Directory UMM :Data Elmu:jurnal:J-a:Journal of Asian Earth Science:Vol18.Issue5.2000:

Journal of Asian Earth Sciences 18 (2000) 519±531

Melting experiment of a Wannienta basalt in the Kuanyinshan
area, northern Taiwan, at pressures up to 2.0 GPa
T.C. Liu a,*, B.R. Chen a, C.H. Chen b
a

Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan, Republic of China
b
Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, Republic of China
Received in revised form 19 November 1999; accepted 6 December 1999

Abstract
Melting experiments involving ®fteen runs were performed at pressures between 1.0 and 2.0 GPa in order to locate the
liquidus temperatures, the solidus temperatures, and the melting intervals of the Wannienta basaltic magma, northern Taiwan.
The experimental results showed that the liquidus and solidus temperatures were raised by 60 GPa and 40 GPa respectively. The
liquidus mineral at 1.0 GPa is orthopyroxene, whereas the liquidus mineral is clinopyroxene at 1.5 and 2.0 GPa. The crystallized
phases are clinopyroxene and plagioclase at temperatures between 1220 and 12708C and pressures between 1.0 and 2.0 GPa.
Garnet appears at 2.0 GPa near the solidus. The geochemical evolution of the residual magma with decreasing temperature
show the following trends: At 1.0 GPa, Al, Na, and K are progressively enriched while depletions occur in Mg. At 2.0 GPa, Si,
Fe and K are progressively enriched with decreasing temperature while depletions occur in Mg, Ca, and Na. The fractionation

trend of the Kuanyinshan volcanic series is similar to the trend observed in residual magmas at pressures between one
atmosphere and 1.0 GPa. These results indicate that the depth for fractional crystallization of the Wannienta basaltic magma to
produce andesites could be modeled at low pressure. The fractionates involved included iron-titanium oxides, olivine,
plagioclase, and clinopyroxene. 7 2000 Elsevier Science Ltd. All rights reserved.

1. Introduction
Taiwan is situated at the junction of the Ryukyu arc
and the Luzon arc in southeastern Asia (Fig. 1a)
within the collision zone between the Philippine Sea
Plate and the Eurasia Plate. The Philippine Sea Plate
is subducted along an E±W hinge line located at about
latitude 248N and dips northward at an angle of 458±
508 to a depth of about 300 km (e.g. Kao and Wu,
1996). On the other hand, the western edge of the Philippine Sea Plate is obducted onto the Eurasia Plate in
eastern Taiwan.
The volcanic provinces in northern Taiwan were
interpreted as the westward extension of the Ryukyu
Arc in previous studies (Yen, 1958; Yen et al., 1981).

* Corresponding author. Tel.: +886-2-2930-9544; fax: +886-28663-7762.

E-mail address: liutc@cc.ntnu.edu.tw (T.C. Liu).

The incompatible trace element patterns of Kuanyinshan basalts are similar to island arc shoshonitic volcanics (Chen, 1982; Juang and Chen, 1989; Liu and
Chen, 1991). Chen (1989), however, proposed that the
volcanic activity in northern Taiwan could be related
to the splitting of the Okinawa Trough based on Nd±
Sr±O isotopic data. The Kuanyinshan area of this
study is located in northern Taiwan and covers an
area of about 30 km2 (Fig. 1b). The depth to the Benio€ Zone at Kuanyinshan is about 150 km (Tsai et al.,
1977).
The Kuanyinshan is a composite volcano mainly
composed of three successive lava ¯ows and agglomerates. Based on the proportion of ma®c minerals in the
rocks, Ichimura (1950) classi®ed the volcanics in this
area into one type of basalt and ®ve categories of
andesites (two pyroxene andesite, hornblende bearing
two pyroxene andesite, hypersthene andesite,
hypersthene bearing hornblende andesite, and

1367-9120/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 1 3 6 7 - 9 1 2 0 ( 0 0 ) 0 0 0 0 2 - X

