Lithogeochemistry Constraints on Assimilation and Fractional
LithogeochemistryLithogeochemistry ConstraintsConstraints onon AssimilationAssimilation andand FractionalFractional CrystallizationCrystallization ProcessesProcesses inin thethe SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
MichaelMichael WhitbreadWhitbread,, ioGeochemistry, Brisbane, Queensland, Australia, [email protected] and: CliffCliff StanleyStanley,, Dept. of Geology, Acadia University, Wolfville, Nova Scotia, B4P 2R6, [email protected] SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
largestlargest peraluminousperaluminous ((SS-type,-type, ilmeniteilmenite seriesseries)) granitoidgranitoid inin thethe AppalachianAppalachian orogenorogen DevonianDevonian age,age, ~380~380 MaMa megacrystic,megacrystic, porphyriticporphyritic emplacementemplacement occurredoccurred inin twotwo stagesstages StageStage 1:1: maficmafic porphyry,porphyry, granodioritegranodiorite && BTBT monzogranitemonzogranite StageStage 2:2: MSMS-BT-BT monzogranite,monzogranite, leucomonzograniteleucomonzogranite && MSMS leucosyenograniteleucosyenogranite majormajor mineralsminerals quartz,quartz, plagioclase,plagioclase, alkalialkali feldspar,feldspar, biotite,biotite, muscovitemuscovite accessoryaccessory mineralsminerals aluminosilicate,aluminosilicate, cordierite,cordierite, garnet,garnet, tourmaline,tourmaline, topaztopaz hosthost toto significantsignificant Sn,Sn, Mo,Mo, UU && MnMn mineralization!mineralization! SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
Windsor Middleton Millet Brook101 Ross Creek Mn U Prospect Deposits
Reeves Sn Walker Mo Prospect Prospect Halifax Long Lake Digby Mo Prospect 12
101 10
8 Atlantic Ocean
Fine-grained leucomonzogranite, leucosyenogranite and porphyry Stage 2 Coarse-grained leucomonzogranite East Kemptville Muscovite-biotite monzogranite Sn Mine Coarse-grained biotite monzogranite and Stage 1 biotite granodiorite Duck Pond 0Sn 25 km Country rock Prospect CoarseCoarse Grained,Grained, PorphyriticPorphyritic StageStage 11 GaspereauGaspereau LakeLake BTBT GranodioriteGranodiorite MediumMedium Grained,Grained, EquigranularEquigranular StageStage 22 MurphyMurphy LakeLake LeucosyenograniteLeucosyenogranite DykeDyke (intruding(intruding StageStage 11 GaspereauGaspereau LakeLake BTBT granodiorite)granodiorite) FineFine Grained,Grained, EquigranularEquigranular StageStage 22 LakeLake LewisLewis MSMS LeucosyenograniteLeucosyenogranite
1 cm FineFine Grained,Grained, EquigranularEquigranular StageStage 22 TantallonTantallon Leucomonzogranite Leucomonzogranite HalifaxHalifax PlutonPluton
Tantallon FG Halifax Leucomonzogranite Haifax CG Leucomonzogranite TA Harrietsfield BT-MS Monzogranite Sandy Bat/Peggy’s Cove BT Monzogranite
Granodiorite
HX
HF N Peggy’s Cove
15 km
Modified from MacDonald and Horne 1988 XenolithXenolithXenolith-Rich--RichRich PortionPortion ofof thethe SouthSouth MountainMountain BatholithBatholith
Photo courtesy of Mike MacDonald, NSDNR HowHow diddid thethe variousvarious meltsmelts inin thethe SouthSouth MountainMountain BatholithBatholith becomebecome evolved?evolved?
