Boninite series: low Ti-tholeiite associations from the 2.7 Ga Abitibi greenstone belt

ELSEVIER Earth and Planetary Science Letters 164 (1998) 303–316

Boninite series: low Ti-tholeiite associations from the 2.7 Ga Abitibigreenstone belt

R. Kerrich a,Ł, D. Wyman b, J. Fan a, W. Bleeker c

a Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, 7N 5E2, Canadab Centre for Strategic Mineral Deposits, Department of Geology and Geophysics, University of Western Australia,

Nedlands, W.A. 6907, Australiac Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0Z8, Canada

Received 20 April 1998; revised version received 10 August 1998; accepted 8 September 1998

Abstract

Boninite series volcanic flows, interfingered with komatiites and tholeiitic basalts, occur at several localities in the¾2.7 Ga Abitibi greenstone belt. Flows from Whitney Township, Ontario, have a compositional range of SiO2 44–60wt%, MgO 24–7.4, Mg# 83–69, and Ni 930–200 ppm. Low TiO2 (0.14–0.31 wt%) but high Al2O3 (13–25 wt%) contentsyield variably high Al2O3=TiO2 ratios of 48–100. These boninite series volcanics are characterized by fractionated HREEwhere Gd=Ybn 0.3–0.7; positive normalized Zr(Hf)=MREE anomalies, and Zr=Hf > 36; generally negative normalizedNb anomalies; and LREE depletion to enrichment (La=Smn 0.72–1.4). Flows with similar compositional affinities occurin the neighbouring Kidd Volcanic Complex and Tisdale volcanic group. Alteration, and=or contamination by continentalcrust can be ruled out as the cause of the distinctive and coherent compositions. If the areally extensive komatiite–tholeiiteassociation represents an ocean plateau derived from a mantle plume and the boninite series formed in a convergent margin,then the interfingering of komatiite and boninite series flows may represent interaction of a plume with a subduction zone. 1998 Elsevier Science B.V. All rights reserved.

Keywords: boninite; Abitibi Belt; komatiite; tholeiitic basalt

1. Introduction and scope

Boninites, and rocks with boninitic affinities havebeen reported from Phanerozoic convergent margins,and modern settings such as the Izu–Bonin–Marianafore-arc and Lau back arc basin [1,2]. They havealso been described from sites of intracontinentalrift magmatism, notably the Stillwater and Bushveldtintrusions [3]. To the authors’ knowledge volcanic

Ł Corresponding author. Tel: C1 306 966-5719; Fax: C1 306966-8593; E-mail: [email protected]

sequences with boninitic compositions have not beenreported from Archean greenstone belts. Siliceoushigh-magnesian basalts (SHMB) of the Yilgarn cra-ton may meet the compositional definition of SiO2 >

53 wt% and Mg# > 60 for boninites [1]. However,Sun et al. [4] drew attention to significant differencesof between SHMB and boninites, that include anabsence of U-shaped REE patterns, and SHMB havebeen interpreted instead as crustally contaminatedkomatiites.

This paper reports geochemical data for volcanicsuites with boninitic affinities from two localities

0012-821X/98/$ – see front matter 1998 Elsevier Science B.V. All rights reserved.PII: S 0 0 1 2 - 8 2 1 X ( 9 8 ) 0 0 2 2 3 - 4

304 R. Kerrich et al. / Earth and Planetary Science Letters 164 (1998) 303–316

Fig. 1. Supracrustal assemblages of the Southern Abitibi greenstone belt in Ontario, with localities of the Whitney, Kidd, and Tisdaleseries flows (modified from Jackson and Fyon [33]).

in the late Archean (2.7 Ga) Abitibi greenstonebelt. New data is presented for volcanic rocks fromWhitney Township, and additional data are reportedfrom the Kidd Volcanic Complex (KVC; [5]) about20 km to the northwest, building on an earlier paperthat dealt with numerous volcanic rock types hostinga massive sulphide deposit in that complex (Fig. 1;[6]).

2. Geological setting

The three localities at which boninite series vol-canic flows have been identified are in the westernsector of the Abitibi greenstone belt, north and eastof the city of Timmins. The boninites are part of

an east–west trending belt of predominantly komati-ites and tholeiitic basalts of the Kidd–Munro, andTisdale lithotectonic assemblages, that includes theclassic Munro Al-undepleted komatiites (Fig. 1; [7];assemblage as in the usage of Thurston et al. [8]).

The volcanic sequence in Whitney Township in-cludes Al-undepleted komatiites, Al-depleted ko-matiites with convex-up REE patterns, tholeiiticbasalts with near-flat REE patterns, and interlay-ered boninite series volcanic flows [9]. Two suitesof boninite series rocks were sampled in northernWhitney Township: a less altered suite with lowerLOI values, and from a neighbouring locality a vari-ably more altered suite with generally higher val-ues of LOI. In Tisdale Township, along strike fromWhitney, boninite series flows interfinger with Al-

R. Kerrich et al. / Earth and Planetary Science Letters 164 (1998) 303–316 305

depleted komatiites having convex-up REE patterns,and tholeiitic basalts [10]. Both volcanic sequencesare part of the Tisdale assemblage (Fig. 1). The baseof the KVC is dominated by Al-undepleted komati-ite flows. Boninite series flows overlie, and possi-bly interfinger with, the top of the komatiites; theboninites have been subdivided into stratigraphicallylower, more magnesian, and stratigraphically higherless magnesian low-Ti tholeiite groups (Lower LOTIand Upper LOTI of [6]). Overlying the boninite se-ries rocks in stratigraphic continuity are primitive arctholeiites [6]. The KVC is part of the Kidd–Munroassemblage (Fig. 1).

