pluton. Measured bulk densities of thegranite range from 2.55 to 2.65, while the calculateddensities range from 2.6l to 2.66. Our knowledge ofthe feldspars, as evidenced from the session preced-

SAMPLE LOCALITIES

LUCERNE PLUTOND. R. TYONES, 1979

o a a a

r rLOt t r t t !

ing this address (Geol. Soc. Amer. Abstracts withPrograms, v. I l, p. 349), permits us to make estimatesof the densities of granitic rocks and to explain theobserved discrepancies.

The fault which separates the northern third fromthe southern two thirds of the pluton may be equiva-lent to the Sunnyside fault described by Bickel (1976)in the Belfast Quadrangle to the southwest. This faulthas displaced the east and west contacts ofthe plutonabout 300 m. The gravity data interpretation bySweeney (1976) suggests that the fault has about akilometer of vertical motion, and that the southern

Fig. 7. Sample localities for modal analysis.


OUARTZ

PLAGIOCLASE K . F E L D S P A R

L U C E R N E P L U T O N

A P L I T EP O R P H Y R I T I C

. S E R I A T E , N O R T H O FSUNNYSIDE FAULT

O S E R I A T E , S O U T H O FS U N N Y S I D E F A U L T

An understalding of the mineralogy of the plutonand the host rocks permits a more detailed inter-pretation of the geophysical data.

Geomorphology and glacial geology

Landsat images (Fig. 13) of the terrain that con-tains the Lucerne pluton show a number of strikingfeatures. The Lucerne pluton, containing quartz andfeldspar, is more resistant to erosion than the carbon-ate and layer-silicate-rich country rocks that it in-trudes. Thus, the Lucerne pluton forms a range ofhills (although in Maine we fondly think of these asmountains) that rise 330 m above the surroundingcountry that is essentially at sea level. A pronouncedtopographic rise along the western contact is part ofthe Penobscot lineament discussed by O'Leary et al.(1976). This prominent feature is the contact betweenthe hornfelsed rocks ofthe contact aureole ofthe Lu-cerne, made up of quartz, plagioclase and biotite,and the lower grade metamorphic rocks pre-dominantly made up of quartz, calcite, muscovite,and cilorite.

The southeastern terminations of the larger lakes

part ofthe pluton represents a deeper level than thenorthern part of the pluton.

Magnetometer data show that the Lucerne plutonhas a distinct signature. Use of a truck-mountedmagnetometer (Kane et al., l97l'1 demonstrated thatthe relatively uniform, magnetite-free granites of theLucerne pluton produce a flat and relativelv uninter-s51ing magnetic profile. The Vassalboro Ld p"o-obscot Formations and the Ellsworth Schist all con-tain sufficient magnetite (Ellsworth) or pyrrhotite(Vassalboro and Penobscot) to give a significant con-trast. Represeptative magnetometer traces across thecontacts are shown in Figure 12. The magnetic con-trast is readily explained by the fact that the plutoncontains no magnetite, except in the mylonitizedzones in the northern portion. There are a few tenthsof a percent modal ilmenite and the major ferromag-nesian mineral in the granite is bibtite.

Much of the southernmost portion of the pluton iscovered by glacial-outwash deposits, and the contactsare not exposed. The truck-mounted and backpack-mounted magnetometers permitted a close resolutionof the contacts in the southern portions of the pluton.

M A F I C S

Fig. 8. Modal analyses of the Lucerne pluton.

M A F I C S


O U A R T Z M A F I C S

PLAG IOCLASE

found within the borders of the Lucerne pluton coin-cide with the eastern contact of the pluton against themetamorphic rocks in the aureole. Apparently glacialscouring took place more easily in the granite than inthe hornfels, so that glacial erosion formed linear SE-striking basins which are dammed by the hornfels.

On the Bubbles, in Acadia National Park, is alarge glacial erratic named Balanced Rock. This er-ratic is coarse-grained, contains large alkali feldspars,and has a modal composition within the range of thegranite of the Lucerne pluton. Glacial striae in therocks in and around the Bubbles indicate that glacialmovements were S20E to Sl5E. Projecting this tra-jectory for Balanced Rock, we find that it coincideswith the Lucerne pluton. This case, although rathersimplistic, demonstrates that detailed knowledge ofthe petrology and minslalegy of plutonic rocks inNew England can aid our understanding of glacialtransport in this region.

Petrography

The coarse grain size, a prominent feature of thegranites of the Luc.erne pluton, makes study of the

K . F E L D S P A R

LUCERNE PLUTON

. A P L I T E

. P O R P H Y R I T I C

. SERIATE, NORTH OFSUNNYSIDE FAULT

SERIATE. SOUTH OFSUNNYSIDE FAULT

rocks in {hin ssctlsl difficult. In this study the rela-tionships among the major minerals were determinedfrom the examination of the stained slabs used formodal analysis. Measurements were made of themaximum and minimum diameters of the majorminerals. and observations were made of their mor-phology.

The Lucerne pluton is predominantly coarse-grained granite with hypidiomorphic seriate texture.

Quartz grains are often in aggregates and are sub-hedral to anhedral; alkali feldspar crystals often oc-cur as Carlsbad twins and range from anhedral to eu-hedral; plagioclase crystals are usually subhedral.Sizes of these three minerals are seriate, within theranges given in Table 1. The biotites are more uni-form in grain size and are subhedral.

Another prominent petrographic feature of thepluton is the presence of plagioclase mantles, onabout 5 percent of alkali feldspar crystals (Fig. 4b, c,e). Forty-one percent of the slabs of seriate granitesouth of the fault showed this texture, and of thatgroup 13 perc€nt of the alkali feldspar crystals weremantled. Of the seriate and porphyritic rocks north

Fig. 9. Average modal analyses of the three facies of the Lucerne pluton'

M A F I C S


Fig. l0 Alkali feldspar aggregates and miarolitic cavity observed in road cuts, Route l, near Upper patten pond. Scale is 6 inches long.

of the fault zone, 48 percent of the slabs containedmantled feldspars, and in those slabs, 15 percent ofthe feldspars larger than I cm were mantled in the se-riate rocks and l0 percent of the phenocrysts in theporphyritic rocks. There is no significant differencein the percentage of mantled alkati feldspars amongthe three facies. I interpret these observations to in-

Table 2. Average modal analyses for granitic rocks ofthe Lucernepluton

dicate that, in spite of the modal differences amongthe three facies, the early crystallization historieswere nearly the same.

