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DTD 5

Lithos xx (2004

Mantle wedge involvement in the petrogenesis of Archaean grey

gneisses in West Greenland

Agnete Steenfelta,*, Adam A. Gardea, Jean-Francois Moyenb,1

aGeological Survey of Denmark and Greenland, aster Voldgade 10, DK-1350 Copenhagen K, DenmarkbUniversite Claude Bernard Lyon-I, 2 Rue Raphael Dubois, 69622 Villeurbanne Cedex, France

Received 16 October 2003; accepted 2 September 2004

Abstract

The Archaean crust in West Greenland is dominated by grey orthogneiss complexes formed in periods of crustal

accretion at around 3.8, 3.6, 3.2, 3.0–2.9 and 2.8–2.7 Ga. The majority of the gneisses have tonalite–trondhjemite–

granodiorite (TTG) compositions, while subordinate quartz–dioritic and dioritic gneisses have calc-alkaline

compositions. The major and trace element chemistry of gneiss samples has been compiled from three large regions

representing different terranes and ages in southern and central West Greenland, the Godth3bsfjord, Fiskefjord and

Disko Bugt regions. The TTG gneisses are typical for their kind and show little variation, except marked Sr

enrichment in the Fiskefjord area and slight Cr enrichment in a unit within the Disko Bugt region. Thus, while most

of the crust has probably formed from magmas derived by slab melting, local involvement of mantle-derived

components is suggested.

Most of the diorites have geochemical signatures compatible with mantle-derived parental magmas, i.e., elevated

Mg, Cr and flat chondrite-normalised REE patterns. A group of quartz–diorite and diorite samples from the Fiskefjord

region exhibits marked enrichment in Sr, Ba, P, K and REE, combined with steep REE patterns. A similar but much

more pronounced enrichment in the same elements characterises Palaeoproterozoic subduction-related monzodiorites

within the Nagssugtoqidian orogen, as well as carbonatites and carbonatitic lamprophyres within the same part of

West Greenland. We argue that the parental magmas of the enriched diorites are derived by partial melting from

regions within the mantle that have been metasomatised by carbonatite-related material, e.g., in the form of

carbonate–apatite–phlogopite veins. Alternatively, ascending slab melts may have reacted with carbonatite-metasoma-

tised mantle.

Carbonatitic carbonates have high Sr and Ba, and carbonatitic apatite has high P2O5 and very steep REE spectra.

Adding such a component to a peridotite-derived magma produces geochemical features similar to those of sanukitoids,

except that high phosphorus is not described as typical of sanukitoids. We observe that the enriched diorites from

0024-4937/$ - s

doi:10.1016/j.lit

* Correspon

E-mail addr1 Now at: D

) xxx–xxx

ee front matter D 2004 Elsevier B.V. All rights reserved.

hos.2004.04.054

ding author. Tel.: +45 38 14 22 16; fax: +45 38 14 22 20.

ess: ast@geus.dk (A. Steenfelt).

epartment of Geology, University of Stellenbosch, Private Bag X1, 7602 Matieland, South Africa.

LITHOS-01184; No of Pages 22

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A. Steenfelt et al. / Lithos xx (2004) xxx–xxx2

Greenland are sanukitoid-like, although they are not sanukitoids by the original definition, and their genesis requires a

twist to the current models for sanukitoid petrogenesis.

D 2004 Elsevier B.V. All rights reserved.

Keywords: TTG gneiss; Sanukitoids; Mantle carbonatite; Mantle metasomatism; Archaean crust; West Greenland

1. Introduction

The bulk of Archaean continental crust consists of

grey gneiss complexes (e.g., Windley, 1995), predom-

inantly sodium-rich granitoid rocks belonging to the

tonalite–trondhjemite–granodiorite (TTG) suite, as

opposed to the more potassium-rich calc-alkaline

granitic rocks that predominate in more recent

continental crust. The major and trace element

characteristics of the TTG suite have been described,

e.g., by Arth and Hanson (1975), Barker (1979),

Drummond and Defant (1990) and Martin (1994).

Archaean TTG complexes are generally polyphase and

record a complex succession of intrusion, deformation

and partial melting events and are commonly asso-

ciated with dioritic orthogneisses of calc-alkaline

affinity. They often also contain amphibolite inclu-

sions, which may both represent disrupted basic dykes

(e.g., Martin, 1994) and remnants of older mafic crust

that was magmatically or tectonically intercalated with

the grey gneiss precursors (e.g., Garde, 1997).

It is nowwell established by experimental data (e.g.,

Wolf and Wyllie, 1994; Rapp and Watson, 1995;

Zamora, 2000) compared with natural rock composi-

tions (e.g.. Barker and Arth, 1976; Martin, 1987;

Drummond and Defant, 1990; Martin, 1994) that TTG

melts are generated by partial melting of hydrous basalt

in the garnet stability field, although the geodynamic

setting of their petrogenesis remains controversial.

Two end-member hypotheses persist (along with

hybrid or intermediate scenarios): (1) Archaean TTGs

were formed in hot plate-tectonic subduction zones, by

partial melting of the subducting slab (Martin, 1986;

Peacock et al., 1994; Martin andMoyen, 2002), and (2)

TTGs were formed by partial melting of underplated

hydrous basalt, either at the base of the continental

crust or in overthickened oceanic crust (basaltic

plateaux; Rudnick et al., 1993; Albarede, 1998).

Regardless which of the two main scenarios is

preferred, it is generally accepted that syn- to post-

kinematic potassium-rich granitic rocks that are com-

monly associated with TTG suites are probably derived

from the latter by local or regional partial melting

(Querre, 1985; Sylvester, 1994; Windley, 1995; Berger

and Rollinson, 1997; Moyen et al., 2003).

It is also well known that Archaean grey gneisses are

more complex than simply TTGs and their melt

products. Recent work has shown that, besides being

derived from partial melting of hydrated basalt, they

may also contain signs of geochemical interaction with

the mantle (e.g., Rudnick et al., 1993; Martin and

Moyen, 2002). It has also been suggested that a

significant part of the late Archaean K-rich components

within grey gneiss complexes may not be related to

crustal recycling, but represent slab melts altered by

geochemical interaction with normal or metasomatised

mantle (Shirey and Hanson, 1984, 1986; Stern et al.,

1989; Stern and Hanson, 1991; Rapp et al., 1999;

Moyen et al., 2001; Martin et al., 2005). Furthermore,

the degree of mantle interaction may have increased

over time—perhaps related to the progressive cooling

of the Earth and an inferred increasing depth of slab

melting (Martin and Moyen, 2002; Smithies and

Champion, 2003; Martin et al., 2005).