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T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

hypersthene bearing biotite hornblende andesite). The
basalt is less abundant. The voluminous dacites occur
in the Chinkuashih gold±copper district, about 45 km
east of the Kuanyinshan volcano. The sequence of
lava ¯ows consist of a clinopyroxene andesite lava
¯ow comprising layer 1, a two-pyroxene andesite lava
¯ow in layer 2, and a hypersthene hornblende andesite
lava ¯ow in layer 3 (Fig. 1b) (Wang, 1958; Chen and
Hwang, 1982; Hwang and Lo, 1986).
Extensive descriptions of the petrography and geochemistry of the Kuanyinshan volcanics were published by Chen (1982). Most of the volcanics are
porphyritic with phenocrysts consisting of zoned plagioclase, olivine, augite, hypersthene, amphibole, and
biotite. Yen (1958) suggested that Kuanyinshan volcanic activity started in the Plio-Pleistocene and ended in
the early or middle Pleistocene based on strata correlation. The volcanic activity in this area was dated
between 0.63 and 0.20 Ma by Juang and Chen (1989)
using the K±Ar method. Wang (1989) traced the earliest volcanic activity in this area back to 1.1 Ma

based on ®ssion track dating.
Fractional crystallization is one of the main mechanisms by which andesitic magmas are derived from

basaltic magmas. Fractionation involves the separation
of magnetite (e.g. Osborn, 1969), olivine (e.g. Nicholls,
1974), amphibole (e.g. Allen and Boettcher, 1978), or
an assemblage of these or other mineral phases (e.g.
Sarkar et al., 1989). Both hydrous (Kay et al., 1982)
and anhydrous (Gill, 1981) fractionation have been
proposed. Several authors (e.g. Singer et al., 1992)
have employed multiple di€erentiation trends in deriving andesites from basalts.
Based on a geochemical study of the Kuanyinshan
shoshonitic series, Chen (1982) proposed that the Kuanyinshan andesites were likely derived from basalts
through separation of an amphibole±plagioclase±magnetite assemblage. Hwang and Lo (1986) suggested
that there are three di€erentiation trends with di€erent
fractionates consisting of amphibole, plagioclase or
magnetite. This fractionation mechanism was con®rmed by the trace elements distributions described by
Chen (1990).
The Wannienta basalt for this study is present in the
Kuanyinshan volcanic province (Fig.1b). The distance

between the Wannienta basalt and Kuanyinshan andesites is less than 3 km. The Wannienta basalt is considered as the most probable parental magma for the
Kuanyinshan andesites based on the major elements,
trace elements, and isotopes in previous studies. In this
study, the crystallization sequences of a Wannienta
basalt were investigated at pressures between 1.0 and
2.0 GPa in order to estimate the depth of fractionation. The di€erentiation trends of the basaltic magma
were determined by analyzing the composition of
glasses and coexisting phenocrysts. The observed crystallization trends at various pressures were then used
to estimate the depth for fractionation of basaltic
magma that di€erentiated to form the Kuanyinshan
andesites.

2. Experimental method
2.1. Starting material

Fig. 1. A general tectonic map of Taiwan (from Lu et al., 1998) and
a simpli®ed Kuanyinshan geologic map (modi®ed from Chen, 1987).

In order to model the fractionation of the basaltic
magmas in the Kuanyinshan group, the rock with the

highest Mg number (64; de®ned as molar Mg/
(Mg+Fe)  100) in this area was chosen. The Wannienta basalt is ®ne-grained and grayish-black in color
with ®ne vesicles. The phenocrysts are olivine, augite,
and plagioclase. The detailed petrography was
described by Chen (1982) and Liu et al. (1998). The
forsterite content of olivine phenocrysts range from
Fo85 in the cores to Fo72 along the rims (Chen, 1982;
Liu et al., 1998). The liquidus temperature at atmospheric pressure is high (12708C) (Liu et al., 1998). All
evidence shows that the composition of the basalt is
near primitive (Draper and Johnston, 1992).

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

The sample powder of Wannienta basalt used in this
study is the same one used in the previous paper (Liu
et al., 1998). The IGPET computer program was
employed to calculate the CIPW norm of the basalt
and to plot the Di-Ol-Sil pseudoternary diagram from
the projection of plagioclase.

