geochemistry of cenozoic basalts in the fukuoka district (northern kyushu, japan): implications for...

Geochemistry of Cenozoic basalts in the Fukuoka district

(northern Kyushu, Japan): implications for asthenosphere

and lithospheric mantle interaction

Nguyen Hoang*, Kozo Uto

Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1-Higashi,

Tsukuba Central 7th, Tsukuba 305-8567, Japan

Received 2 August 2002; accepted 24 December 2002

Abstract

Fukuoka volcanic field in northern Kyushu (Japan) is comprised of scattered small, monogenetic volcanoes with ages

ranging from 1.1 to 4.4 Ma. A set of samples from the area, together with some from nearby localities, was collected and

analyzed for major and trace element abundances and Sr, Nd and Pb isotope compositions. The basalts, unlike lavas from other

nearby centers in northern Kyushu, show the highest FeO*, TiO2 and lowest SiO2 characteristics, which are interpreted to

reflect high melting temperature and pressure; whereas high Sr, Sm and high-field-strength elements (HFSE) such as Zr and Nb,

high light rare earth element (LREE), relatively low Ba, Rb, and broadly oceanic island basalt (OIB)-like primitive mantle

normalized incompatible trace element patterns are interpreted to reflect source characteristics. In addition to lead isotopic

compositions that are the most radiogenic yet analyzed from northern Kyushu and the Sea of Japan, strontium and neodymium

isotopic compositions of Fukuoka lavas free from crustal contamination are among the highest and lowest, respectively

(average, 0.7052 and 0.5126), in the region. The samples show the signature of enriched mantle type 2 (EM2), differing from

most of the other Dupal anomaly bearing lavas reported from the Sea of Japan and elsewhere in northern Kyushu. The EM2-like

characteristics and relatively low concentrations of large ionic lithophile elements (LILE), low LILE/LREE and LREE/high-

field-strength elements (HFSE), and mid-ocean ridge basalt (MORB)-like Rb/Sr and Nb/Zr ratios in the Fukuoka lavas are

explained by melts from an asthenospheric source that experienced previous melt extraction. Because the chemical

characteristics of Fukuoka basalts are strictly, geographically localized, we suggest that, while the mantle beneath most of

northern Kyushu is very much similar to that of the Sea of Japan, represented by a spectrum of depleted MORB-EM1 (Dupal-

like) hybrids, the Fukuoka EM2-rich component may have been added from shallower levels.

D 2003 Elsevier Science B.V. All rights reserved.

Keywords: Kyushu; Basalt; Isotope; Lithospheric mantle; Dupal anomaly

1. Introduction

Two oceanic plates are subducting beneath the

Japanese islands, the Pacific in the northeast and the

0009-2541/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0009-2541(03)00031-7

* Corresponding author. Tel.: +81-298-61-3558; fax: +81-298-

56-8725.

E-mail address: [email protected] (N. Hoang).

www.elsevier.com/locate/chemgeo

Chemical Geology 198 (2003) 249–268

Philippine in the southwest. Subducting slabs,

depending on the direction, dip angles and depths

control the spatial distribution of Cenozoic volcanism

on the islands (Uyeda and Kanamori, 1979; Uto,

1989; Uto and Tatsumi, 1996). Cenozoic volcanic

activity in the southwest of Japan, including northern

Kyushu, however, is believed to not directly relate to

any of the above subducting slabs but rather associ-

ated more with post-opening of the Japan Sea (Uto,

1989; Uto and Tatsumi, 1996). Intraplate basalts in

southwestern Japan show many chemically similar

characteristics, including relatively low ratios between

large ionic lithophile elements and high-field-strength

elements (LILE/HFSE) (Uto, 1989; Nakamura et al.,

1990; Uto and Tatsumi, 1996), elevated 87Sr/86Sr,

low-206Pb/204Pb and high-208Pb/204Pb (Tatsumoto

and Nakamura, 1991). The similarity has not changed

significantly over about 12 my eruption period (Uto

and Tatsumi, 1996). The lavas, while showing little

effect of subduction-related contamination and dis-

playing many chemical features similar to Cenozoic

lavas from China, Korea and especially the Japan Sea

(Uto, 1989; Nakamura et al., 1990; Uto and Tatsumi,

1996), differ fundamentally from the contemporary

subduction-related lavas in the northeast Japan vol-

canic front (e.g. Uto and Tatsumi, 1996; Ikeda et al.,

2001).

Despite a relatively large chemical database for the

Sea of Japan and southwest Japan lavas, thanks to

intensive studies that have been carried out in the

recent years, there are still many volcanic centers left

unknown. In this study, a set of samples was collected

in and around Fukuoka district and analyzed for age,

major and trace elements and Sr, Nd and Pb isotope

Fig. 1. Scheme of Cenozoic basalt distribution in and around Fukuoka; sampling sites, sample labels are indicated. Italicized numbers below

sample names are radiometric ages from Uto et al. (1993). Samples FUK9315 and FUK9316 are located southwest of Fukuoka and north of

large Higashi Matsuura volcanic field (not shown).

N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268250

compositions. The data are interpreted in terms of

temporal and spatial evolution, melting conditions,

possible crustal contamination and mantle isotopic

signature in the context of mantle dynamics.

2. Basalts in the Fukuoka district

Radiometric ages of Cenozoic intraplate basalts in

northern Kyushu are about 9–1 Ma (Uto, 1989;

Matsumoto et al., 1992; Uto et al., 1993). For the

Fukuoka district, age data reveal at least three eruptive

episodes as follows: 4.35–3.4, 2.6–2.4 and 1.6–1.1

million years ago (Matsumoto et al., 1992; Uto et al.,

1993) (Fig. 1). These three episodes of volcanic

activity may reflect renewed extension triggered by

plate kinematic adjustments following the opening of

the Japan Sea (e.g. Seno, 1999). In general, volcanic

activity in Fukuoka shows the following features: (1)

small, monogenetic volcanoes most likely formed by

a single eruption, (2) single volcanoes being within

10–25 km apart from each other, (3) short-lived (ca.

1–2 my) active periods with about 1 my of quies-

cence and (4) chemical homogeneity over a relatively

long period (Uto et al., 1993) (Fig. 1).

In addition to the samples collected in the Fukuoka

district, two samples from Kurose Island, northwest of

Fukuoka district in the Japan Sea (KRH-1 and KRH-

2: 1.13 Ma), and two samples belonging to large

Higashi Matsuura volcanic field, west of Fukuoka

(FUK9315 and FUK9316: 3.19 Ma), were added with

the aim to assess temporal and spatial evolution of the

samples.