One of the volumetrically minor but important

component of the Archaean gneisses is known as

sanukitoids, which generally occur as syn- to late-

tectonic intrusions, occasionally as bdark gneissesQ,interlayered with classical TTGs. In the original

definition of Shirey and Hanson (1984), sanukitoids

are diorites to granodiorites with high Mg# (N0.6),

high Ni (N100 ppm) and high Cr contents (200–500

ppm), together with relatively high K, Sr, Zr and Nb.

They have strong LREE enrichment (CeNN100 and

[Ce/Yb]N=10–50). The term bsanukitoidQ has since

been used for a range of dark diorites to granodiorites

found within the Archaean crust, and ranging from

btrueQ sanukitoids exactly matching the initial defi-

nition to mafic or intermediate rocks associated with

syenites or other alkali intrusives (Lobach-Zhuchenko

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A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 3

et al., 2003; 2005). The term has also been used by

Moyen et al. (2003) for intermediate rocks with high

LREE and [Ce/Yb]N, but with lower Mg# (~0.45) and

Cr (~120 ppm), corresponding to the broader

bsanukitoid suiteQ of Shirey and Hanson (1984).

There is no good agreement on the petrogenesis of

sanukitoids; part of the problem, maybe, arises from

the variety of rocks that have been called bsanukitoidQ.However, two main models have been proposed for

the rocks matching the original definition, which both

call for the involvement of two components, a slab

melt (i.e., TTG-like magma) and a peridotitic mantle

wedge. In the first model (e.g., Balakrishnan and

Rajamani, 1987; Stern and Hanson, 1991; Krogstad et

al., 1995; Smithies and Champion, 2000), sanukitoids

are the product of partial melting of a mantle that has

been metasomatised by slab melts. In the second (e.g.,

Rapp et al., 1999; Moyen et al., 2003), sanukitoids are

formed from hybridised slab melts that have assimi-

lated olivine during their ascent through the mantle.

Both models can account for the high Mg# combined

with a bTTG-likeQ incompatible element signature.

However, despite attempts by, e.g., Martin et al.

(2005), it proves difficult to convincingly decide

between the two models on petrological or geo-

chemical grounds, and they probably represent two

end members of a whole range of processes, depend-

ing on the effective melt/rock ratio (Rapp et al., 1999;

Martin and Moyen, 2002). It should nevertheless be

stated that the first model allows sanukitoids to be

generated at any time after a subduction event and not

necessarily during the subduction itself.

In summary, at least four main components are

likely to have contributed to the petrogenesis of

Archaean grey gneiss complexes: (1) pure slab melts,

i.e., partial melt products of hydrous basalt in the

garnet stability field producing rocks of the TTG

family; (2) partial melts of a peridotitic mantle wedge,

where melting is triggered by fluids derived from

dehydration of the subducting slab producing calc-

alkaline rock suites; (3) melts derived from a

metasomatised mantle wedge or from slab melts

interacting with metasomatised mantle producing

sanukitoids; and (4) partial melts from preexisting

continental crust, such as older TTGs or sedimentary

rocks producing K-rich granodiorites and granites. All

four components are recognised within the generally

well-preserved and excellently exposed Archaean

grey gneiss complexes in Greenland, which have

hitherto largely been overlooked in the debate about

Archaean continental crustal evolution.

In this paper, we present chemical data on grey

gneisses from three large regions in southern and

central West Greenland representing three important

crust forming events between 3.8 and ca. 2.8 Ga. Our

aim is to compare subduction-related gneiss com-

plexes over space and time and discuss mantle

involvement in the genesis of such complexes. Our

data do not support Martin and Moyen’s (2002)

observation that the depth of slab melting and, hence,

the degree of mantle interaction have increased over

Archaean time. Conversely, certain rock associations

in our data have geochemical signatures resembling,

although not matching, those of sanukitoids. They are

spatially associated with 3.0- to 0.16-Ga-old carbo-

natites (see below), and we suggest that their parental

magmas were derived from, or interacted with, a

mantle wedge metasomatised by carbonatite-related

components. Additional data from predominantly

calc-alkaline orthogneisses of Palaeoproterozoic age

in central West Greenland corroborate this suggestion.

2. Geological setting of the study areas

Archaean crust underlies all of West Greenland

(Fig. 1). The Archaean craton, a part of the North

Atlantic craton also comprising areas of Labrador,

East Greenland and Scotland, has escaped post-

Archaean deformation. The exposed Archaean crust

comprises an estimated 85% of orthogneisses domi-

nated by TTG compositions, and 15% supracrustal

associations dominated by mafic metavolcanic rocks.

They have all been metamorphosed at amphibolite to

granulite facies conditions. Previous zircon geochro-

nology of major TTG suites in various parts of West

Greenland documents continental crustal accretion at

around 3.8, 3.6, 3.2, 3.0–2.9 and 2.8–2.7 Ga.

Several tectono-stratigraphic terranes have been

recognised in the Archaean craton. The different

terranes appear to have been assembled by con-

tinent–continent collision around 2.7 Ga (Friend et al.,

1988). To the north, the Archaean craton was variably

reworked during Palaeoproterozoic orogenesis, and to

the south, the slightly younger Ketilidian orogen

(Garde et al., 2002) was accreted to the southern

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Fig. 1. Index map and geological overview of Greenland with study areas. The Palaeoproterozoic metaigneous complexes in the

Nagssugtoqidian orogen are the Arfersiorfik quartz–diorite (AQD) and the Sisimiut intrusive complex (SIS).

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx4

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A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 5

margin of the Archaean block at 1.8 Ga. This orogen

largely consists of a major juvenile continental arc and

its deformed and metamorphosed erosion products.

