Noble gases in the Finero phlogopite-peridotites,western Italian Alps

Takuya Matsumoto a,*, Tomoaki Morishita b, Jun-ichi Matsuda a, Toshiyuki Fujioka a,1,Masamichi Takebe c,2, Koshi Yamamoto c, Shoji Arai b

aDepartment of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, JapanbGraduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan

cDepartment of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Chikusa,

Nagoya, 464-8602, Japan

Received 21 January 2005; received in revised form 16 June 2005; accepted 3 July 2005

Available online 10 August 2005

Editor: K. Farley

Abstract

Here we report results from an investigation of noble gases in a specimen with layers of very fine-grained apatite andorthopyroxene from the Finero ultramafic complex, western Italian alps. We have also examined fresh olivine grains

separated from phlogopite-harzburgites without an apatite layer. Fluid inclusions of these olivine separates appeared richin radiogenic components such as 4He, 21Ne and 40Ar, suggesting the derivation of fluids from a crust-like reservoir. Such acrust-like component also appeared to be contained in the samples with the apatite-opx layer, however, an additional

isotopically distinct component is necessary to explain progressive increases in 3He concentration and decreases in 40Ar / 36Arratios observed approaching the apatite-rich layer. High 3He contents and low 40Ar / 36Ar ratios are consistent with thesignature expected for slab-derived metasomatic fluids. There is a clear mixing trend defined in a 3He / 36Ar vs. 40Ar / 36Ar

diagram with crustal and slab-derived fluids as end-member compositions, suggesting that the complex was metasomatisedby fluids derived from geochemically distinct regions and distinct geotectonic settings. The parent melt or fluids responsiblefor the formation of the apatite-rich layer should be derived from the slab-derived component, which is consistent with thenotion that the Finero mantle was once in the mantle wedge. An in situ component produced in the previously

0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.epsl.2005.07.005

* Corresponding author. Tel./fax: +81 6 6850 5541.

E-mail addresses: matsumoto@ess.sci.osaka-u.ac.jp (T. Matsumoto), moripta@kenroku.kanazawa-u.ac.jp (T. Morishita),

matsuda@ess.sci.osaka-u.ac.jp (J. Matsuda), toshiyuki.fujioka@anu.edu.au (T. Fujioka), takebe@matsue-ct.jp (M. Takebe),

hamchans@nagoya-u.jp (K. Yamamoto), ultrasa@kenroku.kanazawa-u.ac.jp (S. Arai).1 Current address: Research School of Earth Science, The Australian National University, Canberra, ACT0200, Australia.2 Current address: Department of Sciences, Matsue National College of Technology, 14-4, Nishi-ikuma-cho, Matsue, Shimane, 690-8518,

Japan.

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www.elsevier.com/locate/epsl

metasomatised portion of lithospheric mantle, or fluid released from surrounding metamorphic rocks during exhumation arepossible sources for the crust-like component.

D 2005 Elsevier B.V. All rights reserved.

Keywords: noble gas; isotope; mantle metasomatism; subducting slab; subcontinental mantle; He-3/He-4; Finero

1. Introduction

Increasing interest in the noble gas compositionsof the lithospheric part of the upper mantle hasstimulated many investigations of peridotite xenolithsin alkali basalts or of orogenic peridotites (e.g., [1–13]). These studies have identified the subcontinentallithospheric mantle (SCLM) reservoir as a uniquereservoir in which diverse noble gas elemental andisotopic components distinct from those in the sub-lithospheric reservoirs have been built up reflectingprocesses over a long term isolation from the mantleconvection. Previous studies on mantle-derived xeno-liths from Australia identified two distinct noble gascomponents in the SCLM. The first is a trappedcomponent which is often stored in fluid inclusionswith 3He / 4He ratios being indistinguishable fromthose of the convecting upper mantle (8F1 Ra;(eg., [14]); Ra denotes the atmospheric 3He / 4He).The second is a radiogenic and/or nucleogenic com-ponent produced in situ as a result of cryptic ormodal metasomatism which re-fertilized the SCLM.This component is recognized most clearly in thecrystal structure of metasomatic minerals whichoften host noble gas producing radioactive parentssuch as U, Th and K. However, some xenoliths,especially those from the central European litho-spheric mantle, are reported to show significantenrichments in radiogenic noble gases in fluid inclu-sions with characteristically low 3He / 4He ratios of6.3F0.4 Ra[11,12]. This necessitates the fluxing offluids that had already been enriched in radiogenicnoble gases derived from some homogeneous sub-continental reservoirs. Even lower 3He / 4He ratios arefound in xenoliths from far eastern Russia indicatingaddition of fluids with a very low 3He / (U+Th) ratiosassociated with dehydration of a subducting plate[10]. The SCLM is also suggested to be a storagefor the heavier atmospheric noble gases (e.g., Ar)recycled by subduction of a hydrated oceanic plateand its sedimentary cover [7,10]. Thus, it is becoming

clear that the sources and processes responsible fordeveloping peculiar noble gas signatures of theSCLM reservoir are diverse and these issues needto be clarified.

As to the fundamental process of noble gas intro-duction to the SCLM, there is no doubt that thefluxing of metasomatising melts or fluids throughthe SCLM play a key role in modifying its noblegas compositions [1,4,12]. Ineffective diffusivemovement of noble gases within the mantle [15],as well as the occurrence of noble gases in fluidinclusions of mantle minerals (e.g., [10]), requiresadvection of melt charged with noble gas through themantle. These melts should also be responsible forcausing modal or cryptic metasomatism with suchevidence usually found in mantle xenoliths and oro-genic peridotites (e.g., [16,17]). However, there hasbeen only limited direct evidence found so far formetasomatic introduction of noble gases to theSCLM (e.g., [5,8]).

This paper presents new noble gas data obtainedfrom a unique specimen with a distinct apatite-richlayer in a phlogopite-peridotite matrix (Fig. 1). Thespecimen was from the Finero phlogopite-peridotitebody in western Italy. The complex is famous for

Fig. 1. Photograph of phlogopite-peridotite (sawed surface) with the

apatite-rich layer. Labels indicate sample names for noble gas

analysis. Detailed petorographic description of this sample can be

found in Morishita et al. [28].

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 131

the occurrence of unweathered and unaltered oro-genic peridotites, and is believed to be a highlymetasomatised slice of mantle, indicated by theoccurrence of ubiquitous phlogopite and otheraccessory metasomatic phases. The formation ofthe thin apatite-rich layer in the phlogopite-perido-tite matrix is most likely associated with the infil-tration of carbonatitic metasomatizing fluids throughthe peridotitic body. Availability of such a sampleenables us to directly investigate effects of metaso-matism on noble gas signatures within the mantlelithosphere.

2. Sampling and analysis

The Finero mafic–ultramafic complex lies withinthe north-western, basal portion of the Ivrea zone ofthe Italian western Alps. The complex has beendivided into four main units: (1) upper metagabbro,(2) amphibole-peridotite, (3) lower metagabbro, and(4) phlogopite-peridotite [18,19]. They have beenfolded into a tight antiform. The peridotite unitsshow different structural and geochemical character-istics [20,21]. In general, the phlogopite-peridotite

consists of dunite and harzburgite, with smallamounts of chromitite and clinopyroxenite. Plati-num-group minerals and zircon are found withinthe chromitite [22,23]. Zanetti et al. [24] reportedthat apatite and carbonate appear to be randomlydistributed within the phlogopite-peridotite unit.The country rock of the Finero mafic–ultramaficcomplex is the Kinzigite Formation, which consistsof metamorphic wackes, pelites, marbles and volca-nic rocks [25–27].

