Precise age and petrology of Silurian-Devonian plutons in the Benjamin River--Charlo area, northern New Brunswick. (2024)

ABSTRACT

The Late Silurian Landry Brook and Dickie Brook plutons and Charloplutonic suite underlie a combined area of approximately 80 [km.sup.2]in the northeastern part of the Ganderian Tobique-Chaleurtectonostratigraphic belt in northern New Brunswick. The Landry Brookpluton is divided into three units: gabbro to quartz diorite, quartzmonzodiorite to monzogranite, and monzogranite. A sample from the quartzmonzodiorite unit yielded a U-Pb (zircon) crystallization age of 419.63[+ or -] 0.23 Ma. A granodioritic stock located near the Landry Brookpluton has yielded an age of 400.7 [+ or -] 0.4 Ma, indicating that itis a younger unrelated body, herein referred to as the Blue MountainGranodiorite (new name). The Dickie Brook pluton also consists of threeunits: leucogabbro to quartz gabbro, diorite to quartz diorite andquartz monzodiorite to monzogranite. Two samples from the monzograniteunit yielded U-Pb (zircon) crystallization ages of 418 [+ or -] 1 Ma and418.1 [+ or -] 1.3 Ma. The Charlo plutonic suite is a group of smallplutons and dykes, located west of the Dickie Brook and Landry Brookplutons and consists mainly of diabase, quartz monzonite tomonzogranite, rhyolite porphyry, and dacite porphyry. Chemical trendsindicate that the quartz monzodiorite to monzogranite unit of the LandryBrook pluton, all of the units of the Dickie Brook pluton, and thequartz monzodiorite to monzogranite unit of the Charlo plutonic suite,as well as the volcanic host rocks of the Bryant Point and Benjaminformations, are co-magmatic They formed following slab break-off andextension in the waning stages of the Salinic orogeny, which resultedfrom the collision of Ganderia and Laurentia. In contrast, the daciteporphyry of the Charlo plutonic suite may be cogenetic with the youngerBlue Mountain Granodiorite and related to the collision of Avalonia withLaurentia.

RESUME

Les plutons des ruisseaux Landry et Dickie et le corrige plutoniquede Charlo, du Silurien tardif, recouvrent une superficie totaled'environ 80 [km.sup.2] dans la partie nord-est du domainetectonostratigraphique ganderien Tobique-Chaleur, dans le nord duNouveau-Brunswick. Le pluton du ruisseau Landry se compose de troisunites : du gabbro a de la diorite quartzique, de la monzodioritequartzique au monzogranite, et du monzogranite. Un echantillon del'unite de monzodiorite quartzique a produit un age decristallisation de 419,63 [+ or -] 0,23 Ma par la methode de datationU-Pb (sur zircon). Un bloc de granodiorite a proximite du pluton duruisseau Landry a produit un age de 400,7 [+ or -] 0,4 Ma, ce quiindiquerait qu'il s'agit d'un corps de formation plusrecente et non relie, designe ici comme la granodiorite de Blue Mountain(nouveau nom). Le pluton du ruisseau Dickie comprend lui aussi troisunites : du leucogabbro a du gabbro quartzique, de la diorite a de ladiorite quartzique, et de la monzodiorite quartzique a du monzogranite.Deux echantillons de monzogranite ont produit des ages decristallisation de 418 [+ or -] 1 Ma et de 418,1 [+ or -] 1,3 Ma, selonla methode de datation U-Pb (sur zircon). Le cortege plutonique deCharlo est un groupe de plutons et de dykes de petite taille, situe al'ouest des plutons du ruisseau Dickie et du ruisseau Landry, et ilse compose de diabase, de monzonite quartzique a du monzogranite, deporphyre rhyolitique, et de porphyre dacitique. Les tendances chimiquesindiquent une nature comagmatique en ce qui concerne l'unite demonzodiorite quartzique au monzogranite du pluton du ruisseau Landry, latotalite des unites du pluton du ruisseau Dickie, ainsi que l'unitemonzodiorite quartzique au monzogranite du corthge plutonique de Charlo,tout comme pour les roches volcaniques encaissantes des FormationsBryant Point et Benjamin. Ces structures sont apparues apres la rupturede la plaque et son extension aux derniers stades de l'orogenesesalinique, provoquee par la collision des anciens continents de Ganderieet de Laurentie. Par contraste, le porphyre dacitique du corthgeplutonique de Charlo peut s'&re forme sous les m4mes conditionsque celles ayant preside h l'apparition de la granodiorite plusrecente de Blue Mountain et etre associe a la collision des ancienscontinents d'Avalon et de Laurentie.

[Traduit par la redaction]

INTRODUCTION

Central and northern New Brunswick contains voluminousSilurian-Devonian plutonic and volcanic rocks displaying a continuousspectrum from mafic to felsic compositions (e.g., Whalen 1993; Wilson etal. 2008). The focus of this study, the Landry Brook and Dickie Brookplutons anda group of smaller plutons, dykes, and sills referred to hereas the Charlo plutonic suite, are part of this widespread mid-Paleozoicmagmatism, but are spatially isolated from other plutonic manifestationsof the magmatic event. These plutonic rocks range in composition fromgabbro to monzogranite and, collectively, cover an area of approximately80 [km.sup.2] (Fig. 1). Although generally assumed to be consanguineousand Devonian, the ages of these plutons were in fact uncertain prior tothe present study. Stewart (1979) reported an imprecise age of 370 [+ or-] 30 Ma (whole-rock Rb-Sr) for the Landry Brook pluton, and later anunpublished U-Pb (zircon) age of 400 [+ or -] 1 Ma was obtained (V.McNicoll; reported in Wilson et al. 2004) from a separate granodioritestock southwest of the Landry Brook pluton; however, its relationship tothat pluton was uncertain. Data from this latter stock are included inthis study, and geochemical comparisons are made with adjacent intrusiverocks. The Landry Brook and Dickie Brook plutons and Charlo plutonicsuite are excellent targets for petrological and geochronological study,to add new information to models for northern Appalachian magmatic andtectonic evolution.

The purpose of this paper is to describe the field relationshipsand petrology of these plutons, to present new and older (but previouslyunpublished) U-Pb (zircon) data that closely constrain the age of theLandry Brook and Dickie Brook plutons and spatially associated stocks,and to interpret their petrogenesis and tectonic setting at the time ofemplacement. Based on geochemical and age similarities, we furthersuggest that the host volcanic rocks of the Benjamin and Bryant Pointformations are likely genetically related to (i.e., the extrusiveequivalents of) the plutons.

GEOLOGICAL SETTING

The Landry Brook pluton, Dickie Brook pluton, and Charlo plutonicsuite intruded rocks that are part of the mid-Paleozoic Appalachianrealm of Ganderia and its cover sequence (Fig. 2). At regional scale,Ordovician rocks in this area are part of the Popelogan-Victoria arcsubzone (Hibbard et al. 2006; van Staal 2007; van Staal et al. 2009) andare covered by the Silurian-Devonian Chaleur Bay Synclinorium (part ofthe Gaspe Belt; Wilson et al. 2004), which includes rocks of the QuinnPoint, Dickie Cove, Petit Rocher, and Dalhousie groups (Wilson and Kamo2012). The Silurian rocks in the study area include the UpsalquitchFormation (Quinn Point Group), and the Bryant Point, New Mills, andBenjamin formations (Dickie Cove Group; Fig. 1).

The Llandoverian Upsalquitch Formation (Fig. 1) is generallycomposed of calcareous, micaceous siltstone and fine-grained sandstone(McCutcheon and Bevier 1990). It is disconformably overlain by theLudlovian Bryant Point Formation, which is composed of greyish-green tomaroon, locally highly porphyritic and amygdaloidal basaltic flows withplagioclase phenocrysts up to 3 cm in length. It is estimated to beabout 650 m thick at the type locality (Walker and McCutcheon 1995). TheNew Mills Formation overlies the Bryant Point Formation, and is composedof red pebble-cobble conglomerate, sandstone and siltstone, and minormafic and felsic volcanic flows. Cobbles and pebbles in the conglomerateare composed of mafic and felsic volcanic rocks, derived from underlyingand coeval formations. The large size of many of the boulders, theirlack of orientation, and poor stratification suggest deposition assubaerial debris flows (Greiner 1970; Irrinki 1990; Walker et al. 1993;Walker and McCutcheon 1995). The formation is approximately 120 m thick,and is overlain by and interfingers with felsic volcanic rocks of theBenjamin Formation. The latter formation is composed of pale red,flow-banded, sparsely porphyritic rhyolite, and also includes feldsparcrystal tuff, pumaceous lapilli tuff and, at the top of the formation,basalt (McCutcheon and Bevier 1990). The Benjamin Formation is lateLudfordian to early Pridolian in age, and yielded U-Pb (zircon) ages of420.8 [+ or -] 0.4 Ma (Wilson and Kamo 2008) and 419.7 [+ or -] 7 Ma(Wilson and Kamo 2012) at different localities. The former dated samplewas collected 3.5 km north of the northern tip of the Dickie Brookpluton (Fig. 1), and the latter 14 km south of the southern part of theLandry Brook pluton (not shown on Fig. 1).

FIELD RELATIONS AND PETROGRAPHY

Terminology

The Landry Brook pluton was previously termed the "BenjaminRiver intrusive complex" by Stewart (1979), and the Landry Brook,Dickie Brook and Charlo intrusions were later collectively referred toas the "Charlo stocks" (Fyffe et al. 1981). Whalen (1993)considered the Landry Brook and Dickie Brook plutons as two separateplutons forming the "Benjamin River complex". However, toavoid any terminology conflict with some of the host rocks (i.e., theBenjamin Formation), the names Landry Brook and Dickie Brook wereintroduced; both names derive from brooks that are tributaries of theBenjamin River, which transects both plutons. The formal names of theseplutons in the New Brunswick bedrock lexicon are the Landry Brook QuartzMonzonite and Dickie Brook Quartz Monzonite; however, to avoidexclusivity in the various rock types forming them, they are referredherein simply as plutons. The term Charlo plutonic suite is used hereonly for small plutons, dykes, and sills that occur over a large areawest of the Landry Brook and Dickie Brook plutons (Fig. 1). These smallbodies were referred to as the "Charlo stocks" by Whalen(1993); the formal name in the New Brunswick bedrock lexicon is theCharlo Granite. As discussed later in the text, the name Blue MountainGranodiorite is introduced for two granodioritic stocks south andsouthwest of the Landry Brook pluton. The name is derived from BlueMountain, a topographic feature in the area (Fig. 1). However, gabbroicbodies in the same area are interpreted to be part of the Landry Brookpluton, based on petrological features described below.

