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The Moosehorn Plutonic Suite, southeastern Maine and southwestern New Brunswick: age, petrochemistry, and tectonic setting.



ABSTRACT

The Moosehorn Plutonic plu·ton·ic  
adj.
Of deep igneous or magmatic origin: plutonic rocks.



[From Latin Pl
 Suite in the coastal Maine magmatic province covers an area of approximately 250 [km.sup.2] in the area of Calais, Maine Calais is a city in the state of Maine in the United States, situated on the St. Croix River at the border with St. Stephen, New Brunswick, Canada. It is in Washington County, Maine, United States. The population was 3,447 at the 2000 census. , and St. Stephen, New Brunswick New Brunswick, province, Canada
New Brunswick, province (2001 pop. 729,498), 28,345 sq mi (73,433 sq km), including 519 sq mi (1,345 sq km) of water surface, E Canada.
. Based on a compilation of previous work combined with new field mapping, geochronology geochronology

Dating and interpretation of geologic events in the history of the Earth. The classical technique of geochronology was stratigraphy, including faunal succession.
, and petrochemical data, the Moosehorn Plutonic Suite (MPS) is interpreted to consist mainly of five approximately contemporaneous plutons: Staples Mountain Gabbro gabbro: see basalt.
gabbro

Any of several medium- or coarse-grained rocks that consist primarily of plagioclase feldspar and pyroxene. Gabbros are found widely on the Earth and on the Moon.
, St. Stephen Gabbro, Calais Quartz Diorite Quartz diorite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less potassium feldspar. Quartz is present at between 5 to 20% of the rock. , Baring Granite, and Elliott Mountain Diorite diorite

Medium- to coarse-grained igneous rock that commonly is composed of about two-thirds plagioclase feldspar and one-third dark-coloured minerals, such as hornblende or biotite.
. The layered, sill-like Staples Mountain Gabbro is mainly mafic maf·ic  
adj.
Containing or relating to a group of dark-colored minerals, composed chiefly of magnesium and iron, that occur in igneous rocks.
, whereas the larger St. Stephen Gabbro consists of a core of dunite dunite

Yellowish green to green igneous rock composed almost entirely of olivine. Chromite and magnetite also occur in dunite, as do spinel, ilmenite, pyrrhotite, and platinum in some cases. Dunites may be a source of chromium. Places of occurrence include Dun Mtn.
 and troctolite Troctolite is a rare ultramafic intrusive rock type. It consists essentially of variable amounts of olivine and calcic plagioclase along with variable minor pyroxene. It thus is midway between peridotite and anorthosite. , surrounded by olivine olivine (ŏlĭv`ēn), an iron-magnesium silicate mineral, (Mg,Fe)2SiO4, crystallizing in the orthorhombic system.  gabbro and gabbro layers. The latter unit grades to quartz diorite of the Calais Quartz Diorite, the most extensive component of the MPS. The Baring Granite consists of medium-grained biotite biotite (bī`ətīt'), iron-rich variety of phlogopite, most abdunant of the mica minerals.
biotite
 or black mica

Silicate mineral in the common mica group.
 monzogranite, which is widely mingled with quartz diorite and diorite of the Calais Quartz Diorite. The latest pluton plu·ton  
n.
A body of igneous rock formed beneath the surface of the earth by consolidation of magma.



[German, back-formation from plutonisch, plutonic, from Latin
 of the MPS appears to be the Elliott Mountain Diorite, which consists mainly of texturally varied dioritic di·o·rite  
n.
Any of various dark, granite-textured, crystalline rocks rich in plagioclase and having little quartz.



[French, from Greek diorizein, to distinguish : dia-,
 rocks. Each pluton of the MPS is interpreted to have formed by magma differentiation to produce a range of derived compositions. Evidence for mingling and mixing between magmas is also widespread in the MPS, but was not investigated during this study.

A sample from the Baring Granite yielded a U-Pb (zircon zircon

Silicate mineral, zirconium silicate, ZrSiO4, the principal source of zirconium. Zircon is widespread as an accessory mineral in acid igneous rocks; it also occurs in metamorphic rocks and, fairly often, in detrital deposits.
) crystallization Crystallization

The formation of a solid from a solution, melt, vapor, or a different solid phase. Crystallization from solution is an important industrial operation because of the large number of materials marketed as crystalline particles.
 age of 421.1 [+ or -] 0.8 Ma) and phlogopite phlog·o·pite  
n.
A yellow to dark brown mica, K(Mg,Fe)3AlSi3O10(OH)2, used in insulation.



[Greek phlog
 from the olivine gabbro unit of the St. Stephen Gabbro yielded a [sup.40]Ar/[sup.39]39Ar cooling age of 421 [+ or -] 4 Ma. The gabbroic parts of the St. Stephen Pluton and the Calais Quartz Diorite are similar in petrochemistry pet·ro·chem·is·try  
n.
1. The chemistry of petroleum and its derivatives.

2. The branch of geochemistry that deals with the chemical composition of rocks.
 to mafic and intermediate parts of the Bocabec Pluton of the Saint George Saint George, town (1991 pop. 1,648), on St. George's Island, Bermuda. It was the capital of Bermuda until 1815, when it was replaced by Hamilton. During the American Civil War it harbored Confederate blockade-runners.  Batholith batholith, enormous mass of intrusive igneous rock, that is, rock made of once-molten material that has solidified below the earth's surface (see rock). Batholiths usually are granitic (see granite) in composition, have steeply inclined walls, have no visible floors,  whereas the Baring Granite is similar to the granitic parts of the Bocabec Pluton. Plutons of the MPS generally have calc-alkalic to within-plate chemical characteristics, and their slightly negative (-0.4) to moderately positive (+3.4) [[epsilon].sub.Nd] values are consistent with formation by melting of primitive lower crust, such as may have been present below the Mascarcne and Ellsworth terranes. Melting likely occurred in a back-arc setting related to juxtaposition in the late Silurian between these terranes and more outboard terranes of the northern Appalachian orogen.

RESUME

Le cortege plutonique de Moosehorn dans la province magmatique et cotiere du Maine couvre une superficie d'environ 250 kilometres carres dans la region de Calais, au Maine, et de St. Stephen, au Nouveau-Brunswick. Selon une compilation de travaux anterieurs combines a de nouvelles donnees petrochimiques, geochronologiques et cartographiques obtenues sur le terrain, le cortege plutonique de Moosehorn (CPM) est interprete comme un ensemble principalement compose de cinq plutons plus ou moins cinq syngenetiques: le gabbro du mont Staples, le gabbro de St. Stephen, la diorite quartzite quartzite, usually metamorphic rock composed of firmly cemented quartz grains. Most often it is white, light gray, yellowish, or light brown, but is sometimes colored blue, green, purple, or black by included minerals.  de Calais, le granite de Baring et la diorite du mont Elliott. Le gabbro stratifie en filons-couches du mont Staples est principalement mafique, tandis que le gabbro plus vaste de St. Stephen est constitue d'un noyau Noy`au´

n. 1. A cordial of brandy, etc., flavored with the kernel of the bitter almond, or of the peach stone, etc.
 de dunite et de troctolite, entoure de strates de gabbro et de gabbro a olivine. Cette derniere unite se classe parmi la diorite quartzite du pluton de diorite quartzite de Calais, l'element le plus etendu du CPM. Le granite de Baring est constitue de monzogranite a biotite a grain moyen, abondamment mele a de la diorite quartzite et a de la diorite du pluton de diorite quartzite de Calais. Le pluton le plus recent du CPM semble etre la diorite du mont Elliott, principalement constituee de roches dioritiques de textures diverses. Chaque pluton du CPM se serait, selon les interpretations, forme forme (form) pl. formes   [Fr.] form.

forme fruste  (froost) pl. formes frustes   an atypical, especially a mild or incomplete, form, as of a disease.
 par differenciation magmatique ayant produit un eventail de compositions derives. Les indices temoignant d'un melange mé·lange also me·lange  
n.
A mixture: "[a] building crowned with a mélange of antennae and satellite dishes" Howard Kaplan.
 et d'un mixage entre les magmas sont egalement repandus dans le CPM, mais ils n'ont pas ete analyses dans le cadre de la presente etude e·tude  
n. Music
1. A piece composed for the development of a specific point of technique.

2. A composition featuring a point of technique but performed because of its artistic merit.
.

Un echantillon du granite de Baring a ete situe a 421,1 [+ or -] 0,8 Ma par cristallisation au u-Pb (a partir du zircon) et une datation de la phlogopite de l'unite de gabbro a olivine du gabbro de St. Stephen a situe son age de refroidissement [sup.40]Ar/[sup.39]Ar a 421 [+ or -] 4 Ma. Les parties gabbroiques du pluton de St. Stephen et de la diorite quartzite de Calais presentent une petrochimie semblable sem·bla·ble  
adj.
1. Having a resemblance; resembling or like: unfamiliar symbols semblable to religious icons.

2. Seeming; apparent.

n.
 aux parties mafiques et intermediaires du pluton de Bocabec du batholite de Saint George, tandis que le granite de Baring ressemble aux parties granitiques du pluton de Bocabec. Les plutons du CPM possedent generalement des caracteristiques chimiques calco-alcalines a intra-plaque, et leurs valeurs [[epsilon].sub.Nd] legerement negatives (-0,4) a moyennement positives (+3,4) correspondent a une formation par fusion de la croute inferieure primitive, comme celle Celle (tsĕl`ə), city (1994 pop. 73,670), Lower Saxony, N Germany, on the Aller River. Its manufactures include food products, electronic components, chemicals, and textiles. Wax processing and horse breeding are important locally.  pouvant etre survenue au-dessous des terranes de Mascarene et d'Ellsworth. La tusion est probablement survenue dans un cadre arriere-arc apparente a une juxtaposition de ces terranes et des terranes plus limitrophes de l'orogene du nord des Appalaches au cours du Silurien tardif.

[Traduit par la redaction]

INTRODUCTION

The coastal Maine magmatic province (Fig. 1) contains voluminous plutonic and volcanic rocks rocks which have been produced from the discharges of volcanic matter, as the various kinds of basalt, trachyte, scoria, obsidian, etc., whether compact, scoriaceous, or vitreous.

See also: Volcanic
 of Silurian and Devonian age (Geol.) the age next older than the Carboniferous and later than the Silurian; - called also the Age of fishes ltname>. The various strata of this age compose the Devonian formation or system, and include the old red sandstone of Great Britain.  and dominantly mafic and felsic fel·sic  
adj.
Containing a group of light-colored silicate minerals that occur in igneous rocks.



[fel(dspar) + s(ilica) + -ic.
 compositions (e.g., Hogan and Sinha 1989; Seaman et al. 1999). The focus of this study, the Moosehorn Plutonic Suite (MPS), is part of the coastal Maine magmatic province, exposed over an area of about 250 [km.sup.2] in the vicinity of Calais, Maine, and St. Stephen, New Brunswick (Fig. 1). The MPS was previously termed the Moosehorn Igneous ig·ne·ous  
adj.
1. Of, relating to, or characteristic of fire.

2. Geology
a. Formed by solidification from a molten state. Used of rocks.

b. Of or relating to rock so formed; pyrogenic.
 (or Intrusive) Complex (e.g., Ludman and Hill 1986; Hogan and Sinha 1989; Jurinski 1990; Hill 1991), and includes gabbroic, dioritic, and granitic plutons in the vicinity of the Moosehorn Wilderness Preserve south of Calais, Maine. Complex intrusive relationships between the mafic and felsic components of these units were documented by the above authors and also by others such as Abbott (1986) and Hill and Abbott (1989). They described evidence of magma mingling, and concluded that the gabbroic, dioritic, and granitic magmas that formed these plutons were coeval co·e·val  
adj.
Originating or existing during the same period; lasting through the same era.

n.
One of the same era or period; a contemporary.
. Abbott (1977, 1986) demonstrated that the plutonic rocks assigned here to the MPS are older than the Devonian Red Beach Granite and hence suggested a Silurian-Devonian age. A Devonian age was suggested by Ludman and Hill (1990), but Jurinski (1990) suggested that a Silurian age is more likely, based on his U-Pb (zircon) age of 434 [+ or -] 9 Ma.

[FIGURE 1 OMITTED]

The purpose of this paper is to describe the distribution and petrology petrology, branch of geology specifically concerned with the origin, composition, structure, and properties of rocks, primarily igneous and metamorphic, and secondarily sedimentary.  of plutons that make up the Moosehorn Plutonic Suite, to present new U-Pb (zircon) and [sup.40]Ar/[sup.39]Ar data that closely constrain the age of the MPS, and to interpret its petrogenesis pet·ro·gen·e·sis  
n.
The branch of petrology that deals with the origin of rocks, especially igneous rocks.



pet
 and tectonic setting at the time of emplacement. Based on petrological and age similarities, we further suggest that the Bocabec Pluton and Utopia Granite of the Saint George Batholith in southwestern New Brunswick are equivalent to parts of the MPS, and hence that the coastal Maine magmatic province should be extended into southwestern New Brunswick.