2.2. Apparatus and procedures
Melting experiments were performed in a pistoncylinder apparatus (Boyd and England, 1960) at
National Taiwan Normal University. The experimental
techniques for high pressure runs are similar to that
described by Liu and Presnall (1990). The pressure-cell
assembly is the same as that described by Liu et al.
(1997). Platinum tubes were used as sample capsules.
All experiments were of the piston-out type (Presnall
et al., 1978) with no pressure correction. In all cases,
W5Re±W26Re thermocouples were used with no
pressure correction applied to the emf values. Temperatures were corrected to the International Practical
Temperature Scale of 1968 (Anonymous, 1969). The
duration of the experiments ranged from 3.5 to
6 hours. Reported pressures are nominal and no corrections were incorporated for friction.

2.3. Identi®cation and analysis of phases
Experimental charges were mounted in epoxy and
polished in longitudinal section. Phases in the run products were ®rst identi®ed microscopically in re¯ected
light. Characteristic relief, re¯ectivity, and crystal habit
were used for phase identi®cation, along with electron

microprobe analysis and back-scattered electron imaging in questionable cases. The compositions of plagioclase, clinopyroxene, orthopyroxene, garnet, and glass
were determined using the automated JEOL JXA8900R electron microprobe at the Institute of Earth
Sciences, Academia Sinica.
Analyses were obtained using an accelerating voltage
of 15 kV. A beam current of 10 nA with a beam diameter of about 1 mm was employed for all elements. A
synthetic spinel was used as a standard to analyze Al
and Mg elements. For the other elements, a synthetic
glass was applied as a standard. Grains of plagioclase,
clinopyroxene, orthopyroxene, and garnet in the
quenched products chosen for analysis are usually larger than 10 mm in diameter and the diameter of analyzed glass pools is usually larger than 30 mm. Matrix
corrections were made using a ZAF procedure.

521

3. Results and discussion
3.1. Crystallization sequence and melting properties of
the magma
Fifteen runs were performed in order to locate the
liquidus temperatures, the solidus temperatures, and
the melting intervals of the basaltic magma at pressures between 1.0 and 2.0 GPa. Results of the quenching experiments are listed in Table 1. The

temperature±pressure diagram of the Wannienta basalt
(Fig. 2) was constructed based on the data in Table 1
and the data at atmospheric pressure presented by Liu
et al. (1998). It should be emphasized that there is a
small di€erence between the data at atmospheric pressure and the data at high pressure. The experiments by
Liu et al. (1998) were performed at atmospheric pressure under anhydrous conditions. The experiments at
high pressures were, however, performed with rock
powders in which the loss on ignition is about 2%.
The two sets of data were used together to plot the
temperature±pressure diagram of the basalt.
The liquidus temperature of the basaltic magma at
1.0 GPa is determined to be 12808C on the basis of
the quenching experiments (Table 1 and Fig. 2). With
decreasing temperature, the number of crystallized
phases increase beginning with orthopyroxene as the
near-liquidus mineral. Clinopyroxene and plagioclase
crystallize within the lower temperature range of 1250±
12208C during which time orthopyroxene is consumed.
Orthopyroxene re-appears at about 12208C. Back-scattered electron imaging indicates that the run at 11808C
has only a trace amount of glass. The solidus tempera-

Fig. 2. The temperature±pressure diagram of a Wannienta basalt.
Symbols indicate pressures and temperatures of experiments. All the
abbreviations are the same as in Table 1, except Ol: olivine, Ox: oxides, and S: solids. The data, under anhydrous conditions and atmospheric pressure, are from Liu et al. (1998). The data at high
pressures in this study are under hydrous conditions. The solidus
and liquidus curves were, therefore, tentatively drawn as a dashed
line and solid line, respectively, for purposes of discussion.

522

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

Table 1
Quenching experiments
Run no.