Field Relationships

Landry Brook pluton and Blue Mountain Granodiorite

The Landry Brook pluton consists of one main composite intrusionand a few small gabbroic bodies located southwest of the main intrusion(Fig. 1). The latter area is also the location of the Blue MountainGranodiorite stocks, which were originally considered to be geneticallyrelated to the Landry Brook pluton, but are discussed separately here.

The most abundant rock type in the Landry Brook pluton is quartzmonzodiorite to monzogranite, which makes up most of the pluton. Otherlithotypes include gabbro/quartz diorite and late monzogranite.Throughout the area, exposure is poor; hence, cross-cutting and othercontact relations are difficult to observe. In addition to fieldobservations, 16 drill holes were re-logged in order to reassess therelationships with the smaller plutons to the southwest of the mainbody. Based on these observations and prior to geochronological work,the sequence of emplacement was inferred to be gabbro/quartz diorite,followed by medium-grained granodiorite, porphyritic granodiorite andquartz monzodiorite to monzogranite (QMM), and lastly the monzogranite.All these plutonic rocks intruded mafic flows and felsic flows andpyroclastic rocks of the Bryant Point and Benjamin formations,respectively. The gabbro to diorite (of leucogabbro) occurs also asxenoliths in the QMM (Figs. 3a, b); the xenoliths are angular toirregular (e.g., ovoid) in shape and range widely in size (cm to mscale). Contacts between the gabbro and the QMM are gradational to sharpand the late monzogranite clearly cross-cuts both the QMM and gabbro(Fig. 3b), as xenoliths are present in a monzogranite dyke in thenortheastern part of the pluton.

Porphyritic granodiorite (Fig. 3c) and medium-grained granodiorite(Fig. 3d) of the Blue Mountain Granodiorite have clear intrusiverelationships relative to both the early gabbro and the latemonzogranite of the Landry Brook pluton. In both cases contacts aresharp and well define& chilled margins and marginal alteration offeldspar grains were observed in places. The relationship of the BlueMountain Granodiorite to the QMM of the Landry Brook pluton isuncertain, as no contacts were observed. Geochronological andgeochemical analyses of the Blue Mountain Granodiorite (see below)demonstrate that it is unrelated to the Landry Brook pluton, and theproduct of a much younger magmatic event.

Dickie Brook pluton

Like the Landry Brook pluton, the Dickie Brook pluton andassociated dykes intruded mafic flows and felsic flows and pyroclasticrocks of the Bryant Point and Benjamin formations, respectively. Most ofthe northeastern and southern parts of the Dickie Brook pluton consistof medium-grained gabbro to quartz gabbro and quartz diorite (Fig. 1).These areas are also cut by diabasic dykes trending northwest-southeast.The contact between the light-coloured quartz diorite and somewhatdarker gabbro is subtle but visible in some places (Fig. 3e). Thecontact is typically sharp, suggesting that the gabbro had cooled priorto subsequent intrusion of the quartz diorite. Dykes of granodioritecomposition (slightly higher in quartz and K-feldspar) cut the gabbroand quartz diorite and may be related to the quartzmonzodiorite/monzogranite unit that forms more than half of the pluton(Fig. 1). Near the eastern margin, the contact between quartz dioriteand gabbro is irregular (e.g., cuspatelobate margins) but towards thewest, the contact is sharp and angular. Xenoliths of leucogabbro orquartz diorite were also observed in the quartzmonzodiorite/monzogranite (Fig. 3f), indicating that the latter is theyoungest unit in the pluton. Flow during emplacement/cooling issuggested by the presence of schlieren or flow layering in theleucogabbro. Hence, small aphanitic diabasic dykes appear to have beenboudinaged, possibly by host magma movement during their emplacement.Close to its contact with the host rocks of the Bryant Point andBenjamin formations, the quartz monzodiorite/monzogranite containscentimetre- to metre-scale xenoliths of basalt (probably from the BryantPoint Formation). A melanocratic monzogranite dyke in the Bryant PointFormation north of the pluton is interpreted to be related to the quartzmonzodiorite/monzogranite unit based on texture and mineralogy. Diabasicand aphanitic felsic dykes, probably late phases of the pluton, cut thequartz monzodiorite/monzogranite, and are especially visible along theSouth Branch Benjamin River.

Charlo plutonic suite

The plutons, dykes, and sills of the Charlo plutonic suite consistof varied intermediate to felsic rock including quartz monzonite tomonzogranite, quartz-plagioclase rhyolite porphyry, hornblende daciteporphyry, and felsite. They intruded calcareous sedimentary rocks of theUpsalquitch Formation (Fig. 1) and are typically orientedsouthwest-northeast, parallel to regional strike of bedding andcleavage. Diabase dykes, also oriented southwest-northeast, are abundantin the area, and are assumed to be mainly younger than the felsic rocks,based on cross-cutting relationships observed in several places. Some ofthe diabase bodies are concordant with bedding and hence sill-like; vugsat the tops of these sills indicate way-up.

Small areas of skarn were observed in the calcareous rocksthroughout the area adjacent to the intrusions. A drilling project in1996-97 by Noranda Inc. evaluated the potential for skarnmineralization; however, no further work has been carried out sincethen. The drill cores, stored at Madran, New Brunswick, were examinedand the lithotypes intersected in drill core correspond to those seen insurface outcrops.

The quartz monzonite to monzogranite occurs in three plutonicbodies; it is cut by later felsite dykes (Fig. 3g) and has sharpcontacts with the host rocks. It is possible that the felsite andquartz-plagioclase rhyolite porphyry dykes are somewhat younger than thequartz monzonite, assuming they are all comagmatic. This hypothesis issupported by cross-cutting relationships with the quartz monzonite, butalso by their similarity to the late felsite dykes in the Landry Brookand Dickie Brook plutons. Alteration in the rhyolite porphyry ispervasive, indicated by abundant chlorite and calcite veins. Theabundance of aligned miarolitic cavities parallel to primary flow fabricsuggests that these bodies were emplaced at high levels. Nocross-cutting relationships were observed between the hornblende daciteporphyry (Fig. 3h) and the other units.

Petrography

Blue Mountain Granodiorite

Porphyritic (hiatal to seriate) granodiorite has plagioclase(~[An.sub.25]) phenocrysts varying from 3 to 5 mm in size, with ahaltered fine-grained groundmass composed of K-feldspar and quartz (Fig.4a). In contrast, the medium-grained granodiorite consists of quartz,plagioclase ([An.sub.36-41]), biotite, and minor hornblende (Fig. 4b).It is also less altered than the porphyritic granodiorite. Hence theyare texturally and mineralogically distinct, although both hostdisseminated sulphide minerals (e.g. pyrite, chalcopyrite). A summary ofplutonic units and petrographic features are presented in Appendix 1.

Landry Brook pluton

The main body of the Landry Brook pluton varies from quartzmonzodiorite to quartz monzonite and monzogranite, depending mainly onthe relative abundance of K-feldspar. Colour varies from light grey todark brick red with increasing degree of alteration. Most of these rocksare medium-grained and in some areas they are porphyritic with zonedplagioclase phenocrysts (Fig. 4c). They contain abundant xenoliths ofgabbro/diorite and basalt, the latter likely from the host Bryant PointFormation. The youngest component of the pluton is fine- tomedium-grained monzogranite, which in places contains plagioclasephenocrysts in a fine-grained groundmass (Fig. 4d).

Gabbro is generally medium to dark grey and the grain size variesfrom fine to medium; quartz diorite is texturally similar to the gabbrobut lighter in colour. Both the gabbro and quartz diorite consist ofplagioclase ([An.sub.44-63]), diopside and/or calcic hornblende,magnetite and minor quartz (less than 5%).

Dickie Brook pluton

Mafic rocks of the Dickie Brook pluton vary in composition, andinclude gabbro, leucogabbro to quartz gabbro, and diorite to quartzdiorite. Gabbro and quartz gabbro contain a higher proportion ofmaficminerals, mainly clinopyroxene, than the leucogabbro. The diorite/quartzdiorite (Fig. 4e) is lighter in colour that the gabbroic rocks but withsimilar medium to coarse grain size. The quartz content is higher thanin the gabbroic rocks and the main mafic mineral is hornblende ratherthan clinopyroxene.

Quartz monzodiorite/monzogranite (Fig. 4f) is typically light pinkto dark red, medium-grained and equigranular, but in some places it isporphyritic with phenocrysts of plagioclase (~[An.sub.45]). This unit isfairly hom*ogeneous throughout in terms of texture and composition. Maficminerals include biotite and hornblende, and titanite as a prominentaccessory phase.

Charlo plutonic suite

The main rock types in the Charlo plutonic suite are diabase togabbro, quartz monzonite to monzogranite, quartz rhyolite porphyry, andhornblende dacite porphyry. The gabbro and diabase occur both as smallplutons and as dykes; they are dark grey, fine- to medium-grained, andcontain augite-diopside, plagioclase, and magnetite. The quartzmonzonite to monzogranite (Fig. 4g) is fine-to medium-grained, andconsists of zoned phenocrysts of plagioclase (ranging [An.sub.17-57]from rim to core) in a fine-grained groundmass consisting of granophyricquartz and K-feldspar. It is similar in mineralogy and texture to thequartz monzodiorite/monzogranite units in the Landry Brook and DickieBrook plutons, and is likely related to them (see Discussion).Miarolitic cavities are abundant, consistent with high-levelemplacement. The quartz rhyolite porphyry occurs as dykes that vary fromlight grey to dark pink depending on the degree of alteration. Quartzphenocrysts are abundant, as are miarolitic cavities. At some locations,sulphide concentration is relatively high. Hornblende dacite porphyry(Fig. 4h) is medium grey, and has hornblende phenocrysts ranging from 3to 5 mm in size in an aphanitic groundmass. The phenocrysts have a moreor less parallel arrangement.