GEOLOGICAL SETTING

Several fault-bounded geological terranes have been recognized in southern Maine and southwestern New Brunswick (Fig. 1). The MPS stitches the boundary between the St. Croix on the northwest and Mascarene (on the southeast) terranes of Fyffe and Fricker (1987) or St. Croix and Ellsworth terranes of Robinson et al. (1998). Rocks of the St. Croix terrane ter·rane also ter·rain  
n.
1. A series of related rock formations.

2. An area having a preponderance of a particular rock or rock groups.



[Alteration of terrain.]
 intruded by the MPS are mainly shale and quartz-rich sandstone of the Cambrian-Ordovician Cookson Group Cookson Group plc is a leading materials technology company headquartered in London, England, which provides materials, processes and services to customers worldwide. The Group's operations are formed into three divisions – Electronics, Ceramics and Precious Metals. . The Mascarene terrane in the study area is represented by Silurian rocks of the Mascarene Group, including conglomerate, volcanic and volcaniclastic rocks, sandstone, and shale (Fyffe et al. 1999). These Cambrian-Ordovician and Silurian rocks are contact metamorphosed and locally migmatized (Hussey et al. 1967; Ludman and Hill 1990) by the MPS, and also occur as xenoliths and roof pendants in the MPS.

Other plutonic rocks occur around the MPS, including the Pocomoonshine Gabbro-Diorite (Westerman 1972) to the west, the Meddybemps and Charlotte granites to the south and southeast, and the Red Beach Granite to the east (Figs. 1, 2). Small bodies of granite intruded into the Elliott Mountain Diorite may be related to the Red Beach or Charlotte granites (Abbott 1986). All of these granitic bodies intruded plutons of the MPS, although the age difference is not well constrained by existing geochronology (e.g., Hill and Abbott 1989). The Pocomoonshine Gabbro-Diorite, for which a [sup.40]Ar/[sup.39]Ar (hornblende hornblende: see amphibole.
hornblende

Any of a subgroup of amphibole minerals that are calcium-iron-magnesium-rich and monoclinic in crystal structure.
) age of 422.7 [+ or -] 3 Ma has been reported (West et al. 1992), is not in contact with units of the MPS but may be of similar age. The other granitic units are assumed to be significantly younger (Devonian) and not included in the MPS (e.g. Amos 1963; Abbott 1986; Ludman and Hill 1990).

[FIGURE 2 OMITTED]

Although Hogan and Sinha (1989) stopped their map of the coastal Maine magmatic province at the Canadian border, the presence of Silurian-Devonian gabbroic to granitic plutons of the Saint George Batholith (e.g., McLeod 1990; McLeod et al. 1994) suggests that it extends across the international border into southwestern New Brunswick (Fig. 1, 2). The few maps that show details of plutonic units on both sides of the border (e.g., Ruitenberg and McCutcheon 1978) suggest continuity between the Bocabec Pluton of the Saint George Batholith and the unit of the MPS here termed the Elliott Mountain Diorite. The Bocabec Pluton consists of gabbroic, dioritic, granodioritic, and granitic rocks with complex contact relationships (Fyffe 1971; McLeod et al. 1994) that appear analogous to those among some plutons of the MPS. The Utopia Granite part of the Saint George Batholith intruded the Bocabec Pluton, but locally is veined by granodiorite granodiorite

Medium- to coarse-grained rock that is one of the most abundant intrusive rocks. It contains quartz and is distinguished from granite by having more plagioclase feldspar than orthoclase feldspar; its other mineral constituents include hornblende, biotite, and
 of the Bocabec Pluton; the granodiorite was interpreted by McLeod (1990) and Fyffe (1971) as a zone of commingled rocks between the two plutons, and McLeod (1990) referred to the Bocabec and Utopia plutons collectively as the Digdeguash Lake Intrusive Suite.

PLUTONS OF THE MOOSEHORN PLUTONIC SUITE

Terminology

As noted in the Introduction, consistency has yet to be attained in published terminology for plutonic units in the study area. Ludman and Hill (1986) used Moosehorn Intrusive Complex as a collective term for plutonic units in the Calais area; however, Jurinski (1987) and Hogan and Sinha (1989) used the term Moosehorn Igneous Complex. Ludman and Hill (1986) excluded Staples Mountain Gabbro from their Moosehorn Intrusive Complex, although its close spatial association and petrographic pe·trog·ra·phy  
n.
The description and classification of rocks.



pe·trogra·pher n.
 features (Fig. 2, Table 1) appear to justify its inclusion.

Hence, as used here, the MPS consists of five plutons termed the Staples Mountain Gabbro, St. Stephen Gabbro, Calais Quartz Diorite, Baring Granite, and Elliott Mountain Diorite (Fig. 2), each named according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 its dominant and most characteristic rock type, although each contains a variety of components (Table 1). Smaller bodies of gabbro, diorite, and granite are present throughout these main plutons. The individual pluton names were used by previous workers, except for Elliott Mountain, a new name introduced by McLaughlin (2003) for part of the Calais gabbro/diorite of Hogan and Sinha (1989). Hogan and Sinha (1989) included all of the mafic-intermediate plutonic rocks between the Baring and Red Beach granite bodies in the Calais gabbro/diorite; however, we use the term Calais Quartz Diorite only for the gabbro-diorite intrusive complex of Ludman and Hill (1986, 1990), which also contains a substantial component of granite and metasedimentary xenolithic material. We use the name Elliott Mountain Diorite to refer to the gabbro unit of Ludman and Hill (1986, 1990). That unit extends into the adjacent map area of Abbott (1986), who described it as complex mixture of mainly gabbro, diabase diabase: see basalt.
diabase
 or dolerite

Fine- to medium-grained, dark gray to black intrusive igneous rock. Diabase is one of the dark rocks known commercially as “black granite.
, and granodiorite, intruded by younger granite. We consider the Calais and Elliott Mountain units to be different from one another overall, although both contain a wide variety of rock types and distinction between them at the outcrop scale is ambiguous (see below). Similar and probably co-magmatic mafic rock mafic rock

In geology, any igneous rock dominated by the silicates pyroxene, amphibole, olivine, and mica. These minerals are high in magnesium and ferrous iron, and their presence gives mafic rock its characteristic dark colour. It is usually contrasted with felsic rock.
 types also occur throughout the Baring Granite unit, as well as in the Meddybemps Granite to the south. Like previous workers, we exclude clearly younger (Devonian?) granitic plutons in the area, such as Meddybemps, Charlotte, and Red Beach (Fig. 2), from the MPS.

Distinction between gabbro and diorite is problematic in the MPS, especially in outcrop and hand specimen. We use the term gabbro when we consider that the rock is, or was originally before alteration, dominated by pyroxene pyroxene (pī`rŏksēn), name given to members of a group of widely distributed rock minerals called metasilicates in which magnesium, iron, and calcium, often with aluminum, sodium, lithium, manganese, or zinc occur as X in the chemical  as the ferromagnesian fer·ro·mag·ne·sian  
adj.
Containing iron and magnesium.



ferromagnesian  

Containing iron and magnesium. Magnetite and hornblende are ferromagnesian minerals.
 mineral component, and diorite when amphibole amphibole (ăm`fəbōl'), any of a group of widely distributed rock-forming minerals, magnesium-iron silicates, often with traces of calcium, aluminum, sodium, titanium, and other elements.  is the dominant ferromagnesian mineral. Hence we term the hornblende gabbro of some earlier workers (e.g., Abbott 1986) as diorite.

Intrusive relationships

The MPS is characterized by complex zones in which diorite forms enclaves in granite, suggesting that the diorite magma was only partially crystallized at the time of emplacement of the granite magma, and that the two magmas commingled (Hill and Abbott 1989; Jurinski 1990; Ludman and Hill 1990; Hill 1991). These enclaves vary in shape from amoeboid a·moe·boid
adj.
Variant of ameboid.
 to angular, and in size from cm-scale to m-scale, and were described in detail by previous workers (e.g., Hill and Abbott 1989; Jurinski 1990). The dioritic component dominates in the areas included in this study in the Calais Quartz Diorite and Elliott Mountain Diorite, whereas the granitic component dominates in the area shown as Baring Granite (Fig. 2). A complex relationship also appears to exist between dioritic and gabbroic magmas in the MPS, as locally diorite and quartz diorite appears to cross-cut gabbro, and xenoliths of gabbro are present in diorite and quartz diorite, but overall their petrographic and chemical features are gradational gra·da·tion  
n.
1.
a. A series of gradual, successive stages; a systematic progression.

b. A degree or stage in such a progression.

2.
. In this study, the boundary between the St. Stephen Gabbro and Calais Quartz Diorite units is drawn so as to exclude, in so far as possible, gabbroic rocks from the latter pluton. Dykes of granite occur in gabbro in both the Staples Mountain and St. Stephen plutons, indicating that the granite is at least slightly younger than (and not mingled with) the gabbro magma. Because they are similar in appearance, these granite dykes are assumed to be co-magmatic with the granite that dominates the Baring Granite unit of the MPS.

The Elliott Mountain Diorite is dominated by dioritic rocks (gabbro of Abbott 1986 and Ludman and Hill 1990), although granodiorite and granite are also present, especially in the eastern part of the unit (Abbott 1986). Where observed, the contact between the Calais Quartz Diorite and the Elliott Mountain Diorite appears to be sharp and marked by a reduction in grain size in the diorite as the contact is approached, suggesting the presence of a chilled margin. Based on the lack of observed mingling relationships during this study, we suggest that the Elliott Mountain Diorite may be at least somewhat younger that the Baring Granite, but more detailed mapping is needed along their contact in order to confirm this suggestion. The Elliott Mountain Diorite is older than the Charlotte, Magurrewock Lakes, and Red Beach granites that intrude intrude,
v to move a tooth apically.
 it on the south and east, and which are excluded from the MPS.

In addition to units included in the five main plutons, small bodies of dioritic and gabbroic rocks (e.g., Woodland Dump gabbro of Ludman and Hill 1990) also are present in the MPS and adjacent units. A few samples were collected from these units for comparison with the main dioritic and gabbroic units of the MPS.

Petrography pe·trog·ra·phy  
n.
The description and classification of rocks.



pe·trogra·pher n.
 

Petrographic features of die main units of the MPS are summarized in Table 1, and commented on briefly below.

Staples Mountain Gabbro

Coughlan (1986) recognized five units in the Staples Mountain Gabbro, designated I to V from inferred bottom to top: I--gabbro, anorthositic gabbro, and olivine gabbro; II--subophitic augite augite

Most common pyroxene mineral, occurring chiefly as blocky crystals in basalts, gabbros, andesites, and various other dark igneous rocks. It also is a common constituent of lunar basalts and meteorites and may be found in certain metamorphic rocks, such as pyroxenites.
 gabbro; III--interlayered norite nor·ite  
n.
See gabbro.



[Norwegian Norge, Norway + -ite1.]


nor·it
 and anortbosite; IV--unlayered augite gabbro and minor olivine gabbro; V --unlayered gabbronorite, with increased orthopyroxene orthopyroxene  

Any variety of the mineral pyroxene that crystallizes in the orthorhombic system and contains no calcium and little or no aluminum. Enstatite is an orthopyroxene.
 and no olivine, in contrast to unit IV. She interpreted the pluton to be a layered sill-like body, formed by crystal fractionation fractionation /frac·tion·a·tion/ (frak?shun-a´shun)
1. in radiology, division of the total dose of radiation into small doses administered at intervals.

2.
 processes; more details are available in Coughlan (1986).

St. Stephen Gabbro

Paktunc (1989) divided what he termed the St. Stephen Intrusion into ultramafic ul·tra·maf·ic  
adj.
Ultrabasic.



ultramafic  

Containing mainly mafic minerals. Used of igneous rocks and often used interchangeably with ultrabasic. Dunite is an ultramafic rock.
, olivine-bearing mafic, and mafic zones, and interpreted compositional variation and local crude layering to fractional crystallization fractional crystallization  

A process by which a chemical compound is separated into components by crystallization. In fractional crystallization the compound is mixed with a solvent, heated, and then gradually cooled so that, as each of its constituent
. We instead include most of the mafic zone of Paktunc (1989) in the Calais Quartz Diorite, and the remainder of the St. Stephen Pluton is divided into four units: dunite, troctolite, olivine gabbro, and gabbro (Fig. 2). The pluton has crudely concentric zoning in map view, with the central dunite unit surrounded by the locally well layered troctolite unit, then the olivine gabbro unit, and finally the gabbro unit around the margin. Contacts between these units appear to be gradational, implying that they formed as a result of differentiation processes in a single parent magma. The St. Stephen Gabbro contains significant sulphide mineralization of potentially economic importance, especially for Ni and Co (Houston 1986; Kooiman 1996).