In this study, noble gas isotopic compositions ofa phlogopite-peridotite with an apatite-rich layer ofb1 cm thickness was targeted. The sample wastaken from a large boulder buried in river sedi-ments, 0.7!0.4!0.3 m in size, from the Canno-bino River to the west of Finero village. The thinlayer consists of very fine-grained olivine, orthopyr-oxene, spinel, amphibole, phlogopite, sulfide miner-als, and apatite, with small amounts of carbonateand clinopyroxene. In the apatite-rich layer, amphi-bole and carbonate minerals are more abundant thanin the apatite-poor portion, suggesting that an alkali-and phosphate-rich carbonatitic metasomatisingagent existed within the thin layer. A detailed pet-rological investigation of this specimen has already

Table 1

He, Ne and Ar in olivine separates from two Finero Hazburgites (without apatite-opx veins)

FIN-OL1 FIN-OL2

Step-heating Crushing Crushing

800 8C 1800 8C Total

[4He] 1.33 4.34 5.66 2.89 0.45

(10"6 cm3 STP/g) F0.14 F0.44 F0.46 F0.29 F0.053He / 4He 0.155 0.157 0.156 0.155 0.156

(R/Ra) F0.007 F0.004 F0.003 F0.006 F0.008

[22Ne] – 16 4.9 –

(10"12 cm3 STP/g) F4 F0.720Ne / 22Ne 10.1 9.35

F1.3 F0.5921Ne / 22Ne 0.0682 0.0870

F0.0088 F0.0053

[36Ar] 5.8 5.9 11.8 3.7 0.098

(10"10 cm3 STP/g) F0.6 F0.6 F0.9 F0.4 F0.00840Ar / 36Ar 1643 1904 1774 2807 1263

F68 F79 F53 F38 F254He / 40Ar* 3.3 3.1 47

F0.4 F0.5 F6

Quoted errors (1r) in Tables 1–3 include the uncertainties in the correction factors for mass discrimination and sensitivity determined by

repeated analysis of the air-standard (Ne and Ar) and the helium standard of Japan (HESJ [64]), as well as the uncertainties in the blank

correction and interference correction in the case of Ne.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145132

Table 2

Results of step-heating gas extraction on five samples sliced out of the Finero phlogopite-periodotite with apatite-opx veins

A1 (0.721 g) B1 (0.934 g) C1 (1.088 g) D1 (1.042 g) E1 (1.248 g)

800 1300 1800 Total 800 1300 1800 Total 800 1300 1800 Total 800 1300 1800 Total 800 1800 Total

[4He] 1.4 7.5 4.5 13.5 0.49 2.39 5.26 8.14 0.71 1.48 4.03 6.22 0.53 1.19 0.62 2.33 0.91 2.95 3.87

(10"6 cm3

STP/g)

F0.1 F0.8 F0.5 F0.9 F0.05 F0.24 F0.53 F0.58 F0.07 F0.15 F0.41 F0.45 F0.01 F0.12 F0.06 F0.14 F0.01 F0.30 F0.30

3He / 4He 0.38 0.95 1.18 0.97 0.65 0.96 1.03 0.99 0.57 0.87 0.65 0.69 0.405 0.727 0.915 0.704 0.384 0.744 0.659

(R/Ra) F0.02 F0.01 F0.02 F0.02 F0.03 F0.02 F0.01 F0.01 F0.02 F0.02 F0.02 F0.02 F0.022 F0.013 F0.027 F0.012 F0.021 F0.012 F0.012

[22Ne] – – 13.4 – – 20.4 – 1.9 12.9 – – 8.0 6.4

(10"12 cm3

STP/g)

F1.7 F3.5 F1.2 F2.3 F2.6 F5.1

20Ne / 22Ne 9.26 10.6 12.5 9.7 8.5 14

F0.70 F0.9 F4.9 F0.9 F1.6 F621Ne / 22Ne 0.0626 0.0657 0.103 0.065 0.078 0.086

F0.0052 F0.0062 F0.041 F0.006 F0.013 F0.039

[36Ar] 11.7 2.7 4.3 18.7 7.4 2.0 8.1 17.5 6.1 3.2 10.5 19.8 2.3 0.3 2.3 4.9 4.1 6.1

(10"10 cm3

STP/g)

F0.1 F0.3 F0.5 F0.6 F0.7 F0.2 F1.3 F1.5 F0.7 F0.3 F0.1 F0.8 F0.3 F0.1 F0.3 F0.4 F0.4 F0.4

40Ar / 36Ar 320 2831 1153 871 349 3164 2192 1521 342 2498 1997 1565 315 24699 2967 2926 3483 2446

F8 F84 F49 F34 F9 F96 F244 F135 F9 F83 F53 F55 F11 F8618 F197 F685 F130 F1174He / 40Ar* 12.5 3.8 2.5 1.8 2.9

F1.2 F0.6 F0.2 F0.5 F0.3

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been carried out [28], and a geochemical study ofmajor and trace element composition is being under-taken (e.g., [29]). For the noble gas analysis, thesample was first sliced to a thin slab (~1 cm thick)perpendicular to the thin layer. The slab was thencut into ~1 cm intervals parallel to the direction ofthe thin layer. Finally, these were cut into small,~1 cm3 blocks (Fig. 1). Part of these blocks wassubjected to major and trace element analysis [29].One of the blocks contained the apatite-rich layer(A1) and other four (B1, C1, D1 and E1) were fromhost peridotites containing phlogopite. As shown inthe Appendix, abundances of REE’s (and U, Th andSr) in A1 are greater than those in other blocks takenfrom the host phlogopite-peridotite, indicating thatphases associated with the apatite-rich layer hostthese trace elements as well. Note that host peridotites(B1 to E1) also showed enriched LREE patterns, withsmaller La/Yb than A1. These geochemical and petor-ological results suggest that the apatite-layer waslocally formed from a fractionated metasomatisingagent after the main silicate metasomatism recordedin the phlogopite-peridotite [28].

In addition to the sample with the apatite-rich layer,we also examined noble gas compositions of twoolivine separates (FIN-OL1 and FIN-OL2) fromFinero phlogopite-peridotites without an apatitelayer. These two samples were extremely fresh, withabundant fluid or melt inclusions. They form cross-cutting arrays of differing orientations, with isolatedinclusions being rare. Thus, most of fluid inclusionsare of secondary origin and likely to be remnants offluxed fluids. Arrays of fluid inclusions are also abun-dant in olivines of the peridotite containing the apa-tite-rich layer.

Noble gas isotope analysis was carried out usingthe VG5400 noble gas mass spectrometer at OsakaUniversity. Noble gases were extracted from thesamples either by step-heating or crushing. For thephlogopite-peridotite with the apatite layer (A1 toE1), we loaded blocks of ca. 1 gram without mak-ing mineral separates, due to the difficulty of separ-ating a sufficient amount of minor and fine-grainedapatite or other constituents for noble gas analysis.Details of analyses (including sample preparation,cleaning, gas purification and noble gas analysis)are essentially the same as those described pre-viously (e.g., [7]).