GEOCHRONOLOGY

Analytical methods

Samples MLNB-733 (Dickie Brook quartz monzodiorite) and 97-DL-04(Blue Mountain Granodiorite) were collected and analyzed by M.L. Bevierin 1988 and V. McNicoll in 1997, respectively, at the Geological Surveyof Canada, Ottawa. Heavy mineral concentrates were prepared by standardcrushing, grinding, Wilfley table, and heavy liquid techniques. Mineralseparates were sorted by magnetic susceptibility using a Frantzisodynamic separator. Multigrain zircon fractions analyzed were verystrongly air abraded following the method of Krogh (1982). U-Pbanalytical methods were those outlined in Parrish et al. (1987).Treatment of analytical errors follows Roddick et al. (1987), withregression analysis modified after York (1969). Analytical results arepresented in Table 1, where errors on the ages are reported at the 2olevel, and displayed in the concordia plot (Figs. 5a, c).

Samples LB00-1 (Landry Brook quartz monzonite) and 09SHM-BR-50(Dickie Brook quartz monzodiorite) were collected in the summer of 2009by R.A. Wilson and S. McClaneghan, respectively, and analyzed by S. Kamoat the Jack Satterly Geochronology Laboratory of the University ofToronto. The samples were crushed, pulverized and passed over a Wilfleytable. The resulting heavy mineral concentrates were re-processed on

the Wilfley table until a significantly reduced sample size of ~5-10g was achieved (from rock samples weighing ~8-12 kg). The smaller heavymineral concentrates were more rapidly processed through mineralseparation procedures (i.e., magnetic separation and reduced volumes ofmethylene iodide of ~2-8 ml) and no longer required the use of the heavyliquid "bromoform". U-Pb analysis was by isotope dilutionthermal ionization mass spectrometry methods (ID-TIMS) at the JackSatterly Geochronology Laboratory of the University of Toronto. Prior toanalysis, zircon crystals were thermally annealed and partiallydissolved in HF (chemical abrasion), which has the advantage ofpenetratively removing alteration zones where Pb loss has occurred(Mattinson 2005). Grains were placed in a muffle furnace at~1000[degrees]C for 60 hours, followed by leaching in a 50:50 solutionof HF and 6N HCl in Teflon dissolution vessels at 195[degrees]C for 16hours. After selecting the zircons, their dimensions were measured, andthe weights of each grain were calculated. The grains were washed in 8NHN[O.sub.3] acid and ultra-clean acetone prior to dissolution. A[sup.205]Pb-[sup.233]U-[sup.235]U spike (ET535) was added to the Teflondissolution capsules during sample loading. Zircon was dissolved using~0.10 mL of concentrated HF and ~0.02 mL of 7N HN[O.sub.3] in teflonbombs at 195[degrees]C (Krogh, 1973) for five days, and re-dissolved in~0.15 mL of 3N HCI. Uranium and Pb were isolated from the zirconsolutions using 50 microlitre anion exchange columns, dried in diluteH3PO4 acid, and deposited onto outgassed rhenium filaments with silicagel (Gerstenberger and Haase 1997). Uranium and Pb were analyzed with aVG354 mass spectrometer using a Daly pulse-counting system. The deadtime of the measuring system for Pb and U was 21.5 nsec. The massdiscrimination correction for the Daly detector is constant at0.05%/atomic mass unit. Amplifier gains and Daly characteristics weremonitored using the SRM982 Pb standard. Thermal mass discriminationcorrections are 0.10%/atomic mass unit. The total amount of common Pbfor each analysis (Table 1) was attributed to laboratory Pb, thus nocorrection for initial common Pb from geological sources was made.

Results

In geologically young zircons, the [sup.238]U/[sup.206]Pb datingsystem is the most reliable and precise because of the much greaterabundance of [sup.238]U. Therefore, the results (Table 1 and Fig. 5)presented herein refer exclusively to the [sup.206]Pb/[sup.238]U ages.

Four multigrain zircon fractions were analyzed in sample 97-DL-04,representing the various zircon morphologies in the sample, includingequant multifaceted crystals (fraction A), prismatic crystals withaspect ratios of about 2:1 (fractions B1 and B2), and elongate,needle-like grains (fraction C). Most of the zircon grains analyzedcontain minor fluid inclusions. Three of the analyses overlap and arenear-concordant (Fig. 5a). Analysis B2 contains an inherited componentand is not included in the age calculation. A weighted average of the[sup.206]Pb/[sup.238]U ages of fractions A, B1, and C is calculated tobe 400.7 [+ or -] 0.4 Ma (Fig. 5a), which is interpreted to be thecrystallization age of the Blue Mountain Granodiorite.

In sample LB00-1 from the Landry Brook pluton, abundant zircons areeuhedral, sharply-facetted, pink, multi-facetted to 2:1 prismatic, freshand gem-like, and contain abundant bubble-like melt inclusions. The U-Pbdata for four, single, chemically-abraded zircon crystals giveconcordant, highly reproducible data. The weighted mean[sup.206]Pb/[sup.238]U age is 419.63 [+ or -] 0.23 Ma (Fig. 5b) and thisis interpreted as the best age estimate for the Landry Brook pluton,which is significantly older that the previously reported age of 370 [+or -] 30 Ma (whole-rock Rb-Sr; Stewart 1979). It is also older than thespatially related Blue Mountain Granodiorite (401.7 [+ or -] 0.4 Ma).

Two independent age analyses were done at the same location (Fig.2a) on the Dickie Brook pluton. A comparison of sample MLNB-733 with therecently collected sample 09SHM-BR50 enabled us to verify the accuracyof the original age determination. The zircons analyzed in sampleMLNB-733 were pale yellow, clear, stubby to elongate square prisms withsimple terminations. Both samples show three-data-point clusters withweighted mean [sup.206]Pb/[sup.238]U ages of 418.1 [+ or -] 1.3 Ma (Fig.5c) and 418 [+ or -] 1 Ma (Fig. 5d), respectively. In sample 09SHM-BR50,the fourth data point is older and plots outside the error range of thecluster, having a [sup.206]Pb/[sup.238]U age of 420.7 [+ or -] 0.8 Ma.This grain is interpreted as having crystallized 2-3 my prior to thegranite, and was incorporated into the granite magma source or duringemplacement of the granite body. Therefore, the age of the granite isinterpreted to be 418 [+ or -] 1 Ma, making it, within error, coevalwith the Landry Brook pluton.

GEOCHEMISTRY

Introduction

Forty samples from the Landry Brook and Dickie Brook plutons, theCharlo plutonic suite, and Blue Mountain Granodiorite were analysed formajor and trace elements, including rare-earth elements (Appendix 2 and3) at ACME Analytical Laboratories Ltd., Vancouver, Canada.Lithologically hom*ogeneous samples (i.e., barren of enclaves) werecollected with an effort to ensure that the freshest, least alteredsamples were taken. However, the spatial distribution of collectedsamples is, in general, dependant on the available exposed bedrock.

The purpose of this section is to describe the chemicalcharacteristics of the plutons based on these data. In order to comparethe chemical characteristics of the Landry Brook and Dickie Brookplutons and the Charlo plutonic suite, all of the samples are plottedtogether on Harker variation diagrams. The geochemical data of Whalen(1993) also are included on these diagrams to increase the amount ofdata, and include 6 samples from the Landry Brook pluton, 4 samples fromthe Dickie Brook pluton, and 4 samples from the Charlo plutonic suite.

Major Element Compositions

In the Landry Brook pluton and Charlo plutonic suite, gabbro/quartzdiorite and diabase have Si[O.sub.2] concentrations of 47-50 wt. % (Fig.6), anda gap in Si[O.sub.2] separates those rocks from intermediate tofelsic rocks, which vary from 58 to 78 wt. % Si[O.sub.2], Samples fromthe Dickie Brook pluton have a continuous silica spectrum ranging from50% to 72%. Overall, Ti[O.sub.2], [Al.sub.2][O.sub.3],[Fe.sub.2][O.sub.3.sup.t], MgO, and CaO show similar negativecorrelation with Si[O.sub.2] in all three plutons (Fig. 6), consistentwith decreasing abundances of ferromagnesian minerals, plagioclase,titanite, and magnetite. Amounts of Ti[O.sub.2],[Fe.sub.2][O.sub.3.sup.t], MgO, and CaO (Figs. 6a, c-e) are higher ingabbro/quartz diorite samples than in samples from theintermediate-felsic units, reflecting their greater abundance offerromagnesian minerals and calcic plagioclase. Although they varylittle in Si[O.sub.2], the gabbro/quartz diorite samples show a widerange in most other major oxides including Ti[O.sub.2],[Al.sub.2][O.sub.3], [Fe.sub.2][O.sub.3.sup.t], MgO, and CaO (Figs.6a-e), consistent with the varying abundances of clinopyroxene,amphibole, plagioclase, opaque minerals, and titanite observed in thesesamples.

Both [K.sub.2]O and [Na.sub.2]O (Figs. 6f, g) show positivecorrelation with Si[O.sub.2], consistent with the absence of K-bearingminerals (e.g., K-feldspar and biotite) in the mafic rocks. [Na.sub.2]Oshows an increase and then a decrease after about 65 % Si[O.sub.2],which could be linked to fractionation of increasingly Na-richplagioclase as the magma evolved.