3. Analytical methods

Major elements were determined by X-ray fluo-rescence spectrometry (XRF); relative standard de-viations (RSD) are within 5%, and totals were all100 š 1%. Rare earth elements, high field strengthelements (HFSE) and other trace elements listedwere analysed by inductively coupled plasma massspectrometry (ICP-MS, Perkin Elmer Elan 5000)in the Department of Geological Sciences, Univer-sity of Saskatchewan, using the protocol of Jenneret al. [11], with standard additions, pure elemen-tal standards for external calibration, and BIR-1, asa reference material. Th, Nb, Ta, Zr, Hf and theREE were determined using an Na2O2 sinter prepa-ration, and the remaining trace elements by HF–HNO3 dissolution. The sinter technique generatesmore reproducible data for the specified elements inmetavolcanic rocks than acid dissolution [10]. Wetchemistry operations were conducted under cleanlab conditions. Analysis of acids, distilled deionizedwater, and procedural blanks yielded levels of <1ppb for REEs, Th, Nb, Zr and Hf, referenced toconcentrations in rock. Detection limits in ppm, de-fined as 3¦ of the procedural blank, for some criticalelements are as follows: Nb (0.006), Hf (0.008), Zr(0.004), La (0.001),Ce (0.009), Nd (0.004), and Sm(0.03). The precision, at the concentration of trace el-ements in BIR-1 and unknowns, is generally between2 and 4% RSD. BIR-1 is an appropriate referencematerial for high-Mg igneous rocks, inasmuch as theREE and HFSE contents are at comparable levels inthe reference material and unknowns. There is excel-

lent agreement between the recommended values forHFSE and REE in BIR-1, and the running averagefor these elements at the University of Saskatchewanlab. All RSDs are 8% or less, excepting Th (Table 1;[12]). Anomalies of HFSE relative to neighbouringREE are given as Zr=Zr*, Hf=Hf*, and Ti=Ti*; theseare calculated relative to neighbouring elements asfor Eu=Eu*, except that Ti=Ti* is calculated relativeto Sm and Gd, given possible mobility of Eu. Nbanomalies relative to La are expressed as primitivemantle normalized values, given fractionation of Thfrom La in subduction zone magmas (e.g. Nb=Lapm).Mg# is calculated as the molecular ratio of Mg=(MgC Fe2, where Fe2C is assumed to be 90% for thetotal Fe.

4. Results

At the Whitney localities and in the KVC, spinifextextures are preserved in most komatiites and pillowsare present in some basalt flows. The metamor-phic assemblage in boninite series rocks is chlo-rite, clinozoisite, plagioclase, with minor quartz andmuscovite, and some carbonate in the more alteredWhitney suite 2. The six less altered suite 1 boniniteseries flows have LOI values of 4.6 to 7.4 wt%,whereas in the more altered suite 2, LOI is 6.2 to 13wt% (Table 2).

Suite 1 flows are characterized by SiO2 D 44–60wt%, MgO D 24–7.4, Mg# 83–69, and Ni D 930–200 ppm. Low TiO2 D (0.14–0.31 wt%) but highAl2O3 (13–25 wt%) contents yield high Al2O3=TiO2

ratios (48–100; Fig. 2). There are weak negativetrends of Zr, Ti, and Yb with Mg#, and weak pos-itive trends with Ni and Al2O3=TiO2 (Fig. 3). Ondiagrams of Mg# versus elements or ratios suite1 lavas overlap the fields of selected Phanerozoicboninites for Zr, Ti, Ni, and Al2O3=TiO2, but plotto lower Gd=Ybn and generally higher Yb. On aprimitive mantle normalized diagram these volcanicrocks show: (1) fractionated HREE (Gd=Ybn 0.3–0.7); (2) Zr=Y (1.3–1.7) less than the primitive man-tle value of 2.4; (3) generally positive normalizedZr and Hf anomalies, with Zr=Hf generally >36; (4)LREE depletion to enrichment (La=Smn 0.72–1.4);and (5) variably negative Nb anomalies (Nb=Lapm

0.76–0.93; Fig. 4).


Table 1Results for the analyses of selected trace elements in BIR-1 by various techniques and laboratories

PM a Saskatoon b Compiled c Max Plank d

valuesHF–HNO3 Na2O2 sinter LA–ICPMS ID–SSMS ID–SSMS1990 1994Nx e ¦ RSD (%) Nx f ¦ RSD (%) Nx g ¦ RSD (%)

Sc 17.1 46.1 1.4 3 44V 82 346 11 3 313Rb 0.635 0.172 0.03 17 0.3 0.1 33 0.27 0.272 0.24Sr 21.1 112 2.07 2 143 6.7 5 119 7 6 108 109 110Y 4.55 14.6 0.25 2 14.7 0.67 5 14.3 1.2 8 16 17 15.5

Nb 0.74 0.738 0.07 10 0.648 0.07 11 0.6 0.04 7 0.6 0.5 0.5Zr 11.2 15.7 0.5 3 15.1 0.44 3 13.2 1.3 10 15.5 12 15.4Hf 0.309 0.639 0.04 6 0.62 0.06 9 0.6 0.08 13 0.6 0.36 0.51

La 0.687 0.614 0.02 3 0.628 0.04 6 0.8 0.06 8 0.62 0.6 0.61Ce 1.775 1.93 0.05 3 1.92 0.08 4 2.3 0.8 35 1.95 1.8 1.95Pr 0.276 0.382 0.01 3 0.357 0.02 5 0.4 0.04 10 0.38 0.341 0.38Nd 1.354 2.47 0.07 3 2.29 0.15 7 2.6 0.7 27 2.5 2.19 2.34Sm 0.444 1.14 0.06 5 1.08 0.06 6 1.3 0.21 16 1.1 1.07 1.1Eu 0.168 0.524 0.03 6 0.516 0.04 8 0.5 0.07 14 0.54 457 0.52Gd 0.596 1.91 0.06 3 1.81 0.12 7 1.6 0.28 18 1.85 1.52 1.84Tb 0.108 0.351 0.01 3 0.353 0.02 5 0.3 0.06 20 0.36 0.3 0.36Dy 0.737 2.63 0.08 3 2.53 0.13 5 2.7 0.23 9 2.5 2.25 2.51Ho 0.164 0.567 0.02 4 0.57 0.03 5 0.5 0.1 20 0.57 0.55 0.56Er 0.48 1.72 0.04 2 1.68 0.08 5 1.8 0.18 10 1.7 1.5 1.66Tm 0.074 0.26 0.01 4 0.252 0.02 7 0.2 0.02 10 0.26 0.227 0.25Yb 0.493 1.71 0.05 3 1.59 0.08 5 1.6 0.26 16 1.65 1.36 1.63Lu 0.074 0.259 0.01 4 0.248 0.02 8 0.2 0.02 10 0.26 0.227 0.25

