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Journal of Asian Earth Sciences 97 (2015) 393–405
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Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes
Early Cretaceous high-Mg diorites in the Yanji area, northeastern China:
Petrogenesis and tectonic implications
Xing-Hua Ma a, Rui Cao b,⇑, Zhen-Hua Zhou a, Wen-Ping Zhu c
a
Key Laboratory of Metallogeny and Mineral Assessment, Chinese Academy of Geological Sciences, Beijing 100037, China
College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China
c
Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
b
a r t i c l e
i n f o
Article history:
Received 21 March 2014
Received in revised form 4 July 2014
Accepted 6 July 2014
Available online 16 July 2014
Keywords:
High-Mg diorite
Subduction
Dehydration
Sediment melting
NE China
a b s t r a c t
Mesozoic granitic rocks are widely distributed in northeast (NE) China. However, high-Mg dioritic rocks
are considerably rare. Here, we report a newly recognized high-Mg diorite (the Xintun diorite) in the
Yanji area, NE China, to constrain its origin and implications for the tectonic evolution of eastern Asian
continental margin. Zircon U–Pb dating yields a crystallization age of 128 ± 1 Ma for the Xintun diorite.
The diorites are characterized by high MgO (4.4–6.6 wt.%), Cr (119–239 ppm), Ba (419–514 ppm) and Sr
(649–747 ppm) contents and Mg# values (59–64), but low FeOtotal/MgO ratios (1.2–1.4), with geochemical features similar to those of sanukitic high-Mg andesites (HMAs). They show moderate radiogenic Sr
(ISr = 0.7047–0.7050) and Nd (eNd = 0.3–1.1), with high La/Sm ratios, which are indicative of contributions
from sediment components. The mineral assemblage of euhedral hornblende, magnetite and titanite,
implies a water-rich and oxidized signature for their primitive magmas. These features suggest that
the Xintun high-Mg diorites were probably formed via partial melting of the subducting sediments
and subsequent interaction of mantle peridotites with both melts and aqueous ﬂuids. Geochemical modeling reveals that hornblende-dominated fractional crystallization under water-sufﬁcient conditions
enabled the evolved magmas to acquire adakitic signatures. We believe that the Paleo-Paciﬁc subduction
beneath eastern Asian continental margin caused large-scale back-arc extension of NE China in the Early
Cretaceous, and, consequently, induced the asthenospheric ﬂow toward the mantle wedge, reheating
subducting sediments enough to cause melting. Therefore, the occurrence of the Xintun high-Mg diorites
signiﬁes the onset of extensive back-arc extension of eastern Asian continental margin at ca. 128 Ma.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
High-Mg andesites (HMAs) and their intrusive equivalents are a
minor group with unique geochemical characteristics in the family
of intermediate igneous rocks. They are usually characterized by
high MgO (>5%), Mg# (100 Mg/(Mg + Fe)>45), but low CaO
(<10%), FeOtotal/MgO ratios (<1.5), and enrichment in large ion
lithophile element (LILE, e.g., Ba and Sr) as well as compatible elements (e.g., Cr and Ni) relative to typical arc andesites (Tatsumi
and Ishizaka, 1982; Kelemen, 1995; Shimoda et al., 1998;
Heilimo et al., 2010; Tang and Wang, 2010). The HMAs are considered to have contributed greatly to continental-crust formation in
Earth’s early history (e.g., the Archean) (Smithies and Champion,
2000; Halla, 2005). However, they are volumetrically limited in
the modern Earth (Tatsumi, 2001), and mainly found at convergent
⇑ Corresponding author.
E-mail addresses: rcao2007cug@qq.com (R. Cao), wpzhu@pku.edu.cn (W.-P. Zhu).
http://dx.doi.org/10.1016/j.jseaes.2014.07.010
1367-9120/Ó 2014 Elsevier Ltd. All rights reserved.
plate margins, such as the Setouchi volcanic belt of Japan (Tatsumi
and Ishizaka, 1982), Aleutian arc (Kay, 1978) and volcanoes from
Baja California (Rogers et al., 1985), and generally classiﬁed into
four types, as Sanukitoids, Boninites, Adakites and Bajaites
(Kamei et al., 2004). There is a broad consensus that the HMAs
are indicative of subduction-zone related melting under relatively
high temperature conditions in arc systems (Furukawa and
Tatsumi, 1999; Hanyu et al., 2006), therefore, they could provide
important insights into the thermal structure, tectonic setting
and interaction between slab-derived ﬂuids/melts and peridotites
in the mantle wedge (Kelemen, 1995; Shimoda et al., 1998; Rapp
et al., 1999; Hanyu et al., 2006; Tatsumi, 2006).
In this paper, we present zircon U–Pb ages, and petrological,
geochemical and Sr–Nd isotopic data for an Early Cretaceous
high-Mg diorite from the Yanji area, northeast (NE) China. Our
results reveal that the high-Mg diorites were essentially derived
from a mantle source metasomatized by both ﬂuids and sediment-derived melts. Their occurrence indicates an abnormally
394
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Fig. 1. (a) Simpliﬁed geological map showing the location of Yanji area, NE China, modiﬁed after Jahn et al. (2000). (b) Distribution of granitoids in the Yanji area, modiﬁed
after Wu et al. (2011). (c) Geological map showing the Xintun diorite in the Yanji area. NCC, North China Craton.
Fig. 2. Representative photographs of the Xintun diorites showing (a) ﬁeld outcrop, (b) euhedral hornblende, biotite and subhedral to anhedral plagioclase, (c) magnetite
wrapped in the hornblende, and (d) euhedral titanite as early-stage phase. Hb, hornblende; Bt, biotite; Pl, plagioclase; Qz, quartz; Mag, magnetite; Ttn, titanite. The length of
hammer is 50 cm.
high thermal ﬁeld in the mantle wedge related to the upwelling of
asthenosphere caused by the Paleo-Paciﬁc subduction, and signiﬁes the onset of extensive back-arc extension of NE China in the
Early Cretaceous.