Palaeoproterozoic orogeny in central and northern

West Greenland has traditionally been regarded as

comprising two distinct belts, the Nagssugtoqidian

orogen in the south and the Rinkian fold belt in the

north, but recent geochronological and structural

evidence suggests that the two belts may be different

domains within the same large-scale continental

collision zone (Garde et al., 2003; Thrane et al.,

2003). The suture between the two continents has not

been identified with certainty but is probably located

in the central part of the Nagssugtoqidian belt.

Besides intensely reworked Archaean basement, this

region hosts Palaeoproterozoic lithologies likely to be

associated with the opening and closure of an ocean,

including subduction-related calc-alkaline ortho-

gneisses (Kalsbeek et al., 1987; van Gool et al., 2001).

2.1. Early Archaean orthogneiss complexes at

Godthabsfjord, Akulleq terrane

The earliest continental crust in Greenland is the

ca. 3.8- to 3.6-Ga-old Itsaq Gneiss Complex within

the Akulleq terrane (Nutman et al., 1996). The Itsaq

gneiss complex is dominated by tonalites and trond-

hjemites, but also comprises dioritic rocks, besides

rare granodiorites and granites, and was metamor-

phosed under middle to upper amphibolite facies and

locally granulite facies conditions during several early

and late Archaean episodes. The chemistry and Nd

isotopic signature of the 3.8 Ga TTG suite agrees with

an origin as slab melts (Nutman et al., 1996), whereas

late, 3.6-Ga sheets of biotite granite are interpreted as

partial melts of the TTG gneisses. A 3.6-Ga augen

gneiss suite that includes ferrodiorites and ferrogab-

bros was regarded by Nutman et al. (1984, p. 25) as

incomplete mixtures of melted deep sialic crust and

fractionated basic magma ponded at the crust–mantle

interface.

The Akulleq terrane also hosts the 2.8-Ga-old

Ikkattoq gneiss complex (McGregor et al., 1991) of

granodioritic composition, which is related to another

major, late Archaean event of subduction, continental

crustal accretion and regional thrusting. Widespread

anatexis and granite veining at 2.7 Ga in the Akulleq

and neighbouring Akia and Tasiusarsuaq terranes are

related to the assembly of the three terranes and re-

present the first common event that has been recog-

nised in all of them. The youngest Archaean event in

the Akulleq terrane is the intrusion at 2.55 Ga of the

Qorqut granite complex considered to have originated

by partial melting of older TTG gneisses (Friend et al.,

1985). Here, we present chemical data from the

tonalitic Itsaq gneiss complex (13 samples) and of

the augen gneiss suite (12 samples, Table 1, Fig. 2).

2.2. Mid-Archaean orthogneiss complexes at

Fiskefjord, Akia terrane

The high-grade gneiss–amphibolite terrain of the

Fiskefjord area in the central Akia terrane was

studied in detail by Garde (1997) and comprises a

high proportion of grey gneisses with TTG and

dioritic compositions that are intercalated with

amphibolites. The grey gneisses are interpreted as

arc-related magmas generated and accreted during

two major crust-forming events at around 3.2 and 3.0

Ga ago. The dioritic gneisses comprise the 3.2 Ga

Nordlandet diorites with calc-alkaline chemical char-

acteristics and the 3.04 Ga Qeqertaussaq diorite with

distinctly different chemistry, such as high P, Sr, and

Ba and fractionated REE patterns (La/YbNN20). The

latter rock unit contains abundant accessory apatite

besides equant calcite grains (0.1–0.5 mm in size),

which are apparently in equilibrium with the high-

grade metamorphic silicate assemblage. According to

Garde (1997), the chemistry of the TTG gneisses

agrees with an origin as slab melts, while a

considerable mantle component was probably

involved in the generation of the diorites. Garde

(1997) further suggested that the Qeqertaussaq diorite

has sanukitoid affinity, and that metasomatised

mantle was involved in the genesis of the precursor

magmas. Large homogeneous, late-kinematic com-

plexes with TTG compositions were interpreted as

variably fractionated slab melts, whereas several

bodies of late-kinematic granodiorite and granite are

probably the results of crustal remelting from local

grey gneiss sources.

Here, we include chemical data from 121 samples

of TTG gneisses in amphibolite, granulite and

retrogressed granulite facies, besides 20 samples of

Nordlandet diorites and 22 samples of the Qeqertaus-

saq diorite (Table 1, Fig. 2).

AR

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IN P

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SS

Table 1

Compositions of orthogneiss complexes in West Greenland (expressed as median element concentrations), compositions of two whole rocks and apatite from the Qaqarssuk carbonatite (north of the Fiskefjord area) and composition of apatite

from carbonatised mantle

Godth3bsfjord Fiskefjord Disko Bugt Nagssugtoqidian orogen Carbonatitic components

QaqarssukIlulissat Kangaatsiaq

Itsaq

gneiss

Ferrodiorite Amph.

facies

Granulite

facies

Retro

from

gran.

fac.

Nordlandet Qeqertaussaq Grey

gneiss

Ata

tonalite

Ilulissat

diorite

Calc-

alkaline

diorite

Sanukitoid

diorite

AQD AQD SIS SIS Monzo-

diorite

Shon-

kinite

320411

Rock

320511

Rock

320411

Apatite

320511

Apatite

Mantle

apatite

SiO2 N64% b64% N64% N64% N64% b64% b64% N64% N64% b64% b64% b64% N64% b64% N64% b64% b64% b64%

N 13 12 16 19 86 20 22 63 88 4 5 2 4 7 4 10 6 8 1 1

SiO2 69.79 54.37 71.58 70.56 70.74 57.08 59.23 69.74 69.33 61.98 57.89 55.04 66.99 57.59 70.12 59.62 49.37 38.46 3.34 8.24

TiO2 0.31 1.23 0.27 0.29 0.26 0.73 0.61 0.29 0.38 0.70 0.73 1.82 0.54 0.86 0.43 1.13 1.64 1.36 0.15 0.18

Al2O3 16.23 15.35 15.57 15.67 16.02 17.00 17.33 15.58 15.42 16.02 16.12 16.45 15.57 16.93 14.23 15.88 16.03 10.56 0.03 2.06

FeOa 2.12 8.14 1.84 3.34 1.69 7.26 5.49 2.35 2.80 6.15 7.83 7.88 3.30 6.09 3.50 7.73 9.53 9.52 8.76 2.94