3. Results and discussion: characterization ofnoble gases associated with apatite vein and hostperidotite

Two suites of samples were analysed for He, Neand Ar isotopic compositions. One suite consists ofolivine separates from two phlogopite-peridotiteswithout an apatite-rich layer (bunveinedQ peridotites).The other suite consists of five slices prepared froma phlogopite-peridotite with an apatite-rich layer (thebveinedQ peridotite). The analyses were carried outon a whole rock basis for the latter suite. Table 1lists the results obtained from two olivine separates(FIN-OL1 and -OL2) from the unveined peridotites.Noble gas data from the veined peridotite obtainedby step-heating and by crushing are listed in Tables2 and 3, respectively. Uncertainties in noble gaselemental and isotopic compositions listed in tables(and shown in figures) are 1 sigma. Neon isotopicratios obtained by crushing and at some temperaturesteps during step-heating were not reported here,due to the relatively small neon release and conse-quently large CO2

++ interference corrections appliedfor 22Ne peaks lead to N100% uncertainties in iso-topic ratios (shown as b–Q in Table 1). In thissection, we will demonstrate that the sample withthe apatite-rich vein (A1) has a distinct noble gassignature compared with other parts of the sample(B1 to E1). It will also be shown that the unveinedperidotites have noble gas signatures distinct fromthose expected for mantle derived samples.

Table 3

Results of crushing gas extraction on five samples sliced out of the

Finero phlogopite-peridotite with apatite-layer

A1 B1 C1 D1 E1

[4He] 0.75 0.54 1.48 0.28 0.18

(10"6 cm3

STP/g)

F0.08 F0.05 F0.15 F0.03 F0.02

3He / 4He 0.472 0.689 0.655 0.609 0.525

(R/Ra) F0.014 F0.023 F0.016 F0.034 F0.014

[36Ar] 0.6 0.8 2.8 0.4 0.38

(10"10 cm3

STP/g)

F0.1 F0.1 F0.3 F0.1 F0.04

40Ar / 36Ar 840 1209 1883 1595 1396

F24 F28 F10 F108 F114He / 40Ar* 23.8 7.7 3.3 5.8 4.3

F3.9 F1.2 F0.5 F1.1 F0.6

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145134

3.1. He and Ar of unveined samples

Helium isotope ratios in the unveined samples(FIN-OL1 and OL2) are 0.15 Ra and are signifi-cantly lower than the atmospheric ratio. The twoolivine samples yielded quite consistent heliumisotopic ratios in gases released at both 800 and1600 8C, as well as by crushing. This consistencyclearly indicates that helium with 0.15 Ra is froma single component trapped in fluid inclusionswithin the olivines.

Moderately high 40Ar / 36Ar ratios of 2000~3000are observed in the olivine separates and are plottedagainst 3He / 4He ratios in Fig. 2. The peculiarity of Heand Ar in the present samples is clearly demonstratedby the range of 3He / 4He and 40Ar / 36Ar ratios beingsignificantly more radiogenic than mantle-derivedsamples, including orogenic peridotites from Horo-man, northern Japan [7]. The ranges of ratios areconsistent with a reservoir having significantly highertime-integrated U+Th /3He and K/ 36Ar ratios than inthe mantle. Such a signature is generally expected fora crustal environment [30]. An important issue here isthat these quasi-crustal noble gases are released fromfluid inclusions in olivine grains, so the radiogeniccomponent is not an in situ component; thus theradiogenic component would have been obtained bythe fluids before being trapped in inclusions.

3.2. He in the veined samples

Helium isotopic ratios measured from the samplesprepared from the veined sample also yielded 3He / 4Heratios lower than those commonly expected for mantle-derived samples. The range of 3He / 4He ratios ofbetween 0.4 and 1.2 Ra were observed in heliumreleased by step-heating extraction. The heliumreleased at lower temperature steps (see Table 2)yielded consistently lower 3He / 4He ratios than thosereleased at higher temperatures. This indicates a pre-ferential release of in situ radiogenic 4He from thesamples (note that we subjected the whole rock samplesfor the analysis of this suite of samples, with U, Th, K-bearing minerals included in the analysed fractions).Even with an apparent contribution of radiogenic 4He,nominal 3He / 4He ratios released by step-heating wereactually higher than the 0.15 Ra observed in the twoolivine separates from the unveined specimen, indicat-ing the contribution of a helium component with a3He / 4He ratio higher than the highest value observed(1.2 Ra) in the veined samples.

The high 3He / 4He component appears to befocused in the apatite-rich layer. This is shown inFig. 3(a,b) in which the profiles of 3He and 3He / 4Heratios are shown. As reported by Morishita et al. [29](and in Appendix), a metasomatic component withLREE and U–Th enrichments is significantly enriched

Continental Crust

1

10

0.1

102 103 104 105

40Ar/ 36Ar

AIR

Ultramatic (Horoman)

Rad

iog

en

ic 4

He

Mantle-H

e

OL (Hz, Finero)

Radiogenic 40Ar

MORB-source

3H

e/

4H

e (

R/R

a)

Fig. 2. 3He / 4He and 40Ar / 36Ar ratios of olivine separates (filled squares) from two Finero phlogopite-peridotites. Horoman peridotites reported

in Matsumoto et al. [7] are shown for comparison (open circles). The bContinental CrustQ region is from Drescher and Kirsten [30].

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 135

in A1 relative to adjacent host peridotite blocks (B1 toE1) (see Fig. A in Appendix for a gradual decrease intotal REEs from A1 to E1). In terms of helium com-position, a progressive increase in 3He contents andcorrespondingly high 3He / 4He ratios towards sampleA1 was observed. Concentrations of U and Th arealso highest in A1 due to the presence of modalapatite (locally up to 10% of mode; [28]), graduallydecreasing from A1 to E1. It is expected that thecontribution of in situ radiogenic 4He would bemost significant in A1, and 3He / 4He ratios shouldtherefore be lowest in A1. However, as shown in Fig.3b, the highest 3He / 4He ratios were in fact observedin the highest temperature fraction of the sample A1.

We note that the observed 3He / 4He ratios in thissuite of samples are not explained by a nucleogenic3He production by the reaction 6Li(n,a)3H(h")3He.This reaction only significantly increases 3He / 4Heratios of minerals rich in Li and poor in U and Th[31]. Apatite is highly enriched in U and Th and isvirtually devoid of Li [32]. Concentrations of Li inother constituent minerals of Finero peridotites arealso reported to be less than a few ppm [33]. It hasbeen demonstrated experimentally and theoretically

that 3Henucleogenic /4Heradiogenic ratios for minerals

containing a few ppm of Li and U and Th aretypically on the order of 10"7 or lower [31]. There-fore, it is unlikely that a helium component concen-trated in the apatite-rich part of the sample is relatedto the in situ nucleogenic production; rather the3He / 4He ratio higher than air implies a contributionof mantle-He.