Massive olivine alkali basalts are the dominant rock

types in Fukuoka. They are aphyric to moderately

phyric, with olivine being the only phenocryst (3–

7%). The phenocrysts represent several generations

judging from sizes that range from 3� 3 to less than

0.5� 0.5 mm and compositions. Olivine is fresh,

euhedral to sub-euhedral and sometimes aggregated.

The groundmass consists of plagioclase, olivine, cli-

nopyroxene, magnetite and interstitial glass. Magnetite

occurs as euhedral micro-phenocrysts up to 0.5� 0.5

mm (samples FUK9303, FUK9304, FUK9308 and

FUK9313). Two alkali basalts from Kurose Island

(KRH-1 and KRH-2) are the only samples bearing

mantle xenoliths in the region (Arai et al., 2000; Ikeda

et al., 2001).

3. Analytical procedures

All chemical analyses were conducted at the

Institute of Geoscience, Geological Survey of Japan

(GSJ). Powdered samples used for acquiring major

and trace element data were made from fresh parts of

whole rock samples that were crushed to < 1cm size

and pulverized in agate mills. Major elements were

obtained on fused lithium tetra-borate glass disks,

and trace elements such as Rb, Sr, Ba, Nb, Zr, Y, Zn,

Cu, Ni, Cr and V were obtained on pressed pellets

using a Philip PW1404 X-ray Fluorescence spec-

trometer. GSJ standards (JB-1a and JB-1) were

routinely measured as unknown during the measure-

ments. Rare earth elements (REE), Sc, Hf, Ta and

Th, were obtained using instrumental neutron acti-

vation analysis (INAA) equipped with an automatic

sampler and measured using a germanium detector

(ORTEC GEM20180) and a multichannel analyzer

(SEIKO EG&G 7800-8A2). For the analysis, about

50 mg of powdered sample were sealed in a quartz

tube and irradiated at Japan Atomic Energy Research

Institute’s reactor with a thermal neutron flux of

8� 1013 cm2 s� 1 for 40 min. Samples were meas-

ured twice in 7 and 30 days after irradiation with

integration time of, respectively, 7500 and 15000 s.

During the analysis, JB-1, a GSJ standard, was used

as a standard and JB-1a, another standard, was

measured as an unknown to verify the accuracy of

the analysis. In general, data obtained by INAA are

reported in Table 1. The analytical precision and

accuracy, together with the accuracy of the XRF

method relative to JB-1a standard, are reported in

Table 2.

Sr, Nd and Pb isotope compositions were also

acquired at the Geological Survey of Japan. All the

analyzed samples were fresh. Rock chips were

crushed to pieces of 1–2 mm in size and washed

ultrasonically in ultrapure water for about 30 min,

followed by multiple rinses with the water before

being ground in an agate mill. All the acids and

water used during chromatographic work were certi-

fied TAMA-Pure AA-10 grade (e.g. concentrations

of Sr, Pb and Nd are less than 5 pg/ml) and kept

under 20 jC condition. About 50 mg of the powder

(estimate about 300 ng of lead to be analyzed) was

dissolved in concentrated HNO3 and HF (ratio, 1:3),

repeated with HNO3 and followed with HCl. Pb and

N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 251

Table 1

Chemical compositions of Fukuoka basalts

Sample FUK9303 FUK9304 FUK9305 FUK9306 FUK9307 FUK9308 FUK9309 FUK9310 FUK9311

Age 3.74 3.89 3.98 2.49 2.49 2.49 2.49 2.63 2.49

SiO2 46.38 45.56 49.93 48.66 45.23 48.00 47.72 47.14 46.56

TiO2 3.07 3.19 2.38 2.55 3.34 3.07 3.11 3.05 2.99

Al2O3 14.18 14.09 16.02 15.67 14.86 14.65 14.97 14.81 14.81

FeO* 13.46 13.85 10.99 11.66 15.04 12.47 12.23 13.29 13.26

MnO 0.20 0.19 0.16 0.17 0.18 0.17 0.18 0.18 0.18

MgO 8.58 7.88 5.79 6.07 7.12 6.68 6.74 6.81 6.91

CaO 9.08 10.02 8.82 8.94 9.18 8.74 8.91 9.12 9.28

Na2O 2.84 3.05 3.89 4.02 3.19 3.70 3.37 3.31 3.72

K2O 1.49 1.39 1.23 1.32 1.26 1.57 1.85 1.39 1.33

P2O5 0.73 0.79 0.78 0.94 0.58 0.93 0.92 0.90 0.95

Sum 100 100 100 100 100 100 100 100 100

Mg-number 53.2 50.4 48.4 48.1 45.8 48.9 49.6 47.7 48.2

Ba 331 314 307 309 205 363 367 346 307

Rb 27 23 20 24 17 26 31 21 20

Sr 711 777 899 974 1063 943 979 967 942

Zr 189 196 199 198 91 192 189 179 175

Y 27 27 25 22 18 27 25 22 23

Nb 30 33 24 28 14 28 27 28 28

Ni 94 72 25 38 37 41 38 40 43

Cr 213.6 169.1 104.5 130.2 74.9 156.6 160.5 139.2 149.6

Sc 25.5 26.9 30.4 28.6 29.9 29.4 24.6 30.4 24.4

La 30.5 33.5 50.3 56.0 24.6 56.7 40.8 49.7 38.4

Ce 78.6 85.2 111.8 124.9 63.4 117.2 101.6 115.4 92.4

Nd 37.1 61.1 60.7 77.4 45.2 70.7 42.2 67.5 57.1

Sm 8.9 10.0 10.0 11.5 8.6 11.7 10.5 11.4 9.2

Eu 2.5 2.9 3.0 3.2 2.7 3.5 2.7 3.4 2.8

Tb 1.4 1.1 1.2 0.9 1.1 1.1 1.2

Yb 2.1 2.2 2.5 2.6 1.7 2.8 2.0 2.4 1.8

Lu 0.3 0.3 0.4 0.3 0.2 0.4 0.2 0.3 0.2

Hf 4.8 4.8 6.0 6.2 3.5 6.1 5.2 6.0 4.5

Ta 1.9 1.9 1.6 2.1 1.0 2.5 1.9 2.4 1.9

Th 2.7 2.5 5.8 6.4 1.6 4.2 3.7 4.5 3.487Sr/86Sr 0.705173 0.705290 0.705213 0.705245 0.705322 0.705265143Nd/144Nd 0.512662 0.512624 0.512628

eNd 0.47 � 0.27 � 0.20206Pb/204Pb 18.390 18.401 18.426 18.410 18.333 18.413207Pb/204Pb 15.578 15.592 15.601 15.611 15.518 15.605208Pb/204Pb 38.528 38.569 38.619 38.614 38.416 38.601