Sequence of crystallization

Sequence of crystallization can best be determinedby examining mutual grain boundaries and in-clusions; for the Lucerne pluton, the sequence is notobvious. The euhedral to subhedral character of thealkali feldspar tends to give that mineral a "primary"appearance, which is belied by the presence ofqvartz, plagioclase, and biotite inclusions within al-kali feldspar grains. Biotite is a ubiquitous inclusionin all minerals, and the presence of the schlieren andflow banding discussed earlier lends credenc€ to thehypothesis that biotite is the primary phase amongthe major minerals.

Because only 5 percent of the alkali feldspar ismantled, this must have been an early event in thecrystalliallsn of the Lucerne magma, and it is of in-terest to note that the boundary between the alkalifeldspar core and the plagioclase rim is decoratedwith quartz and biotite. Rare euhedral grains of

quar Ez

I

2 7 . 9 9 t 5 . 7 ( s . d . )

2

29-45 ! 5 2

4 r . 4 8 6 . 7

2 4 4 8 4 . 5

4 . 8 5 2 . 4

3

2 7 . 4 3 ! 5 8

4 6 - 2 2 6 . 3

2 2 . 5 6 2 . 7

3 . 9 2 t . 7

Alka1iF e l d s p a r 3 9 . O 2 7 - l

P l a g l o c l a s e 2 6 . 0 6 5 2

Ma f ics( B i o t l E e s ) 6 . 7 2 2 . 1

L . A v e r a g e o f 1 2 4 a n a l y s e s o f s e r l a t e g r a n i t i c , o c k s s o u t ho f S u n n y s i d e F a u 1 t .

Average o f 72 ana lyses o f ser iaEe gran i t i c rocks nor tho f S u n n y s i d e F a u l t .

Average o f 24 anafyses o f porphyr iE ic rocks oor th o fSunnys ide Fau l t .

3

ITONES: LUCERNE PLUTON 425

s i02

Ti02

A1 2O3Fu2o3

Fe0

MnO

Mco

Ca0

Na20

KzoP ^ O _

H2o

"oz

ac

0r

Ab

En

F s

Ilr

I1

Ap

D . I .

Table 3. Average chemical analyses and cnw norms for graniticrocks of the Luccrne pluton

LUCERNE PLUTONH A N C O C K C O U N T Y , M A I N E

G E O L O G Y . D R W O N E S

BOUGUER GRAVITY OATAJ F - S W E E N E Y . 1 9 7 5

4 4 o 4 5 '

O 5 K m

- Geo log ic con loc lContour in fe rvo l - | mgo l

Fig. ll. Bouguer gravity anomaly associated with the Lucernepluton. Gravity data are from Sweeney (1975, 1976). Geologicconlacts are from Fig. 2.

3 k m

Fig. 12. GroundJevel magn€tometer tracings across mntacts ofthc Lucerne Pluton. Dgl, Lucerne pluton; SOp, PenobscotFormation: OCe, Ellsworth Schist.

I

i 1 . 9 5 1 2 . 1 4 ( s . d . )

0 . 2 9 0 . 0 7

1 4 . 7 6 0 . 9 1

0 . 6 6 0 2 8

r . 4 9 0 . 3 1

0 . 0 4 0 . 0 3

0 . 2 8 0 . 1 3

1 0 6 0 . 3 I

3 . 2 3 0 . 2 3

5 . 2 8 0 . 3 9

0 . 1 5 0 . I I

0 . 8 8 0 . 3 7

o . 0 2 0 . o 2

2 9 . 9 r

2 . 2 1

3 t . r 7

2 7 , 3 r

0 . 7 0

1 . 7 9

0 . 9 6

0 . 5 5

0 . 3 6

8 8 . 3 8

2

7 3 . 2 0 ! 1 . 8 2

o . 2 2 0 . 0 3

t 3 . 8 9 0 . A 2

0 . 5 9 0 . 2 2

r . 4 6 0 . 2 4

0 . 0 3 0 . 0 1

0 . 1 6 0 . 0 5

0 9 6 0 . r 9

3 . 0 2 0 . t 7

5 . 5 2 0 . 5 0

0 . 0 6 0 . 0 1

0 . 6 6 0 . 1 1

o . 0 z o . 0 2

3 1 6 5

1 . 4 0

3 2 . 6 9

2 5 . 6 t

4 . 2 5

0 . 4 0

I . 8 9

0 . 8 6

0 . 4 2

0 . 1 4

89 94

3

7 3 . 4 8 1 I . 9 3

0 . 1 6 0 . 0 3

t 3 . 9 2 0 . 8 6

o . 6 4 0 . r . 5

t . 2 0 0 . l 4

0 . 0 6 0 . 0 4

0 . 0 9 0 . 0 1

0 . 8 4 0 . 1 9

3 . 3 8 0 . 2 2

5 . 4 5 0 5 4

0 1 3 0 . 0 5

0 . 6 s 0 0 s

0 . 0 2 0 . 0 t

30 15

1 2 9

3 2 2 0

2 8 . 6 0

3 . 1 9

0 . 2 2

r . 5 2

0 . 9 3

0 . 3 0

0 . 3 1

9 1 . 5 5

A l l a n a l y s e s p e r f o r m e d b y B r a n c h o f A n a l y t i c a l L a b o r a t o r i e s ,U , S . G e o l . S u r v e y , R e s t o n , v r i g l n i a , u s i n g R a p i d R o c k M e l h o d s( S h a p i r o , 1 9 7 5 ) , H , s n i t h , A n a l y s c .

1 . A v e r a g e o f 1 0 a n a l y s e s o f s e r l a t e g r a n i E i c r o c k s s o u l h o fSunnyslde FauI l

2 . A v e r a g e o f 9 a n a l y s e s o f s e r i a t e g r a n i c i c r o c k s n o r t h o fS u n n y s i d e F a u 1 t .

3 . A v e r a g e o f 6 a n a l y s e s o f p o r p h y r i E i c l o c k s n o r E h o fS u n n y s i d e F a u f t .

plagioclase containing 5 to l0 peroent biotite in-clusions also appear to be early phases.