AFCAFC ProcessesProcesses (assimilation(assimilation && fractionalfractional crystallization)crystallization) SidewallSidewall BoundaryBoundary LayerLayer DifferentiationDifferentiation
• Crystallization takes place at cool intrusion margin • Evolved residual melt forms between the crystals at this margin • Residual melt migrates into centre of magma chamber, mixing with less evolved melt, making the mixed melt more evolved • Additional crystallization leads to an even more evolved, mixed melt in the centre of the magma chamber • Process continues … sidewall • Magma chamber becomes boundary concentrically zoned layer ResidualResidual MeltMelt CompositionComposition
SiO2 Water Saturated
Quartz
1 kb
2 kb 5 kb
10 kb Albite K-Feldspar
NaAlSi3O8 KAlSi3O8 FractionationFractionation DuringDuring CrystallizationCrystallization
f (D−1) 100 D(1− f )+ f • Enrichment of incompatible Cliq ⎛ M liq ⎞ = ⎜ ⎟ elements in the Co ⎝ M o ⎠ residual melt can occur during sidewall 0.01 melt path boundary layer 10
crystallization o incompatible
/C elements • Critical factor controlling l mineral deposit C 0.1 1 genesis D = 1 2 compatible 5 10 0.1 elements 010.5 F HowHow diddid thethe variousvarious meltsmelts inin thethe SouthSouth MountainMountain BatholithBatholith becomebecome evolved?evolved? (1)(1) SidewallSidewall BoundaryBoundary LayerLayer DifferentiationDifferentiation ((FractionationFractionation)) additionaddition ofof evolvedevolved meltmelt (essentially(essentially QZ,QZ, ALB,ALB, KSP)KSP) toto thethe originaloriginal melt,melt, causingcausing itit toto becomebecome moremore evolvedevolved enrichmentenrichment ofof incompatibleincompatible elementselements inin thethe moremore evolvedevolved phasesphases PartialPartial MeltMelt CompositionComposition
SiO2 Water Saturated
Quartz
1 kb
2 kb 5 kb
10 kb Albite K-Feldspar
NaAlSi3O8 KAlSi3O8 AssimilationAssimilation
–– ThereThere isis evidenceevidence forfor it,it, butbut muchmuch ofof itit maymay bebe “physical”“physical” FractionationFractionation DuringDuring AssimilationAssimilation
Cliq 1 • Enrichment of incompatible 100 = C D + F()1− D elements can occur in o res res the partial melt during partial assimilation, but only 0.01 melt path if assimilation if 10
incomplete o incompatible
/C elements • If assimilation is complete, l no enrichment can C 0.1 occur unless the 1 D = 1 assimilant is enriched • Critical factor preventing 2 5 compatible mineral deposit elements genesis! 0.1 10 010.5 F Average concentrations (ppm) of Meguma Group Pelites & Psammites, and the granodiorite/monzogranite phases of the SMB
Pelite Psammite SMB Rb 533 398 187 F 2440 1050 620 Li 122 81 76 U 24 6 4 Sn 21 17 7 Nb 14 9 12 Ta 41 1 W 75 1
Meguma Group average concentrations courtesy of Paul Smith, NSDNR HowHow diddid thethe variousvarious meltsmelts inin thethe SouthSouth MountainMountain BatholithBatholith becomebecome evolved?evolved? (2)(2) AssimilationAssimilation partialpartial meltingmelting ofof hosthost rockrock (essentially(essentially QZ,QZ, ALB,ALB, KSP)KSP) andand subsequentsubsequent additionaddition ofof thisthis granitegranite minimumminimum meltmelt compositioncomposition incompatibleincompatible elementselements inin hosthost rockrock cancan partitionpartition intointo partialpartial melt,melt, butbut likelylikely won’twon’t becomebecome enrichedenriched becausebecause partialpartial meltingmelting isis usuallyusually completecomplete (and(and thusthus fractionationfractionation isis limited)limited) additionaddition ofof assimilatedassimilated hosthost rockrock cancan increaseincrease incompatibleincompatible elementelement concentrationsconcentrations byby simplesimple mixing,mixing, butbut thisthis enrichmentenrichment willwill bebe limitedlimited byby thethe hosthost rockrock compositioncomposition CanCan oneone distinguishdistinguish betweenbetween evolvedevolved granitesgranites thatthat havehave undergoneundergone predominantlypredominantly fractionalfractional crystallizationcrystallization fromfrom thosethose thatthat havehave undergoneundergone predominantlypredominantly assimilation?assimilation? NovaNova ScotiaScotia RadiometricRadiometric MapMap