Cs 0.032 0.007 0.01 14 0 0.45 0.01 0.004Ba 6.989 6.47 0.15 2 7.46 0.48 6 7.2 0.6 9 7.7? 8 7.1Pb 0.185 3.13 0.14 5 2.19 0.33 15 8.8 7.2 82 3.2 2.91 2.94Th 0.085 0.06 0.01 17 0.04 0.01 25 0.03 0.031 0.041U 0.021 0.011 0.002 18 0.01 0.01 0.0097

Zr=Hf 36 25 24 22 26 33 30Zr=Sm 25 14 14 10 14 11 14Hf=Nd 0.23 0.26 0.27 0.23 0.24 0.16 0.22Nb=Nb* 1.00 1.41 1.18 0.80 2.41 0.93 0.98Zr=Zr* 1.00 0.65 0.66 0.50 0.93 0.54 0.66Hf=Hf* 1.00 0.96 0.99 0.82 0.89 0.59 0.80

a PM D Primitive mantle values from Sun and McDonough [36]. b Nx average of the analyses; ¦ D standard deviation; RSD D relativestandard deviation. c Compiled values from Govindaraju [12] and Potts et al. [38]; ? D additional uncertainty; italic D from an individualanalysisd ID–SSMS data from Jochum et al. [39,40]. e n D 15. f n D 21. g n D 5. Nb=Nb*, Zr=Zr*, and Hf=Hf* calculated as for Eu=Eu*;see text for details.

Suite 2 flows from Whitney Township are compo-sitionally less coherent than the suite 1, possibly as aresult of more alteration, but some values of LOI arewithin the range for boninites and low Ti-tholeiitesfrom Tasmania [13]. They are characterized by SiO2

D 38–50 wt%, TiO2 D 0.17–0.64, Mg# 80 to 55,and Ni D 370–200 ppm. Al2O3=TiO2 ratios are vari-

able whereas Ti=Zr (84–110) are consistently high(Fig. 2). As for suite 1, they have range of LREEfractionation, and consistent fractionated HREE withnegative slopes, and Zr=Y ratios <2.4. Niobiumanomalies are variably negative to positive, whereasZr and Hf anomalies are consistently positive (Fig. 4;Table 2). They plot as a separate lower Mg# cluster


Fig. 2. Plots of Al2O3 vs. TiO2 (A), and Zr vs. Ti (B). S1 andS2, Whitney suites 1 and 2. Tisdale results plotted from Fanand Kerrich [10]. KC-LLOTI and KC-ULOTI are Kidd VolcanicComplex Lower Low-Ti tholeiites and Upper low-Ti tholeiitesrespectively (Table 2). Fields for Phanerozoic boninites fromHickey and Frey [27] and Cameron [23] are shown for reference.

on Fig. 3, at higher absolute concentrations of ele-ments from La–Yb, but generally lower Al2O3=TiO2

and Gd=Ybn ratios (Table 2). As for suite 1 flows,suite 2 overlap the fields of selected Phanerozoicboninites, but plot to higher Yb (Fig. 3).

The stratigraphically lower boninitic flows of theKidd volcanic complex are more primitive, withSiO2 43–50 wt%, TiO2 0.21–0.34, Mg# 81–74, and

Ni 1010–500 ppm. They have the high Al2O3=TiO2

(67–56) and Ti=Zr (84–90) ratios of most boninites,but are relatively aluminous (Fig. 2; Table 2). LightREE are variably fractionated whereas HREE havepronounced negative slopes in conjunction withZr=Y ratios less than the primitive mantle valveof 2.4. There are variable Nb anomalies but system-atically positive Zr and Hf peaks, where Zr=Hf > 36.

Stratigraphically higher boninitic flows are moresiliceous, trending to lower Mg# and Ni content(SiO2 D 57–53 wt%, Mg# D 57–51, and Ni D430–290 ppm). They show the high Al2O3=TiO2,and Ti=Zr ratios and LREE characteristics as thestratigraphically lower counterparts, albeit at greaterabundances of Al, Ti, and LREE, but overlappingcontents of Th, Nb, MREE and HREE. Overall,HREE and Zr=Y are less fractionated in these flowsrelative to those lower in the section. There areconsistent negative Nb anomalies, whereas Zr=Zr*

and Hf=Hf* are close to unity. Scandium and Vcontents tend to be greater in the stratigraphicallyhigher flows (Sc 37–43 vs 54–64 ppm; V 140–160vs 210–230 ppm). The lower boninites plot close tosuite 1 flows from Whitney Township on plots ofMg# versus selected elements and ratios, whereasthe upper boninites plot as a separate lower Mg#cluster (Fig. 3).

Relative to Whitney suite 2, the Tisdale boniniteseries flows have a comparable range of Mg#, lowerAl2O3=TiO2 ratios, and at a given Mg# greater con-centrations of Zr, Ti, and Yb, but lower Ni, andGd=Ybn ratios (Figs. 2–4; [10]).

5. Discussion

5.1. Alteration or contamination

Boninite series to low-Ti tholeiite flows of theWhitney Township and the KVC are spatially as-sociated with komatiites, as are the counterpartsfrom Tisdale Township directly along strike fromthe Whitney locality [6,10]. Accordingly, it is nec-essary to evaluate if the boninitic rocks, with theirrelatively high Mg# and Ni contents, are intenselyaltered komatiites, or alternatively are komatiites thathave undergone crustal contamination and fractionalcrystallization (SHMB of Sun et al. [4]).


Tabl

e2

Abu

ndan

ces

ofm

ajor

and

trac

eel

emen

tsin

boni

nite

seri

esvo

lcan

icflo

ws

from

the

wes

tern

Abi

tibig

reen

ston

ebe

lt

Whi

tney

Kid

d

Suite

1Su

ite2

Low

erL

OT

IU

pper

LO

TI

PM1

PM3

PM2

PM4

PM6

PM5

WV

-79

WV

-135

A3-

50W

V-8

7N

C-3

3K

C50

6DK

C50

6EK

C50

6A2

KC

533K

KC

533N

KC

533Q

KC

533I

SiO

244

.146

.643

.850

.660

.359

.747

.249

.537

.950

.557

.942

.646

.850

.557

.355

.353

.456

.5T

iO2

0.14

40.

222

0.17

70.

293

0.35

60.

313

0.17

30.

387

0.23

60.

365

0.64

20.

231

0.21

50.