The porphyritic core is presumed to represent aquench event and therefore captures for us the early-crystallized phases: biotite, quartz, alkali feldspar,and plagioclase. Alkafi feldspar crystals predominate,but the others are all present, biotite both as pheno-crysts and as inclusions within the other phases.Plagioclase inclusions within the alkali feldspars maybe partly exsolution products.

The crystallization sequenae appears to be biotitepreceding plagioclase, quartz, and alkali feldspar.Relations among the others are indeterminate.

Mineralogical data

Mineralogical studies have used a combination ofmethods: optical, X-ray powder diffraction, X-rayfluorescence, and electron microprobe. Most of theeffort has been placed on the characteruation of themajor minerals, and relatively little work has been

o


Fig. 13. Landsat image of eastern coastal Maine, with theoutline of the Lucerne pluton superposed.

expended on the accessories, with the exception ofapatite.

Plagioclase

Plagioclase occurs in four typical habits in thegranites of the Lucerne pluton. It usually occurs assubhedral to anhedral polysynthetically-twinnedcrystals of An, to Anro composition scatteredthroughout the matrix of the granitic rocks. The mostcalcic plagioclases observed are Anrr; these are foundin the southern facies of the pluton. Most plagio-clases are sericitized and weakly zoned. plagioclasecrystals also occur as inclusions within alkali feldsparcrystals. These have not been extensively studied, butthe available analyses indicate that they rarely ex-ceed An2o in composition and are commonly An?_,s.The plagioclase mantles in the viborgite (rapakivi)feldspars range from Anro to Anro. plagioclase la-mellae in the perthitic alkali feldspar vary betweenAn, and An .

Alkalifeldspar

Alkali feldspar occurs as coarse- to medium-grained euhedral to subhedral crystals. The crystalsare exsolved to lamellae of low albite about 0.05 mmthick within a matrix of maximum microcline ofcomposition Orru to Or,*. The structural state was es-tablished by X-ray difraction using the method ofWright (1968). Bulk corrpositions of the alkali feld-spars were determined by removing single crystalsfrom rock samples and analyzing them by X-ray flu-orescence methods. They were also sanidinized bv

crushing, pelletizing, and heating to 950oC for sev-eral days. Bulk compositions were then determinedusing the methods of Wright and Stewart (1968). Thetwo methods are compared in Figure 14. The sani-dization procedure always gives estimates of bulkcomposition as more Or-rich than the values deter-mined by X-ray fluorescence. This is probably due tothe inclusions of An, to An,, plagioclase that occur inthe alkali feldspar. This material is not homogenizedinto the alkali feldspar during the sanidization proce-dure but is included in the XRF analysis. I have notattempted to determine the composition by modalanalysis of perthite after microprobe analysis of thehost and lamellae within the perthite. Because of thesize of the lamellae, I did not use the "broad beam"microprobe technique reported by Whitney andStormer (1976). The bulk composition of the per-thites ranges from Orro to Or.o. The compositions ofmutually coexisting plagioclase and alkali feldsparare shown in Figure 15.

Biotite

Biotite occurs as subhedral crystals that rangefrom 0.1 to 0.2 cm in diameter. They frequently con-tain inclusions of apatite, zircon, and in some cases,fluorite. Some of the included minerals are oftenfound in a spiral pattern and are interpreted as "dec-orations" on a crystal of biotite forming by spiral

ooco)oo(l)

o=L

- o 2 4 6 8 t o

Or contenf , K- Feldspor: Sonid in izof ion

Fig. 14. Comparison of the Or content (in mole percent) ofalkali feldspars of the Lucerne pluron determined by X-rayfluorescence of bulk feldspar grains with that determined by X-raypowder diffraction after sanidinization.

or 6

x

oCLo

! t .o

hI

Y

c ^o ) z

coa

o

a

aa

ti.o.a

IVONES: LUCERNE PLUT:ON 427

Table 4. Average structural formulae for biotites of the Lucernepluton

o

oooo-

o

1

s i ru 2 .81 l 05

o r t u r . r 9 . 0 5

e lu t 0 .33 .07

T i 0 . 2 0 . 0 2

F e 1 . 8 5 . 1 2

M n 0 . 0 3 . 0 1

M s 0 . 3 6 . 0 8

c a 0 , 0 1 . , 0 1

N a 0 . 0 1 . 0 1

K 0 . 9 1 . 0 5

F 0 . 1 1 . 0 7

c r 0 . 0 2 . 0 1

I o c E . c a t i o t r s 2 . 1 7

x - 0 . 6 2

Fe/ (Fe + Mg) 0 .86

3 4

2 . 8 6 1 . 0 5 2 . 7 7 ! . 0 5

l . l 4 . 0 5 | . 2 3 . 0 5

0 . 3 5 . 1 7 0 . 5 3 . 0 3

0 . 1 7 . 0 3 0 . 1 7 . 0 3

r . 9 2 , 2 3 r . 5 4 . 1 2

0 . 0 2 . 0 0 3 0 . 0 1 , 0 0 2

0 . 2 5 . 0 9 0 . 5 0 . 1 0

0.004 .002 0 .006 .005

0.005 ,003 0 .004 .005

0 . 8 8 . O 2 0 . 8 3 . 0 5

0 . r 2 . 0 3 0 . 0 9 . 0 5

0 . 0 2 . 0 1 0 . 0 2 . 0 I

2 . 7 1 2 . 7 5

0 . 6 4 0 . 5 1

0 . 8 8 0 . 7 5

2

2 . 8 4 ! . O 2

r . 1 6 . 0 2

o - 2 9 - r 2

0 . 1 9 . 0 2

1 . 9 6 . 1 6

0 . 0 3 . 0 1

0 . 3 0 . 0 4

0 . 0 3 . o 2

0.003 .003

0 . 9 I . 0 r

0 . 1 0 . 0 1

0 . 0 2 . 0 1

2 . 7 7

0 . 6 5

0 . 8 7

Fig. 15. Albite contents (in mole percent) of plagioclase plotted

against albite content of coedsting alkali feldspar. Isotherms forcoexisting sanidine and plagioclase at I kbar are from Stormer(1975). The size of the dashed circle is representative of theuncertainty at each data point.

growth. Biotite, in turn, occurs as inclusions in all ofthe other major minerals of the Lucerne pluton.