2. Geological background
NE China is located in the easternmost segment of the Central
Asian Orogenic Belt (CAOB) that separates the Siberian Craton in
the north from the Tarim and North China Cratons in the south
(Fig. 1a). This area has traditionally been regarded as an important
junction of two different tectonic regimes, as the EW-trending
Paleo-Asian oceanic domain and the NNE-trending Paleo-Paciﬁc
domain, respectively (Fig. 1a). Overall, the tectonic evolution of
NE China may be divided into two stages (Maruyama et al.,
1997; Xiao et al., 2003; Wu et al., 2011): (1) During the Neoproterozoic to Paleozoic, multi-arc systems and accretion complexes
(e.g., Ulan, Baolidao island arcs and Ondor Sum accretion complex)
were developed as a result of subduction of Paleo-Asian oceanic
slabs (Windley et al., 2007; Lehmann et al., 2010), which was
395
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Fig. 3. CL images of representative zircons and U–Pb concordia diagrams of the
Xintun diorites. In the CL images, spots on zircons represent analyzed locations for
U–Pb dating and data listed above zircons are 206Pb/238U ages.
followed by consolidation of multiple terranes with the closure of
Paleo-Asian Ocean until the Late Permian (Ruzhentsev and
Pospelov, 1992; Chen et al., 2000, 2009); (2) Since the Mesozoic,
NE China was dominated by the continental margin accretion
related to the northwestward subduction of Paleo-Paciﬁc plates
(Zhao et al., 1994; Maruyama et al., 1997; Wu et al., 2002; Niu,
2005). Therefore, NE China ultimately became a tectonic collage
of several micro-continental blocks and/or terranes, including the
Erguna in the northwest, the Xing’an and Songliao in the center,
Jiamusi and Nadanhada in the east, and the Liaoyuan Terrane in
the southeast (Zhou et al., 2009; Wu et al., 2011).
During the multiple-stage plate interactions, voluminous Phanerozoic (mostly the Mesozoic) granitoids were developed in the
collaged terranes of NE China. They are mainly distributed in the
western Erguna Massif, Great Xing’an Range, Lesser Xing’an Range,
Zhangguangcai Range and Yanji–Suifenhe area (Jahn et al., 2000;
Zhang et al., 2004; Ma et al., 2009; Wu et al., 2011). Coeval mantle-derived maﬁc to intermediate intrusions are subordinate and
sparsely distributed along the suture zones between the terranes,
such as the Hongqiling, Qinglinzi, Faku gabbros, and the Liukesong,
Taipinggou diorites (Wu et al., 2011). Geochemical investigations
indicate that the granitoids in NE China (as well as other parts of
the CAOB), are mostly I- and A-types, with minor S-type, which
have consistently been considered as signiﬁcant growth of juvenile
crust for their low initial 87Sr/86Sr ratios, high eNd(t) values and
young TDM ages (Wu et al., 2000; Jahn et al., 2001, 2004;
Kovalenko et al., 2004; Chen and Arakawa, 2005).
The Yanji–Suifenhe area, located at the border of China, Russia
and North Korea, is the most southeastern part of NE China
(Fig. 1b). Its basement is mainly composed of Palaeozoic strata
which have undergone variable degrees of metamorphism and
deformation (Shao and Tang, 1995). Massive granitoids, occupying
70% of the exposed rocks in this region (JBGMR, 1988), were
emplaced at three distinct stages, as the Permian (285–245 Ma),
Table 1
LA-ICP-MS U–Pb data of zircons from the Xintun diorites.
Spot no.
U (ppm)
207
1r
207
1r
206
YJ24.1
YJ24.2
YJ24.3
YJ24.4
YJ24.5
YJ24.6
YJ24.7
YJ24.8
YJ24.9
YJ24.10
YJ24.11
YJ24.12
YJ24.13
YJ24.14
YJ24.15
YJ24.16
YJ24.17
YJ24.18
YJ24.19
YJ24.20
YJ24.21
YJ24.22
YJ24.23
YJ24.24
YJ24.25
YJ24.26
YJ24.27
YJ24.28
YJ24.29
YJ24.30
62
64
167
162
181
142
129
101
75
171
94
104
119
161
57
125
43
138
307
77
116
146
74
116
164
273
248
194
75
63
0.0488
0.0486
0.0489
0.0488
0.0487
0.0486
0.0486
0.0491
0.0485
0.0489
0.0490
0.0487
0.0489
0.0487
0.0487
0.0493
0.0489
0.0488
0.0489
0.0488
0.0491
0.0488
0.0487
0.0489
0.0488
0.0487
0.0491
0.0487
0.0488
0.0487
0.0149
0.0181
0.0065
0.0047
0.0042
0.0066
0.0086
0.0099
0.0131
0.0043
0.0098
0.0090
0.0076
0.0072
0.0176
0.0081
0.0362
0.0059
0.0037
0.0124
0.0098
0.0062
0.0127
0.0084
0.0074
0.0049
0.0039
0.0055
0.0119
0.0181
0.1402
0.1331
0.1363
0.1353
0.1306
0.1299
0.1331
0.1353
0.1317
0.1359
0.1365
0.1315
0.1386
0.1349
0.1369
0.1405
0.1379
0.1359
0.1346
0.1352
0.1380
0.1386
0.1377
0.1340
0.1343
0.1314
0.1333
0.1374
0.1356
0.1382
0.0348
0.0292
0.0172
0.0132
0.0112
0.0175
0.0231
0.0253
0.0296
0.0123
0.0253
0.0233
0.0203
0.0192
0.0434
0.0239
0.0455
0.0162
0.0133
0.0286
0.0256
0.0177
0.0302
0.0236
0.0295
0.0131
0.0104
0.0156
0.0281
0.0401
0.0208
0.0199
0.0202
0.0201
0.0194
0.0194
0.0199
0.0200
0.0197
0.0202
0.0202
0.0196
0.0206
0.0201
0.0204
0.0207
0.0204
0.0202
0.0200
0.0201
0.0204
0.0206
0.0205
0.0199
0.0200
0.0196
0.0197
0.0204
0.0201
0.0206
Note:
204
Pb has been corrected.