P (GPa)

Temperature (8C)

Duration (h:min)

Phase(s)a

KYBP4
KYBP1
KYBP6
KYBP2
KYBP3
KYBP5
KYBP10
KYBP8
KYBP11
KYBP12
KYBP13
KYBP9
KYBP14
KYBP16
KYBP15

1.0
1.0
1.0
1.0
1.0
1.0
1.5
1.5
1.5
1.5
2.0
2.0
2.0
2.0
2.0

1300
1280
1260
1240
1200
1180
1340
1300
1240
1200
1340
1325
1280
1260
1220

4:00
4:05
6:00
3:30
5:00
6:00
4:00
4:00
4:30
5:00
3:30
4:00
4:30
6:00
5:00

Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl
Gl

a

+
+
+
+

Opx
Cpx + Pl
Opx + Cpx + Pl
Opx + Cpx + Pl

+ Cpx
+ Cpx
+ Cpx + Pl
+
+
+
+

Cpx
Cpx
Cpx + Pl
Cpx + Pl + Ga

Cpx: Clinopyroxene; Ga: Garnet; Gl: Glass; Opx: Orthopyroxene; Pl: Plagioclase.

ture of the basaltic magma at 1.0 GPa is therefore
taken to be 11808C, indicating a melting interval of
about 1008C. The crystallization sequence at 1.0 GPa
is therefore orthopyroxene, clinopyroxene, and plagioclase.
The liquidus and solidus temperatures at 1.5 GPa
were estimated as 1305 and 11858C, respectively
(Table 1). The crystallization sequence at 1.5 GPa is
clinopyroxene±plagioclase. At 2.0 GPa, the liquidus
temperature is raised to approximately 13338C whereas
the solidus temperature drops below 12208C. The crystallization sequence at 2.0 GPa is clinopyroxene, plagioclase, and ®nally garnet.
The crystallization sequences of the Wannienta
basaltic magma are similar to those of high magnesian
basalt in previous studies (e.g. Gust and Per®t, 1987;
Draper and Johnston, 1992). Iron-titanium oxide is the
liquidus phase and is joined by olivine, plagioclase,
and two pyroxenes at progressively lower temperature
down to 10808C under atmospheric pressure. Above
1.0 GPa, the near liquidus mineral is clinopyroxene.
Garnet appears only at 2.0 GPa in run no. KYBP15
(12208C) whereas garnet is present above 1.5 GPa in
Draper and Johnston's study (1992). Elthon and Scarfe
(1984) only synthesized garnet above 2.5 GPa. Garnet
is absent at lower pressures in their study in which the
data at lower temperatures and pressures are not
available. At successively higher pressures, plagioclase,
clinopyroxene, and garnet are the liquidus phases in
both anhydrous (Johnston, 1986) and hydrous (Baker
and Eggler, 1983, 1987) experiments.
3.2. Mineral chemistry of synthetic phases
Clinopyroxenes in the quenching products were analyzed with an electron microprobe and the results are

presented in Table 2 and also plotted in Fig. 3. The
Wo (CaSiO3) component in the clinopyroxenes range
between 34 and 43% and are therefore classi®ed as
augites following the classi®cation of Morimoto
(1988). The Fs (FeSiO3) component ranges from 11 to
19%.
The orthopyroxenes were synthesized only at 1.0
GPa in this study. Microprobe analyses of orthopyrox-

Fig. 3. The compositions of clinopyroxenes (Cpx) and othopyroxenes
(Opx) in the Wannienta basalt and in the quenched products of this
study. Symbols: solid cross: composition of clinopyroxene as phenocryst in basalt; open cross: composition of clinopyroxene in groundmass of basalt; ®lled squares: compositions of orthopyroxenes at 1.0
GPa; Symbols for the compositions of clinopyroxenes in the quenching products are as follows: ®lled circles: at 1 atm (Liu et al., 1998);
open squares: at 1.0 GPa; open triangles: at 1.5 GPa; ®lled triangles:
at 2.0 GPa.