Biotite compositions [obtained to date] have beendetermined by microprobe. Li and FerO, contentsare unknown, although they can be estimated frombulk rock chemistry. This indicates that 25 to 35 per-cent of the Fe in the biotites occurs as Fe3* and thatalslimurl Li contents are 1000 ppm. Average biotitestructural formulae are given in Table 4, and individ-ual data are plotted in Figures 16-20. There is clearlya range of values, but the range within a single thinsection is frequently as great as the total range ex-pressed in the figures. The only systematic variationin biotite compositions with respect to locationwithin the pluton is in the Fel(Fe + Me) values.These values are systematically higher in rocks foundnorth of the Sunnyside fault, as opposed to thosefound south of the fault. This variation mimics thebulk composition of the rocks.

The variation in Al content in the octahedral lay-ers (AlvI) is much greater than that of Fel(Fe + Mg)(Fig. 16).

The percent variation in Ti content (Figs. (17-19)is not as great as that of Al but is greater than that ofFel(Fe + Me). The substitution of Tin* in biotites for(Fe,Mg)'z* can be compensated in a variety of ways:

Average o f b io t i tes f ron ser ia te rocks sou!h o f Sunnys lde l .au l t

Average o f b io t l tes f ron ser iaEe rocks nor th o f Sumys ide Fau l !

Average o f b ioE i tes f rom porphyr l t l c tocks nor th o f Sunnys ide

F a u l l

Average o f b lo t i tes f i l l i ng e ve in in fe ldspar

Ti' ' + E:2M9"' (2)

Ti"' + 2O'-: (Fe, Mg)"' + 2OH- (3)

In Figure 18, Ti is plotted against Si'" and Fe, andthere does not appear to be any correlation with ei-ther. Figure 19 does not appear to show any correla-tion with total octahedral cations, a relationshipwhich should reflect coupling of Ti substitutions witha vacancy. The most likely type of substitution is ap-parently the TiO, for (Fe,Mg)(OH)' substitution.

1 .

2 ,

3 .

oo

a t t '

^q.

,;".;:o @ ' u

o B '. Norlh ot foul t zone

o soulh of foul t zone O t .

a

BIOT ITE ANALYSESLUCERNE PLUTON

D R W O N E S , t 9 7 9

) r oA N N I T E

o 4

o 3H

o 2

o l

o o o tPHLOGOPITE

Fig. 16. Fe,/(Fe + Mg) of biotites of the Lucerne pluton plottedagainst octahedral aluminum (AlvI).

0 3 0 4 0 5 0 6F e l ( F e + M g )

FELDSPAR ANALYSESLUCERNE PLUTON

D R W O N E S , 1 9 7 9

. S o n p l e s n o r l h o f f o u l t z o n e

O S o m p l e s s o u t h o f f o u l l z o n e

i__,) Averoge voriolon lor eoch somple

A lb i t e i n A l ko l i Fe ldsoo r

Ti't + 2Al'": Mg"I + 2Si'" ( l )

428 WONES: LUCERNE PLUTON

BIOTITE ANALYSESLUCERNE PLUTON

D R W O N E S , 1 9 7 9

a N o r t h o f f o u l l z o n e

O S o u t h o f f o u l l z o n e

A I + M g + M n

Fig. 17. Ternary plot of octahedral AI, Ti, and (Fe + Mg + Mn)contents of biotites of the Lucerne pluton.

2 . 7

2 .

o.2 0.3T i

Fig. 18. Octahedral Ti in biotites from the Lucerne plutonplotted against Si content (upper figure) and mole fraction Fe inthe octahedral layer (lower figure).

. Nor fh o f fou l t zoneO South of foulf zone

o -ooo

I

oooo

o A8ot,

a t 'o c )

o


D R . W O N E S , 1 9 7 9

a

T iFig. 19. Octahedral Ti in biotites from the Lucerne pluton

plotted against total octehedral cations.

This result is contrary to those of Czamanske andWones (1973') for biotites from the Finnmarka com-plex in Norway.

High Al content is characteristic of biotites thatcoexist with aluminosilicates (muscovite, cordierite,

n ?


o.2 o .3F / ( F + O H ) 9 1 . 1 1 1 .

Fig. 20. Xphroaopil€ (mole fraction Mg in octahedral layer)plotted against F/(F + OH) of biotites from the Luc€rne pluton.

2 A

a 2zoF

oJ

E .ol!-FC)oJ, . tZ

o .20 0

a

tf)

) zel!

o

AoEo

Eo-

x

o . l

.o -&S o'


D R W O N E S , 1 9 7 9

o Norfh of foult zoneO South of foult zone


garnet, sillimanite) in granitic rocks. None of thesealuminosilicates have been observed in the Lucernepluton, but the Lucerne biotites are clearly more alu-minous than those that occur with olivine, pyroxene,or amphiboles (Nockolds, 1947).

The alkali contents of the Lucerne biotites are no-table because the Na contents are low, and the bio-tites seem to contain small but fihite quantities of Ca.Using the same analytical techniques employed inthis study, no Ca was detected in analyzed biotitesthat contain no Ca: hence the Ca contents of the Lu-cerne biotites appear to be real. The Na contents arelow. The experimental results of Rutherford (1969)indicate that biotites crystallizing with alkali feld-spars of compositions comparable to those of the Lu-cerne should contain higher amounts of Na. The lowvalues observed may be due to the Al contents ormay result from solidus reequilibration.

F and Cl contents are finite, and low (Table 4,Fig.20). They are characteristic of biotites found in manyorogenic belts but lower than those from alkalic oranorogenic terranes (Ludington, 1974; Ludingtonand Munoz, 1975).

Ilmenite

Representative ilmenites were analyzed for Fe, Ti,Al, Cr, Mg, Si, and Mn. The results, plotted in Figure

I L M E N I T E A N A L Y S E SLUCERNE PLUTON

D. R. WONES, t979

- Apot i le - Phlogopi le- - A p o l i t e - L u c e r n e B i o l i l e

( A n n 6 t - S i d 3 0 - P h g )

. N o r l h o f f o u l t z o n eO Soulh of loul t zone


D R W O N E S , 1 9 7 9

o -o/o 1/ :o

-ugqL'

o :

@

-v o 3+L

o l

o 7

o

co l(D

xoro.;

oc . ^o t uct

ot{)

:F

o 9 5 r o o r o 5 i l o o o 5 o t o o t 5( F e + M n ) / 3 o x y g e n s M n / 3 o x y g e n s

- i o 0 2 0 4 0 6 o e r o

[ F / ( F * o H ) ] a e o r i r "

Fig. 22. F/(F + OH) of biotites plotted against F/(F + OH) ofcoexisting apatites from the Lucerne pluton. Heavy lines are I l00oand 600oC isotherms for pure phlogopite; dashed lines areisotherms calculated for biotite from the Lucerne pluton, based onLudington (1978).