Pb/206Pb
Pb/235U
Pb/238U
1r
206
Pb/238U (Ma)
0.0004
0.0004
0.0002
0.0002
0.0002
0.0002
0.0002
0.0003
0.0003
0.0002
0.0003
0.0003
0.0002
0.0003
0.0004
0.0003
0.0006
0.0003
0.0002
0.0003
0.0003
0.0002
0.0004
0.0003
0.0005
0.0002
0.0002
0.0002
0.0003
0.0004
132.9
126.7
129.1
128.4
124.1
123.7
126.8
127.6
125.6
128.7
129.0
124.9
131.3
128.3
130.0
131.9
130.5
129.0
127.6
128.2
130.0
131.6
130.9
126.9
127.5
124.9
125.6
130.5
128.5
131.2
1r
2.7
2.5
1.3
1.3
1.2
1.3
1.5
2.2
2.2
1.2
1.8
1.9
1.5
2.0
2.5
2.2
3.8
1.7
1.4
2.2
2.0
1.3
2.2
1.8
3.0
1.1
1.0
1.3
1.8
2.3
396
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Table 2
Whole rock chemical compositions of the Xintun diorites.
Sample
Major elements
SiO2
Al2O3
Fe2Ototal
3
CaO
MgO
K2O
Na2O
MnO
TiO2
P2O5
LOI
Total
Na2O/K2O
FeOtotal/MgO
Mg#
YJ-24
(wt.%)
54.4
16.1
8.1
7.7
6.1
1.1
3.6
0.1
1.1
0.3
1.2
99.6
3.2
1.2
64
Trace elements (ppm)
Sc
19.6
Ti
5987
V
169
Cr
213
Mn
970
Co
27.8
Ni
74.1
Cu
26.8
Ga
18.3
Rb
23.1
Sr
650
Y
16.1
Zr
75.5
Nb
6.5
Ba
469
La
15.7
Ce
36.6
Pr
4.8
Nd
20.2
Sm
4.6
Eu
1.4
Gd
4.1
Tb
0.6
Dy
3.5
Ho
0.7
Er
1.6
Tm
0.2
Yb
1.5
Lu
0.3
Hf
2.5
Ta
0.4
Pb
5.3
Th
1.9
U
0.3
dEu
1.01
Sr/Y
40.4
(La/Yb)N
7.4
3. Petrological description
YJ-25
YJ-26
YJ-27
YJ-28
YJ-29
YJ-30
53.9
16.0
8.1
7.6
6.1
1.1
3.6
0.1
1.1
0.3
1.3
99.3
3.2
1.2
64
53.3
16.6
8.4
7.8
5.6
1.2
3.6
0.1
1.1
0.2
2.0
99.8
3.1
1.3
61
53.3
15.8
8.5
7.9
6.6
1.1
3.5
0.1
1.2
0.3
1.3
99.5
3.1
1.2
64
56.3
17.3
7.1
7.4
4.4
1.2
3.7
0.1
0.8
0.2
1.5
100.1
3.2
1.4
59
53.4
17.0
8.3
7.9
5.8
1.0
3.7
0.1
1.0
0.2
1.4
99.8
3.8
1.3
62
54.9
17.0
7.7
7.6
4.9
1.1
3.6
0.1
0.9
0.2
1.6
100.0
3.2
1.4
60
20.6
5987
186
222
1050
29.0
84.0
32.7
19.6
23.5
678
17.3
68.3
7.0
500
17.7
40.9
5.3
22.2
4.8
1.5
4.3
0.6
3.7
0.7
1.7
0.3
1.7
0.3
2.4
0.4
5.5
2.0
0.4
1.00
39.2
7.7
23.3
5715
178
190
1117
27.9
48.6
24.9
19.5
24.4
684
18.1
85.5
5.9
514
14.1
33.6
4.3
18.7
4.3
1.4
4.3
0.6
3.7
0.7
1.8
0.3
1.6
0.3
2.6
0.4
6.0
2.3
0.8
1.01
37.8
6.0
23.6
7099
196
239
1078
32.6
78.9
79.0
19.8
23.1
649
18.7
116.0
7.2
478
16.2
38.2
5.1
21.2
4.8
1.5
4.4
0.7
3.9
0.7
1.9
0.3
1.8
0.3
3.2
0.4
5.3
1.9
0.4
0.99
34.7
6.5
15.0
4444
139
119
1071
20.9
32.3
14.7
18.4
27.2
725
9.5
51.3
5.2
436
13.6
27.0
3.0
11.9
2.5
0.9
2.3
0.3
1.9
0.4
0.9
0.2
0.9
0.2
1.7
0.3
6.3
1.8
0.3
1.18
76.4
10.4
20.4
5620
178
159
1039
27.9
55.6
31.2
18.9
19.1
747
16.6
80.5
6.1
419
14.6
34.8
4.6
19.5
4.4
1.4
4.0
0.6
3.5
0.7
1.6
0.3
1.6
0.2
2.7
0.4
4.9
1.8
0.3
1.01
45.0
6.6
18.7
5064
161
149
1081
24.4
41.6
20.9
18.9
24.9
699
11.5
67.6
5.6
459
13.9
30.5
3.7
15.4
3.5
1.2
3.3
0.5
2.8
0.5
1.3
0.2
1.3
0.2
2.2
0.3
6.0
2.0
0.5
1.07
60.8
8.3
Note: LOI, loss on ignition; Mg# = 100 Mg/(Mg + Fe2+); dEu = EuN/[(1/2) * (SmN + GdN)]; N = chondrite-normalized concentrations.
Late Triassic-Middle Jurassic (210–155 Ma) and Early Cretaceous
(135–100 Ma), respectively (Wu et al., 2011, and references
therein). Of which, the Permian granitoids are rarely exposed in
the west along northern margin of the North China Craton
(Fig. 1b), and generally considered to be associated with the terminal evolution of the CAOB. In contrast, the Late Triassic-Middle
Jurassic and Early Cretaceous granitic rocks are widely distributed
along the NNE-trending Dunhua–Mishan fault (Fig. 1b). These Late
Mesozoic granitoids, combined with those from other areas of NE
China (e.g., the Zhangguangcai Range and Lesser Xing’an Range),
Far East Russia and Japan Islands, have been increasingly regarded
as a magmatic arc belt formed by the subduction of Paleo-Paciﬁc
plates beneath eastern Asian continental margin (Maruyama
et al., 1997; Zhang et al., 2004; Zhou et al., 2009; Guo et al.,
2010; Wu et al., 2011).