In samples from the Landry Brook pluton and Charlo plutonic suite,a gap in MgO of about 2-3 wt. % separates mafic samples andintermediate-felsic samples (Fig. 6d). For example, the abundance ofMg-rich clinopyroxene in the gabbro compared to its minor presence inthe quartz monzodiorite in samples from the Charlo plutonic suite isconsistent with this gap, which does not exist in the[Fe.sub.2][O.sub.3.sup.t] data (Fig. 6c). Samples from the hornblendedacite porphyry dyke in the Charlo plutonic suite and porphyriticgranodiorite in the Blue Mountain Granodiorite tend to diverge from thetrends defined by samples from the other units, with slightly higher[Al.sub.2][O.sub.3], CaO, and MgO and lower Ti[O.sub.2],[Fe.sub.2][O.sub.3.sup.t], and [K.sub.2]O. The quartz rhyolite porphyryin the Charlo plutonic suite is the most felsic unit in the study area,and has very low abundances of all of these components. Overall,[P.sub.2][O.sub.5] shows a wide spread in the more mafic samples, linkedto modal variations in apatite content, and then decreases in the felsicsamples, likely as a result of apatite fractionation, perhaps asinclusions in the fractionating ferromagnesian minerals

Collectively, samples from the four intermediate-felsic units shownegative correlation of [Al.sub.2][O.sub.3], Ti[O.sub.2],[Fe.sub.2][O.sub.3.sup.t], MgO, MnO, and CaO with Si[O.sub.2],consistent with fractionation of ferromagnesian minerals and calcicplagioclase. The mafic units in the Landry Brook pluton and Charloplutonic suite are similar, except that the gabbro in the Charloplutonic suite contains much lower CaO (Fig. 6e) and higher [Na.sub.2]Oand P2Os (Figs. 6f, h). Overall, the samples from all units are similar,although diorite/quartz diorite from the Dickie Brook pluton shows thegreatest deviation from the norm.

Trace and Rare-Earth Element Compositions

Ratios of Zr/Ti[O.sub.2] show a stronger variation than Nb/Y (Fig.Ta) with lower Zr/Ti[O.sub.2] values for the mafic units, consistentwith the negative correlation of Ti[O.sub.2] and Si[O.sub.2] (Fig. 6a).These ratios plotted on a volcanic rock-equivalent discriminationdiagram (Fig. Ta) are more or less consistent with the names determinedusing modal mineralogy. High Zr/Y and Th/Yb ratios (Fig. 7b) associatethe rocks with calc-alkaline affinity, consistent with the range rocktypes present. The rhyolite porphyry plots outside the main data clusterdue to high values of Y relative to Zr. This feature is also shown usingZr/Hf against Zr (Fig. 7c) with high Hf values relative to Zr. Althoughmost of the units are shown in the Chondrite and Cumulate residuefields, the rhyolite porphyry from the Charlo plutonic suite is morelikely to result from the melting of continental crust. La/Yb ratios(Fig. 7d) for all units are similar (<14), whereas the Blue MountainGranodiorite and Charlo dacite porphyry have La/Yb ranging from 22 to48, suggesting that they were generated from a genetically unrelatedsource that probably contained garnet (Thirlwall et al. 1994).

Comparing the chondrite-normalized REE diagrams from pluton topluton (Figs. 8a-c), the Blue Mountain Granodiorite (Fig. 8a) and daciteporphyry of the Charlo plutonic suite (Fig. 8c) are strikingly similar,with significantly lower values in heavy REE and higher La/Yb ratios(Fig. 7c). The gabbro/quartz diorite samples from the Landry Brookpluton tend to have lower total REE than the other units (Fig. 8a),including lower LREE and higher heavy REE, probably linked to theabundance of apatite and other accessory minerals. The REE pattern forthe rhyolite porphyry from the Charlo plutonic suite also shows elevatedheavy REE (Fig. 8c), as do the two samples from the monzogranite unit inthe Landry Brook pluton (Fig. 8a).

Similar sloping profiles of decreasing light to heavy REE'sfor the quartz monzodiorite/monzogranite of the Landry Brook pluton, allof the units of the Dickie Brook pluton, and the quartzmonzodiorite/monzogranite of the Charlo plutonic suite suggest that allof these units are co-magmatic, which is supported by the similaritieson variation and ratio diagrams (Figs. 6-8).

CHEMICAL AFFINITY AND TECTONIC SETTING

Petrographic and chemical characteristics described in previoussections suggest that most of the units in the Landry Brook and DickieBrook plutons and Charlo plutonic suite are comagmatic and potentiallylinked by fractional crystallization, predominantly of plagioclase andamphibole. All three plutons show calc-alkaline trends, although somesamples show moderate iron enrichment and plot on or slightly above thetholeiitic/calc-alkaline dividing line on an AFM diagram (Fig. 9a). Thisdiagram illustrates the bimodality of the Landry Brook pluton comparedto the more continuous trends in the other two plutons; the Landry Brookgabbros may therefore represent part of an unrelated but coeval suitethat appears to be tholeiitic based on the AFM diagram (Fig. 9a). TheBlue Mountain Granodiorite and the dacite porphyry from the Charloplutonic suite are also calc-alkaline, but have relatively higher MgOand hence forma cluster distinct from the trends of the other plutons(Fig. 9a). Given the much younger age obtained for the Blue MountainGranodiorite, its close geochemical similarity with the dacite porphyrysuggests that the latter is probably also Devonian.

AII samples with more than 60% Si[O.sub.2] are metaluminous toperaluminous based on the Si[O.sub.2] vs. A/CNK classification diagramfor granitoid rocks (Fig. 9b). The Landry Brook pluton and Charloplutonic suite straddle the metaluminous-peraluminous fields, althoughnone of these rocks have mineralogical characteristics of peraluminousgranite (such as primary muscovite or other Al-rich minerals) and theapparently peraluminous character is probably related to alkalimobility. Hornblende fractionation could be another factor contributingto the peraluminous character (Cawthorn and Brown 1976). All samples ofaltered rhyolite porphyry from the Charlo plutonic suite areperaluminous, whereas the Dickie Brook pluton, in contrast, is entirelymetaluminous. The Blue Mountain Granodiorite is somewhat moreperaluminous than all other units, with higher alumina relative to sodaand potash; however, the Charlo dacite porphyry is metaluminous (Fig.9b).

On Rb vs. Y + Nb and Hf-Rb-Nb tectonic discrimination diagrams forgranitoid rocks (Figs. 9c, d), intermediate and felsic rocks straddlethe volcanic-arc and within-plate fields, with most points fallingwithin the circular field for post-collisional granitoids (Pearce1996a). The Dickie Brook quartz monzodiorites and monzogranites displaythe most prominent within-plate character on both diagrams, whereas theBlue Mountain Granodiorite and Charlo dacite porphyry have lower Y andNb and plot in the field of volcanic-arc granites (Figs. 9c, d). Onaverage, all samples are more typical of I-type granitoid rocks thanA-type granitoids (Fig. 10). Looking at just the mafic rocks from allthree plutons, most samples from the Dickie Brook pluton plot in thecalk-alkaline field on a Th-Hf-Ta diagram (Fig. 9e), whereas samplesfrom the Landry Brook pluton plot in the alkalic field. Quartzmonzodiorite in the Charlo plutonic suite plots in the calc-alkalicbasah field, although related gabbros overlap two or more fields (Fig.9e). On a La-Y-Nb plot (Fig. 9f) most mafic rocks from all plutons plotin the continental tholeiite field.

Oxygen and Sm-Nd isotope data for these plutons were reported byWhalen (1993). The [[delta].sup.18][O.sub.WR] values are 6.6 in a samplefrom the Dickie Brook pluton, 6.5 in a sample from the Landry Brookpluton, and 7.4 in a sample from the Charlo plutonic suite (Whalen1993). Al1 are within the range expected of granitoid rocks derived frommantle-like

sources (Taylor 1988). The [[epsilon].sub.Nd] isotopic signatures ofthese rocks are relatively high (+1.2, +2.0, and +4.5) which suggestsmainly a mantle source but with some crustal interaction (Whalen 1993).Overall, the values are higher than [[epsilon].sub.Nd] signaturesreported from Ganderia in Newfoundland, which tend to be negative (e.g.,Kerr et al. 1995; Whalen et al. 1994).

Overall, the tectonic setting for these plutons is most likelywithin-plate but the data such as high Zr/Y and Th/Yb ratios indicate asubduction influence, such as in a back-arc setting. Their chemicalcharacteristics are explored in more detail below, together with datafrom the associated and more voluminous volcanic rocks of the DickieCove Group.

RELATIONSHIPS WITH THE HOST ROCKS

The host rocks of the Landry Brook and Dickie Brook plutons, andpart of the Charlo plutonic suite, are the Bryant Point Formation andoverlying Benjamin Formation of the Dickie Cove Group (Fig. 1),consisting mainly of subaerial mafic and felsic volcanic rocks,respectively (Walker and McCutcheon 1995; Wilson and Kamo 2012). Arhyolite flow from near the base of the Bryant Point Formation hasyielded a U-Pb (zircon) age of 422.3 [+ or -] 0.3 Ma, whereas a U-Pb(zircon) age of 419.7 [+ or -] 0.3 Ma was obtained for rhyolite at thetop of the Benjamin Formation (Wilson and Kamo 2012). Emplacement of theLandry Brook quartz monzodiorite at 419.63 [+ or -] 0.23 Ma (Fig. 5) wastherefore essentially coeval with cessation of felsic volcanism.Emplacement of the Dickie Brook quartz monzodiorite/monzograniteoccurred shortly thereafter, at 418 [+ or -] 1 Ma (Fig. 5).

Mafic volcanic rocks of the Bryant Point Formation show chemicalsimilarities to gabbro and leucogabbro (<52 % Si[O.sub.2]) from theLandry Brook and Dickie Brook plutons and Charlo plutonic suite. Likethe plutons, the Bryant Point Formation is mainly calk-alkaline butstraddles the boundary with the tholeiite field (Fig. 11a). On amultielement spidergram (Fig. l lb), the mafic samples show similarpatterns, with negative anomalies in Cs, Rb, K, anda positive anomaly inSr. REE patterns of volcanic and plutonic rocks are similar, with mostshowing parallel patterns and continuous depletion from LREE to HREE,with the exception of slight positive Eu anomalies in a few samples(Fig. 11c). On a Hf-Th-Ta diagram (Fig. 11d), most samples span thecalc-alkalic basalt to within-plate tholeiite/ E-MORB fields; onlygabbros from the Landry Brook pluton plot in the alkaline basalt field.However, most volcanic and plutonic rocks plot in the within-plate fieldon a Ti-Zr-Y diagram (Fig. 11e), and in a cluster that overlaps thewithin-plate and volcanic-arc fields on a Zr-Y-Nb diagram (Fig. 11f). Ingeneral, these strong similarities are consistent with the volcanic andmafic plutonic rocks being co-magmatic and formed in a continentalwithin-plate setting as suggested previously by Dostal et al. (1989).