MnO 0.03 0.13 0.04 0.06 0.03 0.13 0.11 0.03 0.04 0.10 0.14 0.11 0.07 0.13 0.05 0.10 0.12 0.16 0.35 0.24

MgO 0.94 3.06 0.58 0.95 0.72 3.67 3.03 0.83 1.08 2.76 4.11 4.11 2.06 3.15 1.26 2.72 4.53 7.58 14.97 4.69

CaO 3.57 6.05 2.95 3.80 3.08 7.69 5.64 3.06 3.39 5.79 7.28 5.76 4.07 6.48 3.78 5.74 6.72 13.23 30.28 42.36

Na2O 5.06 3.33 4.90 4.38 5.08 4.06 5.30 5.00 4.60 3.41 3.88 3.82 3.65 4.01 3.72 3.65 2.89 2.22 0.53 0.22

K2O 1.08 2.26 1.75 0.73 1.24 0.64 1.30 1.73 1.45 1.44 1.23 2.79 2.06 2.03 1.40 1.68 4.73 5.10 0.10 1.77

P2O5 0.08 0.40 0.09 0.11 0.08 0.17 0.36 0.10 0.11 0.17 0.15 0.69 0.16 0.42 0.12 0.31 1.60 3.73 4.40 6.79

LOI 0.64 0.79 0.17 0.33 0.36 0.52 0.83 0.50 0.70 0.96 0.54 1.11 0.20 0.31 0.39 0.27 1.14 5.16 35.85 28.29

Mg# 0.46 0.27 0.38 0.40 0.43 0.46 0.49 0.39 0.40 0.44 0.48 0.48 0.47 0.48 0.39 0.44 0.47 0.61 0.80 0.79

Ba 136 202 508 364 676 212 1375 457 415 357 150 953 1695 1053 938 1697 7771 6233 53 1185

Co 36 36 21 72 62 55 40 6 60 52 45 24 35 20 11

Cr 14 18 10 11 7 75 29 18 41 102 72 45 32 28 16 31 39 163 0 0

Cu 3 50 5 10 8 14 21 7 8 49 31 26.5 26 26 14 20 22 70 21 68

Ga 22 25 18 18 18 20 22 20 19 21 19 19 19 20 18 2 9

Hf 3.1 1.8 2.8 2.0 2.0 2.7 2.0 4.0 4.5 3.6 4.7 9.0 10.0

Nb 1.5 5.6 3.6 3.0 2.1 5.5 5.4 4.3 4.1 6.0 10.0 3.5 10.2 8.9 23.0 8.0 57.0

Ni 17 38 6 9 5 52 24 9 8 57 29 44 14 18 10 15 19 123 0 13

Pb 10 18 20 7 12 7 18 13 10 9 8 35 73 99 6

Rb 37 35 77 2 11 3 10 63 47 59 14 114 47 60 16 27 94 109 0 33

Sc 5 15 3 8 5 18 14 4 4 15 5 15 10 17 21 12 38 12

Sr 416 259 376 300 681 223 1185 387 422 238 230 1138 598 952 382 583 3182 3372 3381 8295 5560 5560 13175

Th 0.7 1.3 3.5 b0.5 b0.5 b0.5 0.7 6.7 6.1 4.0 3.0 5.0 1.5 1.2 8.4 36.5 0.0 3.0 170

U 0.3 1.1 0.7 b0.5 b0.5 b0.5 b0.5 b0.5 0.9 0.5 0.5 0.0 102

V 20 115 18 31 24 141 105 33 11 105 121 109 61 121 48 123 170 117 103 14

Y 3.5 38.7 5.5 5.0 2.0 19.0 16.0 5.8 8.8 26.5a 21.0 17.0 8 19 11 22 38 48 28 76 125

Zn 50 85 45 53 41 86 92 66 65 93 94 112 68 87 41 96 115 154 51 102

Zr 122 147 94 126 104 114 113 114 122 175 125 132 110 248 210 517 12 56 9

La 5 18 16 14 13 12 45 21 22 17 13 88 35 32 14 34 300 644 168 542 1535 1167 1761

Ce 11 54 26 22 19 22 75 40 42 34 35 176 64 70 30 68 532 1430 663 997 3005 2497 4620

Nd 6 37 10 10 8 12 34 12 20 12 24 81 26 42 15 42 230 731 186 497 1312 1185 1036

Sm 1.3 7.4 1.7 1.5 1.3 2.8 6.2 2 3.7 2.8 6.4 12.2 3.5 7 33 88 29 60 219 201 104

Eu 0.5 1.2 0.5 0.9 0.7 1.0 1.7 0.6 1.0 1.0 1.6 2.9 1.5 1.9 7.0 19.4 6.7 14.3 51.6 49.5 32

Tb 0.2 0.6 0.1 0.3 0.2 0.5 0.7 0.0 0.4 0.0 1.0 0.9 0.3 0.7 2.3 4.2 1.6 4.0 14.6 14.8 60

Yb 0.3 2.5 0.4 0.6 0.4 1.6 1.4 0.4 0.8 2.3 3.0 1.1 1.2 1.9 1.0a 1.9a 2.6 2.5 0.9 3.6 5.5 5.1 6.2

Lu 0.0 0.3 0.1 0.1 0.1 0.2 0.2 0.1 0.1 0.4 0.4 0.1 0.2 0.3 0.4 0.3 0.5 0.8 0.6 0.9

Sr/Y 134.0 6.0 74.8 61.8 357.5 12.2 76.2 62.0 50.0 9.2 58.4 14.9 111.0 43.7 36.7 26.5 83.5 67.7 121 109

(La/Yb)N 13.1 6.0 26.6 13.0 54.1 4.8 23.3 32.7 26.9 5.8 54.0 3.1 30.3 9.3 11.9 15.1 83.1 211 129 104 193 158 197

N : number of samples.

AQD: Arfersiorfik Quartz Diorite (Kalsbeek, 2001). SIS: Sisimiut Intrusive Suite.

Godth3bsfjord data from Nutman et al. (1984, 1996). Qaqarssuk data from Knudsen (1991). Composition of mantle apatite from Belousova et al. (2002).aCalculated concentration of Y or Yb using Y=11.6Yb ; the equation is based on the regression of all TTG gneiss samples for which both Y and Yb have been determined.