D8/4Pb 66.7 69.6 71.4 73.0 62.5 71.3

D7/4Pb 9.4 10.7 11.3 12.4 4.0 11.8

Sample FUK9312 FUK9313 FUK9314 FUK8602 R64030 NOK-1 KRH-1 KRH-2 FUK9316 FUK9315

Age 3.39 3.52 3.51 1.62 1.62 1.13 1.13 3.19 3.19

SiO2 43.70 44.49 44.88 51.39 51.15 47.95 48.82 49.55 48.41

TiO2 3.60 3.73 3.56 2.43 2.15 2.74 2.59 1.74 1.77

Al2O3 14.69 13.57 14.18 16.52 17.57 15.51 15.70 14.98 15.01

FeO* 15.91 15.18 14.56 9.99 10.48 10.86 10.07 10.19 11.45

MnO 0.23 0.21 0.22 0.12 0.2 0.17 0.16 0.16 0.16

MgO 6.79 7.20 7.28 4.90 4.06 7.39 7.91 8.90 8.96

CaO 9.72 9.82 9.57 8.15 8.07 8.90 8.76 9.47 9.36

Na2O 3.23 3.13 3.21 4.07 4.11 4.66 4.48 2.99 3.04


Sr extractions used Sr-spec resin from Eichrom,

following the procedure described by Deniel and

Pin (2001). For the procedure, samples were loaded

in 1.5 ml of 2 M HNO3 into 1-ml pipette tip

columns with a resin bed of about 0.05–0.07 ml.

The samples were rinsed with 1.5 ml of 2 M HNO3

then with 1 ml of cold 7.5 M HNO3. To reduce

possible Rb interference and Sr impurity, about 0.2

ml of ultrapure water was added before Sr being

collected in 1 ml of 0.05 M HNO3. After Sr, the

columns were washed with 0.5 ml of 0.05 M HNO3

followed by 2 ml of 2 M HCl, and Pb was collected

in 1.5 ml of 6 M HCl. The Pb samples were dried

on a hot plate under a lamp in nitrogen gas flow

tank for about 2 h. Solutions after Sr and Pb elution

were used for rough extraction of rare earth ele-

ments using conventional AG50W-X8 resin in small

quartz columns (resin bed is about 4 mm (i.d.) by

50 mm height), followed by Ln-resin (Eichrom) using

0.2 N HCl as eluant to extract Nd, following the

procedure described by Pin and Santos Zalduegui

(1997).

Nd, Sr and Pb isotope ratios were measured on a

multi-collector VG Sector 54 thermal ionization mass

spectrometer at GSJ. Sr and Pb isotopes were obtained

on single Ta and Re filaments, respectively, while Nd

was measured as metal on triple Re filaments. The87Sr/86Sr was normalized to 86Sr/88Sr = 0.1194 and the143Nd/144Nd was normalized to 146Nd/144Nd = 0.7219.

The within-run precision (2r) for 87Sr/86Sr was

F 0.000006 to F 0.000009 and F 0.000007 to

F 0.000012 for 143Nd/144Nd. During the period of

Table 1 (continued )

Sample FUK9312 FUK9313 FUK9314 FUK8602 R64030 NOK-1 KRH-1 KRH-2 FUK9316 FUK9315

K2O 1.07 1.43 1.40 1.60 1.49 1.05 0.85 1.58 1.47

P2O5 1.06 1.24 1.13 0.77 0.75 0.77 0.65 0.43 0.36

Sum 100 100 100 100 100 100 100 100 100.00

Mg-number 43.2 45.8 47.1 46.7 40.9 54.8 58.3 60.9 58.2

Ba 205 341 293 368 730 706 593 527

Rb 10 18 18 31 41 38 36

Sr 701 1033 884 1037 672 477 513

Zr 199 241 220 206 216 133 125

Y 35 35 30 20 28 22 24

Nb 31 40 35 24 61 33 30

Ni 22 28 29 21 143 166 162

Cr 51.5 136.6 143.0 106.5 181 208.1 473.5 489

Sc 27.5 28.7 28.5 20.3 20.7 23.2 21.4 21.4 28.0 27.4

La 27.2 51.7 41.1 43.7 47.6 36.8 38.9 40.6 29.9 29.3

Ce 76.4 124.3 108.3 96.8 95.0 77.0 75.3 78.9 56.0 52.3

Nd 40.3 85.5 52.7 43.5 42.7 35.8 40.0 34.3 25.8 19.6

Sm 10.9 14.1 12.0 7.5 7.8 7.8 7.9 7.7 5.8 5.3

Eu 2.8 3.6 3.2 2.2 2.2 2.2 2.7 2.4 1.7 1.8

Tb 1.4 1.4 1.1 1.4 0.8 1.1

Yb 2.4 2.6 2.4 1.3 1.7 1.8 2.4 2.2 2.1 2.2

Lu 0.3 0.4 0.3 0.2 0.3 0.3 0.3 0.3 0.3 0.3

Hf 5.1 5.1 5.6 4.8 3.9 3.7 2.9 4.9 3.5 3.3

Ta 1.7 2.7 2.2 1.3 1.3 1.4 4.2 3.9 1.9 1.8

Th 0.9 2.9 2.3 5.2 5.2 4.7 6.0 6.2 4.7 4.487Sr/86Sr 0.705118 0.705120 0.705399 0.705496 0.705142 0.704141 0.704416 0.704195 0.704366143Nd/144Nd 0.512713 0.512843 0.512708

eNd 1.46 4.00 1.37206Pb/204Pb 18.375 18.390 18.375 18.366 18.384 18.356 18.387 17.915 17.776207Pb/204Pb 15.589 15.567 15.579 15.562 15.585 15.600 15.609 15.515 15.434208Pb/204Pb 38.514 38.499 38.525 38.491 38.547 38.667 38.697 38.266 38.033

D8/4Pb 67.1 63.9 68.3 65.9 69.3 84.7 84.0 97.9 91.5

D7/4Pb 10.6 8.3 9.7 8.0 10.1 11.9 12.5 8.2 1.6


measurement, 87Sr/86Sr of the NBS 987 Sr standard

was 0.71025F 0.00001 (1r, n= 18) and 143Nd/144Nd

for the JNdi-1 (GSJ) Nd standard (Tanaka et al., 2000)

was 0.512105F 0.000005 (1r, n = 10). Lead isotopic

compositions were corrected for mass fractionation

and are reported relative to the NBS 981 Pb standard

values of (mean, 1r, n = 16) 36.564F 0.025,

15.453F 0.010 and 16.908F 0.009 for 208Pb/204Pb,207Pb/204Pb and 206Pb/204Pb, respectively. Internal

precision of the Pb ratios (2r) is less than 0.01%,

and total blank is smaller than 50 pg. The data are

shown in Table 1.