The dunite typically contains 95-100% olivine with minor plagioclase plagioclase

Any member of the series of abundant feldspar minerals that usually occur as light- to medium-grey-coloured, transparent to translucent grains or crystals. Plagioclase ranges in composition from albite to anorthite.
, pyroxene, and chromite chromite (krō`mīt), dark brown to black mineral. It is an iron-chromium oxide, FeCr2O4, with traces of magnesium and aluminum. , and has a coarse-grained adcumulate texture (Fig. 3a). It is partially serpentinized, and in the smaller satellite bodies, olivine has been completely replaced by serpentine serpentine (sûr`pəntēn, –tīn), hydrous silicate of magnesium. It occurs in crystalline form only as a pseudomorph having the form of some other mineral and is generally found in the form of chrysotile (silky fibers) and  and magnetite magnetite (măg`nətīt), lustrous black, magnetic mineral, Fe3O4. It occurs in crystals of the cubic system, in masses, and as a loose sand. . Sulphide minerals appear to be concentrated in the serpentinized parts of the dunite, suggesting that they also may be secondary. With decreasing cumulus cumulus: see cloud.  olivine and increasing cumulus plagioclase, the dunite grades into troctolite (Fig. 3b). Some parts of the troctolite consist of interlayered olivine-rich troctolite and anorthosite anorthosite

Type of igneous rock composed predominantly of calcium-rich feldspar. It is considerably less abundant than either basalt or granite, but the complexes in which it occurs are often immense.
. Pyroxene, hornblende, and magnetite are minor components of the troctolite. With increasing amounts of pyroxene, the troctolite in turn grades to olivine gabbro (Fig. 3c), olivine gabbronoritc, and anorthositic gabbro all included in the olivine gabbro unit of the pluton. In addition to olivine and plagioclase, both orthopyroxene and clinopyroxene clinopyroxene  

Any variety of the mineral pyroxene that crystallizes in the monoclinic system. Diopside and augite are clinopyroxenes.
 are typically present, as well as varying amounts of amphibole and phlogopite, and accessory apatitc, titanite ti·tan·ite  
n.
See sphene.
, and zircon. The southwestern and southeastern parts of the pluton consist mainly of gabbro, in which large grains of clinopyroxene enclose plagioclase laths, and orthopyroxene is minor or absent (Fig. 3d).

[FIGURE 3 OMITTED]

Although both the St. Stephen and Staples Mountain plutons contain abundant olivine-bearing rocks, the Staples Mountain Gabbro appears to lack the ultramafic component that is present in the St. Stephen Gabbro, and the latter lacks the aligned plagioclase grains that are characteristic of the Staples Mountain body, at least at the current levels of exposure. These differences may be related to the smaller size of the Staples Mountain body.

Calais Quartz Diorite

The Calais Quartz Diorite unit consists mainly of quartz diorite grading to diorite. The rocks are typically fine to medium grained with hypidiomorphic granular to locally ophitic o·phit·ic  
adj.
1. Of or relating to ophite.

2. Having a texture composed of lath-shaped plagioclase crystals in a matrix of pyroxene crystals.
 texture involving amphibole and plagioclase (Fig. 3e). Two types of amphibole are present, an earlier generation of magnesio-hornblende with greenish brown-brown-tan pleochroism Pleochroism

In some colored transparent crystals, the effect wherein the color is quite different in different directions through the crystals. In such a crystal the absorption of light is different for different polarization directions.
 and later pale green-green actinolitic hornblende. Most samples also contain augite and biotite. Interstitial In a separate window. See interstitial ad.

(World-Wide Web) interstitial - A World-Wide Web page that appears before the expected content page. Interstitials can be used for advertising (intermercial, transition ad) or to confirm that the user is old enough to view the
 quartz makes up 5 to 8% of the rock. Minor K-feldspar is present locally, and may reflect places where mixing occurred between mafic and granitic magmas. In some areas, generally near contacts with the Baring Granite unit, quartz diorite has hiatal porphyritic por·phy·rit·ic   also por·phy·rit·i·cal
adj.
1. Of or containing porphyry.

2. Containing relatively large isolated crystals in a mass of fine texture.

Adj. 1.
 texture with plagioclase phenocrysts 2 to 4 cm in length, set in a fine-grained intersertal to intergranular matrix of augite, plagioclase, and quartz. Outcrop-scale areas of gabbro within the Calais Quartz Diorite unit may be xenolithic or mingled material from the Staples Mountain and St. Stephen plutons, although some may be younger intrusions, perhaps related to the Elliott Mountain Diorite.

Baring Granite

Typical granite of the Baring Granite unit is coarse-grained with hypidiomorphic sub-equigranular texture (Fig. 3f, g). Modal composition is mainly syenogranite to monzogranite, with quartz, plagioclase, and potassium feldspar potassium feldspar

A type of alkali feldspar that contains the molecule KAlSi3O8. Microcline and orthoclase are types of potassium feldspar.
 present in approximately equal amounts, and biotite [+ or -] hornblende forming approximately 6 to 8%. Plagioclase locally mantles the potassium feldspar in rapakivi texture. Accessory phases include zircon, apatite apatite (ăp`ətīt), mineral, a phosphate of calcium containing chlorine or fluorine, or both, that is transparent to opaque in shades of green, brown, yellow, white, red, and purple. , allanite Al´lan`ite

n. 1. (min.) A silicate containing a large amount of cerium. It is usually black in color, opaque, and is related to epidote in form and composition.
, and titanite. Near the margins of the pluton, the granite contains numerous xenoliths, composed primarily of metasedimentary rocks from the St. Croix terrane in the west, as well as displaying the complex mingling relations with the Calais Quartz Diorite described by Hill and Abbott (1989), Jurinski (1990), Ludman and Hill (1990), and Hill (1991)

Elliott Mountain Diorite

The Elliott Mountain Diorite unit, although heterogeneous, consists mainly of diorite grading to quartz diorite. Typical diorite (Fig. 3h) is made up of plagioclase, hornblende, augite, orthopyroxene, quartz, magnetite, titanite, and apatite. Augite is typically interstitial to plagioclase, whereas orthopyroxene occurs as relict RELICT. A widow; as A B, relict of C D.  cores in hornblende. The diorite contains pillow-shaped bodies of fine-grained diorite (diabase of Abbott 1986), which appears to be of similar composition to the host diorite. They may have formed by disruption of early crystallized parts of the magma by subsequent magma movement. A swarm of northeast-southwest trending bodies tapering to dykes composed of blue-grey biotite-hornblende granodiorite is present throughout the Elliott Mountain diorite, as mapped by Abbott (1986). These dykes contain numerous angular blocks composed of diorite, and are likely to be related to one of the adjacent younger granitic plutons.

Minor gabbroic and dioritic units

The gabbro body in the vicinity of the Woodland Dump was described by Ludman and Hill (1990) to consist of olivine norite. Our sample (SS00-129; Fig. 2) consists of medium-grained plagioclase, orthopyroxene, olivine, brown amphibole, and phlogopite, and is similar to samples from the olivine gabbro unit of the St. Stephen Gabbro. A mafic dyke-like body (SS00-108) sampled in the Baring Granite consists mainly of plagioclase, with minor quartz, K-feldspar, green-brown amphibole, clinopyroxene, and orthopyroxene.

GEOCHRONOLOGY

U-Pb Dating

Dated sample SS00-124 is a white, medium- to coarse-grained monzogranite, typical of the Baring Granite unit. Zircon grains were separated from a 20 kg sample in the geochronology laboratory at the Massachusetts Institute of Technology by standard techniques, abraded to obtain clean, unaltered grains, and dated using methodology as described by Schmitz and Bowring (2003). Two pale yellow, slender prisms (length:width 2.8:1) with blunt terminations, as well as two fragments of such prisms, were analyzed (Table 2). All four fractions are concordant, yielding a precise crystallization age of 421.1 [+ or -] 0.8 Ma (Fig. 4), at 2 [sigma] error.

[FIGURE 4 OMITTED]

This age is the same, within error, as the age of 423 [+ or -] 3 Ma obtained by the U-Pb (zircon) method for the Utopia Granite (M.L. Bevier, 2001, personal communication to S.M. Barr). The age is similar also to ages of various other plutons of the coastal Maine magmatic province (Fig. 1), such as the South Penobscot Pluton (419 [+ or -] 2 Ma, U-Pb, zircon; Stewart et al. 2001), Spruce Head Pluton (421 [+ or -] 1 Ma, U-Pb, zircon; Tucker et al. 2001), Cadillac Mountain Cadillac Mountain, with an elevation of 1,530 feet (466 m)[1], is the highest point along the East Coast of the United States.  intrusive complex (424 [+ or -] 2 and 419 [+ or -] 2 Ma, U-Pb, zircon; Seaman et al. 1995), and Sedgwick Pluton (419.5 [+ or -] 1 Ma, U-Pb, zircon; Stewart et al. 2001).

[sup.40]Ar/[sup.39]Ar Dating

Sample SS98-36 from the olivine gabbro unit of the St. Stephen Gabbro (location shown on Fig. 2) contained relatively large and abundant interstitial phlogopite suitable for [sup.40]Ar/[sup.39]Ar dating. Phlogopite grains were picked from the crushed sample using tweezers tweezers An instrument with pincers used to grasp or extract. See Optical tweezers.  under a binocular microscope binocular microscope
n.
A microscope having two eyepieces, one for each eye, so that the object can be viewed with both eyes.
. For irradiation in the McMaster University McMaster University, at Hamilton, Ont., Canada; nondenominational; founded 1887. It has faculties of humanities, science, social sciences, business, engineering, and health sciences, as well as a school of graduate studies and a divinity college.  nuclear reactor (in Hamilton, Ontario), the selected grains were placed individually into holes machined in aluminum disks. The flux monitor was the hornblende standard, MMhb-1 (assumed age = 520 Ma; Samson and Alexander 1987). Laser analyses were made with a Nd-YAG system operated in continuous mode with the beam expanded to approximately cover the grain. Power was then increased in a series of steps until complete fusion was achieved. Isotopic analyses were made using a VG 3600 mass spectrometer spectrometer

Device for detecting and analyzing wavelengths of electromagnetic radiation, commonly used for molecular spectroscopy; more broadly, any of various instruments in which an emission (as of electromagnetic radiation or particles) is spread out according to some
.

The single grain ages are plotted against [sup.39]Ar abundance for each analysed grain (Fig. 5). With one exception (Spot 5), no significant differences in apparent age were observed among the fourteen grains. The mean age is 421 [+ or -] 4 Ma (2[sigma] uncertainty, which includes the estimated error in the irradiation parameter, J). This age is interpreted to be the time of cooling of phlogopite through its argon argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0.  closure temperature (ca. 300-400[degrees]C, McDougall and Harrison 1999), and likely approximates the time of crystallization of the gabbro. It is similar within error to a previously reported amphibole K-Ar age of 418 Ma (Wanless et al. 1973) from the St. Stephen Gabbro. However, it is significantly older than the biotite (presumably pre·sum·a·ble  
adj.
That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster.
 phlogopite) K-Ar age from the same pluton (Wanless et al. 1973). It is also similar to the previously reported [sup.40]Ar/ [sup.39]Ar age of 422.7 [+ or -] 3 Ma reported for hornblende from the Pocomoonshine Gabbro-Diorite (West et al., 1992).

[FIGURE 5 OMIITED]

GEOCHEMISTRY geochemistry, study of the chemical changes on the earth. More specifically, it is the study of the absolute and relative abundances of chemical elements in the minerals, soils, ores, rocks, water, and atmosphere of the earth and the distribution and movement of  

Introduction

Although complex mingling, mixing, and gradational contacts characterize relations in the MPS, as described above, heterogeneous rocks were avoided in sampling for geochemistry in this study. We focused on homogeneous-looking samples that appeared characteristic of the main units of the MPS (Table 4). Some of the samples analysed as part of this study (MH designation in Table 4) were obtained from the collection of M. Hill and analyzed as part of the present project. The geochemical data of Gaskill (1999) were integrated into our study after a re-examination of his thin sections and samples. However, we have not included the large chemical data base of Paktunc (1989) because of uncertainty in locations and petrographic features of the analyzed samples. As demonstrated by McLaughlin (2003), they do not significantly change the conclusions of this study.