A.Steen

feltet

al./Lith

osxx

(2004)xxx–

xxx6

ARTICLE IN PRESS

2.3. Late Archaean TTG complexes in the Disko

Bugt region

The study area comprises the Kangaatsiaq and

Ilulissat areas, collectively termed the Disko Bugt

region (Garde and Steenfelt, 1999). The Archaean

basement of the presumed northern continent, in

relation to the inferred Nagssugtoqidian suture zone,

is dominated by TTG orthogneiss complexes with

protolith ages of around 2.8 Ga. The most common

lithology is deformed, polyphase, biotite orthogneiss

in amphibolite facies, except for a few patches in the

southern part of the study area, where granulite facies

conditions were attained. Other lithologies in this

region comprise Archaean, as well as Palaeoproter-

ozoic supracrustal sequences. In the Ilulissat area, two

homogeneous granitoid complexes have been distin-

guished during geological mapping, namely, the Ata

tonalite and the Rodebay granodiorite (Garde and

Steenfelt, 1999; Kalsbeek and Skjernaa, 1999). The

former has TTG chemical characteristics, whereas the

latter has more potassium than typical TTG gneiss and

is not included in this study. Quartz–dioritic to dioritic

orthogneisses are subordinate in the entire region,

making up less than 5% of the outcrop area. Their

field relations show that they are generally older than

the TTG gneisses. Two kinds of dioritic enclaves have

been distinguished: one with calc-alkaline chemistry

and poorly fractionated REE patterns (La/YbNb5 )

and one with fractionated REE (La/YbNN40) and

elevated K and Sr. The latter has tentatively been

considered to be of sanukitoid affinity (Steenfelt et al.,

2003).

The entire region appears to have experienced

crustal melting at ca. 2.7 Ga, whereby small granite

bodies, pegmatite sheets and widespread migmatites

were formed. Palaeoproterozoic heating, on the other

hand, has only rarely resulted in melting.

The chemical data presented here (Table 1, Fig. 3)

comprise 87 samples of grey gneiss with TTG

composition, 88 samples of the Ata pluton and 13

samples of diorite, including 2 with sanukitoid affinity.

ARTICLE IN PRESS

Fig. 3. Simple Precambrian geology and sample locations in the Disko Bugt region with the towns Kangaatsiaq and Ilulissat.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx8

2.4. Palaeoproterozoic calc-alkaline metaigneous

complexes of the Nagssugtoqidian orogen

The Nagssugtoqidian orogen contains the two

juvenile Palaeoproterozoic, calc-alkaline Arfersiorfik

and Sisimiut magmatic complexes. Both were

emplaced between 1.92 and 1.87 Ga, presumably

during the subduction of oceanic crust preceding

continent–continent collision (Kalsbeek and Nutman,

1996; Connelly et al., 2000; van Gool et al., 2001).

The Arfersiorfik complex, which embraces both

intermediate metavolcanic rocks and an intrusive

quartz–diorite, is interpreted as the extrusive and

intrusive members of a volcanic arc. The Sisimiut

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Fig. 4. Simple geology and sample locations in the central Nagssugtoqidian orogen (Arfersiorfik and Sisimiut complexes). The sample locations

to the west of the main Arfersiorfik complex are from folded sill-like intrusions that are not shown at this scale.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 9

complex is a suite of gabbroic, dioritic to granodior-

itic, and monzodioritic to syenitic rocks interpreted as

continental arc rocks. The extent of the Sisimiut

complex is not known in detail, and Fig. 4 only shows

an approximate outline.

Chemical data from the two Palaeoproterozoic

complexes, for which a mantle wedge origin is most

likely, are included here for comparison with similar

Archaean lithologies, for which the involvement of

mantle in their origin is suspected. The chemical

data set included in this paper (Table 1, Fig. 4)

comprises 11 samples from the Arfersiorfik quartz–

diorite (Kalsbeek, 2001) and 20 samples from the

Sisimiut complex (Kalsbeek and Nutman, 1996),

including six monzodiorite samples (Steenfelt, 1994,

1996).

3. Geochemical signatures of grey gneisses in West

Greenland

The gneiss samples from each of the regions

outlined in the previous section are divided into

groups and are plotted on Figs. 6–12 according to

their chemistry and field unit. Following Moyen et

al. (2003) and Martin et al. (2005), samples with

N64% SiO2, Na2O between 3% and 7%, and K2O/

Na2O b0.5 are designated TTG. They make up the

largest number by far of the sample collections from

the Archaean regions. Samples with quartz–dioritic,

monzodioritic and dioritic compositions have SiO2

between 50% and 64%. In the following, quartz–

diorites and diorites are collectively termed diorites.

3.1. TTG gneisses

The diagrams in Figs. 5–7 illustrate that the

Archaean TTG gneiss samples exhibit the general

TTG characteristics of lowMgO and Cr, and high Sr/Y,

but there are also some regional differences. Among the

three Archaean TTG groups, those from Godth3bsfjordhave the lowestMgO, Sr/Yand Cr. The range of Sr/Y in

the Fiskefjord TTGs reaches much higher values than

in the other regions, while the TTGs of the Ata pluton

have higher Cr concentrations than the remaining TTG

suites, both from within and outside the Disko Bugt

region. The high-SiO2 members of the calc-alkaline

Palaeoproterozoic plutonic rocks from the Nagssugto-

qidian orogen are only slightly more enriched in MgO

and Cr than the Archean TTG suites are, but their Y

concentrations reach higher values.

The Ata tonalite is associated in space and time

with bimodal acid-mafic volcanic rocks in a

volcanic arc setting (Garde and Steenfelt, 1999).

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Fig. 5. Variations in SiO2–MgO for orthogneisses and diorites within one Palaeoproterozoic and three Archaean regions and in southern and

central West Greenland. Scales show concentrations in percent. Average Archaean TTG from Martin (1994). C-A: calc-alkaline. Nag orogen:

Nagssugtoqidian orogen. AQD: Arfersiorfik quartz–diorite. SIS: Sisimiut intrusive suite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx10

The major-element characteristics classify the Ata

tonalite as a TTG suite, but it has a higher CaO/

Na2O ratio than the other grey gneisses of the

Ilulissat area, and the elevated Cr may reflect

involvement of mantle wedge material in its

genesis. Alternatively, the Ata protolith, which was

emplaced into a very high crustal level (Garde and

Steenfelt, 1999; Kalsbeek and Skjernaa, 1999),

could have been contaminated during its ascent

through the mafic volcanic complex within which it

resides.