242

0.32

60.

362

0.34

50.

315

Al 2

O3

13.1

23.1

15.8

24.9

17.1

15.8

1618

.221

.317

.716

.412

.914

.414

.118

.219

.219

17.4

Fe2O

310

.57.

5311

.27.

516.

257.

6711

.110

.313

.610

.811

.112

.211

.310

.86.

017.

589.

129.

9M

nO0.

293

0.21

50.

212

0.32

50.

162

0.49

90.

197

0.19

90.

258

0.17

10.

171

0.22

80.

214

0.27

0.18

90.

209

0.29

50.

252

MgO

24.5

14.5

2211

.86.

887.

3720

.710

.317

.110

.96.

1425

.519

.415

3.14

3.71

4.42

4.72

CaO

7.01

6.94

6.68

4.54

5.3

6.59

4.68

8.56

9.37

6.47

3.57

5.06

4.58

6.18

11.7

10.1

9.57

7.61

Na 2

O0.

356

0.84

80.

116

0.06

33.

571.

980.

023

2.44

0.24

71.

664.

060.

239

2.02

2.48

1.86

1.89

2.71

2.78

K2O

––

––

–0.

011

0.00

60.

006

0.00

61.

370.

011

ud–

–0.

316

0.41

80.

137

0.03

1P 2

O5

0.02

20.

032

0.03

10.

039

0.07

10.

057

0.02

30.

044

0.03

40.

034

0.06

40.

043

0.03

20.

032

0.02

10.

031

0.02

10.

021

LO

I4.

815.

415.

394.

637.

394.

9213

.19.

9311

11.5

6.23

7.90

6.5

7.35

4.95

4.25

4.9

4.6

Mg#

8382

8079

7469

8069

7269

5581

7874

5753

5251

Cr

1540

960

1460

600

320

330

1220

210

610

270

7423

0011

6610

5897

187

310

5490

7C

o87

7374

6444

5173

4658

4980

105

73.9

71.3

71.2

71.1

81.5

65.4

Ni

930

590

760

320

210

200

370

110

280

130

200

1010

530

499

323

322

406

295

Sc32

6548

7163

5537

4553

5946

37.1

41.7

43.5

63.8

66.5

53.6

63.1

V13

022

017

027

027

025

015

020

020

015

024

014

015

816

023

025

120

822

6Ta

––

––

––

0.03

0.07

0.03

0.07

0.1

0.03

50.

033

0.03

40.

052

0.05

70.

054

0.05

Nb

0.27

0.54

0.42

0.94

1.7

1.3

0.44

1.4

0.56

1.3

1.9

0.69

50.

814

0.71

40.

856

0.94

71.

030.

885

Zr

1016

1226

3626

9.7

2912

2742

15.4

15.4

15.9

20.4

22.1

2020

.5H

f0.

240.

370.

30.

510.

990.

640.

30.

810.

370.

761.

20.

417

0.39

60.

377

0.62

30.

667

0.65

40.

546

Th

0.03

0.07

0.05

0.15

0.26

0.2

0.05

0.19

0.05

0.14

0.3

0.09

40.

077

0.09

0.11

90.

125

0.14

20.

111

U–

––

––

–0.

020.

030.

010.

030.

160.

022

0.04

30.

011

0.02

80.

032

0.03

70.

026

Y7.

412

915

2117

9.7

1313

1424

8.03

10.4

10.2

11.8

10.3

12.5

9.56

La

0.34

0.73

90.

493

1.15

2.1

1.46

0.59

51.

560.

643

1.15

2.4

0.81

00.

605

0.72

21.

591.

371.

571.

06C

e0.

922

21.

333.

435.

253.

871.

493.

931.

663.

126.

262.

171.

681.

813.

863.

53.

662.

79Pr

0.14

20.

316

0.20

90.

456

0.79

80.

585

0.21

80.

573

0.26

10.

490.

882

0.33

50.

249

0.26

50.

554

0.50

30.

515

0.40

5N

d0.

814

1.62

1.11

2.21

3.71

2.62

1.14

2.82

1.26

2.42

4.27

1.45

1.26

1.33

2.79

2.48

2.77

2.15

Sm0.

295

0.51

70.

389

0.70

10.

956

0.73

90.

322

0.91

80.

427

0.85

81.

370.

468

0.49

60.

447

0.91

10.

827

0.90

30.

696

Eu

0.10

40.

136

0.14

40.

352

0.29

80.

186

0.15

80.

319

0.20

60.

322

0.43

40.

111

0.20

10.

237

0.37

50.

317

0.41

80.

261

Gd

0.50

80.

768

0.62

71.

011.

471.

190.

576

1.27

0.68

81.

311.

920.

592

0.79

30.

668

1.27

1.17

1.28

0.97

7T

b0.

117

0.17

10.

138

0.23

20.

333

0.26

30.

148

0.25

50.

174

0.25

20.

433

0.14

70.

170.

144

0.26

50.

239

0.24

90.

202

Dy

1.12

1.58

1.32

2.22

3.12

2.54

1.28

1.96

1.67

1.91

3.55

1.11

1.36

1.22

2.06

1.83

2.01

1.6

Ho

0.28

70.

425

0.36

40.

587

0.81

70.

651

0.37

10.

508

0.47

40.

505

0.94

0.29

60.

358

0.31

10.

525

0.45

90.

504

0.41

2E

r0.

956

1.61

1.23

1.96

2.76

2.33

1.32

1.66

1.71

1.68

3.06

0.96

91.

190.

954

1.69

1.45

1.63

1.27

Tm

0.16

50.

274

0.21

50.

329

0.5

0.39

0.22

20.

289

0.3

0.28

0.50

20.

154

0.20

70.

168

0.29

0.23

50.

281

0.20

7Y

b1.

162.

151.

492.

263.

623.

031.

631.

932.

211.

993.

421.

131.

441.

192.

051.

571.

931.

51L

u0.

193

0.35

40.

244

0.37

10.

692

0.50

20.

274

0.33

40.

347

0.31

90.

522

0.15

60.

209

0.17

90.

320.