New Ross Pluton Halifax Pluton Davis Lake Pluton SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
Windsor Middleton 101
New Ross Halifax Pluton Digby 12 Halifax 101 10 Pluton
8 Atlantic Ocean
Fine-grained leucomonzogranite, leucosyenogranite and porphyry Stage 2 Coarse-grained leucomonzogranite Davis Lake Muscovite-biotite monzogranite Pluton Coarse-grained biotite monzogranite and Stage 1 biotite granodiorite 0 25 km Country rock NSDNRNSDNR LithogeochemicalLithogeochemical DatabaseDatabase
5,000,000
4,980,000
4,960,000
4,940,000
4,920,000 New Ross
Northing (m) Pluton Halifax GD Pluton BMG 4,900,000 Davis Lake MBMG Pluton CLMG 4,880,000 FLMG MLSG 4,860,000
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 ,0 0 0 0 0 0 0 0 0 0 0 0 7 9 1 3 5 7 9 1 3 5 7 2 2 3 3 3 3 3 4 4 4 4 Easting (m) SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
400 GD 350 BMG MBMG
300 CLMG FLMG MLSG 250
200 Zr (ppm) 150
100
50
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
300 160 GD Sr140 BMG V 250 MBMG 120 CLMG FLMG 200 MLSG 100
150 80 V (ppm) Sr (ppm) 60 100 GD BMG MBMG 40 50 CLMG FLMG 20 MLSG 0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %)
70 30 GD BMG 60 La Sc 25 MBMG CLMG 50 FLMG 20 MLSG
40
15 La (ppm) 30 Sc (ppm)
GD 10 20 BMG MBMG CLMG 5 10 FLMG MLSG 0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %) SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
1,000
Average Meguma Abundances…… GD 900 Pelite Psammite Rb 533 398 BMG F 2440 1050 MBMG 800 Li 122 81 U246 Sn 21 17 CLMG Nb 14 9 FLMG 700 Ta 4 1 W7 5 MLSG 600
500
Rb (ppm) 400
300
200
100
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) SouthSouth MountainMountain Batholith,Batholith, NovaNova ScotiaScotia
1,000 10,000 GD GD 900 9,000 LiBMG F BMG MBMG MBMG 800 8,000 CLMG CLMG 700 FLMG 7,000 FLMG MLSG MLSG 600 6,000
500 5,000 F (ppm) Li (ppm) 400 4,000
300 3,000
200 2,000
100 1,000
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %)
50 200 GD GD 45 180 USnBMG BMG MBMG MBMG 40 160 CLMG CLMG 35 FLMG 140 FLMG MLSG MLSG 30 120
25 100 U (ppm) 20 Sn (ppm) 80
15 60
10 40
5 20
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %) DavisDavis LakeLake Pluton,Pluton, NovaNova ScotiaScotia
1,000
Average Meguma Abundances…… 900 Pelite Psammite GD Rb 533 398 F 2440 1050 MBMG 800 Li 122 81 U246 CLMG Sn 21 17 FLMG 700 Nb 14 9 Ta 4 1 MLSG W7 5 600
500
Rb (ppm) 400
300
200
100
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) DavisDavis LakeLake Pluton,Pluton, NovaNova ScotiaScotia
1,000 10,000
900 GD 9,000 GD LiMBMG F MBMG 800 CLMG 8,000 CLMG FLMG FLMG 700 7,000 MLSG MLSG
600 6,000
500 5,000 F (ppm) F Li (ppm) 400 4,000
300 3,000
200 2,000
100 1,000
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %)
50 200
45 GD 180 GD USnMBMG MBMG 40 CLMG 160 CLMG FLMG FLMG 35 140 MLSG MLSG
30 120
25 100 U (ppm) 20 (ppm) Sn 80
15 60
10 40
5 20
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %) NewNew RossRoss Pluton,Pluton, NovaNova ScotiaScotia
1,000
Average Meguma Abundances…… 900 Pelite Psammite BMG Rb 533 398 F 2440 1050 MBMG 800 Li 122 81 U246 CLMG Sn 21 17 FLMG 700 Nb 14 9 Ta 4 1 MLSG W7 5 600
500
Rb (ppm) 400
300
200
100
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) NewNew RossRoss Pluton,Pluton, NovaNova ScotiaScotia
1,000 10,000
900 BMG 9,000 BMG LiMBMG F MBMG 800 CLMG 8,000 CLMG FLMG FLMG 700 7,000 MLSG MLSG
600 6,000
500 5,000 F (ppm) Li (ppm) 400 4,000
300 3,000
200 2,000
100 1,000
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %)
50 200
45 BMG 180 BMG USnMBMG MBMG 40 CLMG 160 CLMG FLMG FLMG 35 140 MLSG MLSG
30 120
25 100 U (ppm) 20 Sn (ppm) 80
15 60
10 40
5 20
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %) HalifaxHalifax Pluton,Pluton, NovaNova ScotiaScotia
1,000
Average Meguma Abundances…… 900 Pelite Psammite Rb 533 398 BMG F 2440 1050 MBMG 800 Li 122 81 U246 Sn 21 17 CLMG Nb 14 9 FLMG 700 Ta 4 1 W7 5 600
500
Rb (ppm) 400
300
200
100
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) HalifaxHalifax Pluton,Pluton, NovaNova ScotiaScotia
