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

ABSTRACT

The Moosehorn Plutonic Suite in the coastal Maine magmatic province covers an area of approximately 250 [km.sup.2] in the area of Calais, Maine, and St. Stephen, New Brunswick. Based on a compilation of previous work combined with new field mapping, geochronology, and petrochemical data, the Moosehorn Plutonic Suite (MPS) is interpreted to consist mainly of five approximately contemporaneous plutons: Staples Mountain Gabbro, St. Stephen Gabbro, Calais Quartz Diorite, Baring Granite, and Elliott Mountain Diorite. The layered, sill-like Staples Mountain Gabbro is mainly mafic, whereas the larger St. Stephen Gabbro consists of a core of dunite and troctolite, surrounded by olivine 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 monzogranite, which is widely mingled with quartz diorite and diorite of the Calais Quartz Diorite. The latest pluton of the MPS appears to be the Elliott Mountain Diorite, which consists mainly of texturally varied dioritic 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) crystallization age of 421.1 [+ or -] 0.8 Ma) and phlogopite 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 to mafic and intermediate parts of the Bocabec Pluton of the Saint George Batholith 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 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 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 par differenciation magmatique ayant produit un eventail de compositions derives. Les indices temoignant d'un melange 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.

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 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 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 of Silurian and Devonian age and dominantly mafic and felsic 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 (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. 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 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 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 intruded by the MPS are mainly shale and quartz-rich sandstone of the Cambrian-Ordovician Cookson Group. 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) 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 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 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 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, 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 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 as the ferromagnesian mineral component, and diorite when amphibole 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 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. 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 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

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 gabbro; III--interlayered norite and anortbosite; IV--unlayered augite gabbro and minor olivine gabbro; V --unlayered gabbronorite, with increased orthopyroxene and no olivine, in contrast to unit IV. She interpreted the pluton to be a layered sill-like body, formed by crystal fractionation processes; more details are available in Coughlan (1986).

St. Stephen Gabbro

Paktunc (1989) divided what he termed the St. Stephen Intrusion into ultramafic, olivine-bearing mafic, and mafic zones, and interpreted compositional variation and local crude layering to fractional crystallization. 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, pyroxene, and chromite, 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 and magnetite. Sulphide minerals appear to be concentrated in the serpentinized parts of the dunite, suggesting that they also may be secondary. With decreasing cumulus 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. 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 are typically present, as well as varying amounts of amphibole and phlogopite, and accessory apatitc, titanite, 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 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 and later pale green-green actinolitic hornblende. Most samples also contain augite and biotite. Interstitial 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 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 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, allanite, 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 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 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 under a binocular microscope. For irradiation in the McMaster University 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.

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 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 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

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 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 that were inferred to have formed by mixing and hybridization 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 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 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 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 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 (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 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, 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", the details of tectonic activity during this protracted 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 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) for permission to do additional work on his thesis samples, and Dr. D. Lentz, UNB, 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. 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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Editorial responsibility: David Gibson

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, Boston, Massachusetts 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, Halifax, Nova Scotia, 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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