Helium analysis by crushing, however, did notshow a clear mantle-He signature (Fig. 4a). This ismost likely due to the release of radiogenic 4He bycrushing as previously observed in similar experimentson mafic minerals with significant radiogenic 4He[34,35]. This notion is supported by consistentlyhigher 4He / 40Ar* ratios (40Ar* is a non-atmosphericcomponent of 40Ar) measured by crushing than thoseobtained by step-heating, indicating preferentialrelease of radiogenic 4He (Tables 2 and 3). Never-theless, it is important to note that the range of3He / 4He ratios measured by crushing is higher than0.6 Ra, thus higher than the value of 0.15 Ra obtainedfrom the olivine. Thus the 3He / 4He ratio of inclusion-trapped helium in the veined sample should be higherthan in the unveined samples.

A1

B1

C1

D1

E1

A1

B1

C1

D1

E1

(a) (b) (c)

Fig. 3. Concentrations of 3He, 3He / 4He and 40Ar / 36Ar ratios measured by step-heating for samples A1 to E1. Sums of each temperature step are

shown for 3He and 40Ar / 36Ar, whereas ratios measured in high temperature release are shown for 3He / 4He ratios. Exclusion of low temperature

release for 3He / 4He diagram is to minimize the effect of low temperature release of an in situ radiogenic 4He component (although a similar

trend can also be observed even with the total 3He / 4He ratios, Table 1). A1 contains the apatite-rich layer. 1s uncertainties are shown (errors are

smaller than symbols for 3He and 3He / 4He ratios).

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145136

3.3. Ar in veined sample

Argon isotopic ratios measured by heating extrac-tion show a systematic trend (Fig. 3c). 40Ar / 36Arratios gradually increase from 840 (total) in A1 to

2400 in E1. In situ radiogenic 40Ar should contributeto the high 40Ar / 36Ar ratios observed in the samples,since ubiquitous phlogopite [28] hosts the largestproportion of the parental K in the samples [36].In a 40Ar / 36Ar vs. 40K /36Ar plot (Fig. 5), samples

( )

Fig. 5. 40K/ 36Ar vs. 40Ar / 36Ar ratios. A linear regression line is based on four data (except for A1 with bracket) with its slope yielded an

isochron age of 240F41 Ma. K concentrations are listed in the Appendix.

A1

B1

C1

D1

E1

A1

B1

C1

D1

E1

(a) (b)

Fig. 4. 3He / 4He and 40Ar / 36Ar ratios of A1 to E1 measured by crushing extraction.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 137

B1 to E1 show a clear linear trend, this can beregarded as an isochron. A1 lies off the trend dueto heterogeneous K contents. The slope of this iso-chron corresponds to an age of 240F41 Ma with aninitial 40Ar / 36Ar ratio of 1220F90. This age isconsistent with a reported Sm–Nd whole rock ageof 270F57 Ma from Finero amphibole-peridotites[37], a Pb isotope zircon age of 225F12 Ma fromsyenite pegmatitic dikes in the Finero phologopite-peridotite body [38], and a 215F35 Ma age deter-mined by SHRIMP on apatites from the presentsample (e.g., [29]). The significance of these agesare still controversial and will be discussed in a laterpublication, but we stress that the focusing of ages asdetermined by different radiometric methods mostlikely suggests continuous and rapid cooling of theFinero ultramafic body during late stage exhumation.

The gas released by crushing in samples B1 to E1yielded 40Ar / 36Ar ratios lower than those measuredby heating experiments on the same samples (Figs. 3cand 4b), and are less variable (1200 to 1900) com-pared to the variation of 40Ar / 36Ar ratios by crushing.These indicate that argon can be regarded as a mixtureof a trapped components in fluid inclusions and aradiogenic component accumulated in mineral matrixsites. This is also supported by the similarity betweenthe initial 40Ar / 36Ar ratio of the isochron (~1200) and

the range of 40Ar / 36Ar ratios by crushing extraction(it will be shown later that the inclusion trapped argonis likely to be a mixture of two isotopically distinctcomponents, and this binary mixing is responsible forsome variation in 40Ar / 36Ar ratios by crushing). It isalso important to note that the lowest 40Ar / 36Ar ratiofound in the A1 implies the apatite-rich part hosting adistinct argon component, as was the case for heliumisotopic compositions.

3.4. Neon isotopes

Helium and argon results suggest the present sam-ples contain a significant radiogenic component, fromeither in situ production or entrapment as fluid inclu-sions. Neon isotopic ratios of the present samples alsosuggest that there is a significant nucleogenic neoncomponent in addition to air-Ne and mantle-Ne. Thisis shown in Fig. 6 in which the neon results are plottedwith expected mixing trends between possible end-members. All neon ratios plot above the air-nucleo-genic mixing line, and to the right of the MORB-airmixing line, suggesting that these three componentsare required to explain the observed ratios. In the caseof the present samples (especially with the apatite-vein), a nucleogenic neon component should includeF-derived 22Ne (19F(a,n)22Na(h")22Ne [40]) as well

7

8

9

10

11

12

13

14

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

21Ne/

22Ne

20N

e/

22N

e

FIN-OL#1

FIN-OL#1 CrushA1

B1

C1

D1

AIR

MORB-source

AIR-M

ORB mixi

ng

Nucleogenic 21Ne (~ crustal Ne)

Nucleogenic Ne in apatite

Nucleogenic Ne in apatite

Nucleogenic 21Ne (~ crustal Ne)

Fig. 6. Neon isotopic ratios of Finero phlogopite-peridotites. Arrays show directions of mixing trends with MORB-source or air and nucleogenic

neon component expected in the average crustal composition [39] and in the apatite of present samples (see text).

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145138

as 21Ne produced from an 18O(a,n) reaction. Thearrows labeled as bnucleogenic Ne in apatiteQ in Fig.6 show directions of mixing trends between air orMORB-Ne and the nucleogenic neon componentexpected for the apatite estimated from the chemicalcomposition [28] and an empirical relationship foundbetween F /O and nucleogenic 22Ne / 21Ne ratios [41].Also, the presence of a significant 21Ne excess in thecrushing extraction on FIN-OL1 suggests that thecomponent trapped in fluid inclusions is also enrichedin nucleogenic neon. This is consistent with He andAr observations. However, as most of the neon dataare taken by step-heating, and because the differencebetween the crustal neon and in situ nucleogenic neonproduced in the apatite are small compared with theuncertainties with each data point, it is impossible todiscuss if there is a difference in neon isotopic com-position between the olivine separates and the veinedperidotites. Thus, hereafter we will concentrate in Heand Ar results to further discuss the noble gas signa-tures of the present samples and some geochemicalimplications.