247

0.29

0.23

4

La=

Yb n

0.20

0.24

0.23

0.35

0.40

0.33

0.25

0.56

0.20

0.40

0.49

0.50

0.29

0.42

0.54

0.60

0.56

0.49

La=

Smn

0.72

0.89

0.79

1.00

1.40

1.20

1.20

1.10

0.94

0.84

1.10

1.09

0.76

1.01

1.09

1.04

1.09

0.96

Gd=

Yb n

0.36

0.30

0.35

0.37

0.34

0.32

0.29

0.54

0.26

0.54

0.46

0.43

0.45

0.46

0.51

0.62

0.55

0.53

Eu=

Eu*

0.82

0.66

0.88

1.30

0.76

0.60

1.10

0.90

1.20

0.92

0.81

0.64

0.98

1.32

1.06

0.98

1.18

0.96

R. Kerrich et al. / Earth and Planetary Science Letters 164 (1998) 303–316 309Ta

ble

2(c

ontin

ued)

Whi

tney

Kid

d

Suite

1Su

ite2

Low

erL

OT

IU

pper

LO

TI

PM1

PM3

PM2

PM4

PM6

PM5

WV

-79

WV

-135

A3-

50W

V-8

7N

C-3

3K

C50

6DK

C50

6EK

C50

6A2

KC

533K

KC

533N

KC

533Q

KC

533I

Al 2

O3=T

iO2

9110

089

8548

5092

4790

4826

5667

5956

5355

55Z

r=H

f43

4440

5036

4133

3633

3635

3739

4233

3331

38L

a=N

b1.

201.

401.

201.

201.

201.

101.

301.

201.

100.

881.

301.

160.

741.

011.

861.

441.

521.

20T

h=N

b0.

110.

120.

120.

160.

150.

160.

110.

140.

080.

110.

160.

130.

100.

130.

140.

130.

140.

13T

h=L

a0.

090.

090.

100.

130.

120.

140.

080.

120.

070.

130.

130.

120.

130.

130.

080.

090.

090.

10

Zr=

Y1.

401.

401.

301.

701.

701.

601.

002.

200.

941.

901.

701.

921.

481.

561.

732.

151.

602.

14T

i=Z

r83

8189

6960

7111

079

110

8192

9084

9196

9810

492

Ti=

V6.

705.

906.

106.

507.

907.

306.

8012

.00

6.90

14.0

016

.00

9.94

8.15

9.08

8.51

8.62

9.96

8.33

Nb=

Nb*

0.93

0.82

0.92

0.76

0.79

0.81

0.89

0.85

1.10

1.10

0.76

0.86

1.28

0.95

0.67

0.78

0.74

0.87

Zr=

Zr*

1.50

1.20

1.20

1.40

1.30

1.30

1.10

1.30

1.20

1.30

1.20

1.30

1.34

1.43

0.89

1.07

0.87

1.16

Hf=

Hf*

1.20

1.00

1.10

1.00

1.30

1.20

1.20

1.30

1.30

1.30

1.20

1.27

1.26

1.23

0.98

1.17

1.04

1.12

Ti=

Ti*

0.83

0.80

0.81

0.81

0.69

0.75

0.89

0.84

0.99

0.79

0.93

1.06

0.78

1.02

0.71

0.86

0.75

0.89 It is widely accepted that the elements least sus-

ceptible to mobility during subseafloor hydrothermalalteration and greenschist facies metamorphism ofvolcanic piles are Al, Ti, the REE (excepting Ce andEu), the HFSE (Th, Nb, Ta, Zr, Hf), Y, Sc and V [14–17]. However, Ca, Na, K, Mn, Rb, Sr, Ba, and Csare generally mobile. The Whitney suite 1 possesesrelatively uniform Ti=Zr and Zr=Y ratios, has scat-tered Al2O3=TiO2 ratios, consistently fractionatedHREE, and relatively coherent REE and primitivemantle normalized patterns (Fig. 4; Table 2). TheKidd lower and upper boninite series rocks eachplot coherently on Fig. 4, and each has relativelyuniform Al2O3=TiO2, Ti=Zr and Zr=Y ratios. Conse-quently, those elements listed as relatively immobilehave apparently retained their primary magmaticinter-element relationships. Accordingly, the charac-teristics of low Ti contents, high Al2O3=TiO2 ratiosand Gd=Ybn < 1 with Zr=Y < 2.4 of these suites,shared with boninitic rocks, are considered primary.

Collectively, the boninite series flows have Zr andTi contents that overlap those of spinifex textured ko-matiites of Munro Township [7,17,10], but are muchmore aluminous, possess higher Al2O3=TiO2 ratiosand Sc and Yb contents, but lower Gd=Ybn and Zr=Yratios (Fig. 3). Nor do they have the pronounced neg-ative Nb and Ti anomalies with LREE enrichmentof crustally contaminated komatiites [4,18]. Theseboninite series flows are compared to other high-Mglavas from the Abitibi greenstone belt in Fig. 5. Theyplot to consistently higher Al2O3=TiO2 but lowerGd=Ybn than Mg-tholeiites or komatiites. Silicifica-tion or hydration would decrease the absolute contentof these elements but the ratios would remain un-changed. Accordingly, the boninitic series rocks areclearly not altered komatiites or Mg-tholeiites. Nei-ther do the boninite series flow resemble extremelyLREE depleted picrites from Gorgona [19]. The lat-ter have higher TiO2 but lower Al2O3 contents, andlack both the HREE fractionation and positive Zranomalies of the boninite series rocks.

5.2. Type of boninite

The terms boninite series [20] or boninitic (e.g.[21]) have been used for tholeiitic basalts whichshare the low Ti, high Al2O3=TiO2, and fraction-ated HREE of boninites, yet which have lower SiO2


Fig. 3. Plots of selected elements and ratios vs. Mg#. Munro komatiite fields from Fan and Kerrich [10] and Phanerozoic boninite fieldsfrom Hickey and Frey [27] and Cameron [23] are shown for reference. Symbols as in Fig. 2. Tisdale and PH-Ksp are respective boniniteseries lavas from Tisdale Township and spinifex textured komatiites from Pyke Hill, Munro Township [10].

R.K

errichet

al./Earth

andP

lanetaryScience

Letters

164(1998)

303–316311

Fig. 4. Primitive mantle normalized diagrams for two boninite-series volcanic flows: (A, B) Whitney Township; (C) Kidd Volcanic Complex; and (D) Tisdale Township(from Fan and Kerrich [10]. Sample numbers from Table 2. Normalizing values, and normal mid ocean ridge basalt (N-MORB) and ocean island basalt (OIB) from Sun andMcDonough [36]. Average island arc basalt (IAT) from Pearce and Peate [37].