In summary, the Archaean TTG gneisses from each

of the three areas are similar with regard to the elements

depicted in Figs. 5–7, and except for the 2.8 Ga Ata

tonalite, they may be assumed to have derived from

slab melting without significant contribution from a

mantle wedge.

3.2. Diorites

The dioritic rocks vary widely in the components

depicted in Figs. 5–7. With regard to Mg and Cr, the

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Fig. 6. Variations in SiO2–Cr for orthogneisses and diorites within one Palaeoproterozoic and three Archaean regions and in southern and central

West Greenland. Reference line indicates upper limit of TTG field and separates the Ata tonalite from the other TTG gneisses. SiO2 in percent,

Cr in ppm. Average Archaean TTG from Martin (1994). C-A: calc-alkaline. Nag orogen: Nagssugtoqidian orogen. AQD: Arfersiorfik quartz–

diorite. SIS: Sisimiut intrusive suite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 11

highest values relative to SiO2 are displayed by the

Nordlandet diorites of the Fiskefjord region. The

ferrodiorites of Godth3bsfjord have the lowest

concentrations of MgO and Cr, and the remaining

diorites have intermediate and mutually similar

variations. In Fig. 7, the diorites show important

differences; most of the dioritic units have low Sr/Y

combined with high Y, i.e., the characteristics of

calc-alkaline diorites. The exceptions are the Qeqer-

taussaq diorites, the high-K diorites of Kangaatsiaq

and the Sisimiut monzodiorites, in particular, which

are displaced towards higher Sr/Y values at the same

Y values. In Fig. 8, the same three diorite units are

seen to have elevated (La/Yb)N relative to the other

diorites, which have a low (La/Yb)N typical of calc-

alkaline rocks.

In summary, the most common dioritic rocks in this

study display moderately high Sr contents (up to 500

ppm), their REE patterns are poorly fractionated (La/

YbN V10), and in La/Yb vs. Yb or Sr/Yvs. Y diagrams,

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Fig. 7. Variations in Y–Sr/Y for orthogneisses and diorites within one Palaeoproterozoic and three Archaean regions and in southern and central

West Greenland. Y (x-axis) in ppm. C-A: calc-alkaline. Nag orogen: Nagssugtoqidian orogen. AQD: Arfersiorfik quartz–diorite. SIS: Sisimiut

intrusive suite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx12

they plot in the bmodern calc-alkalineQ field of Martin

(1994). They have variable but generally high Cr and

Mg contents; they also have highMg#. By contrast, the

Qeqertaussaq diorite of Fiskefjord area, the

dsanukitoidT diorite of Disko Bugt and the Nagssugto-

qidian monzodiorites display very high Sr contents

above 1000 ppm, strongly fractionated REE patterns

(La/YbN N20) and high Sr/Y; that is, they plot in the

TTG or sanukitoid field (Martin, 1994; Moyen et al.,

2003). Generally, their Cr and MgO contents are equal

to, or lower than, those of the calc-alkaline diorites

within the same area.

4. Discussion

4.1. Sr enrichment in TTG gneisses

Martin and Moyen (2002) investigated the Sr

concentrations of Archaean TTGs and found evidence

that Sr increases relative to CaO+Na2O with decreas-

ing age. The corresponding data for Greenland, shown

in Fig. 9, do not sustain an inverse correlation

between age and Sr content. The highest Sr values

in the Greenlandic TTGs are found within the 3.2–3.0

Ga Fiskefjord region, where also many Qeqertaussaq

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Fig. 8. Variations in YbN–(La/Yb)N for orthogneisses and diorites within one Palaeoproterozoic and three Archaean regions and in southern and

central West Greenland. C-A: calc-alkaline. Nag orogen: Nagssugtoqidian orogen. AQD: Arfersiorfik quartz–diorite. SIS: Sisimiut intrusive suite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 13

diorite samples are enriched in Sr. The much older

TTGs from the Godth3bsfjord region are very low in

Sr, and also the TTGs of the 2.8 Ga Disko Bugt region

are lower in Sr, although a few diorite samples from

the latter region are enriched in Sr.

This observation is apparently in contradiction to

the conclusion of Martin and Moyen (2002), who

proposed that an increasing Sr content during the

Archaean was related to an increasing depth of melting.

Instead, we observe that Sr enrichment is related to

particular sections of the West Greenland crust, i.e., the

Akia terrane and the Nagssugtoqidian orogen.

The Sr enrichment in the TTG and dioritic gneisses

from the Fiskefjord region requires a closer look.

Garde (1997) subdivided the samples from this region

according to their metamorphic grade into amphibolite

facies, granulite facies and those retrogressed from

granulite to amphibolite facies and also identified the

distinctive chemistry of the Qeqertaussaq diorite. Fig.

9 shows that Sr is correlated with Na2O in all the three

metamorphic TTG groups, but that the trend is steeper

for the granulite facies and retrogressed granulite

facies samples (Fig. 9a). Based on petrography, whole

rock and mineral chemistry, Garde (1997) argued that

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Fig. 9. Correlation between Na2O (%) and Sr (ppm) in TTG

gneisses in granulite (upper diagram) and amphibolite facies (lower

diagram).

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx14

the elevated Sr contents in the retrogressed gneisses

were due to the migration of Sr during retrogression,

along with K, Rb and Na. The same author showed

that the Sr enrichment in the Qeqertaussaq diorite is

accompanied by enrichment in P2O5, Ba, La, La/Yb

and K2O (see later). A similar pattern is observed in

some of the TTG gneisses within the outcrop area of

the Qeqertaussaq diorite, and we therefore suggest that

these TTG gneisses are genetically related to the

Qeqertaussaq diorite; accordingly, their high Sr con-

centrations may be primary and not due to metamor-

phic migration.

4.2. Sr enrichments in diorites

The diorites with sanukitoid-like signatures are

distinguished by unusually high Sr (Table 1, Figs. 7

and 10). In Fig. 11, we show that the Sr enrichment

is correlated with enrichment in P, Ba, La, La/Yb

and K. The concentrations of these elements in the

most enriched diorites are much higher than those

obtained in experimental slab melts that have

assimilated peridotitic mantle (Rapp et al., 1999).