Late Silurian felsic volcanic rocks of the Benjamin Formation alsohave chemical similarities to felsic intrusive rocks of all threeplutons. Plotted together on a multi-element variation diagramnormalized to primitive mantle, the volcanic and plutonic rocks showsimilar patterns, including pronounced negative Ba, Nb, Sr, Eu, and Tianomalies (Fig. 12a). The REE profiles are also similar, with strongnegative Eu anomalies, although the volcanic rocks tend to have higherREE overall (Fig. 12b). In terms of tectonic setting, both volcanic andplutonic rocks plot in the within-plate/post-collisional/volcanic-arcgranite fields (Figs. 12c, d), consistent with a co-magmaticrelationship. Dostal et al. (1989) suggested a within-plate settingbased on their study of the volcanic rocks.

TECTONIC IMPLICATIONS

The complex history of the Appalachian orogen can be summarized interms of processes related to the Palaeozoic closure of the Iapetus andRheic oceans, which led to the accretion of arcs, back arcs, andmicrocontinents to Laurentia (e.g., van Staal et al. 2009). Temporally,the emplacement of the Landry Brook and Dickie Brook plutons and Charloplutonic suite was associated with the accretion of Ganderia toLaurentia. However, Ganderia itselfhas a complex tectonic history bothprior to and after accretion to Laurentia (van Staal et al. 2009).Remnants of the Popelogan-Victoria arc and rocks deposited in theassociated Tetagouche-Exploits back-arc basin (e.g., van Staal et al.2003) were accreted to Laurentia (forming the Bathurst SubductionComplex) during the Early Silurian, prior to the arrival of the mainpart of Ganderia (i.e., during the early phase of the Salinic orogeny;Fig. 13a). This was followed by the Devonian Acadian orogeny, which wasassociated with the collision of Avalonia and Laurentia (Fig. 13b).

Based on geological and chemical characteristics of the sedimentaryand volcanic rocks in the region, including Quebec, Wilson et al. (2008)suggested that subduction of the Tetagouche-Exploits back-arc crustceased by the Early Wenlockian (ca. 428 Ma, coincident with the arrivalof the leading edge of Ganderia), and was followed by uplift andextension during the Wenlockian to Pridolian (ca. 428-416 Ma; Fig. 13a).Wilson et al. (2008) suggested that slab-break-off occurred after thelast "gasp" of subduction-related calc-alkaline rocksrepresented by ash tuff dated at ca. 429 Ma (i.e., Pointe Rochette ash;Fig. 14) in the lower part of the Quinn Point Group. Wilson et al.(2008) further suggested that extensional magmatism associated with slabbreak-off is manifested in the bimodal within-plate volcanic rocks ofthe Bryant Point and Benjamin formations (Dickie Cove Group). Theserocks generally post-dated structures formed during the Salinic orogenybut predated development of Acadian structures in the area; that is,they were emplaced to the northwest of the migrating Acadian deformationfront (Bradley and Tucker 2002). The results of this study have shownthat the Landry Brook and Dickie Brook plutons and Charlo plutonic suiteare the intrusive equivalents of these volcanic units.

This sequence of events is consistent with those interpreted tohave occurred along strike in Newfoundland with slab breakoff and upliftfollowing Salinic collision (Whalen et al. 2006). Based on extensivegeochronological, geochemical and isotopic data, Whalen et al. (2006)demonstrated the compositional and spatial variations within themagmatic belt, involving rapid progression from exclusively arc-type tonon-arc-like mafic magmatism, with a short episode of "A-type"granite generation, followed by contemporaneous emplacement ofgranitoids with both within-plate and volcanic-arc characteristics.

Many mantle melts can be influenced by contamination from the crustand hence may display some chemical characteristics of volcanic-arcrocks without being associated temporally with the partial melting of asubducted slab; however, it is most likely that arc-type chemicalsignatures observed in volcanic and plutonic rocks in the study areaarise from contamination of the asthenospheric source by previoussubduction events. This likely explains the I-type granitoidcharacteristics of the three studied plutons.

The Blue Mountain Granodiorite and dacite porphyry of the Charloplutonic suite are temporally related to the collision of Avalonia withcomposite Laurentia (Fig. 13b). Widespread magmatism associated withthis event is attributed to 'flat-slab' subduction (Murphy etal. 1999), somewhat analogous to the Laramide in the western USA and thepresent-day Andes in central Chile and Argentina (Kay and Abruzzi 1996;van Staal et al. 2009). Their chemical volcanic-arc affinities areconsistent with this model, but it is difficult to envisage why suchplutonism would be so sparsely distributed over such a wide area.

CONCLUSIONS

This work has demonstrated that the Landry Brook and Dickie Brookplutons and the Charlo plutonic suite are approximately contemporaneousand Late Silurian in age. The close petrochemical similarity betweenquartz monzodiorite/monzogranite unit of the Landry Brook pluton, allunits of the Dickie Brook pluton, and the quartzmonzodiorite/monzogranite of the Charlo plutonic suite suggest that theyshare a common, or at least similar, mantle source, and a similarpetrogenetic history. The mafic and felsic phases of the plutons showchemical affinities with mafic and felsic volcanic rocks, respectively,of the Benjamin and Bryant Point formations, suggesting that they arecogenetic. The geological and chemical characteristics are consistentwith emplacement in a post-collisional extensional regime. The magma wasprobably generated as a result of slab break-off and resultant high heatflow associated with upwelling asthenosphere under the extinctPopelogan-Victoria arc following closure of the Tetagouche-Exploitsback-arc basin (Salinic collision). Another pulse of magmatic activityoccurred ca. 400 Ma, as indicated by Blue Mountain Granodiorite (andprobably dacite porphyry of the Charlo plutonic suite); however, thecauses of the later magmatic pulse (ca. 400-415 Ma) are not addressed inthis study, and are probably associated with a somewhat differenttectonic setting and different petrogenetic processes.