4. Analytical results

4.1. Major and trace elements

Data for the Fukuoka lavas are reported and com-

pared with data from other northern Kyushu centers

(Hoang and Uto, 2003). Major elements from Fukuoka

basalts show many features that are not observed in

other northern Kyushu basalt centers. For example,

they have the highest FeO*, TiO2, lowest SiO2 and

relatively low K2O accompanied by moderate to low

MgO contents (Table 1, Fig. 2). However, other major

elements are within the range of the latter. Except for a

basalt with SiO2 of 51.39 (wt.%) and FeO* of 10

(wt.%), olivine and alkali basalts range in SiO2 from

ca. 43 to 50 (most less than 47%), FeO* from about 12

to 16 (wt.%) and TiO2 from 2.35 to 3.7 (wt.%) with

MgO at 6–8 (wt.%). Plots of MgO against major

element oxides for Fukuoka basalts (Fig. 2) reveal a

broadly positive correlation with FeO* and CaO, and a

clearly negative correlation with SiO2, Al2O3 and

Na2O and little correlation with TiO2 and K2O (not

shown), indicating possible olivine fractionation. Two

samples from Kurose Island, except those showing

higher TiO2 and Na2O and slightly lower FeO*, plot

within the fields of other northern Kyushu lavas,

including the two samples from Higashi Matsuura,

differing from other Fukuoka samples (Fig. 2).

Compared with other northern Kyushu lavas

(Hoang and Uto, 2003), Fukuoka basalts have the

highest Sr (from 700 to 1100 ppm) and Sm (8–12

ppm) and relatively low Rb and Ba with average

values of, respectively, 20 and 280 ppm compared

with Rb and Ba in olivine alkali basalts from other

nearby centers of 40–600 ppm, respectively, which

are more comparable with reported worldwide alkali

basalts (Weaver, 1991; Chauvel et al., 1995; Hof-

mann, 1997). The basalts show the lowest Ni (most

below 50 ppm) and low Cr (mean value of 135

compared with >300 ppm in other northern Kyushu

centers) (Fig. 3, Table 1). However, the Fukuoka La

(and other light rare earth element [LREE]), Nb (25

ppm average) and Zr (mean value, 190 ppm) are

within the range of other northern Kyushu lavas.

Relative depletion of Rb and Ba and the elevation

of Sr abundances result in low N-MORB-like Ba/Zr

and Rb/Sr (mean value of 1.7 and 0.025), and low Ba/

La and Nb/Zr (Fig. 3). High HREE and HFSE

Table 2

Analytical results of JB-1a standard

XRF JB-1ameasuredF r, n= 6 Ref.a

SiO2 53.31F 0.65 53.40

TiO2 1.32F 0.02 1.30

Al2O3 14.71F 0.09 14.72

FeO* 8.68F 0.43 8.49

MnO 0.14F 0.00 0.15

MgO 7.84F 0.08 7.98

CaO 9.42F 0.09 9.49

Na2O 2.81F 0.05 2.78

K2O 1.43F 0.02 1.43

P2O5 0.27F 0.01 0.26

Sum 100 100

Ba 496.1F1.89 504

Rb 39.0F 0.46 39.2

Sr 439.3F 2.51 442

Zr 145.3F 0.50 144

Y 26.1F1.86 24

Nb 26.3F 1.04 26.9

Ni 141.0F 1.80 139

Cr 406.9F 1.92 392

INAA F r, n= 3 Ref.a

Sc 28.2F 0.3 27.9

La 39.5F 0.4 37.6

Ce 66.8F 1.5 65.9

Nd 23.4F 3.0 26

Sm 5.04F 0.1 5.07

Eu 1.47F 0.02 1.46

Tb 0.69F 0.17 0.69

Yb 2.27F 0.05 2.1

Lu 0.34F 0.01 0.33

Hf 3.32F 0.10 3.41

Ta 1.92F 0.11 1.93

Th 9.04F 0.11 9.03

a Values and analytical sources of the standard may be found at

http://www.aist.go.jp/RIODB/geostand/igneous.html. Major ele-

ments are normalized to 100% volatile-free.


http:\\www.aist.go.jp\RIODB\geostand\igneous.html

Fig. 2. Plots of wt.% major elements vs. wt.% MgO for samples shown in Fig. 1 (Table 1); data for other northern Kyushu basalt centers are

from Hoang and Uto, 2003.


Fig. 3. Plots of wt.% MgO against trace element abundances and ratios, data from Table 1.


accompanied by relatively high LREE concentration

lead to generally higher LREE/HREE, but LREE/

HFSE is slightly lower relative to other northern

Kyushu basalts (Fig. 3).

MgO contents are correlated negatively with La

(and other LREE) and Sr, and positively with Ni, but

are scattered with other trace elements such as Ba, Rb,

Zr and Sm (Fig. 3). Incompatible element distribu-

tions normalized to average primitive mantle (Hof-

mann, 1988) are broadly oceanic island basalt (OIB)-

like (Fig. 4). Except the slight depletion of Rb, Th and

Ba, however, the LREE to HREE slope is much

gentler than normally observed for typical OIB under

garnet control. For instance, average La/Sm in the

Fukuoka basalts is 4.1 compared to 5.4 for OIB

(Hofmann, 1988). In general, while the behavior of

some incompatible trace elements in Fukuoka basalts

is different from those of other northern Kyushu

basalts and may be used to discriminate from the

latter, the concentration of many of the trace elements

in basalts from northern Kyushu centers, including

those in the Fukuoka district, is in the range that is

Fig. 3 (continued).


normally observed for intraplate basalts (Nakamura et

al., 1990; Tatsumoto and Nakamura, 1991; Hoang et

al., 1996). Note that samples from Higashi Matsuura

and Kurose Island show significantly higher Ba,

slightly higher Rb, but lower Sr and Sm than the

other. In addition, samples from Kurose Island have

the highest Nb and Ta (Figs. 3 and 4).