3.5. A binary mixing trend in He and Ar componentsof veined and unveined samples

As noted above, there are two distinct helium andargon components trapped in the present samples.These are: (1) a component having a relatively low

40Ar / 36Ar ratio, concentrated in the apatite-rich partof the sample and (2) a component with a highlyradiogenic argon component similar to the signatureobserved in the two olivine separates from theunveined samples. 3He / 36Ar and 40Ar / 36Ar ratiosreleased from inclusion sites form a linear trendwith the ratios from A1 and FIN-OL1 plotting ateither end of the trend. The 3He / 36Ar ratio of FIN-OL2 is not on the same line and actually plots out therange of Fig. 7 (~0.014). This is due to elementalfractionation favoring helium over argon in this sam-ple, also supported by a fractionated 4He / 40Ar* (~50)compared with the expected unfractionated produc-tion ratio of ~2 to 5 [42]. As noted earlier, the high4He / 40Ar* ratio of A1 is most likely due to a crushrelease of radiogenic 4He from apatite, thus the pro-cess should not affect the 3He / 36Ar ratio of A1. Also,there is no significant elemental fractionation impliedfor the rest of the samples, as their 4He / 40Ar ratios arewithin the expected range. Thus, an interpretation ofpossible disturbance in the observed 3He / 36Ar ratioscaused by elemental fractionation is limited for datapresented in Fig. 7. This suggests that the observedco-variation of 3He / 36Ar and 40Ar / 36Ar ratios is aresult of binary mixing between two components. Thefact that data from A1 plot at the end of the correlationline is particularly important as this block contains asignificant apatite-rich layer, thus the observed noblegas signature in this part of the sample should be the

0

500

1000

1500

2000

2500

3000

3500

0 0.002 0.004 0.006 0.008 0.01

3He/

36Ar

40A

r/ 3

6A

r

FIN-OL1

B1

D1E1

C1

A1

High 3He & Air Ar

Crushing Results Only

Fig. 7. 3He / 36Ar and 40Ar / 36Ar ratios measured by crushing extraction.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 139

closest representative of a true end-member compo-nent; which should directly be associated with theapatite-forming metasomatic agent.

3.5.1. Identity and origin of noble gas component inthe apatite-rich layer and implications to the mantlemetasomatism affected the Finero complex

As discussed in Morishita et al. [28], the apatite-rich layer was formed as a result of introduction ofmetasomatic fluids within the mantle [28], whichalso resulted in significant refertilization in incom-patible elements such as LREE, U and Th ([28],also shown in Appendix). This is shown in Fig. A inwhich the LREE enrichment is the most significant insample A1 compared with the blocks separated fromthe host peridotite (i.e., B1 to E1). It is important tonote that LREE contents gradually decrease from B1to E1, thus the addition of a metasomatic componentassociated with the formation of the apatite-rich layeraffected the host peridotite to some extent. However,there is a gradual increase in abundances of theseincompatible elements from sample E1 to A1, sug-gesting that A1 is the most enriched in the componentadded by the introduction of the infiltrating metaso-matic fluid. This is consistent with the helium andargon signatures noted above, as samples B1 to E1 aremore significantly affected by He and Ar of the othercomponent than in sample A1 (see Fig. 7).

From petrographic evidence, the apatite-rich layerformed during late stage silicate metasomatism ofthe Finero massif [28]. Indeed the apatite in thepresent samples is chlorapatite, with N2% Cl andb1 wt.% F, indicating a metasomatic origin [43].The observation that the metasomatic apatite hostsa distinct noble gas component implies a geneticassociation between the apatite-forming metasomaticagent and its noble gases. Indeed, it has been pre-viously postulated that the fluxing and entrapment ofmetasomatic fluids is responsible for introducingnoble gases into the lithospheric part of the mantlewhich had lost its original noble gas componentduring earlier melting events (e.g., [4]). A clearlink found between the petrographic evidence forthe fluxing of metasomatic fluids (i.e., the apatite-rich vein) and the distinct noble gas component(especially the mantle-He) provides more evidencein support of arguments proposed as a result ofprevious xenolith studies.

Because the analysis on the A1 was carried out onthe blocks (not on the mineral separates) containingboth the apatite-rich part and the host peridotite, itwould be reasonable to regard the observed He and Arcompositions as being affected by the radiogeniccomponent. Thus, the end-member composition forthe apatite-forming metasomatic agent should have3He / 36Ar and 40Ar / 36Ar ratios extrapolated from thecorrelation line in Fig. 7 to higher and lower ratios,respectively. The 40Ar / 36Ar ratio of the apatite-richlayer, therefore, must be smaller than 800, indicating apossible involvement of an argon component with anair-like 40Ar / 36Ar ratio (~300). Likewise, it is con-ceivable that the observed 3He / 4He ratio in A1 is alsoaffected by a helium component from the host peri-dotite, which is probably as low as the ratio found intwo olivine separates from unveined samples (0.15Ra). This suggests that the apatite-rich layer should becharacterized by a helium component with a 3He / 4Heratio higher than 1.2 Ra. Again, the presence ofmantle-He is suggested for the apatite-rich layer(note that if the source of high 3He in the samples isradiogenic 3He, produced from a nuclear reaction onLi, 3He / 36Ar ratios are not necessarily inversely cor-related with 40Ar / 36Ar ratios).

Apatite-forming metasomatic fluids should have ahybrid of air-like argon and mantle-derived helium.Such a noble gas composition is clearly distinguish-able from that expected for any melt of fluid arisingfrom a crustal reservoir, and the combination of man-tle-He and air-Ar is characteristically found in sam-ples associated with a subduction zone setting (i.e.,orogenic and xenolithic ultramafic rocks from volca-nic arc mantle [7,44], arc lava [45] and well gases[46,47]). As demonstrated by Staudacher and Allegre[48], fluids released from altered oceanic crust andsedimentary cover have isotopically air-like argoninherited from dissolved air in seawater. Such fluidsthen acquire mantle-derived helium during their pas-sage through the mantle wedge, and have a homoge-neous 3He / 36Ar ratio corresponding to a mantle-airmixing ratio. The helium and argon signature foundwithin the apatite-rich part of the present sample isconsistent with a signature expected for fluids asso-ciated with slab dehydration. Therefore, this signatureprovides an excellent record of metasomatism thatoccurred when the complex was in a mantle-wedgesetting, during the Variscan. Phlogopite-forming

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145140

metasomatism was also taking place at this stage, byaddition of a slab-derived hydrous silicate melt, whichsubsequently evolved to form apatite-forming carbo-natitic fluids that separated by liquid immiscibilityfrom a SiO2-rich (high CO2/H2O) melt [28]. It islikely that the entire peridotite body had once beenmetasomatised by the slab-derived fluids. The pre-sence of the subduction-related component in theFinero ultramafic body is consistent with previousstudies such as Cumming et al. [49], Hartmann andWedepohl [36], Zanetti et al.[24], and Morishita et al.[28].

3.5.2. A highly radiogenic helium and argoncomponent

In addition to the subduction-related noble gassignatures found in the apatite-rich layer of the sam-ples, we found a crust-like noble gas component in thepresent set of the samples. This component was mostclearly identifiable in the olivine samples fromunveined peridotite, but also affected the noble gascomposition of the blocks of host peridotite preparedfrom the veined samples. Thus, the crust-like noblegas component is an undoubtedly important and per-haps more widespread component that affected theFinero complex than subduction related noble gases.