The Xintun dorites occurred in the southeast of Yanji area
(Fig. 1b), intruding into the Palaeozoic strata and the Jurassic granitoids (Fig. 1c). They appear gray to dark green (Fig. 2a), mediumgrained, and show equigranular texture (Fig. 2b). The mineral
assemblage consists of hornblende (38–50%), plagioclase (32–
45%), biotite (5–8%) and quartz (5%), with minor amounts of
pyroxene (<3%). Accessory phases are apatite, titanite, epidote, zircon and magnetite (Figs. 2c and d).
Hornblende occurs as euhedral and hexagonal crystals (Fig. 2b),
suggesting that it formed very early. Biotite is often euhedral to
subhedral, and locally replaced by chlorite (Fig. 2b). Magnetite is
an earlier phase, wrapped in the hornblende and biotite (Fig. 2b
and c). Plagioclase is mostly subhedral to anhedral (Fig. 2b and
c), and commonly shows compositional and textural zoning.
Quartz is a late-stage phase, interstitial to the cleavage of early
crystallized minerals (Fig. 2b and c). Moreover, apatite is often
stubby. Titanite usually shows wedge-shape and euhedral
(Fig. 2d), indicating its early crystallization.
4. Analytical methods
4.1. Zircon U–Pb dating
Zircon grains were extracted by the combination of heavyliquid and magnetic methods after crushing the fresh rocks, and
further puriﬁed by hand-picking under a binocular microscope.
Zircons were set in an epoxy mount which was polished, and then
vacuum-coated with a layer of 50 nm high-purity gold. Microphotographs and Cathodoluminescence (CL) images were taken to
examine the internal structure of individual grain for situ U–Pb isotopic analyses.
Zircons were dated by the Laser ablation ICP-MS method, conducted on a Thermo Fisher NEPTUNE ICP-MS equipped with a
193 nm laser (1–200 Hz, 15 J/cm2) at the Tianjin Institute of Geology and Mineral Resources, China Geological Survey. The analytical
procedures have been described in detail by Wu et al. (2002). The
spot diameter was 35 lm. Zircon Plesovice (Slama et al., 2008) was
used as the standard and the standard glass NIST610 was used to
optimize the machine. GLITTER program (Jackson et al., 2004)
was used to calculate the U–Pb isotopic compositions. Measured
compositions were corrected for common Pb using the measured
non-radiogenic 204Pb (Andersen, 2002). The age calculations and
Concordia plots were done using ISOPLOT 3.0 (Ludwig, 2003).
4.2. Major and trace element analyses
Whole-rock geochemical analyses were performed at National
Research Center for Geoanalysis. Major elements were determined
by X-ray ﬂuorescence (XRF) using fused glass disks on ARL
ADVANT’ XP+ with accelerating voltage of 50 kV, accelerating
current of 50 mA. The analytical errors are less than 2%. Trace
elements were measured by inductively coupled plasma-mass
(ICP-MS). The analytical uncertainties are 10% for elements with
abundances 610 ppm and better than 5% for those P10 ppm.
International standards, GSR-1 (granite) and GSR-9 (diorite), were
used during data acquisition.
4.3. Sr–Nd isotopes analyses
Separation of Sr and Nd was performed at Key Laboratory of
Orogenic Belts and Crustal Evolution, Peking University. Sample
dissolution was carried out using acid digestion (HNO3 + HF) in a
sealed Savillex beaker on a hot plate (80 °C). Separation of Rb, Sr
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
397
Fig. 4. Plots of major elements against MgO for the Xintun diorites.
and light REE was done through a cation-exchange column (packed
with Bio-Rad AG50Wx8 resin). Sm and Nd were further puriﬁed
using a second cation-exchange column, conditioned and cleaned
with dilute HCl as described by Chen et al. (2000).
Sr–Nd isotope ratios were measured on a negative thermal ionization mass spectrometer (NTIMS) by TRITON, at the Tianjin Institute of Geology and Mineral Resources, China Geological Survey.
87
Sr/86Sr ratios were normalized to 86Sr/88Sr = 0.1194. 143Nd/144Nd
ratios were normalized to 146Nd/144Nd = 0.7219. 87Sr/86Sr ratios
were adjusted to NBS-987 SrCO3 87Sr/86Sr = 0.710250, and the
143
Nd/144Nd ratios to JMC Nd2O3 143Nd/144Nd = 0.511122. The
uncertainty (2r) in concentration measurement by isotope dilution is 1–2% for Rb, 0.5% for Sr, and 0.2–0.5% for Sm and Nd depending on concentrations. Average procedural blanks are: Rb = 100 pg,
Sr = 400 pg, Sm = 50 pg, Nd = 50–100 pg. The decay constants used
in age calculations are 0.0142 Ga 1 for 87Rb and 0.00654 Ga 1
for 147Sm. Nd model ages were calculated based on depleted
mantle assuming a linear revolution of isotopic composition from
eNd(t) = 0 at 4.56 Ga to +10 at the present time.
5. Results
5.1. Zircon U–Pb ages
Cathodoluminescence (CL) images of representative zircons
from the Xintun diorites are shown in Fig. 3a. Zircons are euhedral,
short prismatic, with pyramidal terminations and clear oscillatory
zones, which are indicative of a magmatic origin. Thirty grains
were analyzed by LA-ICP-MS method. The zircon U–Pb isotopic
results are presented in Table 1 and graphically shown in the Concordia diagram (Fig. 3b). Thirty spots yield 206Pb/238U ages ranging
from 123.7 ± 1.3 to 132.9 ± 2.7 Ma, with a weighted mean
206
Pb/238U age of 127.9 ± 0.9 Ma (MSWD = 2.4), which represents
the crystallization age of the Xintun diorites.
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X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Fig. 5. Plots of trace elements against MgO for the Xintun diorites.
Fig. 6. Chondrite-normalized REE patterns (a) and primitive mantle-normalized trace element spidergrams (b) for the Xintun diorites. Normalization values of chondrite and
primitive mantle are from Sun and McDonough (1989).
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X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Table 3
Sr–Nd isotopic compositions of the Xintun diorites.