High FeO* and TiO2 contents accompanying

relatively low MgO may reflect olivine fractionation

as illustrated in Fig. 2. For example, the contents of

FeO* and MgO in sample FUK9312 are 15.9 and

6.67, respectively, which theoretically is in equili-

brium with an olivine of Fo72, assuming Kd (Fe/Mg)ol/liq

is 0.30 (Fe2O3/FeO = 0.10; Roeder and Emslie, 1970).

Thus, Mg-number is too low for a primitive basalt

(see Hirose and Kushiro, 1993; Kushiro, 1996). More-

over, the Fukuoka samples have low Cr (average,

135 ppm) and especially Ni abundances (21–96,

but mostly less than 40 ppm) (Fig. 3) too low to be

considered as primitive. In spite of broadly positive

correlation between MgO and FeO*, the latter does

not form a clear trend with FeO*/MgO (Fig. 2),

suggesting that olivine may not be the only crys-

tallizing phase. Evidence of clinopyroxene and

possibly plagioclase crystallization may be illus-

trated by positive correlation between MgO and

CaO (Fig. 2). In general, the major element varia-

tions indicate that olivine (and possibly pyroxene

and magnetite) was the primary crystallizing phase

in these basalts.

4.2. Strontium, neodymium and lead isotopes

Mantle components have been identified from

isotopic studies of mid-ocean ridge basalt (MORB)

and OIB magmas (Zindler and Hart, 1986), including

(1) depleted MORB (DM) mantle, interpreted to

represent depleted asthenosphere feeding mid-ocean

ridge magmas, (2) enriched mantle (EM1) with rela-

tively low 206Pb/204Pb and 87Sr/86Sr, but high208Pb/204Pb and 207Pb/204Pb, which may represent

ancient Pb-enriched continental crust and (3) a second

enriched mantle (EM2) component with high206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and 87Sr/86Sr,

interpreted as Phanerozoic continental crust and/or

crust-derived sediments.

Northern Kyushu samples lie well above and gen-

erally sub-parallel to the Northern Hemisphere Refer-

ence Line (NHRL) (Hart, 1984), showing collinear

trends between high- (EM2-like) and low-206Pb/204Pb

(EM1-like) extremes and being sandwiched between

high- and low-208Pb/204Pb Ulreung-Dog and Sea of

Japan back-arc basalts, respectively, at the same206Pb/204Pb ratios (Fig. 5a–c). Fukuoka lavas show

the highest 206Pb/204Pb (18.4–18.5) yet analyzed for

basalts in the back-arc side of the Japanese islands,

and among the highest in 208Pb/204Pb (ca. 38.6) and207Pb/204Pb (ca. 15.6) observed from northern Kyushu

lavas (Nakamura et al., 1990; Tatsumoto and Naka-

mura, 1991; Cousens and Allan, 1992) (Fig. 5b–c).

The combination of moderately high 208Pb/204Pb but

Fig. 4. Incompatible element distribution normalized to primitive mantle for representative basalts from Fukuoka, Higashi Matsuura (filled

diamond), Kurose Island (open diamond). Note slight depletion of LILE relative to LREE of the Fukuoka basalts. Also shown is an OIB sample

from Hawaii (dashed line, data from Frey et al., 2000) for comparison. Normalizing data from Hofmann (1988).


Fig. 5. Plots of (a) 207Pb/204Pb and (b) 208Pb/204Pb vs. 206Pb/204Pb and (c) D7/4 Pb vs. D8/4 Pb for the studied samples compared with data

fields for Ulreung-Dog islands and the Japan Sea Basin (data from Tatsumoto and Nakamura, 1991; Cousens and Allan, 1992). Northern

Hemisphere Reference Line (NHRL) and calculation for D7/4 Pb and D8/4 Pb from Hart (1984), mantle components EM1, EM2 and N-MORB

from Zindler and Hart (1986). Data for other northern Kyushu lavas are from Hoang and Uto, 2003.


Fig. 6. Plots of 87Sr/86Sr vs. 143Nd/144Nd (a), 206Pb/204Pb (b) and (c) D8/4 Pb for Fukuoka and offshore basalts compared with data fields of

Ulreung-Dog islands, the Japan Sea Basin (data from Tatsumoto and Nakamura, 1991; Cousens and Allan, 1992) and mantle xenoliths from

southwest Japan (data from Ikeda et al., 2001). Mantle isotopic components are from Zindler and Hart (1986). Data for other northern Kyushu

lavas are from Hoang and Uto, 2003. Note that in all figures, Fukuoka basalts tend toward EM2 relative to the other. See text for details.


very high 206Pb/204Pb results in the Fukuoka basalts

having the lowest D8/4Pb (a deviation from NHRL

and the indicator of Dupal anomaly (Hart, 1984)).

Thus, the Fukuoka samples show the most EM2-like

characteristics of northern Kyushu lavas (Table 1, Fig.

5c).

In addition to high lead isotopic ratios, 87Sr/86Sr

isotopes in the Fukuoka basalts are high, ranging from

0.70519 to 0.70532, and are among the most radio-

genic in the region. High 87Sr/86Sr accompanied by

low 143Nd/144Nd (0.5126–0.5127) trends toward the

EM2 extreme (Fig. 6a). Plots of isotope data from

Fukuoka, together with those from the Sea of Japan

and northern Kyushu, show a complicated, three-

component correlation (Fig. 6b–c). Low 87Sr/86Sr,

low 208Pb/204Pb and D8/4Pb basalts from the Japan

Sea Basin are viewed as the most depleted end

member, forming one of the apexes, high 87Sr/86Sr,208Pb/204Pb and D8/4Pb EM1-like Ulreung-Dog

island lavas define the second, and Fukuoka basalts

having the highest 87Sr/86Sr and 208Pb/204Pb and

lowest D8/4Pb occupy the third EM2-like extreme.

Meanwhile, other northern Kyushu basalts are embed-

ded within the triangle (Figs. 5 and 6). Therefore, any

explanation for the isotopic characteristics of the

basalts should involve at least three above representa-

tive end members.