One possible scenario accounting for the occur-rence of the crust-like noble gases is that the fluidwas derived from dehydration or partial melting ofmetamorphic rocks (i.e., the Kinzigite Formation)around the Finero mafic–ultramafic complex duringvarious stages of its diapiric uplift through the uppermantle to its emplacement in the lower crust, and toassociated crustal uplift. Such processes are recordedas a significant correlation between K2O and87Sr / 86Sr ratios of the external gabbro unit [50]; butthe effect is suggested to be smaller in the case ofFinero ultramafic body. The alternative source for thecrust-like noble gases in Finero phlogopite-peridotitesis the postmetasomatic lithospheric mantle, with someradiogenic ingrowth. A common characteristic ofnoble gases in modally metasomatised mantle xeno-liths is that they are enriched in radiogenic andnucleogenic noble gases (e.g., [4,11,12]). This isbecause metasomatic minerals, such as amphibole,apatite and mica often host the radioactive parentsof noble gases. As these phases are generally lessrefractory than olivine, the radiogenic signature is

easily incorporated into melts or fluids generatedwithin the region, or during infiltration through themantle (e.g., [4,51,52]). Thus, the modally metasoma-tised lithospheric mantle has the potential to host asignificant amount of radiogenic and nucleogenicnoble gases. Noble gas analysis on the wider litholo-gies in the Finero and surrounding mafic–ultramaficcomplexes should help to distinguish between the twoalternative sources for radiogenic noble gases in thepresent samples.

4. Concluding remarks: general implications forthe noble gas reservoir in the SCLM

As discussed above, a significant concentration of3He and air-Ar in the apatite-rich layer was observed.Clear correlations found between the noble gas signa-tures, LREE-enrichment and the occurrence of miner-alogically distinct veining in the Finero peridotite isstrong evidence in support of the importance of meta-somatic fluids as a carrier of noble gases in the litho-spheric part of the mantle. Also, the present resultsreinforce the view that the fluid derived from the sub-ducting slab metasomatised the Finero phlogopite-peridotite body, as proposed by previous geochemicaland petrological investigations of Finero samples.

Finally, we note that results from the present studyprovide some insight into the nature and origin ofnoble gas signatures in the SCLM. Enrichment ofair-Ar in the metasomatised part of the mantle provideadditional evidence to support the storage of recycledsurface noble gases in the wedge mantle. It has beenshown that some vestige of the metasomatically addednoble gas component becomes obscured if the eventoccurred early enough for the production of an in situradiogenic component to overwhelm inherited signa-tures. In the Finero phlogopite-peridotite complex,there have been a few hundreds of million of yearsfor radiogenic noble gas components to accumulate.This is in contrast to the relatively short post metaso-matic history (a few tens of million years [53]) forHoroman complex. A highly radiogenic noble gascomponent has also been found in Jwaneng framesitediamonds from old SCLM [54]. Very low 3He / 4Heratios of 0.3 Ra found in Siberian mantle xenoliths aswell as 0.075 Ra found in Indonesian lavas [55] alsorequire the presence of some helium reservoir

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 141

enriched in radiogenic 4He. This suggests that thelithospheric mantle domains metasomatised throughancient subduction-related process have a potential todevelop and preserve highly radiogenic crust-likenoble gas signatures either by direct recycling ofcrustal material to the SCLM by subduction [54], orby the in situ production of radiogenic isotopes in themetasomatised part of the mantle (this study and [4]).

Absence of such an intense radiogenic signature insome part of the SCLM (especially that beneath Europe[11,12]) suggests that the traces of ancient metasoma-tism and its aging effect have been overwritten by somerecent non-subduction related metasomatic agent withrelatively uniform 3He / 4He ratios [12]. It is also pos-sible that radiogenic noble gas components (and air-like heavy noble gases if affected by ancient subduc-tion-related processes) have been removed from theSCLM by delamination of old, thick lithosphere.Examples of such processes are found in easternChina, where Cenozoic basalts yield MORB-like3He / 4He ratios (7.4 to 8.4 Ra in five megacrysts) with-out an apparent radiogenic 4He signature expected formagma associated with the old SCLM [56,57]. Thishelium signature from the Chinese megacrysts is con-sistent with several independent (geophysical and geo-chemical) lines of evidence supporting the removal ofan Archean keel of lithosphere, presumably by delami-nation, and effective replacement by boceanicQ-likemantle during the Cenozoic [58–60]. The fate of dela-minated material, and its noble gas budget is far beyondthe scope of present study, however it is quite likely thatthe delaminatedmaterials have noble gas elemental andisotopic compositions distinct from those in sublitho-spheric reservoirs. Therefore, the scale and effect ofrecycling noble gases by such processes should beexplored further to better understand the nature ofnoble gas reservoirs in the mantle.

Acknowledgements

The authors thank O. Vaselli, A. Tamura, K. Mat-sukage, N. Abe for their help in sampling rocks usedfor this study. This manuscript benefited fromthoughtful and constructive reviews by P. Sarda andan anonymous reviewer. This work was supported byGrants-in-Aid from the Japan Society for the Promo-tion of Science (14740314 and 17684029) to TM.

Appendix. Major and REE compositions of thepresent samples

The detailed investigations on major and traceelemental compositions of the present samples willbe discussed elsewhere. Here we present only part ofthe data relevant for the sake of the present contribu-tion (bulk K2O, P2O5, U, Th contents of samples A1to E1 in Table A, and their REE abundance patternsin Fig. A). Details of analytical procedures for XRFand ICP-MS will be presented in Morishita et al.,and are also available in previous publications([61,62]).

Fig. A. A. Chondrite-normalized REE patterns of each slice taken

from the Finero phlogopite-peridotite with the apatite-rich layer.

Chondrite values are from McDonough and Sun [63].

Table A

K2O, P2O5, Th and U contents in sliced Finero Phlogopite Peridotite

with apatite rich layer

K2O (wt.%) P2O2 (wt.%) Th (ppm) U (ppm)

A1 0.01 0.43 5.24 1.24

B1 0.08 0.01 n.d. n.d.

C1 0.08 0.01 0.36 0.51

D1 0.10 0.01 0.46 0.06

E1 0.09 0.01 0.35 0.06

K2O, and P2O5 were analyzed by XRF with fused glass beads. P2O5

of 0.01% is upper limit as it is the detection limit.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145142

References

[1] D. Porcelli, R.K. O’Nions, S.Y. O’Reilly, Helium and stron-

tium isotopes in ultramafic xenoliths, Chem. Geol. 54 (1986)

237–249.

[2] T.J. Dunai, H. Baur, Helium, neon, argon systematics of the

European subcontinental mantle: implications for its geo-

chemical evolution, Geochim. Cosmochim. Acta 59 (1995)

2767–2783.

[3] T. Matsumoto, M. Honda, I. McDougall, S.Y. O’Reilly,

Noble gases in anhydrous lherzolites from the newer volca-

nics, southeastern Australia: a MORB-like reservoir in the

subcontinental mantle, Geochim. Cosmochim. Acta 62

(1998) 2521–2533.

[4] T. Matsumoto, M. Honda, I. McDougall, S.Y. O’Reilly, M.

Norman, G. Yaxley, Noble gases in pyroxenites and metaso-

matised peridotites from the newer volcanics, southeastern

Australia: implications for mantle metasomatism, Chem.

Geol. 168 (2000) 49–73.

[5] T. Matsumoto, M. Honda, I. McDougall, I. Yatsevich, S.Y.

O’Reilly, Plume-like neon in a metasomatic apatite from

the Australian lithospheric mantle, Nature 388 (1997)

162–164.

[6] T. Matsumoto, D.L. Pinti, J. Matsuda, S. Umino, Recycled

noble gas and nitrogen in the subcontinental lithospheric

mantle: implications from N–He–Ar in fluid inclusions of

SE Australian xenoliths, Geochem. J. 36 (2002) 209–217.

