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
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268252
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
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 253
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.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268254
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.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 255
Fig. 3. Plots of wt.% MgO against trace element abundances and ratios, data from Table 1.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268256
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).
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 257
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).
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268258
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.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 259
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.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268260
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-
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 261
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.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268262
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
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 263
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
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268264
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).
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 265
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]
References
Anderson, D.L., 1995. Lithosphere, asthenosphere, and perisphere.
Rev. Geophys. 33, 125–149.
Arai, S., Hirai, H., Uto, K., 2000. Mantle peridotite xenoliths from
the Southwest Japan arc: a model for the sub-arc upper mantle
structure and composition of the Western Pacific rim. J. Mineral.
Petrol. Sci. 95, 9–23.
Baker, M.B., Stolper, E.M., 1994. Determining the composition of
high-pressure mantle melts using diamond aggregates. Geo-
chim. Cosmochim. Acta 58, 2811–2827.
Basu, A.R., Wang, J.W., Huang, W.K., Xie, G.H., Tatsumoto, M.,
1991. Major element, REE, and Pb, Nd, and Sr isotopic geo-
chemistry of Cenozoic volcanic rocks of eastern China: impli-
cations for their origin from sub-oceanic type mantle reservoirs.
Earth Planet. Sci. Lett. 105, 149–169.
Carlson, R.W., Hart, W.K., 1988. Flood basalt volcanism in the
Northern United States. In: Macdougall, J.D. (Ed.), Continental
Flood Basalts. Kluwer Academic Publications, pp. 35–61.
Carlson, R.W., Irving, A.J., 1994. Depletion and enrichment history
of subcontinental lithospheric mantle: an Os, Sr, Nd, and Pb
isotopic study of ultramafic xenoliths from northern Wyoming
Craton. Earth Planet. Sci. Lett. 126, 457–472.
Castillo, P.R., 1996. The origin and geodynamic implication of the
Dupal isotopic anomaly in volcanic rocks from the Philippine
island arcs. Geology 24, 271–274.
Chauvel, C., Goldstein, S.L., Hofmann, A.W., 1995. Hydration and
dehydration of oceanic crust controls Pb evolution in the mantle.
Chem. Geol. 126, 65–75.
Cousens, B.L., Allan, J.F., 1992. A Pb, Sr, and Nd study of basaltic
rocks from the Sea of Japan, Legs 127/128. In: Tamaki, K.,
Suyehiro, K., Allan, J., McWilliams, M., et al. (Eds.), Proc.
Ocean Drilling Program, Sci. Results, vol. 127/128, Pt. 2. Col-
lege Sta., TX, pp. 805–817.
Deniel, C., Pin, C., 2001. Single-stage method for the simultaneous
isolation of lead and strontium from silicate samples for isotopic
measurements. Anal. Chim. Acta 426, 95–103.
DePaolo, D.J., 1981. Trace element and isotopic effects of com-
bined wallrock assimilation and fractional crystallization. Earth
Planet. Sci. Lett. 53, 189–202.
Flower, M.F.J., Tamaki, K., Hoang, N., 1998. Mantle extrusion: a
model for dispersed volcanism andDUPAL-like asthenosphere in
East Asia and the Western Pacific. In: Flower, M.F.J., Lo, C.-h.,
Chung, S.-l., Lee, T. (Eds.), Mantle Dynamics and Plate Interac-
tions in East Asia. Geophys. Monogr., vol. 27. American Geo-
physical Union, Washington, DC, pp. 67–88.
Frey, F.A., Clague, D., Mahoney, J.J., Sinton, J.M., 2000. Volcan-
ism at the edge of the Hawaiian plume: petrogenesis of submar-
ine alkalic lavas from the North Arch volcanic field. J. Petrol.
41, 667–691.
Gallagher, K., Hawkesworth, C., 1992. Dehydration melting and
the generation of continental flood basalts. Nature 58, 57–59.
Griffin, W.L., O’Reilly, S.Y., Ryan, C.G., 1992. Composition and
thermal structure of the lithosphere beneath South Africa, Sibe-
ria and China: proton microprobe studies. International Sympo-
sium on Cenozoic Rocks and Deep-Seated Xenoliths of China
and its Environs, Chinese Academy of Sciences, Beijing.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268266
Hart, S.R., 1984. The DUPAL anomaly: a large-scale isotopic
anomaly in the southern hemisphere. Nature 309, 753–756.
Hart, S.R., Hauri, E.H., Oschmann, L.A., Whitehead, J.A., 1992.
Mantle plumes and entrainment: isotopic evidence. Science 256,
517–520.
Hawkesworth, C.J., Mantovani, M., Peate, D., 1988. Lithosphere re-
mobilization during Parana CFBmagmatism. J. Petrol., 205–223
(Special Lithosphere Issue).