doi: 10.4138/atlgeol.2012.006

Appendix 1. Summary of plutonic units and petrographic features *.Plutonic Unit Grain Size Plagioclase (composition)Blue Mountain Granodiorilegranodiorite f.g-m.g. sub-to anhedral ([An.sub.36] to [An.sub.40,7])Landry Brook plutongabbro/quartz diorite f-g--c.fr subhedral, zoned ([An.sub.36] to [An.sub.40,7])quartz monzodiorite/ m.g subhedral, zonedmonzogranite ([An.sub.30,6] to [An.sub.49,3])monzogranite f.g.-m.g subhedral, zoned ([An.sub.18,6] to [An.sub.33,3])Dickie Brook plutonleucogabbro/quartz gabbro m.g.-c.g. subhedral, zoned ([An.sub.50] to [An.sub.60])diorite/quartz diorite m.g.-c.g. subhedral, zoned ([An.sub.25,3] to [An.sub.45,3])quartz monzodiorite/ in.fr subhedral, zonedmonzogranite (albite to [An.sub.45,3])Charlo plutonic suitegabbro/diabase fg-m.g. lath-shaped (labradorite)quartz monzonite/ f.g.-m,g. an- to subhedral,monzogranite zoned ([An.sub.17,3] to [An.sub.57,3])quartz rhyolite porphyry v.f.fr-m.g. anhedral (oligoclase)hornblende-plagioclase v-f-g-f-g- an- to subhedral,dacite porphyry zoned, (nd)Plutonic Unit K-feldspar QuartzBlue Mountain Granodiorilegranodiorite subhedral to interstitial anhedral; orthoclaseLandry Brook plutongabbro/quartz diorite none trace, interstitialquartz monzodiorite/ an- to subhedral; interstitialmonzogranite orthoclasemonzogranite anhedral; nd interstitialDickie Brook plutonleucogabbro/quartz gabbro none minor, interstitialdiorite/quartz diorite none interstitialquartz monzodiorite/ anhedral; nd interstitialmonzograniteCharlo plutonic suitegabbro/diabase trace, interstitialquartz monzonite/ anhedral; nd interstitialmonzogranitequartz rhyolite porphyry anhedral; nd interstitialhornblende-plagioclase anhedral; nd interstitialdacite porphyryPlutonic Unit ClinopyroxeneBlue Mountain Granodiorilegranodiorite noneLandry Brook plutongabbro/quartz diorite 20-30%; diopsidequartz monzodiorite/ nonemonzogranitemonzogranite noneDickie Brook plutonleucogabbro/quartz gabbro 15-25%; augite?diorite/quartz diorite 10-15%; diopsidequartz monzodiorite/ 5%; augite-diopsidemonzogranite and hedenbergiteCharlo plutonic suitegabbro/diabase 15-30%; augite- diopsidequartz monzonite/ nonemonzogranitequartz rhyolite porphyry nonehornblende-plagioclase nonedacite porphyryPlutonic Unit AmphiboleBlue Mountain Granodiorilegranodiorite <3%; ndLandry Brook plutongabbro/quartz diorite 5%; calcic to ferro-hornblendequartz monzodiorite/ 5-15%; calcic tomonzogranite ferro-hornblendemonzogranite 7%; ndDickie Brook plutonleucogabbro/quartz gabbro 10%; nddiorite/quartz diorite 15-25%; edenitequartz monzodiorite/ 10-15%; ferro-edenitemonzogranite with low MgCharlo plutonic suitegabbro/diabasequartz monzonite/ 15%; ndmonzogranitequartz rhyolite porphyry nonehornblende-plagioclase 5%; hornblendedacite porphyryPlutonic Unit Biotite OpaqueBlue Mountain Granodiorilegranodiorite 5-10%; phlogopite cpy, py, mag to anniteLandry Brook plutongabbro/quartz diorite none mag, ilmquartz monzodiorite/ 5-7%; phlogopite ml, secondary?monzogranite to annitemonzogranite 7-8%; phlogopite mag to anniteDickie Brook plutonleucogabbro/quartz gabbro none mag, ilmdiorite/quartz diorite none ndquartz monzodiorite/ none mag, pymonzograniteCharlo plutonic suitegabbro/diabase magquartz monzonite/ 15%; high aluminum ndmonzogranite phlogopite -annitequartz rhyolite porphyry none nonehornblende-plagioclase secondary minordacite porphyryPlutonic Unit AccessoryBlue Mountain Granodiorilegranodiorite apatite, zircon, titaniteLandry Brook plutongabbro/quartz diorite apatite, titanitequartz monzodiorite/ apatite, zircon,monzogranite titanitemonzogranite apatite, zirconDickie Brook plutonleucogabbro/quartz gabbro apatite, titanitediorite/quartz diorite apatite, titanitequartz monzodiorite/ titanite, minormonzogranite apatiteCharlo plutonic suitegabbro/diabasequartz monzonite/ apatite, zircon,monzogranite titanitequartz rhyolite porphyry ndhornblende-plagioclase nddacite porphyryPlutonic Unit Other informationBlue Mountain Granodiorilegranodiorite equigranular to porphyritic, hosts Cu-mineralizationLandry Brook plutongabbro/quartz diorite Intergranular to ophitic cpx-plagquartz monzodiorite/ Granophyric orthoclasemonzogranitemonzogranite interstial granophyric texture; perthitic K-Dickie Brook pluton feldsparleucogabbro/quartz gabbro Intergranular to ophitic cpx-plagdiorite/quartz diorite abundant inclusions of apatite in amphibolequartz monzodiorite/ perthitic K-feldsparmonzograniteCharlo plutonic suitegabbro/diabase pervasive carbonate alterationquartz monzonite/ granophyric andmonzogranite perthitic K- feldsparquartz rhyolite porphyry highly altered, hiatal porphyritichornblende-plagioclase skeletal hornblende,dacite porphyry hiatal plagioclase- phyricAbbreviations: v.f., f, m, and e.g., very fine-, fine-, medium-, andcoarse-grained; cpy, chalcopyrite; cpx, clinopyrox enc; ilm, ilmcnite;mag, magnetite; plag, plagioclase; py, pyrite; nd, not determined.Appendix 2. Chemical data for samples from the Blue MountainGranodiorite, Landry Brook and Dickie Brook plutons, and Charloplutonic suite.Sample Lithology Si[O.sub.2]Blue Mountain GranodioriteJL-09-024 granodiorite 66.40JL-09-057 granodiorite 70.40JL-10-139 granodiorite 66.407020-101 tonalite 67.907012-130 granodiorite 67.307003-295 granodiorite 66.40Landry Brook plutonJL-09-020 monzogranite 71.30JL-09-030 monzogranite 70.10JL-09-037 quartz monzonitc 64.50JL-09-072 quartz monzonitc 64.80JL-10-077 rhyolite/syenogranite 66.10 porphyryJL-10-081 monzogranite 64.40JL-09-086 gabbro 47.00Dickie Brook plutonIL-09-202 monzogranite 67.50JL-09-207 quartz gabbro 59.50JL-09-209 monzogranite 66.00JL-09-214 monzogranite 70.90JL-09-220 monzogranite/granodiorite 70.80JL-09-228 dioritc/gabbro 53.80JL-09-229 hornblende quartz diorite 50.80JL-09 235 quartz monzodiorite 55.70JL-10-304 quartz gabbro 52.40JL-10-311 quartz, monzodiorite 64.10JL-10-322 tonalite 63.60JL-10-373 granodiorite 57.00JL-10-383 quartz monzodiorite 59.60JL-10-386 monzogranite 71.50Charlo Plutonic suiteJL-10-006 quartz monzonite 57.90JL-10-007 quartz monzodiorite 62.60JL-10-019 microgranite 65.30JL-10-039 dacite porphyry 67.50JL-10-058 rhyolite/syenogranite 73.70JL-10-060 rhyolite porphyry 77.20JL-10-092 rhyolite porphyry 73.70JL-10-093 rhyolite porphyry 76.70JL-10-094 alkali rhyolite porphyry 77.00JL-10-104 diabase 46.30JL-10-108 diabase 47.40JL-10-113 monzogranite 66.50JL-10-119 gabbro/quartz gabbro 50.60Sample [Al.sub.2][0.sub.2] [Fe.sub.2][0.sub.3] CaO MgOBlue Mountain GranodioriteJL-09-024 17.02 2.95 2.82 1.44JL-09-057 15.33 1.88 2 14 0.83JL-10-139 16.78 2.98 2.93 1.847020-101 16.35 2.14 3.37 1.187012-130 15.97 2.68 2.76 1.077003-295 15.53 2.48 3.45 1.12Landry Brook plutonJL-09-020 14.52 2.57 0 15 0.21JL-09-030 14.66 2.61 0.79 0.24JL-09-037 15.49 4.82 2.11 1.19JL-09-072 15.57 4.95 2.91 1.21JL-10-077 15.39 4.36 2.57 1.15JL-10-081 15.43 4.57 1.93 1.12JL-09-086 18.80 7.04 12.46 9.27Dickie Brook plutonIL-09-202 14.69 5.63 1 23 0.21JL-09-207 18.27 5.23 5.14 1.45JL-09-209 15.42 5.68 1.26 0.48JL-09-214 14.40 2.22 1 25 0.33JL-09-220 14.05 2 93 0.52 0.23JL-09-228 21.94 4.25 7.30 1.73JL-09-229 20.21 7.99 9.66 2.78JL-09 235 16.96 9.02 5.35 2.28JL-10-304 15.70 11.16 8.43 3.61JL-10-311 16.52 2.50 3.31 2.36JL-10-322 16.11 5.46 2.00 0 95JL-10-373 14.71 8.27 6.19 2.87JL-10-383 16.49 3.46 6.68 2.00JL-10-386 14.15 2.39 0.69 0.13Charlo Plutonic suiteJL-10-006 11.37 8.87 2.56 2.40JL-10-007 15.19 6.53 2.33 1.35JL-10-019 14.38 6.12 1.21 1.11JL-10-039 15.58 2.32 2.78 1.01JL-10-058 13.52 1.84 0.38 0.16JL-10-060 13.33 0.70 0.02 0.15JL-10-092 13.36 2.12 0.18 0.11JL-10-093 12 16 1.20 0.25 0.12JL-10-094 11.83 1.11 0.01 0.05JL-10-104 16.91 11.53 2.21 6.58JL-10-108 16.47 11.96 5.45 6.07JL-10-113 14.94 5.18 1.29 0.81JL-10-119 16.68 9.54 4.91 5.54Sample [Na.sub.2]O [K.sub.2]O MnO Ti[O.sub.2]Blue Mountain GranodioriteJL-09-024 4.97 1.76 0.07 0.43JL-09-057 4.50 2.70 0.02 0.30JL-10-139 1.71 1.42 0.05 0.447020-101 4.53 2.09 0.03 0.407012-130 5.11 1.93 0.07 0 377003-295 3.72 2.31 0.05 0.37Landry Brook plutonJL-09-020 4.91 4.58 0.03 0.30JL-09-030 5.07 4.43 0.04 0.30JL-09-037 4.35 3.71 0.07 0.77JL-09-072 4 60 3.57 0.07 0.75JL-10-077 4.45 3.77 0.08 0.66JL-10-081 4.28 4.24 0.11 0.74JL-09-0S6 1.72 0.54 0.12 0.69Dickie Brook plutonIL-09-202 6.18 2.66 0.12 0.44JL-09-207 7.57 0.59 0.09 0.99JL-09-209 7.30 1.58 0.16 0.49JL-09-214 5.76 3.62 0.03 0.30JL-09-220 5.56 3.78 0.05 0.30JL-09-228 6.17 0.83 0.13 1.03JL-09-229 4.42 0.56 0.11 2.16JL-09 235 5.41 1.65 0.14 1.60JL-10-304 4.27 0.40 0.18 2.40JL-10-311 7.00 0.75 0.04 0.69JL-10-322 6.44 2 49 0.07 0.68JL-10-373 5.29 1.24 0.15 2.06JL-10-383 7.89 1.35 0.08 1.51JL-10-386 5.38 3.72 0.03 0.31Charlo Plutonic suiteJL-10-006 4.68 3.18 0.17 1.47JL-10-007 4.86 3.57 0.14 1.04JL-10-019 3.32 4.10 0.08 0.92JL-10-039 5.55 1.39 0.03 0.42JL-10-058 4.16 4.68 0.03 0.23JL-10-060 4.24 3.04 0.01 0.07JL-10-092 3 34 5.04 0.05 0 20JL-10-093 4.56 3.54 0.02 0.12JL-10-094 2.86 5.19 0.01 0.15JL-10-104 4.38 1.55 0.16 2.07JL-10-108 4.75 0.68 0.15 2.45JL-10-113 5.19 2.57 0.10 0.73JL-10-119 4.19 1.26 0.19 1.70Sample [P.sub.2][O.sub.5] LOI Total Rb Sr BaBlue Mountain GranodioriteJL-09-024 0.15 1.62 99.63 39 707 413JL-09-057 0.07 1.40 99.57 47 388 443JL-10-139 0.09 1.84 99.16 36 523 3657020-101 0.08 0.91 99.03 40 581 5267012-130 0.10 2.35 99.75 31 614 4427003-295 0.10 4.59 100.22 53 271 485Landry Brook plutonJL-09-020 0.04 1.21 99.86 139 68 540JL-09-030 0 0! 