The enriched diorites contain carbonates, and a high

Sr–Ba–P–REE signature with highly fractionated

REE spectra is also characteristic of carbonatites,

as illustrated in Fig. 11 by data for the Qaqarssuk

carbonatite and apatite (Knudsen, 1991), as well as

from carbonatite-metasomatised lherzolite (O’Reilly

and Griffin, 1988, 2000).

4.3. Evidence for a relationship between Sr-enriched

diorites and carbonatites in West Greenland

The Archaean craton in southern West Greenland

has been the site of recurrent carbonatitic magmatism

since the Archaean (Larsen and Rex, 1992). Two

major carbonatite complexes, Qaqarssuk (ca. 0.17 Ga;

Knudsen, 1991) and Sarfartoq (ca. 0.6 Ga; Secher and

Larsen, 1980), and a minor one, Tupertalik (3.0 Ga;

Larsen and Pedersen, 1982; Bizzarro et al., 2002), lie

between the Fiskefjord area and the Palaeoproterozoic

rocks of the Nagssugtoqidian orogen. In addition,

potassic lamprophyres with a high carbonate content

(termed shonkinites by Larsen and Rex, 1992) were

intruded into the southern foreland of the Nagssugto-

qidian orogen, close to the Sarfartoq carbonatite

complex (Fig. 1). Their chemistry strongly resembles

that of Palaeoproterozoic monzodiorites within the

central part of the Nagssugtoqidian orogen, and they

are probably coeval with the latter rocks, having

yielded an imprecise Palaeoproterozoic age (Larsen

and Rex, 1992). It therefore appears that the litho-

spheric mantle in this part of Greenland has been

prone to produce carbonate-rich melts since, at least,

3.0 Ga ago; by contrast, carbonatites have not been

recorded in either of the adjacent Godth3bsfjord and

Disko Bugt regions.

The carbonatites of the Akia terrane and north-

wards comprise calcio- and magnesiocarbonatites

with subordinate ferrocarbonatites. They are rich in

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Fig. 10. Variations in CaO+Na2O–Sr for orthogneisses and diorites within one Palaeoproterozoic and three Archaean regions and in southern

and central West Greenland. CaO+Na2O in percent, Sr in ppm. Notice shift of the Sr scale for the Nag orogen. C-A: calc-alkaline. Nag orogen:

Nagssugtoqidian orogen. AQD: Arfersiorfik quartz–diorite. SIS: Sisimiut intrusive suite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 15

apatite, phlogopite and magnetite and have high

concentrations of REE (Larsen and Rex, 1992). These

features are shared by the shonkinites, although the

latter have much more phlogopite and feldspar than

the former does. The bulk chemistry of the carbo-

natites and shonkinites reflects their mineralogy;

consequently, very high concentrations of P, Sr, Ba

and REE are recorded (Table 1, Fig. 12).

Although the origin of carbonatitic magmas is not

fully understood, it is generally assumed that they

form by melting of a modified (enriched or meta-

somatised) mantle source. Studies of mantle xenoliths

suggest that carbonatite-related metasomatism is

widespread, and chemical analyses of mineral phases

in the metasomatic products, such as carbonates and

apatite, confirm that such metasomatism is accom-

panied by a marked enrichment in LREE, Sr, Ba and

Rb (O’Reilly and Griffin, 1988; Ionov et al., 1993;

Rudnick et al., 1993; Kogarko et al., 1995). Likewise,

apatite residing in metasomatised mantle is very rich

in Sr, U, Th and LREE (Table 1, Fig. 12; O’Reilly and

Griffin, 2000; Xu et al., 2003).

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Fig. 11. Correlation between Sr (ppm) and La (ppm), REE fractionation, Ba (ppm), K2O (%) and P2O5 (%) in normal calc-alkaline (Nordlandet

diorite) and Sr-enriched diorites. The enrichment trends towards the position of carbonatite, apatite in carbonatite and apatite in lherzolite.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx16

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Fig. 12. Chondrite-normalised REE spectra. Upper diagram: Archaean Sr-enriched diorites, Qeqertaussaq diorite and Kangaatsiaq dsanukitoidTdiorite have intermediate positions between TTG and Nordlandet diorite and carbonatite and carbonatite-related apatites. Lower diagram: The

monzodiorite from the Nagssugtoqidian (Nag) orogen has REE spectra similar to shonkinite (Palaeoproterozoic lamprophyre in the

Nagssugtoqidian foreland) and carbonatite and carbonatite-related apatites.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 17

The almost linear trends in the variation dia-

grams of Fig. 11, from a normal calc-alkaline

diorite composition (exemplified by the Nordlandet

diorites) towards the compositions of carbonatite

and apatite in carbonatised mantle, suggest that the

parental magmas of the Sr- and P-rich diorites and

shonkinites in West Greenland have incorporated

variable to high amounts of carbonatised mantle.

Because the Palaeoproterozoic arc magmas of the

Nagssugtoqidian orogen are probably mantle

derived, their carbonatitic signature is assumed to

reflect the presence of carbonatitic components in

the melt source area of the mantle. The carbonatitic

component is probably unevenly distributed because

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A. Steenfelt et al. / Lithos xx (2004) xxx–xxx18

only some of the arc magmas, namely, the

monzodiorites and shonkinites, are enriched in this

component.

Fig. 12 demonstrates that the shape of the REE

patterns in the Sr-enriched diorites resembles that of

carbonatite-related apatite; apatite is probably the

main REE host within these diorites. The very

strongly fractionated REE signature distinguishes

carbonatitic and mantle-derived apatites from apatites

of other lithologies (Belousova et al., 2002). Although

the Archaean Sr-enriched diorites are less enriched

than their Palaeoproterozoic counterparts are, they

occupy similar positions in Fig. 11 and possess

similarly shaped REE-spectra (Fig. 12), which sug-

gests that they have a similar petrogenesis.