Hickey-Vargas, R., Hergt, J.M., Spadea, P., 1995. The Indian
Ocean-type isotopic signature in western Pacific marginal ba-
sins: origin and significance. In: Taylor, B., Natland, J. (Eds.),
Active Margins and Marginal Basins of the Western Pacific.
Geophys. Monogr., vol. 88. American Geophysical Union,
Washington, DC, pp. 175–197.
Hirose, K., Kushiro, I., 1993. Partial melting of dry peridotites at
high pressures: determination of composition of melts segre-
gated from peridotite using aggregate of diamond. Earth Planet.
Sci. Lett. 114, 477–489.
Hoang, N., Flower, M.F.J., 1998. Petrogenesis of Cenozoic basalts
from Vietnam: implication for origins of a ‘diffuse igneous
province’. J. Petrol. 39, 369–395.
Hoang, N., Uto, K., 2003. Origin of mantle isotopic components
beneath southwest Japan. Chem. Geol., to be submitted.
Hoang, N., Flower, M.F.J., Carlson, R.W., 1996. Major, trace ele-
ment, and isotopic compositions of Vietnamese basalts: interac-
tion of hydrous EM1-rich asthenosphere with thinned Eurasian
lithosphere. Geochim. Cosmochim. Acta 60, 4329–4351.
Hofmann, A.W., 1988. Chemical differentiation of the Earth: the
relationship between mantle, continental crust, and oceanic
crust. Earth Planet. Sci. Lett. 90, 297–314.
Hofmann, A.W., 1997. Mantle geochemistry: the message from
oceanic volcanism. Nature 385, 219–229.
Ikeda, Y., Nagao, K., Kagami, H., 2001. Effects of recycled materi-
als involved in a mantle source beneath the southwest Japan arc
region: evidence from noble gas, Sr, and Nd isotopic system-
atics. Chem. Geol. 175, 509–522.
Kerr, R.C., Lister, J.R., 1988. Island arc and mid-ocean ridge vol-
canism, modeled by diapirism from linear source regions. Earth
Planet. Sci. Lett. 88, 143–152.
Kogiso, T., Tatsumi, Y., Shimoda, G., Barsczus, H.G., 1997. High A(HIMU) ocean island basalts in southern Polynesia: new evi-
dence for whole mantle scale recycling of subducted oceanic
crust. J. Geophys. Res. 102, 8085–8103.
Kogiso, T., Hirose, K., Takahashi, E., 1998. Melting experiments on
homogeneous mixtures of peridotite and basalt: application to
the genesis of ocean island basalts. Earth Planet. Sci. Lett. 162,
45–61.
Kurasawa, H., 1968. Isotopic composition of lead and concentration
of uranium, thorium, and lead in volcanic from Dogo of the Oki
Islands, Japan. Geochem. J. 2, 11–28.
Kushiro, I., 1996. Partial melting of a fertile mantle peridotite at
high pressure: an experimental study using aggregates of dia-
mond. In: Basu, A., Hart, S.R. (Eds.), Earth Processes: Reading
the Isotopic Code. Geophys. Monogr., vol. 95. American Geo-
physical Union, Washington, DC, pp. 109–122.
Ludwig, W.J., Murauchi, S., Houtz, R.R., 1975. Sediments and
structure of the Japan Sea. Geol. Soc. Amer. Bull. 86, 651–664.
Mahoney, J.J., LeRoix, A.P., Peng, Z., Fisher, R.L., Natland, J.H.,
1992. Southwestern limits of Indian Ocean ridge mantle and the
origin of low 206Pb/204Pb mid-ocean ridge basalts: isotopic sys-
tematics of the central Southwest Indian Ridge (17j–50jE). J.Geophys. Res. 97, 19771–19790.
Mahoney, J.J., et al., 1994. Isotope and trace element characteristics
of a super-fast spreading ridge: East Pacific Rise, 13–23jS.Earth Planet. Sci. Lett. 121, 173–193.
Matsumoto, H., Yamagata, S., Itaya, T., 1992. K–Ar ages and main
chemical compositions of basaltic rocks from northern Kyushu
and Shimonoseki city, southwest Japan. In: Ishida, S. (Ed.),
Exploration of Volcanoes and Rocks in Japan, China and Ant-
arctica. Yamaguchi Univ., Yamaguchi, Japan, pp. 247–264.
McKenzie, D., Bickle, M.J., 1988. The volume and composition of
melt generated by extension of the lithosphere. J. Petrol. 26,
625–679.
McKenzie, D., O’Nions, R.K., 1983. Mantle reservoirs and oceanic
island basalts. Nature 301, 229–231.
Menzies, M.A., Rogers, N.W., Tindle, A., Hawkesworth, C.J.,
1987. Metasomatic and enrichment processes in lithospheric
peridotites, an effect of asthenosphere– lithosphere interaction.
In: Menzies, M.A., Hawkesworth, C.J. (Eds.), Mantle Metaso-
matism. Academic Press, London, pp. 313–359.