Also included in Table 4 are data for the Bocabec Pluton. The major element data for these samples are from Fyffe (1971), and trace element analyses were obtained from the same sample powders as part of the present study. In addition, four other granitic samples from the thesis collection of Fyffe (1971) were analyzed by K. Thorne and D. Lentz, and those unpublished data are included, with permission, in Table 3. Additional data from Ludman and Hill (1990), Coughlin (1986), McLeod (1990) (including data listed in his Appendix 4), and Thorne and Lentz (2001) are included on the diagrams, but not listed in Table 4.

Major element compositions

Plots against Si[O.sub.2] are used to illustrate chemical characteristics of the units of the MPS (Fig. 6). Dioritic and gabbroic samples from the Staples Mountain, St. Stephen, and Elliott Mountain plutons all have less than about 50% Si[O.sub.2], but show differences in other major element oxides. The Staples Mountain samples show a wide range in most elements, consistent with their wide range in rock types and cumulate features as described by Coughlin (1986). Their most distinctive characteristics compared to the dioritic and gabbroic samples are their high Fe and Ti contents (Fig. 6a, c). The Elliott Mountain samples tend to overlap in composition with gabbro from the St. Stephen Gabbro, but have higher Ti[O.sub.2], [Na.sub.2]O, and [P.sub.2][O.sub.5] and lower MgO contents (Fig. 6a, f, h, d). Compared to samples from the gabbro unit in the St. Stephen Gabbro, the olivine gabbro and troctolite samples have lower Si[O.sub.2] but also a trend toward lower Ti[O.sub.2], [Na.sub.2]O, and [P.sub.2][O.sub.5] contents. Variations in [Al.sub.2][O.sub.3], [Fe.sub.2][O.sup.t.sub.3], MgO, and CaO are consistent with the occurrence of cumulate textures in most of the analysed samples, and can be accounted for by olivine, pyroxene, and plagioclase separation or accumulation. In general, the trend from the more mafic samples of the St. Stephen Gabbro to the higher Si[O.sub.2] samples of the Calais Quartz Diorite can be explained by fractionation of plagioclase, olivine, and pyroxene, and it is likely that these plutons are co-magmatic. In comparison, both the Staples Mountain Gabbro and Elliott Mountain Diorite units show differences in major element compositions which suggest that they are not genetically related to the St. Stephen and Calais plutons. Sample SS00-108 from a gabbroic dyke(?) in the Baring Granite has higher Si[O.sub.2] than any samples analyzed from the Staples Mountain Gabbro, but also shows high [F.sub.2][O.sub.3] and low MgO, as well as high [Na.sub.2]O and [P.sub.2][O.sub.5] contents (Fig. 6f, h). In contrast, sample SS00-129 from the Woodland Dump gabbro of Ludman and Hill (1990) is similar to samples of similar Si[O.sub.2] content from the St. Stephen Gabbro.

[FIGURE 6 OMITTED]

With one exception (granodiorite SS00-142), analyzed samples from the Baring Granite are all of granite composition, and have high Si[O.sub.2] contents (more than 68%), and correspondingly low contents of other major elements except [Na.sub.2]O and [K.sub.2]O (Fig. 6). These chemical features are consistent with the high contents of sodic so·dic  
adj.
Relating to or containing sodium.



[sod(ium) + -ic.]


sodic  

Relating to or containing sodium.
 plagioclase, K-feldspar, and quartz and low abundance of ferromagnesian minerals in the samples. Chemical similarity between the Baring Granite and the Utopia Granite (data from McLeod 1990) is apparent, although the compositional range reported for the Utopia Granite extends to higher Si[O.sub.2] content.

Data from the Bocabec Pluton are also shown on Fig. 6. As described in detail by Fyffe (1971) and McLeod (1990), these samples represent the mafic and felsic components in the suite, and also the intermediate units This is a complete list Pennsylvania's 29 of Intermediate Units by their assigned IU number:

PA Intermediate Unit Web site
  • IU1 - Intermediate Unit 1   IU 1 Web site
  • IU2 - Pittsburg-Mt.
 that were inferred to have formed by mixing and hybridization hybridization /hy·brid·iza·tion/ (hi?brid-i-za´shun)
1. crossbreeding; the act or process of producing hybrids.

2. molecular hybridization

3.
 between the mafic and felsic magmas. The range of compositions encompasses most of the samples from the Calais Quartz Diorite, as well as the gabbro unit of the St. Stephen Gabbro, thus supporting their co-genetic relationship. In contrast, the Staples Mountain and Elliott Mountain samples generally lie outside the Bocabec trend, implying that they are not closely linked to the other mafic magmas. The data also show that the granitic component of the Bocabec Pluton is chemically similar to the Baring Granite, and support the interpretation (Fyffe 1971; McLeod 1990) that the intermediate samples formed by a mixing process. Intermediate sample (SS00-142) from the MPS is chemically similar to intermediate samples from the Bocabec Pluton, suggesting that it may have had a similar origin, as a result of mixing between Baring Granite and Calais Quartz Diorite magmas.

Trace element compositions

Trace element data are more limited than major element data, and are mainly for samples from the present study (Table 4). Trace elements Trace elements
A group of elements that are present in the human body in very small amounts but are nonetheless important to good health. They include chromium, copper, cobalt, iodine, iron, selenium, and zinc. Trace elements are also called micronutrients.
 are available for only one sample from Staples Mountain Gabbro and variable numbers of samples from the Bocabec Pluton and Utopia Granite, depending on the element. Trends in Rb, Sr, and Ba within the mafic and felsic sample sets are generally consistent with feldspar feldspar (fĕl`spär, fĕld`–) or felspar (fĕl`spär), an abundant group of rock-forming minerals which constitute 60% of the earth's crust.  fractionation (Figs. 7a-c). Gabbroic samples have mainly low Rb and Ba, and high Sr, whereas the Calais Quartz Diorite generally has less Sr and more Rb and Ba. Some Utopia Granite samples and one Baring Granite sample have high Rb and low Ba, indicative of a highly evolved composition in which Ba has been partitioned into and removed with K-feldspar (Fig. 6g). However, overall, the Baring Granitc is characterized by high Ba content (up to almost 1100 ppm).

[FIGURE 7 OMITTED]

Elements Zr, Nb, Y, and V display wide variation and few trends on silica variation diagrams (Figs. 8a-d), related to the control of these elements by the abundance of mainly pyroxene and magnetite (e.g., Miyashiro and Shido 1975; Pearce and Norry 1979) Maich vary widely in the dioritic and gabbroic samples. The Utopia Granite overlaps the composition of the Baring Granite, but generally has higher Nb and Y, and lower Zr (Figs. 8a-c). Some of the intermediate to granitic Bocabec Pluton samples have elevated Zr, Nb, and Y, and low V (Fig. 8). High Zr content in intermediate samples may represent the build-up of that element in the magma prior to onset of zircon crystallization.

[FIGURE 8 OMITTED]

Ni and Cr show wide spread in the gabbroic and dioritic samples (Figs. 9a, b) related to variations in olivine and pyroxene contents. The Staples Mountain Gabbro sample (NB00-133) is low in both elements compared to most St. Stephen Gabbro samples, further support for their lack of genetic relationship. Cu and Co also display a wide range in gabbroic to intermediate samples, with a few high values up to 150 and nearly 100 ppm, respectively (Figs. 9c, d). Ni, Cr, and Cu are low in all the granitic samples, but Co contents are high in the Baring Granite compared to most granitic Bocabec Pluton and Utopia Granite samples. Pb and Zn also differ between the Baring and Utopia granites, being generally higher in the Baring samples (Figs. 9e, f). Zn contents are highest in the intermediate rocks.

[FIGURE 9 OMITTED]

Chemical affinity In physical chemistry, chemical affinity, historically, refers to the "force" that causes chemical reactions.[1] A broad definition, used generally throughout history, is that chemical affinity is that whereby substances enter into or resist decomposition.  and tectonic setting

Interpretation of chemical affinity and tectonic setting for units of the MPS is somewhat ambiguous, as illustrated by representative, commonly used diagrams in Fig. 10. With the exception of the Staples Mountain and Woodland Dump samples, which appear tholeiitic, gabbroic and dioritic samples show little iron enrichment, and calc-alkaline affinity is suggested (Fig. 10a). Most samples have low Nb/Y ratios indicative of subalkalic affinity, although some St. Stephen and Bocabec samples plot in alkalic fields (Fig. 10b). Alkalic affinity is not supported by the V-Ti diagram (Fig. 10c), which suggests with in-plate tholeiitic character for mafic samples. On the other hand, the Ti-Zr-Y diagram suggests calc-alkaline (arc) setting (Fig. 10d).

Granitic samples from the Baring Granite have lower Y and Nb contents, consistent with origin in a volcanic arc volcanic arc
n.
A usually arc-shaped chain of volcanoes located on the margin of the overriding plate at a convergent plate boundary.



volcanic arc  
 setting, whereas granitic samples from the Bocabec Pluton and Utopia Granite are generally more evolved and plot mainly in the within-plate granite field (Fig. 10e). Elevated Zr and Ga/Al ratio suggest A-type characteristics for these samples (Fig. 10f).

Rare-earth elements

Rare-earth element rare-earth element
n.
See lanthanide.
 (REE) data were obtained for 15 samples from the MPS during the present study (Table 5). Additional REE data for the MPS were taken from Ludman and Hill (1990) and data for the Bocabec pluton and Utopia Granite are from McLeod (1990). Some of the data from McLeod (1990) show erratic features that suggest analytical error, but the overall patterns are consistent enough to enable comparison with the MPS.

In comparison with the other units, the St. Stephen gabbro has low REE abundance and a relatively flat REE pattern (Fig. 11a). The positive Eu anomalies suggest plagioclase accumulation. The sample with highest REE abundance shows some enrichment in light REE relative to heavy REE, and the pattern is very similar to that of the Calais Quartz Diorite sample with lowest REE abundance. The samples from the Calais Quartz Diorite show parallel chondrite-normalized patterns, with a change from a slight positive to a slight negative Eu anomaly with increasing REE abundance and increasing Si[O.sub.2] content.

[FIGURE 11 OMITTED]

Mafic samples from the Bocabec Pluton display patterns similar to the Calais Quartz Diorite (Fig. 11b). However, an intermediate sample with over 58% Si[O.sub.2] has higher REE abundances and a pattern more similar to those of the Baring Granite samples (Fig. 11c). Three samples from the Elliot Mountain Diorite (Fig. 11c), all from Ludman and Hill (1990) are similar to the Calais Quartz Diorite, but do not show the small negative Eu anomalies that characterize the Calais samples.

Samples from the Baring Granite, Utopia Granite, and granite in the Bocabec Pluton all show strong negative Eu anomalies that could be explained by feldspar fractionation (Fig. 11c, e). They are most pronounced in the Utopia Granite, consistent with its more evolved character (e.g., Fig. 7e). However, in general the REE patterns are indicative of similar and related origins for these units.

Gabbro dyke(?) sample SS00-108 in the Baring Granite has high total REE abundance and a positive Eu anomaly (Fig. 11d). The high REE content, light REE enrichment compared to heavy REE, and strong positive Eu anomaly set it apart from other samples. It may be related to the Staples Mountain Gabbro, as suggested by some of its other chemical features, but no REE data are yet available from Staples Mountain for comparison.

Sm-Nd isotopes

Five samples were analyzed for Sm-Nd isotopes (Table 6). The calculated [[epsilon].sub.Nd] at 421 Ma for gabbro sample SS98-9 from the St. Stephen Gabbro is 0.4, with a depleted mantle model age of 1567 Ma, whereas two dioritic samples from the Calais Quartz Diorite have higher [[epsilon].sub.Nd] values of 1.03 and 3.4 at 421 Ma, with depleted mantle ages of 1184 and 881 Ma, respectively. For the Baring Granite, the [[epsilon].sub.Nd] is only slightly lower at -0.40, with a similar depleted mantle age of 1250 Ma. The gabbro dyke(?) in the Baring Granite has a positive [[epsilon].sub.Nd] of 1.51. All of these values are well below depleted Mantle values (ca. +7 to 8 at ca. 421 Ma), showing that significant crustal crust·al  
adj.
Of or relating to a crust, especially that of the earth or the moon.

Adj. 1. crustal - of or relating to or characteristic of the crust of the earth or moon
 material was inched to produce even the mafic units in the MPS. On the other hand, the [[epsilon].sub.Nd] values, even for the Baring Granite, are too high for the magmas to have had an ancient crustal source (likely to be -7 or less at ca. 421 Ma; DePaolo 1988).