21, show that there is a slightly higher conoentrationof Mn in the ilrnenites from the soutlern part of thepluton and that all of the ilmenites tend to be moreenriched in Fe than in Ti. This implies that there is 3to 5 mole percent MnTiO, (pyrophanite) component,and 0 to 9 mole p€rcent FerO, (hematite) componentin the ilmenite. Ilmenite most commonly occurs asinclusions included in all other minerals as well.Biotites that include ilmenite do not appear to bericher in TiO, than those that do not.

Magnetite

Magnetite is only found in areas of mylonitizationwhere it is always associated with chlorite in pseudo-morphs after biotite. These grains are almost pureFerOo. No magnetite has been observed in a primarytextural relationship with any primary mineral.

Chlorite

Small amounts of this secondary mineral occur in-terleaved with biotite in nearly every rock. In my-lonitized rocks, most of the biotite grains have beenaltered to chlorite, sphene and, rarely, epidote. Thechlorite is more aluminous than the biotite andnearly always preserves the Fel(Fe + Mg) value ofthe associated biotite. Chloritization is much moreintense in the porphyritic zone of the pluton, as is thedevelopment of secondary sphene.

Sphene

This mineral only occurs in chlorite pseudomorphsafter biotite.

. NORTH OFFAULT ZONE

O SOUTH OFFAULT ZONE

o 9

Fig. 21. Ti vs. (Fe * Mn) and Mn contents of ilmenites from theLucerne pluton. Upper diagram shows scatter between analyricalpoints. Lower diagram shows scatter between averaged handspecrmens.


Apatite

Apatite nearly always occurs as fine-grained sub-hedra usually associated with biotite. Microprobeanalyses were performed on the apatites to explorethe F and Cl fractionation between apatite and bio-tite (Stormer and Carmichael, l97l; Ludington,1978). The analyses are not stoichiometric and implythat there are other substituent anions such as car-bonate and sulfate as well as excess F in the apatite.Figure 22 is a plot of the F/(F + OH) of biotiteagainst that of apatite. The irregular fractionation ofF between the biotites and apatites indicates somedisequilibrium between the two and may be due tosubsolidus loss of F from the biotite.

Tourmaline

This mineral occurs in sprays on Springy pondMountain, near the NW boundary of the porphyriticfacies of the pluton. Tourmaline also occurs in thesingle outcrop of pegmatite observed near the west-ern margin of the pluton 800 m north of MooseBrook. Aplite dikes observed at the Craig Brook FishHatchery and on Blackcap Mountain containtourmalines. Trace amounts of tourmaline have beenobserved in 2 samples of the seriate facies of the plu-ton. The Fel(Fe + Mg) ratio varies between 0.65 and0.69.

Amphibole

This mineral was observed in only one thin sec-tron.

Zircon

The mineral is ubiquitous, and nearly always oc-curs associated with biotite.

Fluorite

This mineral was observed in only one specinen asthin lamellae interleaved with biotite.

Contact metamorphism

Novak (1979) determined that the thermal effectsofthe Lucerne pluton on its host rocks extend aboutI kn from the contacts. The major effect is recrys-tallization of the Vassalboro Forrration from quartz-calcite-muscovite-chlorite assemblages characteristicof the regional grade to plagioclase-biotite assem-blages, similar to the situation at the Togus plutonsto the southwest (Ferry, 1976). Quartz-calcite veins,deformed into tabular masses, react at higher gradesto form assemblages that contain tremolite, diopside,

and zoisite. The more pelitic layers within the Vassal-boro react to form andalusite- and corundum-bear-ing assemblages. Novak did not observe sillimaniteor garnet in any of the metamorphic assemblages,even those adjacent to the pluton at the contacts.

The inferred composition of the gas phase presentduring the prograde metamorphism of the Vassal-boro is relatively COr-rich. However, the later reac-tion of calcite-plagioclase assemblages to zoisite (orepidote) indicates a late-stage gas phase that wasHrO-rich.

The granite of the Wallamatogus pluton, whichlies a few hundred meters SW of the Lucerne plutonand predates the Lucerne, contains garnet and sil-limanite as accessory minerals and is confined to thePenobscot Formation. Novak found that biotite-cor-dierite assemblages within the Penobscot Formationprobably represent an earlier metamorphism thatpredated the intrusion of the Lucerne pluton.

The sequence of events as worked out by Novak is:(l) a prograde metamorphism of the Vassalboro For-mation that generated COr-rich fluids, followed by(2) the introduction of aqueous fluids into the meta-morphic rocks. Ferry (1978) suggested a similar se-quence for the Togus plutons, followed by the incor-poration of fluids into the crystallized granite pluton.In the Lucerne pluton there is little evidence forlarge-scale introduction of fluids into the granite af-ter its crystallization. There is some deuteric altera-tion and minor silicification along joints, but no ex-tensive metasomatism and retrograde reaction.Finally, restricted mylonitization and deformationtook place within specific portions of the pluton.

Intensive variables

One of the groat accomplishments of experimentalpetrology during the past two decades has been thedevelopment of a number of mineralogical methodsof determining the values of intensive parametersduring geological events. Such parameters have tra-ditionally been pressure and temperature, but nowwe can make approximate determinations of the ac-tivities or fugacities of chemical components. Currentwork may establish values for reaction rates, strainrates, and thermal histories as well.

Granitic rocks are the result of a long seeling his-tory beginning with a magma of uncertain origin.The total crystallization interval of such a magmacould range from 400" (Carmichael,1967) to only afew tens of degrees. This could be followed by sub-solidus recrystallization. Thus the mineral assem-blages that we observe in the rocks today are the re-

WONES: LUCERNE PLUT:ON 431

sult of a long integrated history of differenttemperatures, pressures, and fluids. These problemshave been repeatedly encountered in studies apply-ing the ilmenite-magnetite geothermometer-oxyba-rometer of Buddington and Lindsley (1964) to gra-nitic rocks (Haggerty, 1976).