Fig. 5. Plot of Al2O3=TiO2 vs. Gd=Ybn showing the difference between the boninite series volcanic rocks, and boninite series (Type2) lavas from Tisdale [10], vs. other high-Mg lavas from the Abitibi greenstone belt. Fields for Tisdale Mg-tholeiites (Type 1), TisdaleAl-depleted komatiites (ADK) and Pyke Hill Al-undepleted komatiites (AUK) from Fan and Kerrich [10].

and=or Mg# than in the boninite definition of Craw-ford et al. [1]. For depleted tholeiites associated withboninites Brown and Jenner [13] use the term low-Titholeiite (LOTI). If the major element oxides are ad-justed to the primary water content of about 2 wt%estimated for boninites, then four of the KVC suitevolcanic rocks and one of the Whitney suite meet thestrict compositional definition of boninite of SiO2 >

53 wt% and Mg# > 60 given by Crawford et al. [1].Based on TiO2, Al2O3, and Sc contents they conformmost closely to the low-Ca Type 2 classification ofCrawford et al. [1], and overlap in Ti and Al contentswith boninites from the Koh ophiolite [22]. Theyalso share the relatively high Ti=Zr ratios and Sccontents of Koh boninites [23,22].

The Tisdale suite shares the fractionated HREE,low Zr=Y ratios, and positive Zr and Hf anomaliesof Whitney and KVC counterparts, and of boniniteseries rocks in general, but plot to higher abso-lute abundances, and have lower Ni contents andAl2O3=TiO2 ratios than the Whitney or Kidd suites(Figs. 3 and 4). Sample T14 is close to the strict defi-nition of a boninite (Fig. 4; [10]). This suite overlapsthe LOTI from the Black Hill area, Tasmania, inTiO2 and Al2O3, and shares their negative HREE butnot pronounced positive LREE fractionation [13,10].

Given the apparently continuous trend of increasingTiO2, Al2O3, and REE abundances with decreasingMg# and Ni content from boninites sensu stricto tolow-Ti tholeiites, in these three groups of spatiallyassociated flows in Abitibi belt, we adopt the termboninite series-low Ti tholeiite association (Figs. 3and 4; Table 2).

The stratigraphically higher boninite series flowsof the Kidd volcanic complex are less refractorythan their lower counterparts. This trend may stemfrom olivine fractional crystallization, but fractiona-tion alone cannot account for the higher Zr=Y andGd=Ybn ratios, or the switch from positive to zero Zrand Hf anomalies. In the Cambrian greenstone beltsof SE Australia there is a stratigraphically upwardsuccession from less to more refractory boninites,with increasing large ion lithophile element (LILE)enrichment. These trends have been interpreted interms of boninite liquids being derived from a pro-gressively more refractory source, that in turn re-quires larger quantities of LILE enriched fluids toflux [24,25]. Consequently, the two KVC boninitesuites must have been derived from mantle sourceswith more and less refractory nature stemming fromdifferent degrees of depletion. The Tisdale boni-nite series flows were derived from a less refractory


source than Whitney flows along strike, and in addi-tion fractionated an aluminum phase, as seen in thesharp downturn from Lu to Al (Fig. 4).

5.3. Origin of boninites

There is a general consensus that melts ofboninitic composition require a two stage process. Instage one, single or multiple extractions of basalticmelts leave a residue more refractory than the sourceof mid ocean ridge basalt (MORB), where the or-der of increasing depletion is from Lu to La andlithophile elements. During stage two, the refractoryresidue is fluxed by fluids and=or melts generatedfrom a subducted slab, that are enriched in Si, Na,LILE, and for some boninites Zr and Hf [1,14,26–28]. According to some workers, an ocean islandbasalt (OIB)-like enriched silicate melt componentmay also be involved, to account for the Zr and Hfenrichment, and Zr–Hf fractionation to values vari-ably greater than the primitive mantle ratio of 36(Table 2; [27,29–31]).

The combined processes generate the variablyLREE depleted to enriched patterns and negativelyfractionated HREE of boninites and LOTI, and insome suites positive Zr and Hf anomalies. If an en-riched OIB asthenosphere component is responsiblefor positive Zr and Hf anomalies in some boniniteseries rocks, then this is present in all Whitney andTisdale samples, and lower but not upper boniniteseries to low Ti tholeiites of the KVC. In general, theAbitibi boninite series flows do not have Zr or Hfanomalies as large as observed in some Phanerozoicboninites, but overlap with the field for Phanerozoicboninites (Fig. 6A).

Collectively boninites have a large range of LREEfractionation. Those from the Koh ophiolite are char-acterized by LREE depletion to mild enrichment,with an upturn at Sm, whereas Nepui and NorthTonga boninites have pronounced LREE enrichmentwith an upturn at Ho–Tb, and deep negative Nband Ti anomalies [23] (see [22]; fig. 10 for a com-pilation). Tholeiites associated with the Koh andNepui boninites have relatively unfractionated REE,whereas LOTI in Tasmania share the HREE frac-tionation of boninites. In summary, the Abitibi boni-nite series flows share the HREE fractionation ofall Phanerozoic boninites, and possess only minor

Fig. 6. Plots of Zr=Zr* (A) and Nb=Lapm (B) vs. Mg#. Phanero-zoic boninite fields from Hickey and Frey [27] and Cameron[23], are shown for reference. The third field includes other datafor Phanerozoic boninites and low-Ti tholeiites [22,13,21,34,2].

LREE depletion to enrichment and small Nb or Tianomalies, like the Koh boninites. There are smallpositive to generally negative Nb anomalies com-pared to a much larger range of positive to negativeanomalies in Phanerozoic boninites (Fig. 6B). Con-sequently, these rocks all feature strong signaturesof stage one boninite genesis, but a weak secondstage subduction zone LREE enrichment. All ofthe Whitney and KVC boninite series rocks havea pronounced trough at V relative to Lu and Sc.


This feature is common to some arc tholeiites andmany boninites, but further sets these lavas apartfrom other high Mg-lavas in the Abitibi belt such asMg-tholeiites and komatiites (Figs. 4 and 6).