These results are consistent with those reported by Whalen et al. (1994), which were in the order of +2 to +3 for the Utopia Granite and granite in the Bocabec Pluton. Gabbro in the Bocabec Pluton yielded a higher value of +5 (all values recalculated to 421 Ma).

PETROGENSIS

Field relations and petrological features, as well as geochronology, are consistent with a co-magmatic relationship among the St. Stephen Pluton, Calais Quartz Diorite, Bocabec Pluton, and Baring Granite. The Staples Mountain Gabbro may also be closely related to this suite, but it shows some chemical differences that need to be investigated further.

A likely model is that a mafic magma (possibly mantle derived) of the MPS was emplaced first and underwent substantial crystal fractionation to produce the mafic and ultramafic St. Stephen Gabbro and the more evolved dioritic magma represented by the Calais Quartz Diorite. The evolved dioritic magmas then mingled with crustal melts of granitic composition, represented by the Baring Granite, to locally produce hybrid rocks such as the granodiorite documented by Fyffe (1971) in the Bocabec Pluton. Disruption of earlier layered mafic bodies by younger granite magmas was proposed by Amos (1963). However, in their study of the Cadillac Mountain intrusive complex, similar to the MPS in age and range of rock types, Wiebe et al. (1997) demonstrated that felsic magmas interacted with subsequent infusions of mafic magma. Such later infusions of mafic magma are represented in the MPS by the Elliott Mountain Diorite and small gabbroic and dioritic bodies scattered through the MPS.

Although the mafic component in the coastal Maine province has generally been considered a mantle melt, the low epsilon Nd values and especially the small difference in epsilon Nd between the Baring and Utopia granites and the Calais Quartz Diorite suggests a major component of crustal material. Isotopic studies of other plutonic suites in the region may enable a better understanding of magma generation processes.

TECTONIC IMPLICATIONS

The late Silurian (ca. 421 Ma) age for components of the MPS is similar to ages reported for other mafic-felsic plutonic complexes of the Coastal Maine magmatic province, although voluminous younger Devonian plutons are also present (e.g., Hogan and Sinha 1989; McLeod 1990; Tucker et al. 2001). Like the MPS, many of the other Silurian plutons are bimodal bi·mod·al  
adj.
1. Having or exhibiting two contrasting modes or forms: "American supermarket shopping shows bimodal behavior
, and display mingling relationships that suggest that the mafic and felsic components were contemporaneous (e.g., Hogan and Sinha 1989; Wiebe et al. 1997). Although these plutons are generally considered to be related to the "Acadian orogeny Acadian orogeny

Mountain-building event that affected the northern portion of the Appalachian Geosyncline from present-day New York to Newfoundland during the Devonian period. The orogeny was most intense in northern New England.
", the details of tectonic activity during this protracted pro·tract  
tr.v. pro·tract·ed, pro·tract·ing, pro·tracts
1. To draw out or lengthen in time; prolong: disputants who needlessly protracted the negotiations.

2.
 orogenic event are unclear. Widespread evidence for voluminous late Silurian volcanic and plutonic activity throughout the coastal Maine magmatic province and adjacent New Brunswick shows that igneous activity was a major characteristic of this event, but the specific tectonic setting is uncertain.

The bimodal character of the plutons, and their tendency to A-type affinities, has led to the suggestion that the magmatism was related to regional extension and mafic underplating (e.g., Hogan and Sinha 1989). However, regional tectonic models (e.g., Robinson et al. 1998; van Staal et al. 1998; Tucker et al. 2001) are more consistent with plate convergence and subduction sub·duc·tion  
n.
A geologic process in which one edge of one crustal plate is forced below the edge of another.



[French, from Latin subductus, past participle of
 in the Late Silurian. Although somewhat ambiguous, chemical data front the MPS are more indicative of calc-alkalic affinity and a subduction environment than within-plate extension (Fig. 10). One interpretation that may be consistent with both ideas is that Late Silurian plutons in the coastal Maine magmatic province formed in a back-arc position with respect to the early Silurian Kingston arc (Fyffe et al. 1999; Barr et al. 2002). Isotopic data do not indicate a major component of directly mantle-derived magmas in these suites, although isotopic data are not yet available from the more mafic components. Melts may have been generated by large-scale melting of relatively primitive arc-type crust underlying the Mascarene and Ellsworth terranes. The presence of such crust has been suggested by isotopic data from southern New Brunswick (Whalen et al. 1994; Samson et al. 2000).

CONCLUSIONS

This work has demonstrated that the St. Stephen Gabbro, Calais Quartz Diorite, and Baring Granite components of the Moosehorn Plutonic Suite are approximately contemporaneous and late Silurian in age. The close petrochemical similarity of the St. Stephen Gabbro and Calais Quartz Diorite to the mafic and intermediate components of the Bocabec Pluton of the Saint George Batholith suggests that all of these plutons were comagmatic. The granitic component of the Bocabec Pluton is generally more similar to the Baring Granite than to the Utopia Granite, which is more evolved. The Elliott Mountain Diorite shows petrological differences that suggest that it may be somewhat younger than the other units of the MPS, although the number of samples is limited and more work is required to better define the characteristics of the Elliott Mountain Diorite and its relationship to the Bocabec Pluton and Calais Quartz Diorite. The Staples Mountain Gabbro is unlike the other mafic plutons of the MPS in its iron-enrichment trend, and is therefore likely to be a separate intrusion, although of similar age. Neodymium isotopic data show that even the mafic parts of these plutons have a significant crustal component in their source, but the values even in granitic samples are too high for significant amounts of ancient crustal material to be involved. Their petrochemical features are most consistent with origin in a supra-subduction zone extensional environment (back-arc basin) in relatively young continental crust.
Table 1. Summary of petrographic features of main units * in the MPS.

                Staples Mountain Gabbro          St. Stephen Gabbro

Principal    olivine gabbro, anorthositic    dunite, troctolitc, oli-
rock types   gabbro, norite, anorthosite,    vine gabbro, anorthositic
             gabbro                          gabbro, anorthosite,
                                             norite, gabbro
Primary      olivine ([FO.sub.53-55]),       olivine ([Fo.sub.80-58]),
minerals     plagioclase ([An.sub.72-53]),   plagioclase
             cpx (augite and pigeonite),     ([An.sub.95-35]), opx
             hornblende (ferroan             ([En.sub.80-70]), cpx
             pargasite), [+ or -] ortho-     (augite-diopside),
             pyroxene ([En.sub.70-62])       [+ or -] hornblende
                                             (pargasite-pargasitic
                                             hornblende), phlogopite-
                                             biotite (Fe/Fe+Mg = 12-40)
Accessory    magnetite, ilmenite, apatite    apatite, titanite,
minerals                                     pyrrhotite, chalcopyrite,
                                             pentlandite,
Textures     layering, cumulate              layering, cumulate,
                                             ophitic
                 Calais Quartz Diorite             Baring Granite

Principal    quarts diorite, diorite,        syenogranite,
rock types   tonalite, granodiorite,         monzogranite,
             quartz monzonite                granodiorite, tonalite
Primary      plagioclase ([An.sub.80-20]),   plagioclase
minerals     brown amphibole (ferroparga-    ([An.sub.29-19]), K-
             sitic hornblende to edenitic    feldspar (microcline),
             hornblende); green              quartz, biotite
             amphibole                       (Fe/Fe+Mg=72-80), [+ or -]
             (magnesiohornblende to          hornblende
             actinolite), cpx (augite),
             opx (En50), quartz, biotite
             (Fe/Fe+Mg = 40-60)
Accessory    apatite, magnetite, zircon,     apatite, zircon
minerals     titanite
Textures     medium-grained (m.g.)           m.g. hypidiomorphic
             hypidiomorphic                  inequigranular/ seriate
             inequigranular, sub-ophitic     porphyritic

                Elliott Mountain Diorite

Principal    diorite, quartz diorite,
rock types   tonalite, gabbro
Primary      plagioclase ([An.sub.60-25]),
minerals     amphibole
             (magnesiohornblende-
             actinolite), cpx (augite-
             diopside), opx ([En.sub.50]),
             quartz, [+ or -] K-feldspar
Accessory    magnetite, apatite, zircon
minerals
Textures     m.g. hypidiomorphic
             inequigranular, sub-ophitic

* Compiled mainly from McLaughlin (2003), except Staples Mountain
Gabbro data from Coughlan (1986).

Table 2. U-Pb data for sample SS00-124

                                Concentrations                Ratios

Sample                 Weight       U      Pb      Pb(c)   [sup.206]Pb/
Fractions            ([micro]g)   (ppm)   (ppm)    (pg)    [sup.204]Pb
                        (a)                         (b)        (c)

z1                      2.9        138      9.3     0.5       3659.1
z3                      2.2        284     19.3     0.6       4863.6
z4                      4.5        169     11.7     0.8       3945.1
z5                      3.7        334     23.7     0.4      14419.9
Weighted Mean Age:
     [+ or -]
       MSWD

                                      Ratios

Sample               [sup.206]Pb/   [sup.206]Pb/
Fractions            [sup.238]Pb     [sup.238]U       err
                         (d)            (e)        (2[sigma]%)

z1                      0.105         0.067557        0.30
z3                      0.111         0.067560        0.08
z4                      0.136         0.067636        0.07
z5                      0.165         0.067616        0.06
Weighted Mean Age:
[+ or -]
MSWD

                                      Ratios

Sample               [sup.207]Pb/                 [sup.206]Pb/
Fractions            [sup.206]Pb       err         [sup.238]U
                         (e)        (2[sigma]%)       (e)

z1                      0.5143         0.32         0.05522
z3                      0.5147         0.12         0.05525
z4                      0.5150         0.10         0.05522
z5                      0.5147         0.08         0.05520
Weighted Mean Age:
[+ or -]
MSWD

                       Ratios                Age (Ma)

Sample                  err        [sup.207]Pb/   [sup.207]Pb/
Fractions            (2[sigma]%)    [sup.238]U     [sup.235]U

z1                      0.11          421.4          421.4
z3                      0.09          421.4          421.6
z4                      0.07          421.9          421.8
z5                      0.06          421.8          421.6
Weighted Mean Age:                    421.7          421.6
[+ or -]                                0.4            0.3
MSWD                                    1.58           0.29

                           Age (Ma)

Sample               [sup.207]Pb/   corr.
Fractions            [sup.206]Pb    coef.

z1                      421.1       0.937
z3                      422.5       0.641
z4                      421.3       0.729
z5                      420.5       0.718
Weighted Mean Age:      421.1
[+ or -]                  0.8
MSWD                      0.91

Notes: (a) Sample weights are estimated by using a video monitor and
are known to within 40%. (b) Total common-Pb in analyses. (c) Measured
ratio corrected for spike and fractionation only. (d) Radiogenic Pb.
(e) Corrected for fractionation, spike, blank, and initial common Pb.
Mass fractionation correction of 0.15%/amu [+ or -] 0.04%/amu (atomic
mass unit) was applied to single-collector Daly analyses and 0.12%/amu
[+ or -] 0.04% for dynamic Faraday-Daly analyses. Total procedural
blank less than 0.4 pg for Pb and less than 0.1 pg for U. Blank
isotopic composition: [sup.206]Pb/[sup.204]Pb=19.10 [+ or -] 0.1,
[sup.207]Pb/[sup.204]Pb =15.71 [+ or -] 0.1, [sup.208]Pb/[sup.204]Pb
= 38.65 [+ or -] 0.1. Corr. coef. = correlation coefficient; err =
error. Age calculations are based on the decay constants of Steiger and
Jager (1977). Common-Pb corrections were calculated by using the model
of Stacey and Kramers (1975) and the interpreted age of the sample.

Table 3. [sup.40]Ar/[sup.39]Ar data for sample SS98-36.