System Ab-An-Q-HrO

One of the earliest suggestions for establishingtemperatures and pressures of granitic magma crys-tallization was that of Tuttle and Bowen (1958),namely that the composition of the liquid coexistingwith alkali feldspar, quartz, and a vapor phase in thesystem Ab-Or-Q-HrO had unique values, and thatthe residual liquids in a crystallizing magma mightbe modeled after the synthetic system. Recent addi-tions to this study by Luth et al. (1964), Steiner et al.(1975), and James and Hamilton (1968) show thathigh pressure, low activities of HrO, and the additionof the anorthite component can modify the composi-

tions of the melt coexisting with two feldspars,quartz, and gas.

Normative compositions of selected samples of theLucerne pluton are projected onto the Q-Ab-Or ter-nary diagram in Figure 23. Also plotted on the figureare the compositions of the ternary minipsal liquidsas determined by Tuttle and Bowen (1958) and thecomposition of liquids coexisting with quartz, plagio-clase, alkali feldspar, and vapor at I kbar as deter-mined by James and Hamilton (1968) for An, andAn, compositions in the more general system Q-Ab-An-Or-HrO. Most of the samples from the Lucernepluton plot within the alkali feldspar region ratherthan on the phase boundary between quartz andfeldspar. The most siliceous rocks plot near the three-phase boundary at 500 bars total pressure or near thefour-phase boundary at An3 composition at I kbar.As can be seen from Table 3, the porphyritic facies ofthe Lucerne pluton contains about 3 weight percentAn component.

NORMATIVE COMPOSITIONSLUCERNE PLUTON

D. R . WoNES, t979

-s An con len f ,S-phose po in l. Nor lh o f fou l to Soufh of foul tr A p l i f e sa Ternory min imum

AbFig. 23. Ternary projection of normative Q-Ab-Or contents of the rocks of the Luccrne pluton. Also plotted are minimum melting

compositions (triangles) for the system Q-Ab-Or-H2O of Tuttle and Bowen (1958) at 0.5, 1.0, 2.0,3.0, and 4.0 kbar (from right to left)and for the composition of the melt coexisti.g with quartz, plagioclase, alkali feldspar and vapor at An, and An5 compositions at I kbar(after James and Hamilton, 1968).

Or


The normative data are projected onto the An-Ab-Or ternary (Fig.24), as is the boundary curve be-tween plagioclase and alkali feldspar given by Jamesand Hamilton (1968) for I kbar. Compositions of theplagioclases and alkali feldspars observed within theLucerne pluton are given as well. The rocks of theLucerne pluton plot near the four-phase boundary.

The porphyritic facies of the Lucerne pluton con-tains miarolitic cavities. This fact, and the porphy-ritic texture, suggest that this facies of the pluton mayhave partially crystallized in the presenoe of a gasphase. Porphyritic texture can result from the ex-solution of gas from a phenocryst-bearing melt as theHrO pressure within the crystallizing nagma exceedsthe ambient pressure.

Abbott (1978) and Cherry and Trembath (1978)have examined the available information concerningthe coexistence of the two feldspars and liquid. Theyhave suggested that viborgitic (rapakivi) texture isdue to a change in ambient conditions, rather thanthe result ofperitectic reaction as suggested by Stew-art and Roseboom (1962). Such an event, if their

analysis is correct, would have taken place when 5percent of the alkali feldspar had crystallized, wouldhave been effective throughout all the presently ex-posed part of the pluton, and could have happenedwhen the magma moved into its present position.The porphyritic core region would have been the lastpart of the pluton to crystallize and would have accu-mulated the residual HrO from the rest of the systemduring crystallization of the anhydrous quartz andfeldspar.

Two-feldspar geothermometry

The use of the two-feldspar geothermometer hasbeen recently enhanced by the formulation of Stor-mer (1975) and the applications by Whitney andStormer (1976). Although the formulation was doneoriginally for sanidine, recent data are available formicrocline (Whitney and Stormer, 1977). The habitof the alkali feldspars in the granites of the LucernePluton is monoclinic, so that I have plotted the iso-therms for coexisting plagioclase and alkali feldsparsas originally given by Stormer (1975). Indicated terr-

NORMATIVE COMPOSITIONSLUCERNE PLUTON

D . R . W O N E S , 1 9 7 9

rfsld5por composit ions. Norlh of foulto Soulh of foullr Ap l i tes

PLAGIOCLASE

K - F E L D S P A R

AbFig. 24. Ternary projection of normative An-Ab-Or contents of the rocks of the Lucerne pluton. Boundary curve between alkali

feldspar and plagioclase at I kbar afler James and Hamilton (1968).


peratures ofequilibration range from 775" to 550"C.The range in composition of the alkali feldspars islimited, so that the range in temperatures reflects thevarying composition of plagioclase. The plagioclaseand alkali feldspar must have undergone somereequilibration and subsolidus recrystallization dur-ing cooling. The lower inferred temperatures couldreflect the decrease in the An content of the plagio-clase due to sericitization and,/or the reaction ofplagioclase with exsolving albite during the forma-tion of microcline perthite. The best estimate for thetemperature of the feldspar mantling event is about675"C.

Plotting the granite minimum melting curve at gassaturation as a function of pressure and temperatureyields a value ofabout I to 3 kbar for the pressure atwhich the Lucerne pluton crystallized (Fig. 25). Alsoplotted in Figure 25 is the boundary curve betweenthe AlrSiO, polymorphs, andalusite and sillimanite,as determined by Holdaway (1971) and by Richard-son et al. (1969). The lack of sillimanite in the contactmetamorphic rocks near the Lucerne pluton has twointerpretations. If we assume that the data on thequartzo-feldspathic phases are correctly interpreted,then the andalusite-sillirnanite curve established byHoldaway must be at too low a pressure, and thecurve of Richardson et al. is more nearly correct. Onthe other hand, if Holdaway's determination is cor-rect, it appears that the temperature estimates of theLucerne magma at low pressures are too high, andthat the actual curve of the granite minimum is not agood estirnate of the minimum melting conditions ofthe Lucerne magma. This entire analysis assumesthat the rocks immediately adjacent to the contactwere heated to magmatic temperatures.