Note that the Kurose (KRH-1,KRH-2: 1.1 Ma) and

especially Higashi Matsuura samples (FUK9315–16:

3.2 Ma) tend more toward EM1-like, differing from

the rest of the Fukuoka samples. However, Fukuoka

samples FUK8602 and R64030 (1.6 Ma) and

FUK9312–14 (3.4 Ma) have similar isotopic compo-

sitions and plot within the field of other Fukuoka

samples. Therefore, there does not appear to be a

temporally related change in source.

5. Discussion

5.1. Crustal contamination

The strontium isotopic compositions of the Fukuoka

samples are high (most >0.705), although many are in

the range of those reported for the Sea of Japan and

elsewhere in southwest Japan (Kurasawa, 1968;

Nohda et al., 1988; Morris and Kagami, 1989; Naka-

mura et al., 1990; Tatsumoto and Nakamura, 1991),

but the test for any crustal contamination is essential.

The extent of wall rock contamination in continental

basalts is controversial and difficult to identify unless

chemical compositions of both contaminant and mag-

matic source are independently known (Carlson and

Hart, 1988). In general, the addition of crustal material

to basaltic magmas or their source region is expected

to result in a positive covariance of 87Sr/86Sr with

parameters such as SiO2, Rb/Sr and K2O/P2O5 (Carl-

son and Hart, 1988), although this relationship may be

complicated by assimilation-fractional crystallization

and partial melting effects (DePaolo, 1981).

Fig. 7a,b shows that 87Sr/86Sr and 206Pb/204Pb

change only slightly over the range of MgO, suggest-

ing that assimilation-fractional crystallization (AFC,

DePaolo, 1981) process is unlikely to have been

responsible for the enrichment of the Fukuoka lavas.

Plots of 87Sr/86Sr against Rb/Sr for the Fukuoka

samples shown in relation to N-MORB and continen-

tal crust compositions (Fig. 8a) show that the samples

cluster around a narrow range of Rb/Sr (0.01–0.04)

apart from other northern Kyushu centers. In addition,

crustal involvement results in increasing Ba/Zr, Rb/Zr

and Sr/Zr relative to Ti/Zr (Hoang and Flower, 1998).

Fig. 8b shows Ba/Zr ratios of the Fukuoka samples,

which are within the N-MORB range, plot within the

mantle array providing further indication that crustal

contamination is minimal.

5.2. Mantle signature inferred from major and trace

element compositions

Cenozoic OIB-like basalts along the Sea of Japan

margin in southwest Japan are characterized by low

LILE/HFSE and high LREE/HFSE, and are different

from those lavas influenced by the subduction-related

dehydrated fluids (Uto, 1989; Morris and Kagami,

1989; Uto and Tatsumi, 1996).

Experimentally determined compositions of basal-

tic melts (Hirose and Kushiro, 1993; Baker and

Stolper, 1994; Kushiro, 1996) have shown that their

SiO2 contents are primarily pressure-dependent and

decrease with increasing pressure. Concentrations of

FeO also strongly depend on pressure (see Hirose

and Kushiro, 1993 and references therein), decreas-

ing with increasing melting pressure and, unlike

MgO, decreasing with increasing melt fraction. In

addition, FeO contents increase with increasing melt-


ing temperature (Hirose and Kushiro, 1993). Kogiso

et al.’s (1998) experiments showed that melting of

peridotite–basalt mixtures tends to produce silica-

undersaturated magmas enriched in Fe and Ti

(Kogiso et al., 1998). Generally, FeO (TiO2)-rich

(OIB-like) basalts in continental settings are com-

monly interpreted to reflect melting from a fertile

asthenospheric source (e.g. Hawkesworth et al.,

1988; Gallagher and Hawkesworth, 1992; Turner

and Hawkesworth, 1995).

In general, other than high FeO abundances, major

element characteristics of Fukuoka basalts, while

differing from other northern Kyushu samples, are

closely similar to many intraplate alkali basalts and

basanites both from oceanic (Hawaiian) and continen-

tal (northeast China and elsewhere) settings (e.g. Uto,

unpublished data; Tu et al., 1991; Turner and Hawkes-

worth, 1995), and moreover, regardless of the anom-

aly in abundance of some trace elements that may not

be readily explained by fractionation from each other

Fig. 7. Plots of wt.% MgO vs. (a) 87Sr/86Sr and (b) 206Pb/204Pb for the studied samples. Note no significant variation of the isotopic

compositions observed for Fukuoka samples over a range of MgO. Samples from Kurose Island and Higashi Matsuura plot outside the range of

the Fukuoka.

Fig. 8. (a) Plots of 87Sr/86Sr vs. Rb/Sr and (b) Ti/Zr vs. Ba/Zr for the studied samples (Fig. 1, Table 1) in relation to N-MORB (Regelous et al.,

1999), continental crust (CC) (Taylor and McLennan, 1981), OIB hypothetical distribution line extrapolated based on data from Kogiso et al.

(1997) and Frey et al. (2000) and primitive mantle (PM) (Hofmann, 1988). See text for detailed discussion.


by melting, the incompatible trace element distribu-

tion patterns are generally OIB-like (Fig. 4); we

propose that major and trace element compositions

of Fukuoka alkali basalts are consistent with basaltic

melts derived from an asthenospheric source that is

fertile to slightly depleted.

5.3. Asthenosphere dynamics

Asthenosphere dynamic effects responsible for

partial melting may include secondarily induced con-

vection at passive margins (Mutter et al., 1988) or a

plume ‘head’ impacting at the base of the lithosphere

(McKenzie and Bickle, 1988). When high temperature

asthenosphere rises from lower levels by convection,

following lithosphere stretching, it will melt partially,

and the melting degree will increase because of the

pressure decrease. Some molten parts of the astheno-

spheric mass flow may obtain buoyancy and Ray-

leigh–Taylor instability that happens because the

density of the upwelling mass becomes lower than

the overlying mantle (Kerr and Lister, 1988 cf. Mutter

et al., 1988). Thus, the small dimension mass flow

may start to penetrate the overlying mantle as diapirs.

Mantle diapirs should stop when their density is about

the same as of the surrounding material or when they

are forced to stop at the base of the mantle lithosphere

acting as rigid wall. Partial melt will then segregate

from the diapirs and pool before erupting to the

surface, with or without interaction with the mantle

lithosphere and/or crust.