Spot    Code        mV 39    Age [+ or -] 1[sigma]    % ATM
                                     (Ma)

  1     C66-3-1     197.1     417.7 [+ or -] 7.3       1.2
  2     C66-7-2     154       422.3 [+ or -] 9.1       0.8
  3     C66-2-2     228.9     427.5 [+ or -] 6.2       0
  4     C66-6-1      40.8     420.2 [+ or -] 31        6
  5     C66-11-2     86       440.4 [+ or -] 6.5       0.6
  6     C66-14-2    200.9     425.0 [+ or -] 3.7       2.6
  7     C66-4-2     250.9     420.2 [+ or -] 3         1.6
  8     C66-5-2     157.2     424.6 [+ or -] 4         0.6
  9     C66-1-2     613.4     417.1 [+ or -] 2.1       1.4
 10     C66-8-1     289       416.8 [+ or -] 2.7       1.6
 11     C66-9-1     222.8     417.4 [+ or -] 3.2       2.3
 12     C66-10-2    138       432.6 [+ or -] 4.9       5.5
 13     C66-12-2    226       423.0 [+ or -] 3.1       0.4
 14     C66-13-2    113.9     417.8 [+ or -] 5.6       6.6

Spot    [sup.37]Ar/    [sup.36]Ar/    [sup.39]Ar/    % IIC
        [sup.39]Ar     [sup.40]Ar     [sup.40]Ar

  1        1.17         0.000041       0.009593      0.16
  2        1.19         0.000030       0.009504      0.16
  3        0.38         0.000001       0.009460      0.05
  4        3.47         0.000204       0.009041      0.47
  5        1.13         0.000023       0.009092      0.15
  6        0.23         0.000089       0.009276      0.03
  7        0.07         0.000054       0.009496      0.01
  8        0.06         0.000021       0.009478      0
  9        0.30         0.000048       0.009595      0.04
 10        0.12         0.000054       0.009584      0.01
 11        0.36         0.000080       0.009494      0.05
 12        0.8          0.000186       0.008826      0.1
 13        0.53         0.000014       0.009540      0.07
 14        0.99         0.000224       0.009068      0.13

Mean age = 421 [+ or -] 4 Ma (2[sigma] uncertainty, including error in
J). Grain 4 omitted from mean age calculation because probably
polymineralic. J = 0.002533 [+ or -] 0.000025 (0.9%).
[sup.27]Ar/[sup.39]Ar, [sup.36]Ar/[sup.40]Ar, and [sup.39]Ar/[sup.40]Ar
are corrected for mass spectrometer discrimination, interfering
isotopes, and system blanks. % IIC--Interfering isotopes correction.

Table 4. Chemical data for samples from the Moosehorn Plutonic Suite,
Bocabec Pluton, and spatially associated units

                                             [Al.sub.2]    [Fe.sub.2]
Sample         Si[O.sub.2]    Ti[Os.ub.2]    [O.sub.3]     [O.sub.3]

Staples Mountain Gabbro
SS00-133          44.19          4.40          16.16         15.86

St. Stephen Gabbro
troctolite
SS98-26A          47.71          0.22          23.34          5.77
SS98-52           43.58          0.22          19.26          9.01

olivine gabbro
SS00-110          46.27          0.51          21.50          6.57
SS98-02B          43.82          0.39          15.50         10.11
SS98-31B          47.33          0.30          25.07          5.02
SS98-36           45.29          0.89          16.93         10.92
SS98-45           42.26          0.23          22.39          9.15

gabbro
SS97-1-151        48.87          1.12          15.99         11.58
SS97-5-54.5       51.51          1.93          18.05         12.02
SS98-29           48.51          0.57          19.23          6.71
SS98-32a          48.87          0.64          17.13         10.21
SS98-54           49.31          1.31          16.43          9.94
SS98-67           49.25          0.47          19.33          9.04
SS98-90           46.76          0.61          20.35          9.53

Calais Quartz Diorite
MH-79             49.99          2.28          15.94         12.04
MH-1758           59.77          0.99          15.88          7.39
SS00-119          56.56          1.33          15.55          8.43
SS00-120          53.50          1.25          15.33         10.62
SS00-122          54.77          1.57          15.74         10.21
SS00-123          58.14          0.87          15.21          8.27
SS00-131          55.98          0.76          17.91          7.98
SS00-140          51.49          1.45          17.38         10.71
SS00-144A         59.14          1.34          16.54          7.58
SS00-144B         57.83          1.44          16.07          8.19
SS98-09           54.26          1.00          17.06          7.99
SS98-72           56.33          1.43          16.11          9.31

Baring Granite
MH-153            74.31          0.25          12.88          2.34
MH-159            74.81          0.24          12.86          2.30
LH-258            76.06          0.15          13.83          1.28
MH-382            73.16          0.26          13.81          2.51
SS00-104          72.66          0.29          14.18          2.72
SS00-107          72.69          0.27          14.62          2.60
SS00-113          72.11          0.36          14.77          3.21
SS00-117          72.12          0.32          14.88          2.89
SS00-118          71.96          0.31          14.54          2.53
SS00-121          68.80          0.51          15.02          3.93
SS00-124          72.73          0.36          14.68          2.39
SS00-137          71.25          0.34          14.33          2.64
SS00-139          72.38          0.32          14.45          2.48
SS00-141          69.67          0.36          15.05          2.80
SS00-142          63.34          0.75          16.53          6.59
SS00-148          71.96          0.32          15.41          2.60

Elliot Mountain Diorite
MH-43             50.18          1.51          16.86         10.38
MH-58A            48.30          2.26          16.07         12.65
LH-58             48.06          2.26          15.65         11.93
LH-72A            49.05          2.05          16.56         11.00
LH-72B            48.38          2.28          15.52         12.04
SS00-126          49.47          2.40          13.87         12.17
SS00-127          48.41          2.10          16.32         12.08

Unnamed Gabbro Diorite Bodies
SS00-108          52.88          1.66          14.31         16.64
SS00-129          47.79          1.22          17.69          9.96

Bocabec Pluton
Fyffe04           50.10          1.20          14.70         10.29
Fyffe13           69.15          0.68          13.12          5.45
Fyffe17           60.60          1.30          14.80          8.90
Fyffe32           68.80          0.50          14.50          3.32
Fyffe33           60.00          1.40          14.20          9.29
Fyffe35           60.90          1.30          15.20          8.85
Fyffe38           68.78          0.65          13.32          5.01
Fyffe42           68.80          0.65          13.21          5.00
Fyffe43           68.20          0.67          13.26          5.29
Fyffe49           53.00          1.50          14.00         11.44
Fyffe59           61.60          0.80          15.90          4.93
Fyffe6l           52.80          1.30          15.00          8.61
Fyffe64           62.50          1.00          14.90          7.59
Fyffe67           46.70          1.00          18.20          8.85
Fyffe72           64.10          0.80          15.20          4.75

Sample         MnO      MgO      CaO     [Na.sub.2]O    [K.sub.2]O

Staples Mountain Gabbro
SS00-133       0.21     6.34    10.64       2.78           0.33

St. Stephen Gabbro
troctolite
SS98-26A       0.10     5.20    10.98       2.82           0.75
SS98-52        0.11    15.03     9.97       1.48           0.10

olivine gabbro
SS00-110       0.10     9.04    11.95       1.94           2.78
SS98-02B       0.14    16.56    10.99       0.62           0.10
SS98-31B       0.08     5.30    13.69       2.07           0.12
SS98-36        0.15    12.78     8.15       1.96           0.48
SS98-45        0.08     8.85    11.05       1.49           0.67

gabbro
SS97-1-151     0.17    11.20     7.22       2.00           1.30
SS97-5-54.5    0.16     4.91     6.06       2.55           1.14
SS98-29        0.11     7.25    12.90       2.56           0.31
SS98-32a       0.17    10.59     9.96       1.42           0.12
SS98-54        0.16     8.09     9.51       2.73           0.75
SS98-67        0.14     9.06     9.46       1.34           0.28
SS98-90        0.13     7.70    10.72       2.17           0.41

Calais Quartz Diorite
MH-79          0.19     5.42     8.21       3.46           1.23
MH-1758        0.14     2.97     5.32       3.55           2.39
SS00-119       0.14     4.55     7.61       3.08           2.08
SS00-120       0.17     5.97     8.38       3.13           1.69
SS00-122       0.17     4.12     7.73       3.23           1.44
SS00-123       0.14     4.75     7.33       3.13           2.07
SS00-131       0.17     3.74     6.66       3.12           3.07
SS00-140       0.20     5.40     8.24       3.03           1.19
SS00-144A      0.15     2.47     5.70       3.85           1.80
SS00-144B      0.13     3.00     6.05       3.56           1.94
SS98-09        0.13     5.71     7.07       3.20           1.89
SS98-72        0.17     3.61     6.87       3.36           2.04

Baring Granite
MH-153         0.06     0.21     0.79       3.21           5.01
MH-159         0.06     0.22     0.55       3.34           4.63
LH-258         0.03     0.78     0.48       4.47           4.57
MH-382         0.05     0.24     1.43       3.56           4.59
SS00-104       0.06     0.34     1.58       3.62           4.54
SS00-107       0.06     0.27     1.02       3.89           5.02
SS00-113       0.07     0.43     1.56       3.61           4.53
SS00-117       0.06     0.39     1.75       3.41           4.68
SS00-118       0.06     0.50     1.68       3.50           4.60
SS00-121       0.08     0.94     2.72       3.67           3.78
SS00-124       0.05     0.29     1.58       3.52           5.28
SS00-137       0.05     0.56     1.87       3.54           3.94
SS00-139       0.06     0.38     1.58       3.44           5.14
SS00-141       0.06     0.79     2.33       3.80           3.27
SS00-142       0.15     0.92     3.11       3.50           3.33
SS00-148       0.06     0.68     2.37       4.08           3.34

Elliot Mountain Diorite
MH-43          0.14     5.51     8.71       3.19           1.21
MH-58A         0.20     6.60     8.83       3.42           1.10
LH-58          0.18     6.69     8.82       3.84           1.12
LH-72A         0.17     6.14     8.95       4.58           0.93
LH-72B         0.19     6.20     9.10       4.39           1.21
SS00-126       0.20     5.09     8.09       3.25           1.30
SS00-127       0.19     6.11     9.30       3.33           0.66

Unnamed Gabbro Diorite Bodies
SS00-108       0.61     1.68     6.75       4.12           1.50
SS00-129       0.15     9.76     9.16       2.74           0.60

Bocabec Pluton
Fyffe04        0.20     6.60     9.10       3.40           1.10
Fyffe13        0.15     0.61     1.14       4.57           2.83
Fyffe17        0.23     1.80     4.40       4.20           2.10
Fyffe32        0.05     2.40     2.80       3.50           2.40
Fyffe33        0.22     2.10     4.80       4.00           2.10
Fyffe35        0.19     1.40     4.20       4.40           2.00
Fyffe38        0.11     0.62     1.73       4.11           3.24
Fyffe42        0.15     0.58     1.93       4.12           3.28
Fyffe43        0.15     0.62     2.04       4.27           3.19
Fyffe49        0.30     5.00     8.70       3.40           0.90
Fyffe59        0.08     2.10     4.80       4.80           1.40
Fyffe6l        0.15     5.80     8.20       3.40           1.30
Fyffe64        0.17     1.10     3.00       3.70           3.10
Fyffe67        0.16     7.60    10.50       2.40           0.70
Fyffe72        0.08     1.80     4.30       3.70           2.60

               [P.sub.2]
Sample         [O.sub.5]    LOI     Total      Ba     Rb     Sr

Staples Mountain Gabbro
SS00-133         0.47       0.09    101.47       3     14    446

St. Stephen Gabbro
troctolite
SS98-26A         0.03       3.82    100.74     315     49    513
SS98-52          0.03       1.54    100.33     101     27    244

olivine gabbro
SS00-110         0.09       2.00    102.75      23     17    316
SS98-02B         0.02       1.96    100.21     191     26    199
SS98-31B         0.02       1.08    100.08       0     32    341
SS98-36          0.12       1.45     99.12      87     33    316
SS98-45          0.04       4.07    100.28     117     41    400

gabbro
SS97-1-151       0.19       0.71    100.35     229     46    278
SS97-5-54.5      0.13       1.34     99.80     304     47    305
SS98-29          0.02       2.13    100.30     270     35    328
SS98-32a         0.03       0.78     99.92       0     25    233
SS98-54          0.09       0.88     99.20       0     38    269
SS98-67          0.03       0.87     99.27       5     33    271
SS98-90          0.06       2.06    100.50     356     34    380

Calais Quartz Diorite
MH-79            0.45       1.50    100.71      50    170    374
MH-1758          0.19       1.30     99.88     280     75    250
SS00-119         0.23       0.81    100.37     353     70    285
SS00-120         0.19       0.65    100.88     495     46    294
SS00-122         0.23       0.84    100.05     386     44    257
SS00-123         0.12       0.93    100.96     561     59    240
SS00-131         0.11       1.11    100.62     674     87    310
SS00-140         0.19       0.98    100.26     381     39    331
SS00-144A        0.38       0.76     99.72     338     74    342
SS00-144B        0.31       1.13     99.65     275     68    326
SS98-09          0.17       0.93     99.41     588     75    336
SS98-72          0.30       0.87    100.40     606     59    325