5.4. Implications for geodynamic setting

Boninite series volcanic suites all form in conver-gent margin environments, and are rare compared toother volcanic rocks. They have been described fromPaleozoic and Mesozoic ophiolites that include ophi-olites from Appalachia and Troodos from terranessuch as the Marianas intraoceanic arcs as at CapeVogel; the Lau basin back-arc; and the continentalmargin convergent setting of Baja, California andSW Japan [1]. According to Meffre et al. [22] thecomposition of basalts associated with boninites mayprovide constraints on their geodynamic setting. Forexample, back arc basalts overlie the Koh ophioliteboninites. Boninites have also been reported from aProterozoic volcanic terrane [35].

At the Kidd volcanic centre boninite series lavasare underlain and overlain by komatiites, and thereis a stratigraphic upward trend from primitive toevolved arc tholeiites. According to Wyman et al. [6]the conjunction of these two magma associations isinterpreted in terms of a mantle plume interactingwith a subduction zone. Similarly, the Tisdale boni-nite series — low Ti tholeiites interfinger in the fieldwith komatiites, a relationship interpreted in terms ofconvergent margin–plume interaction [10]. A similarassociation of komatiites with boninite series rocksis present in Whitney Township [9].

Crawford et al. [1] summarized the conditionsnecessary for boninite genesis, namely hydrous flu-ids and high temperatures in a shallow subductionzone environment. The high temperatures have vari-ably been attributed to MORB source diapirs im-pinging under an arc during extension, or a sub-ducted active spreading centre. Stern and Bloomer[32] developed a model of subduction zone infancyfor intraoceanic arcs, with catastrophic melting in-duced by rapid adiabatic decompression. Given theassociation of plume-derived komatiite with boniniteseries — low Ti tholeiites at three locations in thewestern Abitibi greenstone belt, a hot plume imping-ing on an arc satisfies the constraints of a shallowheat source in a subduction environment.

Acknowledgements

The authors thank P. Hollings and A. Polat for in-cisive critiques of a provisional draft. We are gratefulfor journal reviews by J. Dostal and R. Hickey-Var-gas that have greatly improved the manuscript. TheWhitney samples were part of a study funded by anNSERC operating grant top R.K., and samples fromthe Kidd Volcanic Complex were part of a studyfunded by a MITEC grant to R.K. and D.W. TheICP-MS lab is partially supported by an NSERCMFA grant to the University of Saskatchewan. [CL]

References

[1] A.J. Crawford, T.J. Falloon, D.H. Green, Classification, pet-rogenesis and tectonic setting of boninites, in: A.J. Craw-ford (Ed.), Boninites and Related Rocks, Unwyn Hyman,London, 1989, pp. 1–49.

[2] J.A. Pearce, R.J. Arculus, B.J. Murton, T. Ishii, D.W. Peate,I.J. Parkinson, Boninite and harzburgite from Leg 125(Bonin-Mariana forearc); a case study of magma genesisduring the initial stages of subduction, Pro. Ocean Dril.Prog. Sci. Res. 125 (1992) 623–659.

[3] C.J. Hatton, M.R. Sharpe, Significance and origin ofboninite-like rocks associated with the Bushveld Complex,in: A.J. Crawford (Ed.), Boninites and Related Rocks, Un-win Hyman, London, 1989, pp. 174–207.

[4] S.S. Sun, R.W. Nesbitt, M.T. McCulloch, Geochemistry andpetrogenesis of Archaean and early Proterozoic siliceoushigh-magnesian basalts, in: A.J. Crawford (Ed.), Boninitesand Related Rocks, Unwyn Hyman, London, 1989, pp.148–173.

[5] W. Bleeker, R.R. Parrish, Stratigraphy and U–Pb zircongeochronology of Kidd Creek; implications for the forma-tion of giant volcanogenic massive sulphide deposits andthe tectonic history of the Abitibi greenstone belt, Can. J.Earth Sci. 33 (1996) 1213–1231.

[6] D.A. Wyman, W. Bleeker, R. Kerrich, A 2.7 Ga plume,proto-arc, to arc transition and the geodynamic setting ofthe Kidd Creek deposit: evidence from precise ICP MStrace element data, The Giant Kidd Creek VolcanogenicMassive Sulfide Deposit, Western Abitibi Subprovince,Canada, Econ. Geol. Monogr. 10 (1998) in press.

[7] N.T. Arndt, R.W. Nesbitt, Geochemistry of Munro Town-ship basalts, in: N.T. Arndt, E.G. Nisbet (Eds.), Komatiites,Allen and Unwin, London, 1982, pp. 309–329.

[8] P.C. Thurston, I.A. Osmani, D. Stone, Northwestern Supe-rior Province: Review and terrane analysis, Geology of On-tario Special Volume 4, Ontario Geological Survey, 1991,pp. 81–144.

[9] J. Fan, Geochemistry and petrogenesis of unaltered and al-


tered volcanic sequences in the southern Abitibi GreenstoneBelt, PhD Thesis, University of Saskatchewan, 1995.

[10] J. Fan, R. Kerrich, Geochemical characteristics of Al-depleted and undepleted komatiites and HREE-enrichedtholeiites, western Abitibi greenstone belt: variableHFSE=REE systematics in a heterogeneous mantle plume.,Geochim. Cosmochim. Acta 61 (1997) 4723–4744.

[11] G.A. Jenner, H.P. Longerich, S.E. Jackson, B.J. Fryer,ICP-MS — A powerful tool for high precision trace-ele-ment analysis in earth sciences: evidence from analysis ofselected USGS reference samples, Chem. Geol. 83 (1990)133–148.

[12] K. Govindaraju, 1994 compilation of working valuesand sample description for 383 geostandards, Geostand.Newslett. 18 (Spec. Issue) (1994) 158.

[13] A.V. Brown, G.A. Jenner, Geological setting, petrology andchemistry of Cambrian boninite and low-Ti tholeiite lavasin western Tasmania, in: A.J. Crawford (Ed.), Boninites andRelated Rocks, Unwyn Hyman, London, 1989, pp. 232–263.

[14] S.-s. Sun, R.W. Nesbitt, Geochemical regularities and ge-netic significance of ophiolitic basalts, Geology 6 (1978)689–693.