[7] T. Matsumoto, Y. Chen, J. Matsuda, Concomitant occurrence

of primordial and recycled noble gases in the Earth’s mantle,

Earth Planet. Sci. Lett. 185 (2001) 35–47.

[8] T. Matsumoto, M. Honda, I. McDougall, I. Yatsevich, S.Y.

O’Reilly, Isotope fractionation of neon during stepheating

extraction? a comment on dre-interpretation of the existence

of a primitive plume under Australia based on neon isotope

fractionation during step heatingT by Gautheron and Moreira

(2003), Terra Nova 16 (2004) 23–26.

[9] M. Trieloff, H.W. Weber, G. Kurat, E.K. Jessberger, J. Janicke,

Noble gases, their carrier phases, and argon chronology of

upper mantle rocks from Zabargad Island, Red Sea, Geochim.

Cosmochim. Acta 61 (1997) 5065–5088.

[10] J. Yamamoto, I. Kaneoka, S. Nakai, H. Kagi, V.S. Prikhod’ko,

S. Arai, Evidence for subduction-related components in the

subcontinental mantle from low 3He/ 4He and 40Ar / 36Ar ratio

in mantle xenoliths from far eastern Russia, Chem. Geol. 207

(2004) 237–259.

[11] C. Gautheron, M. Moreira, Helium signature of the subconti-

nental lithospheric mantle, Earth Planet. Sci. Lett. 199 (2002)

39–47.

[12] C. Gautheron, M. Moreira, C. Allegre, He, Ne and Ar com-

position of the European lithospheric mantle, Chem. Geol. 217

(2005) 97.

[13] A. Buikin, M. Trieloff, J. Hopp, T. Althaus, E. Korochant-

seva, W.H. Schwarz, R. Altherr, Noble gas isotopes suggest

deep mantle plume source of late Cenozoic mafic alkaline

volcanism in Europe, Earth Planet. Sci. Lett. 230 (2005)

143.

[14] C.J. Allegre, M. Moreira, T. Staudacher, He-4 /He-3 disper-

sion and mantle convection, Geophys. Res. Lett. 22 (1995)

2325–2328.

[15] T. Trull, M.D. Kurz, Experimental measurements of 3He and4He mobility in olivine and clinopyroxene at magmatic

temperatures, Geochim. Cosmochim. Acta 57 (1993)

1313–1324.

[16] S.Y. O’Reilly, W.L. Griffin, Mantle-metasomatism beneath

western Victoria, Australia: I. Metasomatic processes in Cr-

diopside lherzolites, Geochim. Cosmochim. Acta 52 (1988)

433–447.

[17] W.L. Griffin, S.Y. O’Reilly, A. Stabel, Mantle metasomatism

beneath western Victoria, Australia: II. Isotopic geochemistry

of Cr-diopside lherzolites and Al-augite pyroxenites, Geochim.

Cosmochim. Acta 52 (1988) 449–459.

[18] G. Lensch, Die ultramafitite der Zone von Lvrea und ihre

geologische interpretation, Schweiz. Mineral. Petrogr. Mitt.

48 (1968).

[19] R.G. Cawthorn, The amphibole peridotite-metagabbro com-

plex, Finero, northern Italy, J. Geol. 83 (1975) 437–454.

[20] M. Coltorti, F. Siena, Mantle tectonite and fractionate perido-

tite at Finero (Italian western Alps), Neues Jahrb. Mineral.

Abh. 149 (1984) 225–244.

[21] F. Siena, M. Coltorti, The peterogenesis of a hydrated mafic–

ultramafic complexes and the role of amphibole fractionation

at Finero Italian western Alps), N. Jb. Miner. Mh. 6 (1989)

255–274.

[22] C.C. Ferrall, Evidence for Honolulu volcanic series eruptions

less than 12,000 years before present, EOS Trans. AGU 62

(1981) 432.

[23] G. Grieco, A. Ferrario, A. Von Quadt, V. Koeppel, E.A.

Mathez, The zircon-bearing chromitites of the phlogopite

peridotite of Finero (Ivrea zone, southern Alps): evidence

and geochronology of a metasomatized mantle slab, J. Petrol.

42 (2001) 89–101.

[24] A. Zanetti, M. Mazzucchelli, G. Rivalenti, R. Vannucci, The

Finero phlogopite-peridotite massif: an example of subduc-

tion-related metasomatism, Contrib. Mineral. Petrol. 134

(1999) 107–122.

[25] A. Zingg, The Ivrea and Strona-Ceneri Zones (southern Alps,

Ticino and N-Italy)—a review, Schweiz. Mineral. Petrogr.

Mitt. 63 (1983) 361–392.

[26] J.D. Sills, J. Tarney, Petrogenesis and tectonic significance of

amphibolites interlayered with meta-sedimentary gneisses in

the Ivrea zone, southern Alps, northwest Italy, Tectonophysics

107 (1984) 187–206.

[27] B. Schnetger, Partial melting during the evolution of the

amphibolite-facies to granulite-facies gneisses of the Ivrea

zone, northern Italy, Chem. Geol. 113 (1994) 71–101.

[28] T. Morishita, S. Arai, A. Tamura, Petrology of an apatite-rich

layer in the Finero phlogopite-peridotite, Italian western Alps;

implications for evolution of a metasomatising agent, Lithos

69 (2003) 37–49.

[29] T. Morishita, K. Terada, T. Matsumoto, S. Arai, Apatite-rich

layer in the Finero phlogopite-peridotite massif: metasoma-

tism and its timing, Geochim. Cosmochim. Acta 67 (2003)

A306.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 143

[30] J. Drescher, T. Kirsten, The rare gas inventory of the conti-

nental crust, recovered by the KTB continental deep drilling

project, Earth Planet. Sci. Lett. 154 (1998) 247–263.

[31] B.A. Mamyrin, I.N. Tolstikhin, Helium Isotopes in Nature,

Elsevier, New York, 1984, 230 pp.

[32] S. Klemme, C. Dalpe, Trace-element partitioning between

apatite and carbonatite melt, Am. Mineral. 88 (2003)

639–646.

[33] H.-M. Seitz, A.B. Woodland, The distribution of lithium in

peridotitic and pyroxenitic mantle lithologies — an indicator

of magmatic and metasomatic processes, Chem. Geol. 166

(2000) 47.

[34] P. Scarsi, Fractional extraction of helium by crushing of oli-

vine and clinopyroxene phenocrysts: effects on the 3He / 4He

measured ratio, Geochim. Cosmochim. Acta 64 (2000)

3751–3762.

[35] T. Matsumoto, A. Seta, J. Matsuda, M. Takebe, Y.L. Chen,

S. Arai, Helium in the Archean komatiites revisited: sig-

nificantly high He-3 /He-4 ratios revealed by fractional

crushing gas extraction, Earth Planet. Sci. Lett. 196 (2002)

213–225.

[36] G. Hartmann, K.H. Wedepohl, The composition of peridotite

tectonites from the Ivrea complex, northern Italy — residues

from melt extraction, Geochim. Cosmochim. Acta 57 (1993)

1761–1782.