The concept of the formation and rise of mantle

diapirs appears to explain the volcanic activity in

Fukuoka in terms of the small volume and areal

distribution of the volcanoes, and possibly the perio-

dicity of eruption, on the one hand, and source

homogeneity and the similarity of melting conditions,

on the other. However, there are several aspects that

need to be accounted for. Is the chemical heteroge-

neity among Cenozoic basalts in northern Kyushu due

to differences in the depth of origin of the mantle

diapirs (asthenosphere) or to interaction with the

overlying mantle (continental lithospheric mantle)

where they stop rising, which may be further compli-

cated by crustal contamination?

Asthenosphere is believed to be fertile but depleted

in the most incompatible trace elements. It is hot and

chemically well mixed due to vigorous convection. In

contrast, the continental lithospheric mantle (thermal

boundary layer) is not involved in convection and is

believed to be variably refractory but enriched in

incompatible elements (Anderson, 1995). As reported

elsewhere, heterogeneity is commonly observed for

the continental lithospheric mantle, which records

histories of melt addition and removal (e.g. Carlson

and Irving, 1994), and ancient and recent metasoma-

tism (e.g. Menzies et al., 1987), and leaves heteroge-

neous and complexly enriched, diversified EM1-,

EM2-rich reservoirs.

The Fukuoka lavas, which appear to be free from

crustal contamination, have features that are consis-

tent with their derivation from a fertile and variably

depleted asthenospheric source. We therefore assume

that the EM2-like isotopic enrichment of the Fukuoka

basalts is an asthenospheric characteristic of these

magmas, assuming that the EM2 component (recycled

sediment?) introduced into the asthenosphere lowers

the solidus, following the breakdown of hydrous

phases that allows decompression melting to com-

mence deeper, and this component happens to be

beneath the region for the last several million years.

If this is true, and because the enrichment is geo-

graphically localized, we need to explain how the

supposedly small-sized, deep and enriched source still

remains beneath Fukuoka and survives despite the

asthenospheric convection over several millions of

years.

Tatsumoto and Nakamura (1991) observed that206Pb/204Pb from southwest Japan alkaline rocks

shows a smooth decrease from northeast to southwest

Japan and then to inland China. Most northeast China,

southwest Japan and Ulreung-Dog island lavas have

D8/4Pb values higher than 60, indicating that rocks

from the Eurasian margin were derived from a source

having high Th/U for a long time. Because within the

Japan Sea and southwest Japan there are a number of

continental remnants believed to be eastward exten-

sions of the Korean Peninsula, including Yamato

Bank, Ulreung and Oki flanks (Ludwig et al., 1975),

the regional variation of 206Pb/204Pb may be inter-

preted to reflect either contamination effects of the

EM1-rich (Sino-Korean) cratonic lithospheric rem-

nants (e.g. Ulreung-Dog islands) or heterogeneity of

the underlying asthenosphere (e.g. Tatsumoto and

Nakamura, 1991; Cousens and Allan, 1992). Nohda

et al. (1988) observed a temporal shift in basalts from


enriched Nd and Sr characters during the preopening

stage of back-arc spreading of the Sea of Japan to a

depleted signature during the post-opening stage, and

interpreted the temporal shifts as a result of decreasing

involvement of subcontinental lithosphere as it be-

comes thinner during back-arc spreading. This model

implies that melts of homogeneous MORB-like asthe-

nosphere could be variably enriched depending on the

age and type of the penetrated lithosphere. However,

the EM1 component affects all Japan-area basalts

including those from the Japan Sea Basin (Tatsumoto

and Nakamura, 1991; Cousens and Allan, 1992), and

thus appears to be an intrinsic component of the

asthenospheric source in this area. In contrast, we

observe that the isotopic compositions of basalts from

different centers (localities) in northern Kyushu plot

within distinct fields and show a general correlation

between low-206Pb/204Pb, low-87Sr/86Sr (EM1-like)

and high-206Pb/204Pb, high-87Sr/86Sr (EM2-like)

among the others, regardless of eruption age (Figs.

5–7; Hoang and Uto, 2003), suggesting that, beside

possibly a common (EM1-like) source shared by the

centers, there may be a spatial factor that controls the

EM2-like chemical diversity. Various peridotites

recovered in southwest Japan, including northern

Kyushu, reveal a heterogeneous upper mantle in terms

of degree of depletion and enrichment (Arai et al.,

2000; Ikeda et al., 2001). Isotopic data reported for

recovered xenoliths are limited, but the data from

Ikeda et al. (2001) show a large range of Sr and Nd

isotopic compositions (Fig. 6a), suggesting EM2-like

presents in the lithosphere mantle (Ikeda et al., 2001)

that controls the local-scale chemical diversity. There-

fore, we suggest that the mantle heterogeneity in-

ferred beneath southwest Japan might reflect both the

depth of origin of asthenospheric diapirs and/or the

effects of their interaction with overlying lithospheric

mantle.

5.4. Isotopic mixing model

Finally, reports of the existence of the Dupal-like

anomaly in East and Southeast Asia are not new

(Mukasa et al., 1987; Tatsumoto and Nakamura,

1991; Tu et al., 1991; Hoang et al., 1996). The

anomaly (pervasive EM1) defined by Hart (1984) as

an enriched component with low 206Pb/204Pb, high208Pb/204Pb, 87Sr/86Sr>0.705 and D8/4Pb> + 60 orig-

inally was applied to basalts from the Indian Ocean

and was believed to belong to mantle domains in the

Southern Hemisphere (Hart, 1984). Several workers

have observed the similarity of Dupal-like East Asian

and western Pacific (WPAC) asthenosphere to Indian

Ocean (I)-MORB (Mahoney et al., 1992) and sug-

gested that it reflects a common mantle reservoir

formed by northward flow of the Indian Ocean mantle

(Mukasa et al., 1987; Hickey-Vargas et al., 1995;

Castillo, 1996). Of endogenous enrichment, Tatsu-

moto and Nakamura (1991) appealed that it is a

distinct reservoir generated by (deep) mantle plumes.

In contrast, Tu et al. (1991) and Hoang et al. (1996)

followed by Flower et al. (1998) proposed a delami-

nated Sino-Korean cratonic mantle for the following

reasons. Firstly, WPAC thermal (low velocity) anoma-

lies are shallow and not indicative of deep mantle

plume (Zhang and Tanimoto, 1993). Secondly, mantle

contamination is strongest beneath the Sea of Japan,

proximal to the Sino-Korean craton, where volcanic

rocks and mantle-derived xenoliths show extreme

enrichment in an EM1-like contaminant (Basu et al.,

1991; Tatsumoto and Nakamura, 1991), and to lesser

extent, Taiwan and Indochina, and concentration gra-

dients inconsistent with either north–south flow or

provenance beneath WPAC basins. Thirdly, there are

strong indications that Archean lithospheric mantle

has been removed from the Sino-Korean craton since

the Mesozoic (Griffin et al., 1992; Tatsumoto et al.,

1992). Thus, asthenospheric EM1 may have been

incorporated by east-flowing asthenosphere associated

with Tethyan closure (Hoang et al., 1996; after

McKenzie and O’Nions, 1983).