Baring Granite
MH-153           0.08       0.80     99.93     685    175     55
MH-159           0.08       0.99    100.08     631    175     47
LH-258           0.03       0.30    101.98     160    204     25
MH-382           0.06       0.50    100.17     803    198     87
SS00-104         0.06       0.28    100.33     802    191     90
SS00-107         0.06       0.28    100.77    1073    152    100
SS00-113         0.08       0.28    101.00    1092    131    133
SS00-117         0.13       0.40    101.03     973    172    113
SS00-118         0.06       0.59    100.32     124    148    140
SS00-121         0.09       0.72    100.25     786    118    192
SS00-124         0.06       0.18    101.11     853    199     92
SS00-137         0.09       0.78     99.39     745    160    128
SS00-139         0.06       0.20    100.49     869    173    100
SS00-141         0.12       0.59     98.84     604    134    236
SS00-142         0.24       0.99     99.45    1412     85    233
SS00-148         0.11       0.48    101.41     671    152    214

Elliot Mountain Diorite
MH-43            0.18       0.78     98.65      52     34    344
MH-58A           0.38       0.89    100.70      --     27    348
LH-58            0.37       0.90     99.82     224     36    349
LH-72A           0.36       1.00    100.79     210     27    394
LH-72B           0.40       1.00    100.71     219     36    363
SS00-126         0.48       1.22     97.53     102     29    304
SS00-127         0.34       0.81     99.65      49     16    325

Unnamed Gabbro Diorite Bodies
SS00-108         0.63       0.00    100.78     970     28    428
SS00-129         0.23       0.99    100.29      50     18    353

Bocabec Pluton
Fyffe04          0.20        --      96.89      --     59    363
Fyffe13          0.23        --      98.70     628     74    137
Fyffe17          0.30        --      98.63      --     36    213
Fyffe32          0.10        --      98.37      --     93    188
Fyffe33          0.20        --      98.31      --     23    345
Fyffe35          0.40        --      98.84      --     57    214
Fyffe38          0.21        --      98.92     599    110    121
Fyffe42          0.20        --      98.25     564    118    122
Fyffe43          0.21        --      97.44     561    115    121
Fyffe49          0.20        --      98.44      --     88    192
Fyffe59          0.20        --      96.61      --     60    177
Fyffe6l          0.20        --      96.76      --    138    167
Fyffe64          0.20        --      97.26      --     59    208
Fyffe67          0.00        --      96.11      --     42    246
Fyffe72          0.00        --      97.33      --     31    187

Sample          Y      Zr     Nb    Th    Pb     Ga      Zn     Cu

Staples Mountain Gabbro
SS00-133         17     72     6     3    1.5      17     67     17

St. Stephen Gabbro
troctolite
SS98-26A          6     48     7     0     14      --     43     24
SS98-52          12     36    14     0      8      --     59     28

olivine gabbro
SS00-110         14     47     2     1      5      15     42     25
SS98-02B         16     43    17     2     13      --     57     69
SS98-31B          7     36     6     0      4      --     29     25
SS98-36          21     82    20     0      0      --     71     38
SS98-45          16     47    17     0     17      --     39    544

gabbro
SS97-1-151       31    109    24     1     64      --     92    150
SS97-5-54.5      34    150    29     5     22      --    121    106
SS98-29          11     37    10     0      9      --     41     18
SS98-32a         19     39    19     0     10      --     90     49
SS98-54          26     86    21     0      8      --     79     25
SS98-67          15     41    14     0      0      --     72     14
SS98-90          17     57    16     1     11      --     73     89

Calais Quartz Diorite
MH-79            50    233    24    13     39      20    101     <4
MH-1758          38    154     9     5      7      19     79     <4
SS00-119         31    186    11     7     11      19     77      4
SS00-120         28    125    12     7     10      17     84     65
SS00-122         34    259    12     6     10      20     87     17
SS00-123         27    107     9     6     10      17     71     62
SS00-131         58    130    13     3     11      20     99     33
SS00-140         29    158    11     3      4      20    101     12
SS00-144A        26    191    15    10      8      20     96      2
SS00-144B        42    178    14     6      8      19     80      6
SS98-09          26    107    14     5     29      --     68     58
SS98-72          43    196    21     7     19      --     99     19

Baring Granite
MH-153           52    243    16    20     39      20     69     <4
MH-159           52    247    19    21     39      22     64     <4
LH-258           71    134    14    19     12      17     31     --
MH-382           64    217    11    13     43      19     53     <4
SS00-104         45    220    10    16     53      20     51      2
SS00-107         43    226     7    14     31      18     41      2
SS00-113         40    263    10    12     32      21     65      4
SS00-117         34    245     9     8     34      19     51      2
SS00-118         29    188     5    14     30      16     40      2
SS00-121         32    286    16    15     25      19     55      2
SS00-124         42    172    14    15     34      19     47      2
SS00-137         42    169    13    12    120      17     48      5
SS00-139         29    207    16    14     49      17     45      2
SS00-141         37    176    11    15     28      18     45      2
SS00-142         56    598    23    13     23      23    120      2
SS00-148         33    167     7    13     28      18     43      2

Elliot Mountain Diorite
MH-43            23    130     9     5      6      16     70     55
MH-58A           30    205    19     4    1.5      22     95     36
LH-58            35    200    20     2    --       21    102     41
LH-72A           33    184    16     3    --       18     98     54
LH-72B           39    196    16     3    --       19    111     64
SS00-126         35    239    21     4      7      19     99     11
SS00-127         30    187    19     4      3      19     93     43

Unnamed Gabbro Diorite Bodies
SS00-108       52.1    127     9     3      7      21    126      2
SS00-129         22    144     8     4      6      18     75     39

Bocabec Pluton
Fyffe04          40    190    --    10     24             78     --
Fyffe13          89    506    31    13     14    19.1     96     --
Fyffe17          31    122    --     5      9      --    134     --
Fyffe32          52    476    --    12      9      --    115     --
Fyffe33          21     89    --     1     10      --    127     --
Fyffe35          56    503    --     8      9      --     82     --
Fyffe38          77    438    35    15     11    19.5     86     --
Fyffe42          85    447    36    15    0.5    19.3     93     --
Fyffe43          92    500    25    13      6    20.5     84     --
Fyffe49          37    141    --    10     13      --     71     --
Fyffe59          56    209    --     9     11      --     89     --
Fyffe6l          45    184    --    13     25      --     75     --
Fyffe64          60    245    --     7     10      --    130     --
Fyffe67          28    112    --     5      7      --    130     --
Fyffe72          53    104    --     4     11      --    143     --

Sample          Ni      V      Cr      Co      U

Staples Mountain Gabbro
SS00-133         14    551      17      53       1

St. Stephen Gabbro
troctolite
SS98-26A         22     45     150      24       0
SS98-52          19     72     159      58       0

olivine gabbro
SS00-110        138     83     122      52       2
SS98-02B        331    176     898      81       0
SS98-31B         86     99     336      33       0
SS98-36         121    121     297      67       0
SS98-45        1022     47     193      77       0

gabbro
SS97-1-151      142    139     240      77       1
SS97-5-54.5     148    257     103      60       2
SS98-29           7    153     342      42       0
SS98-32a        112    235     376      61       0
SS98-54          41    172      66      52       0
SS98-67          57    151     224      48       0
SS98-90         307    108     293      70       0

Calais Quartz Diorite
MH-79            31    288     118      93       5
MH-1758           5    149       9      59       3
SS00-119         15    201     120      44       2
SS00-120         63    221     159      51       1
SS00-122         15    243      52      58       2
SS00-123         47    162     104      48       3
SS00-131         23    127      27      39       2
SS00-140          6    252      52      45       1
SS00-144A         3    169       2      46       2
SS00-144B       1.5    202      16      41       2
SS98-09          99    149     167      42       2
SS98-72          10    204      10      41       3

Baring Granite
MH-153           <3     34      <4      75       6
MH-159           11     33      <4      77       6
LH-258            6     16     1.7    0.82    4.91
MH-382           <3     35      <4      84
SS00-104        1.5     41       2      59
SS00-107        1.5     38       2      47
SS00-113          5     47       2      51
SS00-117          9     43       2      53
SS00-118         14     43       2      65
SS00-121         10     66       2      53
SS00-124          7     37       2      57
SS00-137        1.5     46       2      57
SS00-139          3     40       2      52
SS00-141          4     51       2      62
SS00-142         24     88       2      45
SS00-148          5     45       2      59

Elliot Mountain Diorite
MH-43            54    252      68      64
MH-58A           60    288      90      48
LH-58            69    268      93    44.1
LH-72A           64    245    81.3    39.7
LH-72B           64    297     102    43.9
SS00-126         14    297     128      57
SS00-127         59    272     105      66

Unnamed Gabbro Diorite Bodies
SS00-108        1.5    142       2      47
SS00-129         88    172     309      61

Bocabec Pluton
Fyffe04          22    112      52      31
Fyffe13          13     19       7      23
Fyffe17          94    203     179      50
Fyffe32           5    121      35      41
Fyffe33         101    186     156      49
Fyffe35         2.5    128      37      58
Fyffe38           9     23       7      50
Fyffe42           7     20      10      54
Fyffe43           8     24       6      13
Fyffe49          18    110      44      49
Fyffe59         2.5    181      41      34
Fyffe6l          18     70      47      37
Fyffe64         2.5    154      37      59
Fyffe67          35    215     170      48
Fyffe72          34    230     148      41

Notes: Major element analyses for Fyffe samples are from Fyffe (1971)
but trace element data were obtained on the same powders during the
present study, except 13, 38, 42, and 43, which were provided by K.
Thorne and D. Lentz. Data for LH samples are from Ludman and Hill
(1990). M. Hill provided the MH samples for analysis. Analyses were
done by X-ray Fluorescence at the Regional Geochemical Centre, Saint
Mary's University, Halifax, Nova Scotia (see
http://www.stmarys.ca/academic/science/geology/rgc/rgc home.htm for a
description of the methodology, and information about accuracy and
precision). Analytical error is generally less than 5% for major
elements and 2-10% for trace elements. [Fe.sub.2][O.sub.3] is total Fe
as [Fe.sub.2][O.sub.3]. LOI is loss on ignition at 1000[degrees]C. Dash
means is not determined and 0 indicates below or 2 ppm.

Table 5. Rare-earth element, Hf, and Ta data * from the Moosehorn
Plutonic Suite and spatially associated units.

 Sample      La        Ce         Pr        Nd        Sm        Eu

St. Stephen Gabbro-gabbro unit
SS98-29       1.164      2.800     0.476     2.707     0.933    0.619
SS98-32a      2.636      5.672     0.766     3.609     0.986    1.081
SS98-54       8.780     19.863     2.620    11.520     2.846    1.194

Calais Quartz Diorite
SS00-120     20.845      43.10     5.304    21.625     4.980    1.458
SS00-122     18.748     39.687     5.416    24.120     5.746    1.675
SS00-123     15.910     36.634     4.457    18.291     4.538    1.350
SS00-140     16.516     36.574     4.775    20.900     5.630    1.689
SS00-144A    23.569     51.282     6.259    26.133     6.065    1.689
SS98-09      11.956     26.073     3.414    15.001     3.490    1.248
SS98-72      27.125     57.960     7.316    31.034     7.129    1.902

Baring Granite
SS00-104     25.574     79.216     6.992    28.172     6.713    1.106
SS00-121     32.520     64.693     7.713    26.695     5.957    1.201
SS00-124     36.197     79.388     9.359    36.224     8.428    1.063
SS00-139     44.236     85.748    10.161    39.640     7.897    1.095

Diorite dyke(?) in Baring Granite
SS00-108     54.481    124.342    15.847    49.000    13.389    7.952

 Sample      Gd        Tb       Dy        Ho       Er       Tm

St. Stephen Gabbro-gabbro unit
SS98-29       1.302    0.215     1.424    0.279    0.797    0.110
SS98-32a      1.284    0.222     1.537    0.323    1.012    0.158
SS98-54       3.230    0.539     3.444    0.663    1.991    0.291

Calais Quartz Diorite
SS00-120      5.790    0.947     5.903    1.136    3.285    0.490
SS00-122      7.016    1.149     7.323    1.392    3.983    0.588
SS00-123      5.287    0.896     5.802    1.030    3.111    0.478
SS00-140      6.591    1.055     6.807    1.129    3.260    0.468
SS00-144A     6.421    1.000     6.115    1.022    2.981    0.433
SS98-09       3.902    0.625     3.972    0.778    2.341    0.336
SS98-72       7.537    1.213     7.516    1.477    4.297    0.628

Baring Granite
SS00-104      6.829    1.212     7.772    1.544    4.567    0.687
SS00-121      6.431    1.047     6.718    1.269    3.711    0.575
SS00-124      9.012    1.458     9.334    1.574    4.580    0.673
SS00-139      7.243    1.080     6.498    1.073    3.139    0.477

Diorite dyke(?) in Baring Granite
SS00-108     14.539    2.151    12.605    2.238    5.997    0.784

 Sample      Yb       Lu       Hf       Ta

St. Stephen Gabbro-gabbro unit
SS98-29      0.705    0.098    0.428    0.187
SS98-32a     1.107    0.162    0.359    0.271
SS98-54      1.899    0.268    2.561    0.538

Calais Quartz Diorite
SS00-120     3.200    0.466    3.305    0.597
SS00-122     3.383    0.547    4.500    0.584
SS00-123     3.360    0.563    3.013    0.815
SS00-140     3.134    0.519    3.720    0.437
SS00-144A    2.909    0.486    3.715    1.047
SS98-09      2.275    0.318    3.153    0.467
SS98-72      4.126    0.611    6.024    0.922

Baring Granite
SS00-104     4.582    0.651    5.916    2.184
SS00-121     3.808    0.549    5.051    1.185
SS00-124     4.473    0.716    4.253    1.391
SS00-139     3.250    0.537    5.021    1.492

Diorite dyke(?) in Baring Granite
SS00-108     4.860    0.703    2.344    0.437

* Analyses at Memorial University of Newfoundland by ICP-MS, using the
[Na.sub.2][O.sub.2] sinter method (Longerich et al. 1990).