Morris, P.A., Kagami, H., 1989. Nd and Sr isotope systematics of
Miocene to Holocene volcanic rocks from Southwest Japan:
volcanism since the opening of the Japan Sea. Earth Planet.
Sci. Lett. 92, 335–346.
Mukasa, S.B., McCabe, R., Gill, J.B., 1987. Pb-isotopic composi-
tions of volcanic rocks in the West and East Philippine arcs:
presence of the Dupal isotopic anomaly. Earth Planet. Sci. Lett.
84, 153–164.
Mutter, J.C., Buck, W.R., Zehnder, C.M., 1988. Convective partial
melting: 1. A model for the formation of thick basalt sequen-
ces during the initiation of spreading. J. Geophys. Res. 93,
1031–1048.
Nakamura, E., McCulloch, M.T., Campbell, I.H., 1990. Chemical
geodynamics in the back-arc region of Japan based on the trace
element and Sr–Nd isotopic compositions. Tectonophysics 174,
207–233.
Nohda, S., Tatsumi, Y., Otofuji, Y., Matsuda, T., Ishizaka, K., 1988.
Asthenospheric injection and back-arc opening: isotopic evi-
dence from the northeast Japan. Chem. Geol. 68, 317–327.
Pin, C., Santos Zalduegui, J.F., 1997. Sequential separation of light
rare-earth elements, thorium and uranium by miniaturized ex-
traction of chromatography: application to isotopic analyses of
silicate rocks. Anal. Chim. Acta 339, 79–89.
Regelous, M., Niu, Y., Batiza, R., Greig, A., Collerson, K.D.,
1999. Variations in the geochemistry of magmatism on the
East Pacific Rise at 10j30VN since 800 ka. Earth Planet.
Sci. Lett. 168, 45–63.
Roeder, P.L., Emslie, R.F., 1970. Olivine– liquid equilibria. Con-
trib. Mineral. Petrol. 29, 275–289.
Seno, T., 1999. Syntheses of the regional stress fields of the Japa-
nese islands. Isl. Arc 8, 66–79.
Tanaka, T., et al., 2000. JNdi-1: a neodymium isotopic reference
in consistency with La Jolla neodymium. Chem. Geol. 168,
279–281.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268 267
Tatsumoto, M., Nakamura, Y., 1991. DUPAL anomaly in the Sea
of Japan: Pb, Nd, and Sr isotopic variations at the eastern
Eurasian continental margin. Geochim. Cosmochim. Acta 55,
3697–3708.
Tatsumoto, M., Basu, A.R., Huang, W., Wang, J., Xie, G., 1992. Sr,
Nd, and Pb isotopes of ultramafic xenoliths in volcanic rocks of
eastern China: enriched components EMI and EMII in subcon-
tinental lithosphere. Earth Planet. Sci. Lett. 113, 107–128.
Taylor, S.R., McLennan, S.M., 1981. The composition and evolu-
tion of the continental crust: rare earth element evidence from
sedimentary rocks. Philos. Trans. R. Soc. Lond. 301, 381–399.
Tu, K., Flower, M.F.J., Carlson, R.W., Zhang, M., Xie, G.-H., 1991.
Sr, Nd, and Pb isotopic compositions of Hainan basalts (south
China): implications for a subcontinental lithosphere Dupal
source. Geology 19, 567–569.
Turner, S., Hawkesworth, C., 1995. The nature of the sub-continen-
tal mantle: constraints from the major element composition of
continental flood basalts. Chem. Geol. 120, 295–314.
Uto, K., 1989. Neogene volcanism of Southwest Japan: its time and
space based on K–Ar dating. PhD thesis, University of Tokyo,
Tokyo. 184 pp.
Uto, K., Tatsumi, Y., 1996. Quaternary volcanism of the Japanese
islands. Isl. Arc 5, 250–261.
Uto, K., Hirai, H., Arai, S., 1993. K–Ar ages for Quaternary
alkali basalts from Kurose, Fukuoka Prefecture and Kifume,
Yamaguchi Prefecture, SW Japan. Bull. Geol. Surv. Jpn. 44
(11), 693–698.
Uyeda, S., Kanamori, H., 1979. Back-arc opening and the mode of
subduction. J. Geophys. Res. 84, 1049–1061.
Weaver, B.L., 1991. The origin of ocean island basalt end-member
compositions: trace element and isotopic constraints. Earth
Planet. Sci. Lett. 104, 381–397.
Zhang, Y.-s., Tanimoto, T., 1993. High-resolution global upper
mantle structure and plate tectonics. J. Geophys. Res. 98,
9793–9823.
Zindler, A., Hart, S., 1986. Chemical geodynamics. Annu. Rev.
Earth Planet. Sci. 14, 493–571.
N. Hoang, K. Uto / Chemical Geology 198 (2003) 249–268268