[15] J. Ludden, L. Gelinas, Trace element characteristics ofkomatiitic basalts from the Abitibi metavolcanic belt ofQuebec, in: N.T. Arndt, E.G. Nisbet (Eds.), Komatiites,Allen and Unwin, London, 1982, pp. 331–346.

[16] S.E. Humphris, The mobility of the rare earth elementsin the crust, in: P. Henderson (Ed.), Rare Earth ElementGeochemistry, Elesevier, Amsterdam, 1984, pp. 317–342.

[17] K.P. Jochum, N.T. Arndt, A.W. Hofman, Nb–Th–La in ko-matiites and basalts: constraints on komatiites petrogenesisand mantle evolution, Earth Planet. Sci. Lett. 107 (1991)272–289.

[18] I.S. Puchtel, D.Z. Zhuravlev, A.V. Samsonov, N.T. Arndt,Petrology and geochemistry of metamorphosed komatiitesand basalts from the Tungurcha greenstone belt, AldanShield, Precamb. Res. 62 (1993) 399–417.

[19] A.C. Kerr, G.F. Marriner, N.T. Arndt, J. Tarney, A. Nivia,A.D. Saunders, R.A. Duncan, The petrogenesis of Gorgonakomatiites, picrites and basalts: new field, petrographic andgeochemical constraints, Lithos 37 (1996) 245–260.

[20] A. Meijer, Primitive arc volcanism and a boninite series;example from western Pacific Island arcs., Geophys. Mon.23 (1980) 269–282.

[21] R.A. Coish, Boninitic lavas in Appalachian ophiolites; areview, in: A.J. Crawford (Ed.), Boninites and RelatedRocks, Unwyn Hyman, London, 1989, pp. 264–287.

[22] S. Meffre, J.C. Aitchison, A.J. Crawford, Geochemical evo-lution and tectonic significance of boninites and tholei-ites from the Koh ophiolite, New Caledonia, Tectonics 15(1996) 67–83.

[23] W.E. Cameron, Contrasting boninite–tholeiite associationsfrom New Caledonia, in: A.J. Crawford (Ed.), Boninitesand Related Rocks, Unwyn Hyman, London, 1989, pp.314–338.

[24] A.J. Crawford, W.E. Cameron, Petrology and geochemistry

of Cambrian boninites and low-Ti andesites from Heath-cote, Victoria, Contrib. Mineral. Petrol. 91 (1985) 93–104.

[25] A.J. Crawford, R.R. Keays, Petrogenesis of Victorian Cam-brian tholeiites and implications for the origin of associatedboninites, J. Petrol. 28 (1987) 1075–1109.

[26] G.A. Jenner, Geochemistry of high-Mg andesites from CapeVogel, Papua New Guinea, Chem. Geol. 33 (1981) 307–332.

[27] R.L. Hickey, F.A. Frey, Geochemical characteristics ofboninite series volcanics; implications for their source,Geochim. Cosmochim. Acta 46 (1982) 2099–2116.

[28] R. Hickey-Vargas, M.K. Reagan, Temporal variation ofisotope and rare earth element abundances in volcanic rocksfrom Guam; implications for the evolution of the MarianaArc, Contrib. Mineral. Petrol. 97 (1987) 497–508.

[29] W.E. Cameron, M.T. McCulloch, D.A. Walker, Boninitepetrogenesis: chemical and Nd–Sr isotopic constraints,Earth Planet. Sci. Lett. 65 (1983) 75–89.

[30] R. Hickey-Vargas, Boninites and tholeiites from DSDP Site458, Mariana Forearc, in: A.J. Crawford (Ed.), Boninitesand Related Rocks, Unwin Hyman, London, 1989, pp.339–356.

[31] S.M. Eggins, J.D. Woodhead, L.P.J. Kinsley, G.E. Mor-timer, P. Sylvester, M.T. McCulloch, J.M. Hergt, M.R. Han-dler, A simple method for the precise determination of > orD 40 trace elements in geological samples by ICPMS usingenriched isotope internal standardisation, Chem. Geol. 134(1997) 311–326.

[32] R.J. Stern, S.H. Bloomer, Subduction zone infancy; ex-amples from the Eocene Izu Bonin-Mariana and JurassicCalifornia arcs, Geol. Soc. Am. Bull. 104 (1992) 1621–1636.

[33] S.L. Jackson, J.A. Fyon, The Western Abitibi subprovincein Ontario, in: P.C. Thurston, H.R. Williams, R.H. Sutcliffe,G.M. Stott (Eds.), Geology of Ontario, Special Volume 4,Ontario Geological Survey, 1991, pp. 405–482.

[34] N.W. Rogers, C.J. MacLeod, B.J. Murton, Petrogenesis ofboninitic lavas from Limassol Forest Complex, Cyprus, in:A.J. Crawford (Ed.), Boninites, University of Tasmania,Geology Department, Hobart, Tasmania, 1989, pp. 288–311.

[35] B. Wolde, Z. Asres, Z. Desta, J.J. Gonzalez, Neoproterozoiczirconium-depleted boninite and tholeiitic series rocks fromAdola, southern Ethiopia, Precambrian Res. 80 (1996) 261–279.

[36] S.-s. Sun, W.F. McDonough, Chemical and isotopic system-atics of oceanic basalts: implications for mantle composi-tion and processes, in: A.D. Saunders, M.J. Norryt (Eds.),Magmatism in the Ocean Basins, Geol. Soc. Spec. Publ. 42(1989) 313–345.

[37] J.A. Pearce, D.W. Peate, Tectonic implications of the com-position of volcanic arc magmas, Annu. Rev. Earth Planet.Sci. 23 (1995) 251–285.

[38] P.J. Potts, A.G. Tindle, P.C. Webb, Geochemical ReferenceMaterial Compositions, Whittles Publishing, CRC Press,Boca Raton, 1992, 313 pp.

[39] K.P. Jochum, H.M. Seufert, M.F. Thirlwall, Multi-element


analysis of international standard rocks by isotope-dilutionspark source mass spectrometry, Geostand. Newslett. 14(1990) 469–473.

[40] K.P. Jochum, M. Rehkamper, H.M. Seufert, Trace elementanalysis of basalt BIR-1 by ID SSMS, HPLC and LIMS,Geostand. Newslett. 18 (1994) 43–51.

Documents

Boninite series: low Ti-tholeiite associations from the 2.7 Ga Abitibi greenstone belt