[37] H. Voshage, J.C. Hunziker, A.W. Hofmann, A. Zingg, A Nd

and Sr isotopic study of the Ivrea zone, southern Alps, N-Italy,

Contrib. Mineral. Petrol. 134 (1987) 380–404.

[38] V. Stahle, G. Frenzel, A. Michard, W. Schneider, Zircon

syenite pegmatites in the Finero peridotite (Ivrea zone): evi-

dence for a synite from a mantle source, Earth Planet. Sci. Lett.

101 (1990) 196–205.

[39] I. Yatsevich, M. Honda, Production of nucleogenic neon in the

Earth from natural radioactive decay, J. Geophys. Res. 102

(1997) 10291–10298.

[40] G.W. Wetherill, Variations in the isotopic abundances of neon

and argon extracted from radioactive minerals, Phys. Rev. 96

(1954) 679–683.

[41] H. Hunemohr, Edelgase in U-und Th-reichenMineralen und die

Bestimmung der 21Ne-Dicktarget-Ausbeute der 18O(a,n)21Ne-Kernreaction im Bereich 4.0–8.8 MeV, Ph.D., Johannes-Guten-

berg-Universitat, Mainz, 1989.

[42] F.M. Stuart, P.G. Burnard, R.P. Taylor, G. Turner, Resolving

mantle and crustal contributions to ancient hydrothermal

fluids: He–Ar isotopes in fluid inclusions from Dae Hwa

W-Mo mineralisation, South Korea, Geochim. Cosmochim.

Acta 59 (1995) 4663–4673.

[43] S.Y. O’Reilly, W.L. Griffin, Apatite in the mantle: implications

for metasomatic processes and high heat production in Pha-

nerozoic mantle, Lithos 53 (2000) 217–232.

[44] K. Nagao, E. Takahashi, Noble gases in the mantle wedge and

lower crust: an inference from the isotopic analyses of xeno-

liths from Oki-Dogo and Ichinomegata, Japan, Geochem. J. 27

(1993) 229–240.

[45] D.B. Patterson, M. Honda, I. McDougall, Noble gases in mafic

phenocrysts and xenoliths from New Zealand, Geochim. Cos-

mochim. Acta. 58 (1994) 4411–4427.

[46] Y. Sano, H. Wakita, Geographical distribution of 3He / 4He

ratios in Japan: implications for arc tectonics and incipient

magmatism, J. Geophys. Res. 90 (1985).

[47] T. Matsumoto, T. Kawabata, J. Matsuda, K. Yamamoto, K.

Mimura, He-3 /He-4 ratios in well gases in the Kinki district,

SW Japan: surface appearance of slab-derived fluids in a non-

volcanic area in Kii Peninsula, Earth Planet. Sci. Lett. 216

(2003) 221–230.

[48] T. Staudacher, C.J. Allegre, Recycling of oceanic crust and

sediments: the noble gas subduction barrier, Earth Planet. Sci.

Lett. 89 (1988) 173–183.

[49] G.L. Cumming, V. Koppel, A. Ferrario, A lead isotope study

of the northeastern Ivrea zone and the adjoining Ceneri zone

(N-Italy) — evidence for a contaminated subcontinental man-

tle, Contrib. Mineral. Petrol. 97 (1987) 19–30.

[50] M.H. Lu, A.W. Hofmann, M. Mazzucchelli, G. Rivalenti, The

mafic–ultramafic complex near Finero (Ivrea–Verbano zone).2.

Geochronology and isotope geochemistry, Chem. Geol. 140

(1997) 223–235.

[51] A. Dodson, A.D. Brandon, Radiogenic helium in xenoliths

from Simocoe, Washington, USA: implications for metaso-

matic processes in the mantle wedge above subduction zones,

Chem. Geol. 160 (1999) 371–385.

[52] M. Martelli, P.M. Nuccio, F.M. Stuart, R. Burgess, R.M.

Ellam, F. Italiano, Helium–strontium isotope constraints on

mantle evolution beneath the Roman comagmatic province,

Italy, Earth Planet. Sci. Lett. 224 (2004) 295–308.

[53] G. Kimura, The latest Cretaceous–early Paleogene rapid

growth of accretionary complex and exhumation of high pres-

sure series metamorphic rocks in northwestern Pacific margin,

J. Geophys. Res. 99 (1994) 22147–22164.

[54] M. Honda, D. Phillips, J.W. Harris, I. Yatsevich, Unusual

noble gas compositions in polycrystalline diamonds: prelimin-

ary results from the Jwaneng kimberlite, Botswana, Chem.

Geol. 203 (2004) 347–358.

[55] D.R. Hilton, J.A. Hoogewerff, M.J.v. Bergen, K. Hammer-

child, Mapping magma sources in the east Sunda–Banda Arcs,

Indonesia: constraints from helium isotopes, Geochim. Cos-

mochim. Acta 56 (1992) 851–859.

[56] Z. Fang, T. Matsumoto, S.J. Xu, J.I. Matsuda, J.H. Yu, R.C.

Wang, Absence of lithospheric mantle helium signature in

megacrysts of SE China, Geochim. Cosmochim. Acta 67

(2003) A89.

[57] S.J. Xu, Z. Fang, T. Matsumoto, J. Matsuda, M. Yasuda, J.H.

Yu, R.C. Wang, W.Z. Liu, He and Ar isotopes in mantle

megacryst minerals from Nushan and Yingfengling in south-

east China, Chin. Sci. Bull. 48 (2003) 1624–1630.

[58] W.M. Fan, H.F. Zhang, J. Baker, K.E. Jarvis, P.R.D. Mason,

M.A. Menzies, On and off the North China craton: where is

the Archaean keel? J. Petrol. 41 (2000) 933–950.

[59] M.A. Menzies, Y.G. Xu, Geodynamics of the North China

craton, in: M.F.J. Flower, et al., (Eds.), Mantle Dynamics and

Plate Interactions in East Asia, Geodynamics Ser., vol. 27,

American Geophysical Union, Washington, D.C., 1998,

pp. 155–165.

[60] X. Xu, S.Y. O’Reilly, W.L. Griffin, X. Zhou, X. Huang, The

nature of the Cenozoic lithosphere at Nushan, eastern China, in:

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145144

M.F.J. Flower, et al., (Eds.), Mantle Dynamics and Plate Inter-

actions in East Asia, Geodynamics Ser., vol. 27, American

Geophysical Union, Washington, D.C., 1998, pp. 167–219.

[61] M. Takebe, K. Yamamoto, Geochemical fractionation between

porcellanite and host sediment, J. Geol. 111 (2003) 301–312.

[62] M. Takebe, Carriers of rare earth elements in Pacific deep-sea

sediment, J. Geol. 113 (2005) 201–215.

[63] W.F. McDonough, S.-s. Sun, The composition of the Earth,

Chem. Geol. 120 (1995) 223–253.

[64] J. Matsuda, T. Matsumoto, H. Sumino, K. Nagao, J. Yama-

moto, Y. Miura, I. Kaneoka, N. Takahata, Y. Sano, The He-3 /

He-4 ratio of the new internal He standard of Japan (HESJ),

Geochem. J. 36 (2002) 191–195.

T. Matsumoto et al. / Earth and Planetary Science Letters 238 (2005) 130–145 145