Sample Rb
(ppm)
Sr
(ppm)
87
87
±2r
ISr(t)
Sm
(ppm)
Nd
(ppm)
147
YJ-24
YJ-25
YJ-26
YJ-27
YJ-28
YJ-29
YJ-30
663
678
684
649
725
681
699
0.101
0.101
0.103
0.103
0.109
0.081
0.103
0.705039
0.705028
0.705145
0.705049
0.704979
0.704968
0.704842
0.000006
0.000012
0.000013
0.000004
0.000010
0.000005
0.000006
0.7049
0.7048
0.7050
0.7049
0.7048
0.7048
0.7047
4.64
4.8
4.29
4.78
2.52
4.43
3.5
20.2
22.2
18.7
21.2
11.9
19.5
15.4
0.1389
0.1307
0.1387
0.1363
0.1280
0.1373
0.1352
23.1
23.5
24.4
23.1
27.2
19.1
24.9
Rb/86Sr
Sr/86Sr
Sm/144Nd
143
Nd/144Nd ±2r
eNd(0) fSm/Nd (143Nd/144Nd)t eNd(t) TDM
(Ma)
0.512612
0.512613
0.512646
0.512623
0.512626
0.512604
0.512626
0.000001
0.000002
0.000002
0.000002
0.000021
0.000328
0.000003
0.5
0.5
0.2
0.3
0.2
0.7
0.2
0.29
0.34
0.29
0.31
0.35
0.30
0.31
0.51250
0.51250
0.51253
0.51251
0.51252
0.51249
0.51251
0.4
0.6
1.1
0.7
0.9
0.3
0.8
886
873
831
865
850
896
859
Note:
eNd = ((143Nd/144Nd)S/(143Nd/144Nd)CHUR 1) 10,000,
fSm/Nd = (147Sm/144Nd)S/(147Sm/144Nd)CHUR 1,
TDM1 = 1/k ln(1 + ((143Nd/144Nd)S (143Nd/144Nd)DM)/
((147Sm/144Nd)S-(147Sm/144Nd)DM)), TDM2 = TDM1 (TDM1 t)(( 0.4 fSm/Nd)( 0.4 0.08592)), 143Nd/144NdCHUR = 0.512638, 147Sm/144NdCHUR = 0.1967, 143Nd/144NdDM =
0.51315, 147Sm/144NdDM = 0.2137; kRb = 1.42 10 11/year, kSm = 6.54 10 12/year.
5.2. Whole-rock geochemistry
Major and trace element compositions are listed in Table 2 and
presented in Figs. 4 and 5. The Xintun diorites have relatively high
contents of SiO2 (53.3–56.3 wt.%), Al2O3 (15.8–17.3 wt.%) and TiO2
(0.8–1.2 wt.%), and are characterized by high MgO (4.4–6.6 wt.%)
and Mg# (59–64), but low CaO (7.4–7.9 wt.%) and FeOtotal/MgO
ratios (1.2–1.4), which are approximately equivalent to the compositions of typical HMAs (Tatsumi and Ishizaka, 1982; Kelemen,
1995). Na2O and K2O abundances are 3.5–3.7 wt.% and 1.0–
1.2 wt.%, respectively, with considerably high Na2O/K2O ratios
(3.1–3.8). They show mediate-K calc-alkaline characteristics. In
the major element Harker diagrams, the SiO2 and Al2O3 are negatively correlated with MgO (Fig. 4a and b), while CaO, FeO, P2O5
and Na2O + K2O show opposite trends (Fig. 4c–e).
The Xintun diorites have remarkably high Ba (419–514 ppm)
and Sr (649–747 ppm) contents (Fig. 5), and show signiﬁcant
enrichment in light rare earth element (LREE) and LILE (e.g., Pb,
Rb and Th), and depletion in high ﬁeld strength elements (HFSE;
e.g., Nb, Ta, Ti and Zr) (Fig. 6). Compatible elements, such as Cr
(119–239 ppm) and Ni (32–84 ppm), are relative high, which are
consistent with their high MgO contents and Mg# values (Table 2).
Moreover, they have strong fractionated LREE, but weak fractionated medium rare earth element (MREE) relative to heavy rare
earth element (HREE), displaying concave chondrite-normalized
REE patterns with negligible Eu anomalies (dEu = 0.99–1.18)
(Fig. 6a).
(e.g., Sr, Ba and Pb) and, depleted in HFSE (e.g., Nb, Ta and Ti)
(Fig. 6). These features indicate an arc-related magma series for
the Xintun diorites. However, the high MgO (4.4–6.6%), Mg#
(59–64), and low CaO (7.4–7.9%) and FeOtotal/MgO ratios (1.2–
1.4) make them quite akin to typical HMAs. As shown in the diagram of SiO2 vs. MgO (Fig. 4a), all the samples fall in the HMAs ﬁeld
due to higher MgO contents than that of normal andesites at equivalent SiO2. Further evidence comes from their considerably high Sr
and Ba contents. In addition, high concentrations of compatible
elements, such as Cr and Ni are also common features of HMAs.
Therefore, the Xintun diorites have geochemical afﬁnities to the
typical HMAs, probably representing the intrusive equivalents of
the HMAs.
As mentioned earlier, the HMAs can be divided into four subtypes according to their unique geochemical characteristics. The
sanukitic HMAs are characterized by high LILE, Cr, Ni contents
and Mg# (>60) (Martin et al., 2005), and relatively high Y
(>10 ppm), Yb (>0.8 ppm), and low Sr/Y (<40), (La/Yb)N (<10) ratios
(Kamei et al., 2004). They are believed to be generated by equilibrium reaction of mantle peridotites with silicic melts derived from
partial melting of subducting slab/sediments (Yogodzinski et al.,
1994; Shimoda et al., 1998; Tatsumi, 2001). Adakitic HMAs show
signiﬁcantly higher Sr (>400 ppm), Sr/Y and (La/Yb)N ratios, lower
low Y (<18 ppm) and Yb (<1.9 ppm) (Kay, 1978; Defant and
Drummond, 1990; Martin, 1999) than sanukitic HMAs, and are
usually derived from melting of a subducting oceanic slab
(Defant and Drummond, 1990) or over-thickened lower crust
5.3. Sr–Nd isotope data
Sr and Nd isotopic analyses are presented in Table 3 and Fig. 7.
The Xintun diorites have homogeneous and slightly depleted
Sr–Nd isotopic compositions, with ISr = 0.7047–0.7050, and
eNd(128 Ma) = +0.3 to +1.1, respectively. Nd model ages (TDM) of
the Xintun diorites are relatively young, ranging from 831 to
896 Ma. As shown in Fig. 7, the isotopic compositions of the Xintun
diorites are different from the Cenozoic adakites of the Yanji area
(Guo et al., 2009). All samples plot on the extension of the subcontinental mantle of that time, overlapping with the Setouchi HMAs
from NE Japan arcs (Hanyu et al., 2006).