0.96 99.27 142 121 526JL-09-037 0 19 2.19 99.43 111 230 488JL-09-072 0.20 O.20 99.63 135 224 461JL-10-077 0 1S 1.34 100.15 127 204 460JL-10-081 0.18 2.39 99.49 131 236 495JL-09-086 0.04 2 52 100.26 18 463 88Dickie Brook plutonIL-09-202 0.06 0.54 99.62 42 124 583JL-09-207 0.30 0.55 100.01 6 461 400JL-09-209 0.09 1.29 99.56 25 149 634JL-09-214 0.04 0.69 99.67 51 179 709JL-09-220 0.03 0.86 99.19 91 116 497JL-09-228 0.25 2.00 99.49 15 700 391JL-09-229 0.09 0.69 99.52 9 593 214JL-09 235 0.45 1.14 99.77 38 428 430JL-10-304 0.34 0.90 99.86 7 380 214JL-10-311 o.os 1.65 99.00 18 368 129JL-10-322 0.23 1.51 99.90 60 296 473JL-10-373 0.44 0 34 99.08 24 329 295JL-10-383 0.55 1.15 99.78 7 478 141JL-10-386 0.03 0.87 99.28 59 111 733Charlo Plutonic suiteJL-10-006 0.41 2.55 98.68 104 437 567JL-10-007 0.28 1.67 99.60 111 217 643JL-10-019 0.23 2.91 99.75 136 83 413JL-10-039 0.09 2.96 99.69 26 601 263JL-10-058 0.03 1.06 99.83 162 62 4116JL-10-060 0.01 1.27 100.06 91 68 163JL-10-092 0.01 1.51 99.65 157 62 411JL-10-093 0.01 0.79 99.47 96 61 266JL-10-094 0.02 1.18 99.42 205 25 193JL-10-104 0.28 6.34 98.73 44 1747 941JL-10-108 0.41 4.03 99.93 15 915 913JL-10-113 0.21 1.84 99.74 77 220 566JL-10-119 0.30 4.78 99.76 30 690 1027Sample Zr Nb Y V Ni Cu Co Pb Zn Th UBlue Mountain GranodioriteJL-09-024 136 7 7 32 10 17 39 2 90 5 1JL-09-057 118 7 8 22 4 108 53 2 13 7 2JL-10-139 122 5 7 38 6 394 46 1 32 4 17020-101 126 5 7 28 5 506 57 1 20 5 17012-130 148 5 6 24 7 30 40 3 63 4 17003-295 146 5 6 25 7 9 23 1 27 4 1Landry Brook plutonJL-09-020 293 15 11 8 1 3 54 3 21 16 3JL-09-030 314 15 24 8 1 9 60 15 34 19 4JL-09-037 346 21 33 55 3 3 44 6 34 17 5JL-09-072 395 23 36 53 2 2 58 7 23 19 4JL-10-077 336 20 30 44 4 4 60 15 42 15 6JL-10-081 319 19 33 58 3 2 59 16 78 16 4JL-09-086 31 3 8 109 50 11 53 1 19 1 0Dickie Brook plutonIL-09-202 453 27 55 8 0 4 57 6 56 10 5JL-09-207 579 11 42 58 1 3 59 2 14 6 1JL-09-209 657 28 49 8 0 4 50 4 61 10 3JL-09-214 462 25 51 8 1 1 73 4 11 19 4JL-09-220 413 27 52 8 0 2 72 7 28 17 5JL-09-228 614 10 25 167 11 18 44 45 93 5 1JL-09-229 125 9 16 311 4 27 55 5 23 2 1JL-09 235 231 26 51 93 1 6 55 3 16 7 2JL-10-304 289 23 40 310 6 43 51 2 18 5 1JL-10-311 197 9 21 83 2 0 33 1 5 10 3JL-10-322 561 28 41 24 2 7 44 2 31 14 5JL-10-373 371 22 53 192 3 10 48 6 38 8 3JL-10-383 553 33 73 54 1 2 49 2 10 10 5JL-10-386 399 25 51 8 2 1 70 4 17 16 4Charlo Plutonic suiteJL-10-006 286 25 49 122 2 8 33 4 97 10 3JL-10-007 467 26 50 60 3 9 55 15 77 12 3JL-10-019 496 26 47 51 4 9 35 8 61 15 4JL-10-039 121 4 7 38 4 2 41 4 23 4 1JL-10-058 231 17 31 8 1 2 95 12 26 23 6JL-10-060 130 73 73 8 1 1 45 5 51 15 7JL-10-092 225 15 38 8 1 2 48 3 29 21 8JL-10-093 110 20 42 8 0 2 55 38 170 26 7JL-10-094 105 21 45 8 0 0 65 1 15 20 8JL-10-104 176 13 26 275 52 34 51 2 77 2 1JL-10-108 276 15 32 172 34 23 48 2 72 2 1JL-10-113 350 16 47 32 1 9 42 8 61 12 3JL-10-119 247 23 27 144 20 22 37 5 61 5 2Notes: Analyses were done by X-ray Fluorescence for major oxides andICP-MS for trace elements at the ACME Laboratory in Vancouver, BritishColumbia, Canada. Anaiytical error is generally less than 5% for majorelement and 2-10% for trace elements. [Fe.sub.2][0.sub.3] is total Feas [Fe.sub.2][O.sub.3]. LOI is loss on ignition at 1000[degrees]C.Appendix 3. Rare earth element, Hi, and Ta data * from the BlueMountain Granodiorite, Landry Brook and Dickie Brook plutons,and Charlo plutonic suite.Sample La Ce Pr Nd Sm Eu GdBlue Mountain GranodioriteJL-09-024 20.4 38.9 4.22 16.1 2.33 0.73 1.75JL-09-057 21.8 41.9 4.35 16.2 2.44 0.59 1.72JL-10-139 13.4 25.2 2.80 10.6 1.87 0.65 1.497020-101 23.2 45.0 4.66 16.4 2.48 0.66 1.667012-130 23.6 46.8 4.75 17.3 2.39 0.70 1.597003-295 21.1 41.3 4.22 15.3 2.28 0.69 1.48Landry Brook plutonJL-09-020 11.8 42.1 2.83 10.9 1.94 0.33 1.42JL-09-030 28.1 59.0 5.94 21.6 3.86 0.68 3.34JL-09-037 36.4 76.4 8.47 32.5 5.94 1.28 5.37JL-09-072 42.4 91.0 9.67 37.0 6.57 1.28 5.91JL-10-077 36.0 74.5 8.17 31.5 5.71 1.23 4.90IL-10-081 40.5 78.3 9.10 35.1 6.37 1.34 5.63JL-09-086 5.0 10.8 1.43 6.6 1.43 0.75 1.64Dickie Brook plutonJL-09-202 39.8 93.2 11.00 47.1 9.25 2.33 9.40JL-09-207 21.4 52.1 7.11 33.7 7.41 2.96 7.89JL-09-209 35.4 79.5 9.59 41.3 8.20 2.54 7.82JL 09-214 16.6 52.1 7.83 34.7 7.69 1.33 7.74JL-09-220-1 44.8 96.4 11.08 45.0 8.54 1.20 8.01JL-09-228 14.8 32.9 4.19 18.3 4.12 1.40 4.31JL-09-229 10.6 23.3 2.82 12.3 2.74 1.29 2.94IL-09-235 37.1 79.9 9.97 42.4 8.79 2.67 9.20JL-10-304 22.6 51.3 6.63 29.9 6.78 1.97 7.45JL-10-311 14.9 34.1 3.78 14.8 3.27 0.84 3.35JL-10-322 53.3 110.2 11.95 46.1 7.86 1.91 6.95JL-10-373 34.1 81.6 10.02 44.2 9.33 2.47 9.71JL-10-383 49.1 137.6 16.91 70.7 14.12 3.91 13.72JL-10-386 25.6 66.0 9.15 40.3 8.12 1.36 7.95Charlo Plutonlc suiteJL-10-006 37.6 85.3 10.48 46.0 9.00 2.41 9.10JL-10-007 43.6 97.4 11.57 47.8 9.17 2.12 8.91IL-10-019 46.0 100.7 11.86 49.0 9.09 1.71 8.45JL-10-039 15.2 28.4 3.30 13.0 2.15 0.63 1.56JL-10-058 45.0 79.1 9.13 33.7 6.31 0.64 5.68JL-10-060 1.0 20.8 0.64 3.4 2.78 0.23 5.79IL-10-092 24.5 50.3 5.61 21.9 4.02 0.45 4.43JL-10-093 34.0 66.5 7.84 30.6 7.14 0.27 7.29JL-10-094 4.4 31.0 1.12 4.3 1.64 0.10 3.19JL-10-104 14.3 35.0 4.54 22.2 4.52 1.50 4.86JL-10-108 22.0 54.1 7.02 31.1 6.37 2.13 6.46JL-10-113 36.8 80.7 9.44 39.2 7.61 1.84 7.58JL-10-119 23.1 52.9 6.38 27.9 5.46 1.61 5.32Sample Tb Dy Ho Er Tm Yb Lu HfBlue Mountain GranodioriteJL-09-024 0.27 1.37 0.23 0.62 0.10 0.61 0.08 3.6JL-09-057 0.27 1.38 0.25 0.70 0.11 0.72 0.10 3.3JL-10-139 0.23 1.18 0.22 0.59 0.09 0.58 0.09 3.17020-101 0.23 1.13 0.21 0.58 0.08 0.56 0.09 3.27012-130 0.23 1.12 0.19 0.54 0.08 0.51 0.07 3.57003-295 0.22 1.14 0.21 0.51 0.07 0.50 0.07 3.4Landry Brook plutonJL-09-020 0.30 1.92 0.43 1.49 0.26 1.82 0.29 7.0JL-09-030 0.61 3.71 0.78 2.43 0.40 2.51 0.40 8.3JL-09-037 0.95 5.49 1.11 3.37 0.54 3.52 0.54 9.1JL-09-072 1.04 6.04 1.25 3.71 0.61 3.81 0.57 10.1JL-10-077 0.87 5.06 1.04 3.06 0.49 3.20 0.48 8.6IL-10-081 0.98 5.60 1.12 3.28 0.52 3.32 0.48 8.2JL-09-086 0.27 1.51 0.29 0.77 0.13 0.73 0.10 0.9Dickie Brook plutonJL-09-202 1.63 9.65 1.97 5.75 0.91 5.70 0.87 10.7JL-09-207 1.30 7.37 1.49 4.23 0.64 3.95 0.58 11.5JL-09-209 1.38 8.29 1.72 5.14 0.82 5.34 0.85 14.7JL 09-214 1.37 8.55 1.69 5.12 0.82 5.46 0.85 11.8JL-09-220-1 1.44 8.38 1.76 5.30 0.84 5.52 0.83 11.1JL-09-228 0.71 4.15 0.86 2.61 0.38 2.65 0.41 13.3JL-09-229 0.50 2.94 0.57 1.67 0.23 1.60 0.22 3.2IL-09-235 1.50 8.86 1.75 5.01 0.75 4.83 0.71 5.9JL-10-304 1.24 7.33 1.48 4.00 0.56 3.90 0.55 6.8JL-10-311 0.59 3.67 0.73 2.15 0.34 2.30 0.35 5.1JL-10-322 1.20 7.17 1.39 4.20 0.65 4.53 0.70 12.5JL-10-373 1.60 9.64 1.92 5.52 81 5.34 0.79 9.7JL-10-383 2.32 13.84 2.74 7.81 1.12 7.50 1.05 12.7JL-10-386 1.40 8.57 1.78 5.32 0.79 5.37 0.78 10.1Charlo Plutonlc suiteJL-10-006 1.50 8.83 1.74 5.06 0.76 4.68 0.69 8.0JL-10-007 1.50 8.73 1.74 5.14 0.80 4.85 0.75 11.8IL-10-019 1.43 8.33 1.66 4.93 0.77 4.92 0.74 12.4JL-10-039 0.24 1.23 0.23 0.64 0.09 0.58 0.08 3.4JL-10-058 0.97 533 1.04 3.01 0.49 3.23 0.47 7.3JL-10-060 1.50 10.61 2.35 7.72 1.32 8.48 1.23 7.7IL-10-092 0.92 5.82 1.27 4.03 0.64 4.12 0.62 7.4JL-10-093 1.28 7.50 1.52 4.55 0.71 4.58 0.67 4.9JL-10-094 0.94 7.01 1.56 4.91 0.78 5.01 0.72 4.9JL-10-104 0.81 4.93 0.94 2.71 0.42 2.63 0.38 4.4JL-10-108 1.03 5.94 1.14 3.18 0.48 2.94 0.43 6.0JL-10-113 1.31 7.95 1.62 4.91 0.79 5.02 0.74 9.6JL-10-119 0.86 4.90 0.94 2.76 0.40 2.53 0.37 5.7Sample TaBlue Mountain GranodioriteJL-09-024 0.8JL-09-057 1.2JL-10-139 0.97020-101 0.97012-130 0.87003-295 0.6Landry Brook plutonJL-09-020 1.9JL-09-030 2.1JL-09-037 2.1JL-09-072 2.4JL-10-077 2.1IL-10-081 1.8JL-09-086 0.4Dickie Brook plutonJL-09-202 2.1JL-09-207 1.1JL-09-209 2.2JL 09-214 2.4JL-09-220-1 2.5JL-09-228 1.0JL-09-229 0.9IL-09-235 1.8JL-10-304 1.6JL-10-311 0.9JL-10-322 2.3JL-10-373 1.8JL-10-383 2.3JL-10-386 2.1Charlo Plutonlc suiteJL-10-006 1.8JL-10-007 1.9IL-10-019 2.1JL-10-039 0.7JL-10-058 2.5JL-10-060 7.8IL-10-092 1.9JL-10-093 2.7JL-10-094 2.4JL-10-104 0.9JL-10-108 1.0JL-10-113 1.5JL-10-119 1.6* Analyses at ACME Laboratory in Vancouver, British Columbia, Canada,using ICP-MS.