1,000 10,000
900 9,000 LiBMG F BMG MBMG MBMG 800 8,000 CLMG CLMG 700 FLMG 7,000 FLMG
600 6,000
500 5,000 F (ppm) Li (ppm) 400 4,000
300 3,000
200 2,000
100 1,000
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %)
50 200
45 180 USnBMG BMG MBMG MBMG 40 160 CLMG CLMG 35 FLMG 140 FLMG
30 120
25 100 U (ppm) 20 Sn (ppm) 80
15 60
10 40
5 20
0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TiO2 (wt. %) TiO2 (wt. %) HalifaxHalifax Pluton,Pluton, NovaNova ScotiaScotia
2.0
1.8 BMG MBMG 1.6 Feldspar CLMG Control 1.4 FLMG (m = 1)
1.2 m = 1.00 1.0
0.8
(2Ca+Na+K)/Zr (ppm) 0.6 Muscovite 0.4 Control (m = 1/3) 0.2 Projected from Quartz 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Al/Zr (molar) DavisDavis LakeLake Pluton,Pluton, NovaNova ScotiaScotia
2.0
1.8 GD MBMG 1.6 CLMG Feldspar FLMG Control 1.4 MLSG (m = 1)
1.2
1.0 m = 0.80 0.8
(2Ca+Na+K)/Zr (ppm) 0.6 Muscovite 0.4 Control (m = 1/3) 0.2
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Al/Zr (molar) NewNew RossRoss Pluton,Pluton, NovaNova ScotiaScotia
2.0
1.8 BMG MBMG 1.6 CLMG Feldspar FLMG Control 1.4 MLSG (m = 1)
1.2 m = 0.84 1.0
0.8
(2Ca+Na+K)/Zr (ppm) 0.6 Muscovite 0.4 Control (m = 1/3) 0.2
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Al/Zr (molar) 2.0 1.9 1.8 1.7 Halifax 1.6 Davis Lake 1.5 1.4 New Ross CLMG 1.3 FLMG 1.2 1.1 1.0 0.9 0.8 0.7 (K-OH/2)/Zr (Molar) (K-OH/2)/Zr (Molar) 0.6 0.5 0.4 0.3 0.2 0.1 Projected from Muscovite and Quartz 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Na/Zr (molar) MLSG 0.3
Halifax Davis Lake New Ross 0.2 Muscovite
0.1 MLSG (Al/3-Na/3-K/3)Zr (Molar) (Molar) (Al/3-Na/3-K/3)Zr
Projected from Feldspar Quartz 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 (Si-3Na-3K)/Zr (molar) MLSG 2.5
Halifax m = 0.5 2.0 Davis Lake New Ross
1.5 Feldspar Control (m = ∞ )
1.0 (Al-Ca-3/2*OH)/Zr (ppm) (Al-Ca-3/2*OH)/Zr
0.5 Quartz MLSG Control (m = 0 )
0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 (Si-2Ca-3Na-3K)/Zr (molar) FractionationFractionation CompositionComposition
SiO2 Water Saturated Liquidus Surface
Halifax fractionating Davis Lake QZ, ALB, KSP Quartz composition New Ross (by either process) 1 kb
2 kb 5 kb
10 kb Albite K-Feldspar
NaAlSi3O8 KAlSi3O8 FractionationFractionation CompositionComposition
Quartz Water Saturated Liquidus Surface
Halifax
Davis Lake
Variation New Ross
Feldspar Muscovite SomeSome KeyKey PointsPoints
Major element, and therefore mineralogical, differences are subtle However, even utilising a ‘poor man’s water’, we can demonstrate repeatable differences between ‘fertile’ and ‘barren’ plutons within the SMB by examining their most evolved components Major and trace elements are telling us the same story! Gives more confidence in the interpretation Proper water analyses would have helped greatly, and might allow interpretation of major element data against mineral phase boundaries Structural water…. Analyse for it! If you are looking for variations in hydrous minerals! Point Counting might help… but time consuming and is it really more reliable? Use the whole rock traces and majors to rapidly assess many samples ConclusionsConclusions • two processes operated to cause magma evolution in the South Mountain batholith: • fractional crystallization, and • assimilation • Only the former leads to significant lithophile element enrichment • Think PROCESS • The Halifax pluton hosts no significant known mineralization, does not exhibit significant lithophile element enrichment, and did not become very peraluminous during evolution (probably as a result of assimilation) • The New Ross and Davis Lake plutons have significant mineralization, exhibit lithophile element enrichment, and became very peraluminous during evolution (probably as a result of fractional crystallization) ThanksThanks to:to:
NSERCNSERC DiscoveryDiscovery GrantGrant toto CRSCRS MikeMike MacDonaldMacDonald && LindaLinda Ham,Ham, NSNSNS-DNR--DNRDNR ChristinaChristina GilesGiles BarrieBarrie ClarkeClarke andand SaskiaSaskia Erdmann,Erdmann, DalhousieDalhousie
Questions?Questions?