Table 6. Sm-Nd isotopic data for the Moosehorn Plutonic Suite

                                     [sup.143]Nd/
Unit                      Sample     [sup.144]Nd     2 [sigma]

St. Stephen Gabbaro      SS98-32a      0.512581      0.000050
Calais Quartz Diorite    SS98-09       0.512687      0.000050
Calais Quartz Diorite    SS00-123      0.512571      0.000020
Raring Granite           SS00-124      0.512484      0.000013
Gabbro dyke(?)           SS00-108      0.512568      0.000017

                         [sup.147]Sm/
Unit                     [sup.144]Nd     [micro]g/g Nd    [micro]g/g Sm

St. Stephen Gabbaro         0.1691           3.752             1.05
Calais Quartz Diorite       0.1514          14.75              3.70
Calais Quartz Diorite       0.1533          18.92              4.70
Raring Granite              0.1485          34.59              8.32
Gabbro dyke(?)              0.1431          64.43             14.95

                         [[epsilon].sub.Nd]
Unit                          (421 Ma)          T(DM)

St. Stephen Gabbaro             0.37           1567 Ma
Calais Quartz Diorite           3.40            881 Ma
Calais Quartz Diorite           1.03           1184 Ma
Raring Granite                 -0.41           1250 Ma
Gabbro dyke(?)                  1.52           1086 Ma

Notes: Analyses by Alain Potrel, Memorial University of Newfoundland.
Sm and Nd contents and Nd isotopic composition were analyzed using a
multicollector Finnigan Mat 262 mass spectrometer in static mode. Nd
isotopic ratio are normalized to [sup.146]Nd/[sup.144]Nd = 0.7219. The
reported values were adjusted to La Jolla Nd standard
([sup.143]Nd/[sup.144]Nd = 0.511860). During the course of data
acquisition replicates of the standard gave a mean value of
[sup.143]Nd/[sup.144]Nd = 0.511886 [+ or -] 26 (2[sigma], n=18). The
in-run precisions on Nd isotopic ratio are given at 95% confidence
level. Error on Nd isotopic compositions are <0.002% and errors
on the [sup.147]Sm/[sup.144]Nd ratio are estimated to be less than
0.1%. The [[epsilon].sub.Nd] values are calculated using a
[sup.147]Sm/[sup.144]Nd = 0.1967 and [sup.143]Nd/[sup.144]Nd = 0.512638
values for the present day chondrite uniform reservoir (CHUR).
[sup.147]Sm decay constant is 6.54 [10.sup.-12][y.sup.-1] (Steiger and
Jager, 1977). The depleted mantle model ages, TDM, were calculated both
with respect to a D.M. with a [[epsilon].sub.Nd0] value of +10 isolated
from the CHUR since 4.55 Ga and following a linear evolution with
respect to the De Paolo (1988) mantle model.


ACKNOWLEDGEMENTS

We thank L.R. Fyffe (NB Department of Natural Resources Many sub-national governments have a Department of Natural Resources or similarly-named organization:
Australia
  • Queensland Department of Natural Resources and Mines
Canada
  • Natural Resources Canada
) for permission to do additional work on his thesis samples, and Dr. D. Lentz, UNB UNB University of New Brunswick
UNB Universidade de Brasília (University of Brasilia)
UNB United News of Bangladesh (news agency)
UNB Unclassified News Board
UNB Unbuffered
, for providing the thin sections and sample powders from the thesis collection. Kay Thorne and Dave Lentz kindly allowed us to include their unpublished chemical data in our Table 4 (samples Fyffe 13, 38, 42, 43). Owen Gaskill permitted us to use some photographs from his B.Sc. honours thesis in Fig. 3. Field work by M. Hill was supported by the Maine Geological Survey The term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information.

A geological survey
. Comments by journal reviewers Spike Berry and Malcolm McLeod were helpful in improving the manuscript and especially in motivating the authors to change the name to Moosehorn Plutonic Suite.

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PEARCE, J.A. AND CANN CANN Canadian Association of Neuroscience Nurses , J.R. 1973. Tectonic setting of basic volcanic rocks determined using trace element analysis. Earth and Planetary Science planetary science or planetology, study of planets and planetary systems as a whole. Planetary science applies the theories and methods of traditional disciplines such as astronomy, geology, physics, chemistry, and mathematics to the study of  Letters, 19, pp. 290-300.

PEARCE, J.A., & NORRY, M.J. 1979. Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks. Contributions to Mineralogy and Petrology, 69, pp. 33-47.

PEARCE, J.A., HARRIS, N.B.W., & TINDLE, A.G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, pp. 956-983.

ROBINSON, P., TUCKER, R.D., BRADLEY, BERRY, H.N., & OSBERG, P.H. 1998. Paleozoic orogens in New England, USA. GFF GFF Gain Flattening Filter (used in Erbium Doped Fiber Amplifier)
GFF Glass Fiber Filter
GFF Grain Foods Foundation
GFF Generic File Format (application data)
GFF Government Furnished Facility
, 120, pp. 119-148.

RUITENBERG, A.A., & MCCUTCHEON, S.R. 1978. Field guide to lower Paleozoic sedimentary and volcanic rocks of southwestern New Brunswick. In Ludman, A., editor, New England Intercollegiate Geological Conference Guidebook, 70th Annual Meeting, pp. 133-144.

SAMSON, S.D., & ALEXANDER JR., E.C. 198Z Calibration of the inter-laboratory [sup.40]Ar/[sup.39]Ar dating standard, MMhb-1. Chemical Geology, 66, pp. 27-34.

SAMSON, S.D., BARR, S.M., WHITE, C.E. 2000. Nd isotopic characteristics of terranes within the Avalon Zone, southern New Brunswick. Canadian Journal of Earth Sciences, 37, pp. 1039-1052.

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n.
A mineral that is present in a minor amount in rocks and is not considered an essential constituent of the rock.



accessory mineral 
 thermochronometry of lower crustal xenoliths, southern Africa. Contributions to Mineralogy and Petrology, 144, pp. 592-618.

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SEAMAN, S.J., SCHERER, E.E., WOBUS, R.A., ZIMMER, J.H., & SALES, J.G. 1999. Late Silurian volcanism volcanism
 or vulcanism

Any of various processes and phenomena associated with the surface discharge of molten rock or hot water and steam, including volcanoes, geysers, and fumaroles.
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STEWART, D.B., TUCKER, R.D., AYUSO, R.A., & LUX A unit of measurement of the intensity of light. It is equal to the illumination of a surface one meter away from a single candle. See candela. , D.R. 2001. Minimum age of the Neoproterozoic Seven Hundred Acre island Formation and the tectonic setting of the Islesboro Formation, Islesboro Block, Maine. Atlantic Geology, 37, pp. 41-59.

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VAN STAAL, C.R., DEWEY, J.F., NIOCAILL, C.M., & MCKERROW, W.S. 1998. The Cambrian-Silurian tectonic evolution of the northern Appalachians and British Caledonides: history of a complex, west and southwest Pacific-type segment of lapetus. In Lyell: the Past is the Key to the Present. Edited by D.J. Blundell and A.C. Scott. Geological Society, London, Special Publications, 143, pp. 199-242.

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WEST, D.P., LUDMAN, A., LUX, D.R. 1992. Silurian age for the Pocomoonshine gabbro-diorite, southeastern Maine and its regional tectonic implications. American Journal of Science, 292, pp. 253-273.

WESTERMAN, D.S. 1972. Petrology of the Pocomoonshine Gabbro-Diorite, Big Lake, Quadrangle, Maine. Ph.D. dissertation, Lehigh University Lehigh University, at Bethlehem, Pa.; coeducational; chartered and opened 1866 by Asa Packer. It has undergraduate colleges of arts and science, business and economics, and engineering and applied science, as well as several graduate programs. , 175 p.

WHALEN, J.B., CURRIE, K., & CHAPPELL, B.W. 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95, pp. 407-419.

WHALEN, J.B., JENNER, G.A., CURRIE, K.L., BARR, S.M., LONGSTAFFE, F,J, HEGNER, E. 1994. Geochemical and isotopic characteristics of granitoids of the Avalon Zone, southern New Brunswick: possible evidence for repeated delamination delamination /de·lam·i·na·tion/ (de-lam?i-na´shun) separation into layers, as of the blastoderm.

de·lam·i·na·tion
n.
1. A splitting or separation into layers.

2.
 events. The Journal of Geology, 102, pp. 269-282.

WIEBE, R.A., HOLDEN, J.B., COOMBS Coombs can refer to:
  • Coombs test, a test for the presence of antibodies or antigens
  • Coombs reagent, the reagent used in the Coombs test
  • Coombs' method, a type of voting designed by the psychologist Clyde Coombs
, M.L., WOBUS, R.A., SCHUH, K.J., & PLUMMER, B.P. 1997. The Cadillac Mountain intrusive complex, Maine: The role of shallow-level magma chamber A magma chamber is a large underground pool of molten rock lying under the surface of the earth's crust. The molten rock in such a chamber is under great pressure, and given enough time and pressure can gradually fracture the rock around it creating outlets for the magma.  processes in the generation of A-type Granites. In The Nature of Magmatism in the Appalachian Orogen. Edited by A.K. Sinha, J.B. Whalen, and J.P. Hogan. Geological Society of America. Memoir 191, pp. 397-418.

WINCHESTER, J.A., & FLOYD, P.A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile im·mo·bile
adj.
1. Immovable; fixed.

2. Not moving; motionless.



immo·bil
 elements. Chemical Geology, 20, pp. 325-343.

Editorial responsibility: David Gibson
For the American football player, see David Gibson (football player)
For the Scottish soccer player, see Dave Gibson


David Gibson, (March 9 1804 – January 25 1864), was a surveyor, farmer and political figure in Upper Canada.
 

K.J. McLAUGHLIN (1), S.M. BARR (1) *, M.D. HILL (2), M.D. THOMPSON (3), J. RAMEZANI (4), AND P.H. REYNOLDS (5)

(1.) Department of Geology, Acadia University, Wolfville, Nova Scotia, Canada B4P 2R6

(2.) Northeastern University Northeastern University, at Boston, Mass.; coeducational; founded 1898 as a program within the Boston YMCA, inc. 1916, university status 1922, fully independent of the YMCA 1948. , Boston, Massachusetts “Boston” redirects here. For other uses, see Boston (disambiguation).
Boston is the capital and most populous city of Massachusetts.[3] The largest city in New England, Boston is considered the unofficial economic and cultural center of the entire New
 02115 USA

(3.) Geology Department, Wellesley College, Wellesley, Massachusetts 02481 USA

(4.) Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 USA

(5.) Department of Earth Sciences, Dalhousie University Dalhousie University (dălhou`zē), at Halifax, N.S., Canada; nonsectarian; coeducational; founded 1818 by the 9th earl of Dalhousie. Except for a few years between 1838 and 1845, Dalhousie did not function as a university until 1863. , Halifax, Nova Scotia For other uses, see Halifax.
Halifax, Nova Scotia may refer to any of the following:
  • Halifax Regional Municipality, capital of Nova Scotia, Canada
, Canada B3H 3J5

* Corresponding author: <sandra.barr@acadiau.ca>

Date received: September 12, 2003 & Date accepted: March 3, 2004
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Author:McLaughlin, K.J.; Barr, S.M.; Hill, M.D.; Thompson, M.D.; Ramezani, J.; Reynolds, P.H.
Publication:Atlantic Geology
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Date:Jul 1, 2003
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