Oxygen fugacity estimates

The use of magnetite-ilmenite pairs to estimatetemperatures and oxygen fugacities is not applicableto the Lucerne pluton as no magmatic magnetite hasbeen observed. The occurrence of ilrnenite with acomposition of llmrrPy,oHm, gives a range of oxygenfugacity-temperature values that approximate thoseof the assemblage fayalite-magnetite-quartz (Lindsley,1976,1978; Hewitt, 1978; Chou, 1978). If we assumethat the oxygen fugacity-temperature range of themagma approximates the FMQ assemblage, then wecan calculate anf^,o-T curve for the stability of thebiotites found in the Lucerne (Fig. 25). These in turncan be expressed in PH,o-f diagrams and superposedon the data for the quartzo-feldspathic components.With the data of Wones and Eugster (1965), as modi-

Temperof ure, oC

Fig. 25. Pressure vJ. temp€rature plot for the ternary minimumat water saturation in the system Q-Ab--Or-HrO after Tuttle andBowen (1958). Boundary curves between andalusite andsillimanite after Holdaway (1971) (solid) and Richardson et al.(1969) (dashed). The stippled area is the estimated temperaturerange of the crystallization of the Lucerne magma. The curvelabeled "Lucerne biotite" is the upper stability of biotites in theLucerne pluton at oxygen fugacities defined by the quartz-magnetite-fayalite assemblage (Hewitt, 1978). See text and Fig.26.

fied by Wones (1972), we can calculate a curve on theassumption that the Fe in the biotites is all Fe'*.

The biotites within the Lucerne pluton are limitedin mole fraction of Fe2* in the structural formula to0.51 to 0.71 of the octahedral constituents. In thistreatment, vacancies were counted as constituents, aswere Ti and Al; the ratio, Fel(Fe + Mg), is not ap-propriate. The stability curve calculated for thesealuminous biotites lies close to that determined byRutherford (1969) for the stability of synthetic alu-minous femrginous biotites. In Figure 25, the calcu-lated biotite stability curve intersects the granite min-imum ctrve of Tuttle and Bowen (1958), within therange of the feldspar temperature estimates, and atabout I kbar pressure. The P",o values of this curveare for biotites coexisting with magnetite. Actual Pr,o

oL

od)(l)

=tnano(L

\:.:..',.' r.,.,,, r.,,r,,rr:i : i , l l , , i ' '

, ,,:,,\. l , l . i .. . ' , l i i t .: l

tr i .,.,,,\ ' ' : ' . : ' : "" ' l l .

, ' , , : , \ , . , , , , . ,: : : , : ,

R 'G ' A B' ' 1969

,Fgtd9pg.r1,,,,Theimomeliy

TVONES: LUCERNE PLUTON

values for the Lucerne magma would be lower, asmagnetites are not present as magmatic phases.

Carmichael (1967; personal communication) hassuggested that the TiO, contents of biotites coexistingwith ilmenite or sphene are a fun-ctiq[ of temper-ature. Czamanske and Wone$ (1973) showed thatthis was true for the rocks of the Finnmarka com-plex. TiO, contents of the biotites from the Lucernepluton are comparable to those of the granites of theFinnmarka complex, for which Czamanske andWones estimated a crystalltzation temperature be-tween 675o and 7fr)oC. These data are also com-parable with those of Robert (1976) for synthetic Mg-biotites.

If we assume that the total pressure of the crystal-lizing Lucerne magma was about I kbar, then we canassume HrO pressures near that value and plot oxy-

- ) 6 q- -500

gen fugacity vr. temperature (Fig. 26) for the Lucernebiotites as if they coexisted with a spinel (magnetite).The biotite stability is limited by two curves, one forthe reaction to sanidine and spinel (magnetite) andone of,biotite plus quartz to sanidine and fayalite, or-thopyroxene, or cordierite depending upon the Fe-Mg-Al ratios. The frrst curve puts a boundary on theoxygen fugacity, the second on temperature. Both areplotted in Figure 25 for the 1rye limiting biotite com-positions. The maximum calculated temperatures forbiotite stability are given by the intersection of thetwo curves. This constraint shows good agreementwith the temperature estimates made from the two-feldspar thermometer and from the system Q-Ab-Or-An-HzO.

Crystallization sequence

Another approach is to use the data of Whitney(1975\ and of Maaloe and Wyllie (1975) that relatethe sequence of crystallization of the minerals to thetemperature, pressure, and water content of themagma. Biotite was the primary phase of the essen-tial minerals. and the occurrence of biotite-richschlieren within the pluton indicates that it musthave been a stable liquidus phase at the time of in-trusion.

The occurrence of the miarolitic cavities in theporphyritic core zone indicates that the magma didnot reach saturation with a vapor phase until wellover 90 percent ofthe presently exposed surface hadcrystallized. Thus, there was a gas-undersaturatedmagma in which biotite was stable, and in which thequartz, plagioclase, and alkali feldspar begin to crys-trlhze simultaneously. On the basis of the biotite andilmenite data, the oxygen fugacity of the melt musthave been relatively reducing, but exact limits cannotbe detennined.

Maaloe and Wyllie (1975) established crystalliz4-don sequences for a granitic magma for a series ofHrO contents. They used the Ni-NiO buffer to estab-lish oxygen fugacities in their experiments, and hadmagnetite as the early crystallizing phase. As a con-sequence, their data for biotite stability probablyyield terrperatures that are too low for direct appli-cation to the Lucerne pluton. the Fel(Fe + Mg) val-ues for their granite are lower than the values for theLucerne pluton. Their data for quartz and the feld-spars should be applicable. Whitney (1975) collectedsimilar data for a synthetic sample that did not con-tain ferromagnesian constiluents but was clos-e to theoompo$ition of the Lucerne pluton in terms of thequartuo-feldspathic components,

- t o

C)oo r - 1 4f

ll-

cq)ctl

xo9 - t 6crro

J

Temperoture, "CFig. 26. Log,o oxygen fugacity yr. tempetature. Dashed

boundary curves for hematite-magnetite and quartz-magnetite-fayalite are from Chou (1978). Solid curve for the quartz-magnetite-fayalite assemblage is after Hewitt (1978). The heavyline labeled Ann 5l is the stability curve ofa biotite in equilibriumwith sanidine and dagnetite that contains 5l mole percent Fe inthe octahedral layers. The dotted curve is th: equivalent for ?'lrhole percent Fe., The d4sh-dot curve is the estimated,upFe.rstability of the biotite + quaftz assefublagb .for AnB 71, and ,tleheavy. 66tr"4 line iS th€ equivalent curve for ,A,nfl 5I.