6. Discussion
6.1. Analogy to high-Mg andesites
The Xintun diorites are characterized by abundance of euhedral
hornblende (Fig. 2b), primary magnetite and titanite (Fig. 2c and d),
which imply a H2O-rich (P4 wt.%; Ridolﬁ et al., 2010) and relatively oxidized (Foley and Wheller, 1990) signature of their initial
magmas. Geochemically, they are enriched in LREE as well as LILE
Fig. 7. 143Nd/144Nd(t) vs. 87Sr/86Sr(i) plot for the Xintun diorites. Sr–Nd isotopic
data of the Yanji adakites are from Guo et al. (2009). Data of the Setouchi HMAs,
altered oceanic crust and sediments are from Tatsumi (2006) and Hanyu et al.
(2006).
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X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
of TiO2 vs. MgO/(MgO + FeOtotal), Sr/Y vs. Y, and (La/Yb)N vs. YbN
can effectively distinguish them from each other (Kamei et al.,
2004). As shown in Fig. 8, the Xintun diorites possess relatively
high TiO2 (0.8–1.2 wt.%), Y (10–19 ppm), and Yb (0.9–1.8) contents,
but low Sr/Y (35–76) and (La/Yb)N (6–10) ratios, which are analogous to those of sanukite from the Setouchi Volcanic Belt.
6.2. Origin of the Xintun high-Mg diorites
Fig. 8. TiO2 vs. MgO/(MgO + FeOT), Sr/Y vs. Y, and (La/Yb)N vs. YbN discrimination
diagrams for the Xintun high-Mg diorites (after Kamei et al., 2004).
(Atherton and Petford, 1993). Bajaites have extremely high Sr (up
to 4000 ppm), Ba (>1000 ppm) and Sr/Y ratios, which are widely
considered to be generated by disequilibrium reaction of mantle
peridotites with slab-derived melts (Saunders et al., 1987). Boninites contain very low TiO2 (<0.5 wt.%), Y (<10 ppm) and Yb
(<0.8 ppm), but high SiO2 (>52 wt.%) and MgO (>8 wt.%), and are
usually generated by hydrous melting of depleted residual mantle
in supra-subduction zone setting (Crawford et al., 1989; Taylor
et al., 1994; Macpherson and Hall, 2001). Discrimination diagrams
The origin of HMAs remains a subject of considerable debate
(Kelemen, 1995; Shimoda et al., 1998; Tatsumi, 2001; Hanyu
et al., 2006). Proposed possible processes of HMAs magma generation include: (1) partial melting of a subducting oceanic crust and
subsequent melt–mantle interaction (Yogodzinski et al., 1994;
Kelemen, 1995); (2) partial melting of subducting sediments followed by equilibration with mantle peridotites (Shimoda et al.,
1998; Tatsumi, 2001); (3) direct hydrous melting of mantle peridotites by addition of ﬂuids released from the dehydrating slab
(Kushiro, 1969; Crawford et al., 1989; Hirose, 1997). In this case,
it is crucial to identify the nature of metasomatic agents overprinted in the mantle wedge.
The model of oceanic crust melting is not favored for the Xintun
high-Mg diorites due to the following reasons. First of all, trace element characteristics of the Xintun high-Mg diorites are quite different from those of oceanic crust-derived melts, which possess
higher Sr/Y ratios and lower Y (<18 ppm) as well as Yb
(<1.9 ppm) concentrations than the former (Defant and
Kepezhinskas, 2001; Kelemen et al., 2003). Moreover, although
the Xintun high-Mg diorites are enriched in LREE relative to HREE,
few show strong MREE enrichments relative to HREE (Fig. 6a), precluding their origination from partial melting of an eclogite-face
source region where oceanic crust melts are generally produced
(Defant and Drummond, 1990; Richards and Kerrich, 2007). This
is also supported by their high contents of Al2O3 (15.8–17.3 wt.%)
and Sc (15–24 ppm) (preferably hosted in the garnet) which could
be indicative of a garnet-free residue in the source. Furthermore,
the Ba/Th ratios should be markedly increased if oceanic crustderived melts are involved in the production of magmas
(Tatsumi, 2006), which is inconsistent with their low Ba/Th ratios
(226–256) (Fig. 9a). Besides, the Xintun high-Mg diorites have
moderate
radiogenic
Sr
(ISr = 0.7047–0.7050)
and
Nd
(143Nd/144Nd(t) = 0.51249–0.51253) (Fig. 7), rather than strikingly
depleted isotopic compositions of the MORB and oceanic crust
(Tatsumi, 2006).
Instead, sediment components, as a major metasomatic agent,
may have played an important role in the formation of Xintun
high-Mg diorites, based on the facts below: (1) In the ISr vs.
143
Nd/144Nd diagram (Fig. 7), the Xintun high-Mg diorites show
isotopic trends toward the sediments, suggesting signiﬁcant contribution of sediment components. (2) Addition of sedimentderived melts could notably enhance La/Sm ratios of the magma
(Fig. 9a), but could not change Ba/Th ratios (Tatsumi, 2006), which
are consistent with features of the Xintun high-Mg diorites. (3)
Geochemical modeling by Tatsumi (2001) and Hanyu et al.
(2006) has demonstrated that sediment melts could be produced
at 1050 °C and 1.0 GPa and subsequent interaction of such melts
with overlying mantle peridotites could result in element compositions close to the Setouchi HMAs (Imaoka et al., 1993; Shimoda
et al., 1998; Kamei et al., 2004). The Xintun high-Mg diorites are
akin to the sanukitic HMAs; therefore, they are likely to share common generation mechanism.
However, in addition to sediment-derived melts, we propose
that H2O-rich ﬂuids are another metasomatic agent also involved
in the production of the Xintun dioritic magmas. As mentioned
above, the common presence of hydrous minerals (hornblende
and biotite) suggests that primitive parental melts are hydrous. This
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
401
Fig. 9. Ba/Th vs. (La/Sm)N and Th/Yb vs. Ba/La discrimination diagrams for metasomatic agents added to the mantle wedge. Data of Choshi, Setouchi HMAs and normal arc
rocks are from Tatsumi (2006) and Hanyu et al. (2006).