523

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

enes are listed in Table 3 and also plotted in Fig. 3.
The En (MgSiO3) component of the orthopyroxenes in
this study decreases with decreasing temperature
whereas the Fs component increases. The results are
consistent with the fractionation trends of pyroxenes
within the Skaergaard and Bushveld complexes (Deer
et al., 1992).
Plagioclase is abundant at pressures between 1 atm
and 2.0 GPa. The compositions of plagioclase in this
study are listed in Table 4 and plotted in Fig. 4. They
range from labradorite to andesine in composition.
The An (CaAl2Si2O8) component of the synthesized
plagioclases in this study all decrease with decreasing
temperature in both the 1.0 and 2.0 GPa experiments
which is consistent with the results of previous studies
(Bowen, 1913; Schairer, 1957; Yoder et al., 1957; and
Johannes, 1978). The synthesized plagioclases at high
pressures are more calcic than those formed at low
pressures (Table 4 and Fig. 4). The compositions of
plagioclase phenocrysts in the Wannienta basalt clustered around An83 as determined by Chen (1982) and
around An80 in study by Liu et al. (1998). The plagioclases in this study having An contents (An77 to An79)

close to those values only appeared at pressures of 1.5
and 2.0 GPa. The composition of the synthesized plagioclase (An61) at 10878C and atmospheric pressure,
however, is similar to the composition of plagioclase
(An63) in the groundmass of the Wannienta basalt
(Liu et al., 1998). This indicates that the clinopyroxene
and plagioclase phenocrysts in the Wannienta basalt
were formed at high pressures whereas minerals in the
groundmass were formed at pressures between 1 atm
and 1.0 GPa. Garnet is only present in run no.
KYBP15 at 12208C and 2.0 GPa and has a composition of Py61Alm34Spes5 (Table 5).
3.3. Evolution of the basaltic magma
The glasses in the quenched products at 1.0, 1.5,
and 2.0 Gpa were analyzed by microprobe and are
listed in Tables 6±8. Most of the glass analyses totaled
between 98 and 101%. They were normalized to 100%
to be plotted in the variation diagrams for comparison.
The compositions of glasses at each speci®c temperature and pressure are analogous to the compositions of
the residual magmas under these conditions. Several

Table 2
Clinopyroxene compositions in the runs
Run No.
P (GPa)
T (8C)
Average of

KYBP2
1
1240
4

Wt(%)
SiO2
48.69 (0.95)a
TiO2
0.62 (0.58)
Al2O3
8.74 (1.12)
Cr2O3
0.11 (0.01)
tFeO
9.15 (1.25)
MnO
0.31 (0.24)
MgO
16.47 (0.67)
CaO
15.03 (0.06)
Na2O
0.73 (0.02)
K2O
0.04 (0.01)
Total
99.88
Cations per 6 Oxygens
Si
1.790
Ti
0.017
Al
0.210
Cr
0.003
Fe
0.281
Mn
0.010
Mg
0.903
Ca
0.892
Na
0.052
K
0.002
Total
4.160
Wo
43
Fs
14
En
43
Mg ]
76
a

KYBP3
1
1200
3

KYBP5
1
1180
1

KYBP8
1.5
1300
3

48.87 (0.92)
0.69 (0.21)
6.68 (1.46)
0.13 (0.16)
9.42 (2.01)
0.24 (0.11)
15.46 (1.81)
17.94 (1.07)
0.62 (0.23)
0.05 (0.04)
100.11

47.38
0.91
7.89
0.00
11.69
0.24
14.76
15.99
0.89
0.04
99.74

49.66
0.05
6.22
0.32
8.96
0.24
17.07
17.01
0.20
0.05
99.78

1.813
0.019
0.187
0.004
0.292
0.008
0.855
0.713
0.045
0.002
3.940
38
16
46
75

1.776
0.026
0.224
0.000
0.336
0.006
0.825
0.642
0.065
0.002
3.940
36
19
46
71

1.835
0.001
0.271
0.009
0.276
0.008
0.940
0.673
0.014
0.002
4.029
36
14
50
77

Standard deviation in parentheses.