In explaining the triangular relationship of isotopic

compositions of the Fukuoka basalts with respect to

other southwest Japan intraplate lavas, including the

Sea of Japan, we adopt the isotopic mixing model

reported by Hoang et al. (1996) and Flower et al.

(1998). Based on existing geophysical evidence and

EM1 concentration gradients relative to the Sino-

Korean craton, they proposed that the East Asian

‘low velocity component’ (LVC) might be identified

assuming that the mantle isotopic variation may be by

variable EM1-like enrichment of DM and HIMU

(high 238U/204Pb mantle component, Zindler and Hart,

1986) hybrids, and followed by contamination of the

asthenosphere (or partial melts) by crust-derived

EM2. Using end members defined in terms of Sr


and Pb elemental contents and isotopic ratios of87Sr/86Sr and 206Pb/204Pb from the literature, these

were calculated as a basis for understanding LVC

mass balances and illustrated by plots of 87Sr/86Sr vs.206Pb/204Pb (Fig. 9). Mixing of HIMU and DM (curve

A) appears to be a fundamental constraint on global

suboceanic mantle (Hart et al., 1992). East Pacific

Rise (13–23j) N-MORB compositions lie on the

HIMU/DM mixing line, and an average of these is

taken to be the N-MORB end member for the East

Asian WPAC asthenosphere. Curve B illustrates

development of the East Asian–WPAC domain by

addition of EM1 to the N-MORB (Mukasa et al.,

1987; Tu et al., 1991) prior to its contamination by, or

mixing with, lithospheric EM2, as presented by curves

C1–C6 (Fig. 9). East Asian–WPAC asthenosphere

may thus reflect EM1-enriched N-MORB mantle

with, for example, small, subducting slab-derived

additions of fluid and sediment melt.

According to the model, the most depleted samples

from the Sea of Japan spreading center that form one

of the apexes of the triangle (Figs. 5 and 6) are

consistent with addition from 1% to 2% of the defined

EM1 component to the N-MORB before EM2 was

added. The configuration of other northern Kyushu

centers is almost similar to the Japan Sea Basin

basalts, which reflects EM2 addition to EM1-rich

compositions (e.g. Tatsumoto and Nakamura, 1991),

with maximum additions of ca. 2% EM1 and 5% of

EM2. Note that, while northern Kyushu and the Japan

Sea Basin variation may be consistent with the addi-

tion of EM2 to EM1-rich melts, Ulreung-Dog com-

positions that make the second apex, showing the

highest EM1-rich addition, may be explained by

reaction with EM1-rich wall rocks as suggested by

Cousens and Allan (1992). Meanwhile, Fukuoka

compositions, which form the third apex, showing

the highest EM2 addition, about 7%, and being differ-

Fig. 9. Plots of 87Sr/86Sr against 206Pb/204Pb for the studied samples compared with data from other northern Kyushu (Hoang and Uto, 2003),

data fields of Ulreung-Dog islands, the Sea of Japan spreading center (data source is in Figs. 5 and 6). Hypothetical mixing lines are constructed.

Line A: N-MORB (DM/HIMU hybrid) with 87Sr/86Sr = 0.70265 and 206Pb/204Pb = 18.45 (average values of East Pacific Rise MORB, data from

Mahoney et al., 1994), Sr = 20 (ppm), Pb = 0.05 (ppm); mixing line B: the N-MORB+EM1 (87Sr/86Sr = 0.707, 206Pb/204Pb = 16.84, Sr = 180

(ppm) and Pb = 17 (ppm)) giving rise to heterogeneous, EM1-rich sub-Asian WPAC asthenosphere; mixing line C1–C6: N-MORB/EM1

hybrids (increments of 0.1%, 0.5%, 1%, 2%, 5% and 10% EM1) + EM2 (87Sr/86Sr = 0.710 and 206Pb/204Pb = 18.82, Sr = 180 (ppm) and Pb = 17

(ppm)) reflecting variable addition of EM2 to the Asian WPAC asthenospheric melts. EM1 and EM2 elemental and isotopic compositions are

modified from Taylor and McLennan (1981) and Zindler and Hart (1986).


ent from the others, may be explained by reaction with

EM2-rich material in the lithospheric mantle.

6. Conclusions

(1) Olivine and alkali basalts occurred periodically in

three major episodes, at 4.35–3.4, 2.6–2.4 and

1.6–1.1 Ma, forming scattered small, monogen-

etic volcanoes in the Fukuoka district, one of the

centers of northern Kyushu intraplate basalts. The

composition of the lavas appears to be relatively

homogenous and temporally insensitive and

different significantly from center to center,

suggesting a spatial factor may be more important.

(2) High FeO* and TiO2 and low SiO2 concentrations

possibly indicate melting at high temperature and

pressure from a fertile asthenospheric source.

Primitive mantle normalized trace element pat-

terns are OIB-like; however, relatively low LILE

contents, low LILE/HFSE and LREE/HFSE and

N-MORB Rb/Sr and Ba/Zr ratios suggest that the

source may have experienced previous melt

extraction.

(3) The high 87Sr/86Sr, low 143Nd/144Nd of the crustal

contamination-free Fukuoka basalts, and the facts

that they have the highest lead isotope ratios

among the northern Kyushu lavas may reflect the

addition of EM2-rich material from wall rocks

probably in the lithosphere mantle to EM1-rich

contaminated asthenospheric melts. The latter is a

Dupal-like component believed to be present

throughout the East Asian asthenosphere.

Acknowledgements

We thank Japan International Science and Technol-

ogy Exchange Center (JISTEC) for their financial

support. T. Kamioka, A. Matsumoto and T. Kani are

thanked for assisting in clean laboratory and mass

spectrometer work. We are grateful to Richard Carlson

(DTM) and Martin Flower (UIC) for patiently reading

and commenting on an earlier version that helped

improve the manuscript significantly. We thank Yasuo

Ikeda and Ryuichi Shinjo for their constructive

criticism. Editorial comments by R. Rudnick are

acknowledged. [RR]

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