// et, ' x , // *v't


These combined data suggest that the Lucernemagma, upon intrusion at its present level, must havebeen saturated with qrartz, plagioclase, alkali feld-spar, and biotite but undersaturated with water. Wehave observed that the amount of water or other vol-atiles within the magma could not have been great,because of the large volume of the pluton that crys-tallized before the formation of the porphyritic corefacies. From Figure 25 we see that the magma musthave contained a finite amount of HrO correspond-ing to an HrO pressure of I to 2kbat. However, if themagma contained another volatile substance thatpromoted lower melting temperatures, then the bio-tite stability and the water contents could be morecompatible.

Boron as a possible component

Chorlton and Martin (1978) have demonstratedthat BrO. will lower the solidus of granitic magmas.Accessory tourmaline within the Lucerne pluton andlate quartz and tourmaline veins indicate that boronwas present in the magma. Boron would make themagma less viscous, and because of its tendency tobreak up silica polymers within the melt could sup-press crystal nucleation and lead to the coarse grainsize of the pluton.

Boron might also influence the position of theboundary curves between the feldspar5. \{a11ling ofalkali feldspar by plagioclase could be the result ofenriching the residual melt in BrO, during crystalli-zation of quartz and feldspar, thus shifting the phaseboundary toward alkali feldspar.

Origin of the Lucerne magma

Mineralogical studies can place a surprising num-ber of constraints on the origin of granitic magmas,although geochemical studies are essential for thebest resolution of such a problem. The magmaclearly originated from a potassiun-rich source, hadits water content controlled by reactions involvingbiotite, and was intruded from greater depths to itspresent level. The Al-rich biotites of the Lucerne plu-ton have not come to equilibrium with each other inregard to Ti and Al contents and may represent abiotite residuum from the source or disaggregated in-clusions. The presence of tourmaline suggests a bo-ron-enriched source. A quartz-plagioclase-biotitegneiss derived from the metamorphism of a gray-wacke-type sediment is a most hkely source material.

An earlier metamorphic event that could have de-pleted the source in nuscovite and HrO would havemade such a gneiss even more appropriate as a

source material. The Lucerne magma, once formed,would have carried residual qtartz, plagioclase, al-kali feldspar, and biotite to the site of the intrusion.

These concepts essentially follow the models thatWhite and Chappell (1977) have proposed for gran-ites derived from a sedimentary source ("S" gran-ites), and are in great contrast to the model proposedby Barker et al. (1975) for the Pikes Peak Batholith.The Lucerne pluton is one tenth the size of the PikesPeak Batholith, contains more plagioclase, and crys-talTtzed biotite at an earlier stage. According to themodel of Barker et al. (1915), the Lucerne plutonmust have formed in a less mature continental crustthan did the Pikes Peak Batholith.

Summary

I have attempted to demonstrate how studies ofmineralogy permit us to map rocks, to interpret theirhistory and deformation, to define conditions ofmagma crystallization, to constrain source regions ofmagmas, and even to understand geomorphic andglacial processes better. I am confident that manyother apphcations await us, once we have the visionto see them.

Acknowledgments

A large number of people have contributed to the data I havesummarized herein, and I would like to acknowledge their contri-butions. I thank the U.S. Geological Survey and the National Sci-ence Foundation for their support The pluton was mapped underthe auspices of the U.S. Geological Survey, and some of the recentmineralogical and chemical work was obtained through NationalScience Foundation Grant EAR 78-03655.

My field assistants, who have taught me more than I may havetaught them, were Robert M. Hazen, Robert L. Trithart, DavidMiller, Kenneth Shay, Nelson L. Hickling, and Robert A. Ayuso.The modal data summarized in this report were collected by Hick-ling and Ayuso. I am also indebted to Jane M. Hammarstrom, J.S. Huebner, and Cristina Silber Zen for their help in the labora-tory. U S. Geological Survey provided much of the analytical dataincluded in this summary. M. F. Kane of the U.S. Geological Sur-vey made available the use of a truck-mounted magnetometer.

Douglas G. Brookins and Robert E. Zanman have contributedto the resolution of the geochronology of the Lucerne pluton.

My understanding of the Iocal geology has been aided im-measurably by long discussions with P. H. Osberg, Olcott Gates,Arthur M. Hussey, and Allan Ludman, although they disagreewith some of my interpretations. I owe a special debt to my col-league, David B. Stewart, who originally suggested that the Lu-cerne pluton was appropriate for study. Stewart has mapped theBlue Hill and Castine quadrangles that include the southern lobeof the Lucerne pluton (Stewart, 1974; Stewart and Wones, 1974).

The text of the manuscript has been improved through reviewsby R. A. Ayuso, G. K. Czamanske, and Priestley Touknin, III. Iam grateful to my wife, Connie, for logistical and emotional sup-port during this project, and to my sons Edward and Andrew for


literal support during field investigations of numerous cliffs withinthe margins of the Lucerne pluton.

Finally, I would like to acknowledge the inspiration and chal-lenge that Paul C. Bateman of the U.S. Geological Survey hasgiven me. Paul patiently took me through a mutual project in theSierra Nevada (Bateman and Wones, l972a,b) and challenged meto produce data for New England that would complement the datathat he and his colleagues have put together for the Sierra Nevadabatholith (Bateman et al., 1963; Bateman and Clarke, 1974; Bate-man, 1979). This study is part of the answer to that challenge.

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- and - (1972b) Huntington Lake quadrangle, centralSierra Nevada, California-analyic data. U.S. Geological Sur-vey Prof. Pap. 724-A,18.

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- (1978) Fluid interaction betwcen granite and sedimentduring metamorphism, south-central Ma;ne. Am. J. Sci., 278,1025-1056.

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Holdaway, M. J. (1971) Stability of andalusite and the aluminumsilicate phase diagram. Am. J. Sci., 271,97-131.

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Manuscript received, February 11, 1980;

acceptedfor publication, February 13, 1980.

Documents

Contributions of crystallography, mineralogy, and petrology to the geology of the Lucerne pluton