KYBP11
1.5
1240
3

KYBP12
1.5
1200
3

(1.02) 50.03 (1.24) 49.06 (1.21)
(0.01) 0.06 (0.25) 0.57 (0.34)
(1.31) 7.81 (0.33) 6.13 (2.55)
(0.01) 0.03 (0.01) 0.17 (0.04)
(1.45) 9.19 (1.44) 9.58 (1.55)
(0.02) 0.25 (0.02) 0.03 (0.01)
(0.05) 15.32 (1.15) 16.36 (1.14)
(1.55) 17.66 (1.56) 17.88 (1.24)
(0.01) 0.24 (1.44) 0.58 (0.24)
(0.02) 0.06 (1.48) 0.05 (0.11)
100.65
100.38
1.831
0.002
0.327
0.001
0.282
0.008
0.836
0.693
0.017
0.003
3.990
34
18
58
75

1.815
0.016
0.267
0.005
0.296
0.001
0.902
0.709
0.042
0.002
4.055
37
16
47
75

KYBP9
2
1325
5

KYBP14
2
1280
5

KYBP16
2
1260
4

KYBP15
2
1220
4

49.06 (1.61)
0.62 (0.29)
7.90 (1.25)
0.27 (0.19)
8.31 (1.05)
0.30 (0.99)
14.99 (0.99)
17.92 (2.40)
0.82 (1.23)
0.04 (0.02)
100.23

50.08 (1.25)
0.35 (0.20)
7.58 (1.29)
0.31 (0.05)
6.70 (1.40)
0.26 (0.10)
15.66 (0.52)
18.55 (1.20)
0.92 (0.50)
0.03 (0.03)
100.44

51.07 (1.66)
0.58 (0.33)
6.37 (1.45)
0.41 (0.21)
7.21 (1.54)
0.23 (0.02)
15.01 (1.21)
18.66 (2.18)
0.65 (0.23)
0.03 (0.03)
100.22

50.95
0.86
4.81
0.21
6.83
0.19
14.73
20.63
0.32
0.03
99.55

1.807
0.017
0.343
0.008
0.256
0.009
0.823
0.707
0.059
0.002
4.031
38
16
46
76

1.828
0.010
0.326
0.009
0.204
0.008
0.852
0.725
0.060
0.001
4.032
42
11
47
81

1.868
0.016
0.276
0.012
0.221
0.007
0.819
0.731
0.046
0.001
3.997
41
12
47
79

1.884
0.024
0.210
0.006
0.211
0.006
0.812
0.817
0.023
0.001
3.994
44
11
45
79

(1.29)
(0.32)
(0.49)
(0.20)
(0.77)
(0.04)
(0.61)
(1.43)
(0.03)
(0.03)

524

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

Table 3
Orthopyroxene compositions in the runs
Run no.
P (GPa)
T (8C)
Average of

KYBP6
1
1260
4

Wt(%)
SiO2
53.15 (0.50)a
TiO2
0.22 (0.02)
Al2O3
5.59 (0.73)
0.27 (0.09)
Cr2O3
tFeO
8.48 (0.37)
MnO
0.31 (0.03)
MgO
28.36 (0.43)
CaO
2.69 (0.31)
Na2O
0.12 (0.02)
K2O
0.01 (0.01)
Total
101.2 (0.06)
Cations per 6 Oxygens
Si
1.908
Ti
0.006
Al
0.136
Cr
0.007
Fe
0.245
Mn
0.009
Mg
1.462
Ca
0.100
Na
0.008
K
0.000
Total
3.881
Wo
06
Fs
14
En
80
a

KYBP3
1
1200
1

KYBP5
1
1180
3

53.13
0.31
7.43
0.30
9.56
0.30
27.17
2.55
0.14
0.02
100.91

49.66
0.36
9.21
0.08
13.04
0.34
24.70
2.47
0.17
0.04
100.06

1.855
0.008
0.306
0.008
0.279
0.009
1.414
0.095
0.009
0.001
3.984
05
16
79

(1.19)
(0.10)
(2.43)
(0.07)
(1.21)
(0.05)
(1.29)
(0.65)
(0.05)
(0.06)
(0.06)
Fig. 4. The compositions of plagioclase in the Wannienta basalt and
in the run products of this study. The data for natural plagioclase
and synthesized plagioclase at atmospheric pressure are reproduced
from Liu et al. (1998). The data for natural plagioclase in Wannienta
basalt published by Chen (1982) are similar to that of Liu et al.
(1998) and are not plotted. Symbols for the compositions of plagioclases in the quenching products: ®lled circles: at 1 atm (Liu et al.,
1998); open rhombus: at 1.0 GPa; open triangles: at 1.5 Gpa; ®lled
triangles: at 2.0 GPa.