Fig. 10. SiO2 vs. Th/La and U/Nb (a and b), and MgO vs. eNd(t) and ISr(t) (c and d) diagrams for the Xintun diorites. CC, crustal contamination. FC, fractional crystallization.
is further supported by the observation that plagioclase crystallized
later than hornblende; because experimental results indicate that
early crystallization of plagioclase is suppressed by high water content of the melts (Müntener et al., 2001). Such H2O-rich magmas
usually solidify upon ascent as the Xintun high-Mg dioritic pluton,
rather than reach the surface. Moreover, addition of sediment components to the mantle wedge could elevate the Th/Yb ratios due to
high Th/Yb in sediments. Meanwhile the Ba/La ratios would also be
elevated accordingly if additional ﬂuids were involved, because Ba
is more soluble in aqueous ﬂuids than La (Hanyu et al., 2006). As
presented in Fig. 9b, the Xintun diorites possess trace element signatures transitional between the two trends. Therefore, we infer
that not only sediment-derived silicic melts but also aqueous ﬂuids
have been overprinted in the original mantle wedge and subsequently involved in the magma generation.
6.3. Magmatic evolution
High MgO contents, Mg# values (mostly over 60), and high concentrations of compatible elements (e.g., Cr and Ni) indicate that
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X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
Fig. 11. Sr/Y vs. Y (a) and (La/Yb)N vs. YbN (b) discrimination diagrams for adakites and typical arc rocks (after Drummond and Defant (1990) and Martin (1986)). The
calculated trend line in (a) represents residual liquids after variable proportions of fractionation of Hb (46%) + Cpx (42%) + Ttn (5%) + Ap (4%) + Mag (3%), based on the
Rayleigh law, and the partition coefﬁcients are from Rollinson (1993). Cpx, clinopyroxene; Hb, hornblende ; Ttn, titanite ; Ap, apatite; Mag, magnetite.
Fig. 12. Possible petrogenetic model of the Xintun high-Mg diorites in the Yanji area, NE China (modiﬁed after Hanyu et al., 2006 and Wu et al., 2011). (a) Slab dehydration
and partial melting of the lithospheric mantle were major processes to form normal arc magmas during 210–155 Ma. (b) Long-lasting subduction of the Paleo-Paciﬁc Plate
induced the initiation of back-arc extension in the Xing’an area at 155–130 Ma. (c) Since the 130 Ma, extensive upwelling and injection of asthenospheric materials resulted
in high-temperature conditions in the whole mantle wedge, reheating the subducted sediments enough to cause melting.
X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
the most primitive parental magmas to the Xintun high-Mg diorites were in equilibrium with mantle peridotites. Even so, magmatic differentiation may have taken place during the ascent of
magmas from the subarc mantle to the upper crust, as revealed
by the regular chemical compositions variations in Harker diagrams (Figs. 4 and 5).
Crustal contamination and fractional crystallization are two
possible processes responsible for the chemical variations. Chen
et al. (2013) have ever presented petrological and isotopic data of
the high-Mg dioritic rocks from the North China Craton and
proposed a process of magma mixing between mantle- and crustderived magmas for their origin. However, mixing and contamination evidence cannot be observed for the Xintun diorites, such as
the presence of enclaves or xenoliths, textural and compositional
disequilibrium in plagioclase phenocrysts (Chen et al., 2013). Moreover, from primitive mantle-normalized trace element spidergrams
(Fig. 6b), it can be seen that Th and U are mostly depleted relative to
the LREE, precluding signiﬁcant involvement of crustal components
during the magma ascent (Taylor and McLennan, 1985). This is
supported by the constant Th/La and U/Nb ratios with increasing
SiO2 content (Fig. 10a and b). Furthermore, the diagrams of eNd(t)
and ISr vs. MgO are constructed to evaluate the role of crustal
contamination for the Xintun high-Mg diorites (Fig. 10c and d).
However, the eNd(t) and ISr values do not show remarkable
variations and linear trends with MgO contents, also suggesting
that the magmas were not notably affected by crustal materials.
Instead, a process of fractional crystallization may have played a
dominated role during the magmatic evolution. In Harker diagrams, the positive correlations of CaO, FeO (Fig. 4c and d), Co
and Sc (Fig. 5a and b) with MgO indicate a signiﬁcant fractionation
of ferromagnesian phases such as clinopyroxene and hornblende,
which is well veriﬁed by the concave REE patterns (Fig. 6a),
because clinopyroxene and hornblende show preference for MREE
over HREE (Rollinson, 1993). Moreover, experimental studies
reveal that hornblende crystallization from basaltic to intermediate magmas shifts the residual melts toward high SiO2 and
Na2O + K2O contents (Foden and Green, 1992), which is consistent
with the negative correlations of SiO2 and Na2O + K2O with MgO
(Fig. 4a and f). The presence of Ti anomalies in the primitive mantle-normalized spidergrams (Fig. 6b) and positive correlation
between Ti and MgO (Fig. 5c) are possibly attributed to the early
precipitation of titanite under high fO2 conditions (Foley and
Wheller, 1990). In addition, the positive correlations of V and Cr
with MgO (Fig. 5d) imply a signiﬁcant fractionation of magnetite.
Simultaneous apatite fractionation is also important as revealed
by the depletion of Y (strong enrichment in apatite) (Fig. 5e) and
the positive correlation between P2O5 and MgO (Fig. 4e). However,
the absence of negative Eu anomalies (Fig. 6a) indicates that segregation of plagioclase is negligible, which coincides with the
increasing Sr contents with decreasing MgO (Fig. 5f). So, fractional
crystallization of assemblage of hornblende, clinopyroxene, as well
as accessory minerals such as apatite and titanite, has controlled
the magmatic differentiation of the Xintun high-Mg diorites.
More importantly, the magmas of Xintun high-Mg diorites
evolve following curved trends in Sr/Y vs. Y and (La/Yb)N vs.
(Yb)N diagrams (Figs. 8 and 11), and appear an adakitic signature
progressively. For example, two evolved samples (YJ-28 and YJ30) possess high Sr (699–725 ppm) but low Y (9.5–11.5 ppm)
and Yb (0.9–1.3 ppm) concentrations, with high Sr/Y and (La/Yb)N
ratios (60–76 and 8–10, respectively), which are comparable to
those of typical adakitic rocks (Martin, 1986, 1999). Trace element
modeling results, based on Rayleigh law, suggest that fractionation
(10–25%) of combined phases of hornblende (46%) + clinopyroxene
(42%) + titanite (5%) + apatite (4%) + magnetite (3%), has contributed to the high Sr/Y ratios and low Y of the evolved samples.