ACKNOWLEDGEMENTS

This paper results from a M.Sc. thesis by J-L. Pilote at AcadiaUniversity. We thank journal reviewers J. B. Whalen and L.R. Fyffe fortheir helpful comments and suggestions. Funding and logistical supportwere provided by the New Brunswick Department of Natural Resources, aResearch Grant to J-L. Pilote from the Geological Society of America,and Discovery Grant to S.M. Barr from the Natural Sciences andEngineering Research Council of Canada.

Date received: 19 April 2012 [paragraph] Date accepted: 02 July2012

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Editorial responsibility: David P. West

JEAN-LUC PILOTE (1) *, SANDRA M. BARR (1), REGINALD A. WILSON (2),SEAN MCCLENAGHAN (2), SANDRA KAMO (3), VICKI J. MCNICOLE (4), AND MARYLOU BEVIER (5)

(1.) Department of Earth and Environmental Science, AcadiaUniversity, Wolfville, Nova Scotia, B4P 2R6 Canada

(2.) Geological Surveys Branch, New Brunswick Department of NaturalResources, Bathurst, New Brunswick, E2A 3Z1 Canada

(3.) Jack Satterly Geochronology Laboratory, Department of Geology,University of Toronto, Toronto, Ontario, M5S 3B1 Canada

(4.) Geological Survey of Canada, Ottawa, Ontario, K1A 0E4 Canada

(5.) Department of Earth and Ocean Sciences, The University ofBritish Columbia, Vancouver, British Columbia, V6T 1Z4 Canada

* Corresponding author: <[emailprotected]>

Table 1. U-Pb isotopic data for chemically abraded single zircongrains from samples 97-DL-04, LB00-1, MLNB-733, and 09SHM BR-50. PbSample Weight U Pbtol (a) Pb Th/U (b) (c) ([micro]g) (ppm) (pg) (ppm) (pg)97 DL-04A 61 127 -- 8 -- 3BI 70 140 -- 9 -- 5B2 40 138 -- 9 -- 4C 64 155 -- 10 -- 8LBO0-11 55 100 -- 6.9 0.46 0.42 5.0 177 -- 12.5 0.54 0.43 2.7 164 -- 115 0.51 0.64 4.7 92 -- 6.4 0.50 0.3MLNB-733A 25 272 -- 19 -- 18B 13 406 -- 29 -- 43C 16 279 -- 19 -- 1709SHM-BR-501 6.3 108 47 -- 0.52 0.52 2.6 16i 29 -- 0.47 0.93 2.1 157 22 -- 0.41 1.44 3.1 104 22 -- 0.42 0.7Sample [sup.206] Pb/ [sup.206]Pb/ 2[sigma] [sup.204] Pb (d) [sup.238]U (e) measured97 DL-04A 9982 0.06415 0.00006BI 8468 0.06409 0.00005B2 5498 0.06521 0.00006C 4949 0.06417 0.00005LBO0-11 5661 0.067307 0.0000682 10119 0.067262 0.0000723 3401 0.067222 0.0000624 5780 0.067134 0.000421MLNB-733A 1525 0.06693 0.00007B 527 0.06708 0.00008C 1112 0.06706 0.0000709SHM-BR-501 6007 0.06693 0.000072 2099 0.06707 0.000133 1053 0.06706 0.000144 2097 0.06744 0.00014Sample [sup.207]Pb/[sup.235]U 2[sigma] (e)97 DL-04A 0.4833 0.0005BI 0.4838 0.0005B2 0.4976 0.0005C 0.4818 0.0005LBO0-11 0.5134 0.00152 0.5121 0.00133 0.5135 0.00224 0.5112 0.0035MLNB-733A 0.50876 0.00094B 0.51027 0.00174C 0.51246 0.0011509SHM-BR-501 0.5103 0.00182 0.5111 0.00373 0.5i01 0.00584 0.5131 0.0034Sample [sup.206]Pb/[sup.238]U 2[sigma] Age (Ma)97 DL-04A 400.8 0.7BI 400.5 0.6B2 407.3 0.7C 4110.9 0.6LBO0-11 419.91 0.412 419.64 0.433 419.40 0.384 418.87 2.54MLNB-733A 417.6 0.8B 418.6 1.0C 418.4 0.809SHM-BR-501 417.61 0.782 418.45 0.813 418.45 0.834 420.73 0.83Sample [sup.207]Pb/[sup.235]U 2[sigma] Age (Ma)97 DL-04A 400.3 0.7BI 400.6 0.7B2 410.1 0.7C 401.3 0.7LBO0-11 420.7 1.02 419.9 0.93 420.8 1.44 419.3 2.3MLNB-733A 417.6 1.3B 418.6 2.3C 420.1 1.509SHM-BR-501 418.6 1.22 419.2 2.53 418.5 3.94 420.6 2.3Sample [sup.207]Pb/[sup.206]Pb 2[sigma] %Disc Error Age (Ma) (f) Corr (g)97 DL-04A 397.8 2.0 -0.8 0.900BI 401.7 1.8 0.3 0.924B2 426.1 2.3 4.6 0.879C 403.9 1.9 0.8 0.914LBO0-11 425.2 5.4 1.3 0.6692 421.3 4.3 0.4 0.7143 428.5 8.3 2.2 0.6084 421.6 5.0 0.7 0.944MLNB-733A 417.5 5.8 0.0 0.732B 419.1 12.1 0.1 0.684C 429.3 7.9 2.6 0.65509SHM-BR-501 424 1 1.6 116922 423 14 1.1 0.5193 419 23 0.1 0.5104 420 13 -0.3 0.526Notes (a) Pblot is total amount of Pb exclding blank. (b) Th-Ucalculated from radiogenic [sup.208]Pb-[sup.206] Pb ratin and[sup.207]Pb-[sup.206]Pb age assuming concordance. Correction for[sup.230]. Th disequilibrium in 206/238 and 207/206 assuming Th-U of4,2 in the magma, (c) PbC is total common Pb (assuming isotopiccomposition of laboratory blank for zircon and for titamite usingStacey and Kramers (1975) for intial Pb in excess of blank):laboratory Pb isotopic composition 206/204: 18.221; 207/204: 15.612;208/204 39.360; 2[sigma] errors of 1% (d) Measured ratio for spike andfractionation only. (e) Pb-U ratio are corrected for fractionation,common Pb in the spike, and blank, (f) Disc is percent discordance forthe given [sup.207] Pb-[sup.206]Pb age. (g) Error Corr is correlationcoefficients of X-Y errors on the concardia plot. Decay constants arethose of Jaffey et al. (1971).