Evidence for carbonatite emplacement in a sub-

duction setting is provided from a study of the 2.7-Ga-

old alkaline Skjoldungen igneous province in southern

East Greenland, some 500 km southeast of Fiskefjord

(Blichert-Toft et al., 1995). Still farther to the east, on

the eastern Lewisian part of the North Atlantic craton,

subduction-related mela-syenites have a similar high

Sr–Ba–P–REE signature with extremely high concen-

trations of these elements. Themela-syenites have been

interpreted by Tarney and Jones (1984) as resulting

from partial melting of an apatite–phlogopite–carbo-

nate–veined mantle wedge.

We therefore propose that subduction-related

diorites that carry a carbonatite-related geochemical

signature are derived from melting within a mantle

wedge containing domains or patches of apatite-

and carbonate-rich materials or from the interaction

of slab-derived magma with such metasomatised

mantle.

4.4. Greenlandic carbonatite-enriched diorites and

sanukitoids

The Greenlandic diorites (both normal and

enriched) examined in this study have Mg# less than

0.6 and generally moderate Cr contents; that is, they

are not high-Mg diorites or sanukitoids in the sense

proposed by Shirey and Hanson (1984). Models for

the genesis of sanukitoids implicate interaction

between slab melts and mantle to explain their

combined elevated LILE and Mg–Cr–Ni concentra-

tions and steep REE patterns. However, in our view,

such models can only explain the high P2O5 observed

in the enriched diorites from West Greenland, as well

as the extremely high concentrations of Sr, Ba and

REE (i.e., not only LREE), as well as carbonate

contents observed in some of the enriched diorites

(Table 1), if the involved mantle was different from

normal peridotite. Even if it is accepted that the least

enriched of the sanukitoid-like diorites, namely, the

Qeqertaussaq diorite, could be generated in the same

way as current models proposed for other sanukitoids

(despite its low MgO, Ni and Cr contents), a different

petrogenetic model would still have to be adopted for

the Palaeoproterozoic enriched diorites. Our preferred

model, which essentially ascribes the high Sr–Ba–P–

REE signature to incorporation of mantle-derived

apatite, phlogopite and carbonate, can be applied to all

rocks with this signature that are presented in this

study.

In the diagrams of Fig. 13, it can be observed that

sanukitoids of the Superior province (Shirey and

Hanson, 1984; Shirey and Hanson, 1986; Stern et al.,

1989) share their high Sr and P and the correlation

between Sr and REE fractionation with the enriched

diorites in West Greenland (Fig. 13a), while sanuki-

toids from other parts of the world, such as the

Dharwar and Pilbara cratons, do not (Fig. 13b; Reddy,

1991; Krogstad et al., 1995; Smithies and Champion,

2000). It therefore remains possible that the mantle

involved in the generation of the Sr- and P-rich

sanukitoids of the Superior Province was also

carbonatite metasomatised, as suggested here for

several parts of the North Atlantic craton. It may also

be speculated that the chemical differences among the

abovementioned sanukitoids reflect craton-scale dif-

ferences in the chemical character of the underlying

lithospheric mantle.

5. Conclusions and implications

(1) Archaean TTGs in West Greenland have uni-

form compositions, close to the average Arch-

aean TTGs of Martin (1994). The TTG

complexes range in age from 3.8 to 2.8 Ga.

Chemical differences, e.g., in Sr, Mg or Cr

concentrations, are observed between terranes,

but the variations cannot be related to emplace-

ment ages. The chemistry of the suites is

compatible with more or less pure slab melting,

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Fig. 13. Comparison of Qeqertaussaq diorite with sanukitoids; all samples shown have SiO2 less than 64%. Upper diagrams: Sanukitoids from

Superior craton (Shirey and Hanson, 1984; Stern, 1989) show same order of Sr and P enrichment, as well as REE fractionation, as the

Qeqertaussaq diorite from Fiskefjord does. Lower diagrams: Sanukitoids from Dharwar and Pilbara cratons have less Sr and P2O5.

A. Steenfelt et al. / Lithos xx (2004) xxx–xxx 19

although elevated Cr in the Ata complex might

reflect mantle involvement. Slab melting appa-

rently prevailed throughout Archaean times.

(2) Diorites of calc-alkaline composition with mod-

erate to high Mg and Cr contents and flat

chondrite-normalised REE spectra are also sim-

ilar irrespective of age and location, implying

that mantle melting has been active since 3.6 Ga.

(3) Some subduction-related diorites, quartz–dio-

rites and monzodiorites of various ages are

enriched in Sr, Ba, P and REE, have fractionated

REE patterns, and occur in a certain section of

the Archaean crust, where carbonatites and

carbonatitic lamprophyres have been generated

in both subduction and cratonic environments

since at least 3.0 Ga. The REE spectra of the

enriched diorites are governed by apatite, and we

propose that their parental magmas resulted from

partial melting of carbonatite-veined parts of a

mantle wedge.

(4) The abundance of Sr in magmas is not tied

exclusively to plagioclase; in this study, we have

shown that when, e.g., apatites and carbonates

are involved in the magma genesis, they strongly

influence Sr concentrations. This implies that

care must be taken when Sr is used as indicator

of plagioclase stability.

(5) Some care should also be exercised when using

the term bsanukitoidQ: There are Mg-rich diorites

in the Archaean which are not sanukitoids. In

West Greenland, the carbonatite-related diorites

exhibit compositions which, in some respect,

resemble that of sanukitoids, but their genesis

requires a phosphorus-bearing component that is

not accounted for in current genetic models for

sanukitoids. However, in the light of the present

investigation, it is possible that the geochemical

signature of some of the rocks classified as

sanukitoids in the literature also reflects involve-

ment of variably carbonatised mantle.

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A. Steenfelt et al. / Lithos xx (2004) xxx–xxx20

Acknowledgements

This investigation has made use of partly

unpublished chemical analyses derived from data-

bases of the Geological Survey of Denmark and

Greenland. In addition to data acquired by the

authors, samples and analyses have been acquired

by Feiko Kalsbeek (Ata tonalite, Arfersiorfik quartz-

diorite, Sisimiut quartz-diorite), Hanne Tv&rmose

Nielsen and Lotte M. Larsen (shonkinites), Jeroen

van Gool, Sandra Piazzolo and Kristine Thrane

(orthogneisses from the Kangaatsiaq area). The

authors are grateful for constructive criticism by

W. L. Griffin and R. P. Rapp. The Geological

Survey of Denmark and Greenland authorised the

publication of this manuscript.

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