Therefore, we propose that hornblende-dominated fractional
403
crystallization under water-sufﬁcient conditions could readily
yield melts with adakitic signatures. It is therefore concluded that
oceanic crust melting is not required to produce those adakitic
rocks (e.g., adakites or adakitic HMAs) which usually accompany
with the sanukitic HMAs.
6.4. Tectonic implications
The HMAs are generally related to the subduction of a young
and/or hot oceanic slab (e.g., ridge subduction) (Rogers and
Saunders, 1989; Furukawa and Tatsumi, 1999). On the other hand,
some workers have recently pointed out that the HMAs magmas
could be also produced in a relatively old subduction zone if the
subducting slab is reheated by 200 °C or higher (Hanyu et al.,
2006). Therefore, the existence of the Xintun high-diorites in NE
China is of great signiﬁcance to understand the thermal conditions
and tectonic evolution of eastern Asian continental margin.
It is well known that NE China is a junction of the Central Asian
Orogenic Belt and the Paciﬁc margin accretion belt (Fig. 1a). Previous studies have shown that the ﬁnal closure of the Paleo-Asian
Ocean between North China Craton and Siberian Craton along the
Solonker-Xra Moron suture took place in the Late Permian
(Ruzhentsev and Pospelov, 1992; Chen et al., 2009; Xu et al.,
2013), which was followed by the post-orogenic adjustment in
the Early Triassic (Dewey, 1988; Zhang et al., 2008). After a tectonic
quiescence, NE China was signiﬁcantly affected by subduction of
the Paleo-Paciﬁc plates since the Late Mesozoic (Zhao et al.,
1994; Maruyama et al., 1997; Wu et al., 2011). Jurassic to Cretaceous accretionary terranes and calc-alkaline I-type granitoids
were widely developed along the eastern Asian continental margin,
including NE China, Far East Russia and the Japan islands
(Wickham et al., 1995; Jahn et al., 2004; Wu et al., 2007; Sorokin
et al., 2010). In NE China, the Heilongjiang complexes, with blueschist facies high-pressure metamorphism ages of 185–165 Ma
(Cao et al., 1992; Zhou et al., 2009), are increasingly recognized
as a mélange recording the process of Paciﬁc margin accretion
(Wu et al., 2007; Zhou et al., 2009). Moreover, according to
Maruyama et al. (1997), the mid-oceanic ridge between the Paciﬁc
and Izanagi plates was not subducted beneath the NE China margin
until the Late Cretaceous (90 Ma). Therefore, it is unlikely that a
young and hot slab subduction has caused the formation of the
Xintun high-Mg diorites in the Early Cretaceous.
We prefer a model that thermal disturbance has triggered partial melting of the subducting sediments under high temperature
conditions (Honda and Saito, 2003; Hanyu et al., 2006), which is
associated with a possible scenario as follows (Fig. 12): The early
Paleo-Paciﬁc subduction toward the Eurasia plate took place at
210–155 Ma, and arc magmas were generated along the eastern
Asian continental margin (Fig. 12a). The long-lasting subduction
caused the initiation of extension on the back-arc side of the NE
China (e.g., the Xing’an and Songliao areas) at 155–130 Ma
(Fig. 12b). During the Early Cretaceous (130–110 Ma), extensive
back-arc extension occurred (Fig. 12c) (Tatsumi and Kimura,
1991; Ge et al., 2005; Ma et al., 2013), as indicated by the formation of NNE-striking sedimentary basins (Liu et al., 2010; Zhang
et al., 2011; Ge et al., 2012), and the occurrence of immense volumes of I- and A-type granites (Wu et al., 2000, 2005; Jahn et al.,
2001, 2009) and metamorphic core complexes (Wang et al.,
2011). Lithospheric extension induced signiﬁcant passive asthenospheric injection or upwelling (Niu, 2005; Shao et al., 2007).
Asthenospheric ﬂow from the west beneath the Xing’an area
toward the subduction zone caused high temperature conditions
in the whole mantle wedge (Fig. 12c), and ﬁnally led to a result that
the relative cold slab was effectively reheated to cause sediment
melting (Hanyu et al., 2006). The transition from dehydration to
sediment melting corresponds to the change of metasomatic
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X.-H. Ma et al. / Journal of Asian Earth Sciences 97 (2015) 393–405
agents, from prevailing ﬂuids to sediment-derived melts. Therefore, the occurrence of the Xintun high-Mg diorites signiﬁes high
temperature conditions in the mantle wedge and commencement
of extensive back-arc extension at 128 Ma, although the backarc opening in NE China failed later due to the heat consumption
in the Japan arc-trench system (Tatsumi and Kimura, 1991).
7. Conclusions
1. The Xintun pluton is a newly recognized high-Mg diorite in the
Yanji area, NE China, which is characterized by high MgO, Cr, Ni
contents, and low FeO/MgO ratios, with geochemical afﬁnities
to sanukitic HMAs.
2. Geochemical and isotopic compositions suggest that the Xintun
high-Mg diorites were formed via partial melting of the subducting sediments and subsequent interaction of mantle peridotites with hydrous silicic melts. Hornblende-dominated
fractional crystallization in H2O-rich melts enabled the evolved
magmas to possess adakitic signatures. Oceanic crust melting is
not required to produce those adakitic rocks which usually
accompany with the sanukitic HMAs.
3. The occurrence of the Xintun high-Mg diorites indicates a hot
asthenospheric injection in the mantle wedge, signifying the
onset of extensive extension on the back-arc side of NE China
at ca. 128 Ma, associated with the long-lasting Paleo-Paciﬁc
subduction beneath the eastern Asian continental margin.
Acknowledgments
We would like to thank H.F. Yuan and J.W. Liu for their assistance in U–Pb and Sr–Nd isotopes analysis. Financially, this
research has been supported by the State Key Basic Research and
Development program (#2013CB429804), Natural Science Foundation of China (#41202033) and Project of China Geological Survey
(#12120113093600).
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