1.783
0.010
0.217
0.002
0.329
0.010
1.322
0.095
0.012
0.002
3.782
05
22
73

Standard deviation in parentheses.

Table 4
Plagioclase compositions in the runs
Run no.
P (GPa)
T (8C)
Average of

KYBP2
1
1240
4

Wt(%)
SiO2
49.70 (1.60)a
Al2O3
30.77 (1.48)
tFeO
1.05 (0.06)
CaO
14.62 (1.55)
Na2O
3.28 (0.68)
K2O
0.42 (0.23)
Total
99.84 (0.23)
Cations of 8 oxygens
Si
2.283
Al
1.666
Fe
0.040
Ca
0.719
Na
0.292
K
0.025
An
69
Ab
28
Or
3
a

Standard deviation in parentheses.

KYBP3
1
1200
4

KYBP5
1
1180
4

KYBP12
1.5
1200
3

KYBP16
2
1260
3

KYBP15
2
1220
3

52.38
28.80
1.08
12.50
4.20
0.69
99.65

55.53
26.62
1.31
9.44
4.74
2.07
99.71

52.48
29.51
2.01
13.41
2.20
0.60
99.74

48.23
30.11
1.15
18.24
2.45
0.32
99.5

48.27
32.24
1.20
16.13
2.30
0.42
100.55

(0.90)
(0.01)
(0.62)
(0.26)
(0.16)
(0.01)
(0.23)

2.400
1.555
0.041
0.613
0.373
0.040
60
36
4

(0.53)
(0.10)
(0.05)
(0.09)
(0.22)
(0.09)
(0.23)

2.517
1.422
0.050
0.458
0.417
0.120
46
41
12

(1.54)
(3.12)
(0.11)
(3.31)
(1.25)
(0.33)
(0.23)

2.389
1.583
0.077
0.654
0.194
0.003
77
22
1

(1.31)
(2.45)
(0.15)
(2.45)
(1.13)
(0.30)
(0.23)

2.241
1.649
0.006
0.908
0.221
0.019
79
19
2

2.206
1.750
0.042
0.800
0.201
0.019
78
20
2

(1.21)
(1.09)
(0.11)
(1.44)
(1.22)
(0.34)
(0.23)

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

525

workers have pointed out that the glass composition
can be signi®cantly altered by the formation of quench
crystals in the experiments (e.g. Jaques and Green,
1979, 1980). In this study, some quench crystals were
found. In another study (Liu and Presnall, 2000), we
had found that the glass compositions only changed
within a few microns of the quenched crystals. The
results estimated from the glass composition determined by microprobe are consistent with the results of
the quenching experiments in that study. Therefore,
the glass compositions are believed to represent the
compositions of the melt coexisting with the crystallized assemblage in that run. All the spots for glass
analyses in this study are at least 10 mm away from
crystallized phases.
The di€erentiation trends at each pressure are discussed below.
3.4. 1.0 GPa
The compositions of glasses change irregularly
between Ol-normative and Qz-normative with decreasing temperature (Table 6). The compositions of glasses

Table 5
Garnet composition in this study
Run no.
P (GPa)
T (8C)
Average of
Wt(%)
SiO2
TiO2
Al2O3
Cr2O3
tFeO
MnO
MgO
CaO
Na2O
K2O
Total
Cations per 24 Oxygens
Si
Al
Ti
Mg
Fe
Ca
Na
K
Cr
Mn
Total
Pyrope
Almandine
Spessartine
a

Standard deviation in parentheses.

KYBP15
2
1220
3

Fig. 5. Variations of SiO2, Al2O3, total Fe as FeO, MgO, CaO,
Na2O, and K2O of residual glasses versus temperature at 1.0 GPa.
The KYBP] are the run numbers listed in Table 1.

at 1.0 GPa are plotted versus temperature in Fig. 5.
With decreasing temperature (read from right to left in
Fig. 5), glasses become progressively enriched in
Al2O3, Na2O, and K2O and depleted in MgO, while
total iron contents change irregularly. The SiO2 content ¯uctuates within the range of 52 and 55%. The

39.67 (0.26)a
0.14 (0.02)
21.92 (0.09)
0.05 (0.08)
15.56 (0.17)
0.67 (0.12)
15.48 (0.12)
5.72 (0.04)
0.11 (0.03)
0.01 (0.01)
100.32 (0.01)
5.585
3.811
0.127
3.402
1.919
1.903
0.031
0.001
0.005
0.288
16.111
61
34
05

Fig. 6. The di€erentiation trend of residual liquids in Harker's diagram at 1.0 GPa. Symbols: solid dots: the glass compositions at 1.0
GPa. open circles: average compositions of each rock type in Kuanyinshan volcanic group from Chen (1990): 1: augite olivine basalt;
2: augite basalt; 3: biotite hornblende andesite; 4: augite andesite; 5:
hornblende bearing two pyroxene andesite; 6: hypersthene hornblende andesite.

526

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

Table 6
Glass compositions in the runs at 1.0 GPa
Run no.
T (8C)
No. of analyses
Wt(%)
SiO2
TiO2
Al2O3
Cr2O3
tFeO
MnO
MgO
CaO
Na2O
K2O
Total
CIPW Norm
Il
Or
Ab
An
Di
Hy
Q
Ol
Mg ]
a

KYBP1
1280
2

KYBP6
1260
2

KYBP2
1240
2

KYBP3
1200
3

KYBP5
1180
5

51.54 (0.39)a
0.80 (0.06)
17.58 (0.20)
0.06 (0.08)
6.90 (0.04)
0.21 (0.06)
7.69 (0.06)
9.38 (0.02)
2.74 (0.04)
1.58 (0.01)
98.48

53.98
0.91
17.72
0.00
3.36
0.14
8.03
10.01
2.78
1.54

52.76
0.99
17.65
0.02
6.61
0.22
6.73
9.58
2.90
1.69

53.37
1.29
17.06
0.03
8.08
0.10
4.62
7.50
2.83
2.93

54.75 (0.75)
0.35 (0.20)
24.01 (1.51)
0.03 (0.03)
2.65 (0.97)
0.07 (0.04)
1.41 (1.17)
10.10 (0.87)
4.52 (0.26)
1.99 (0.23)
100.48

1.52
9.34
23.19
31.00
12.65
10.07
0.00
10.63
57.21

1.73
9.10
23.52
31.32
14.60
17.98
0.21
0.00
57.11

(0.23)
(0.08)
(0.17)
(0.00)
(0.05)
(0.08)
(0.01)
(0.05)
(0.07)
(0.04)
98.47

2.54
17.31
23.95
25.19
9.98
17.40
0.00
1.49
51.27

(0.26)
(0.06)
(0.34)
(0.05)
(0.27)
(0.05)
(0.21)
(0.05)
(0.12)
(0.06)
97.81

0.66
11.76
34.56
39.35
8.97
0.00
0.00
2.54
53.24

Standard deviation in parentheses.

Table 7
Glass compositions in the runs at 1.5 GPa
Run no.
KYBP10
T (8C)
1340
No. of analyses 4

KYBP8
1300
4

Wt(%)
SiO2
TiO2
Al2O3
Cr2O3
tFeO
MnO
MgO
CaO
Na2O
K2O
Total
CIPW Norm
Il
Or
Ab
An
Di
Hy
Ol
Mg ]

1.73
11.11
31.35
27.37
12.75
0.00
15.39
46.61

a

1.88
9.99
24.54
30.15
14.18
12.08
0.00
6.31
55.13

(0.20)
(0.05)
(0.16)
(0.02)
(0.06)
(0.04)
(0.01)
(0.07)
(0.09)
(0.07)
99.15

KYBP11
1240
4

KYBP12
1200
4

compositions of the Kuanyinshan volcanics. The
extensive fractionation is shown by the wide compositional spread of the Kuanyinshan natural volcanics
whereas the glasses at 1.0 Gpa cluster within a small

52.33 (0.71)a 53.57 (0.18) 53.35 (0.65) 52.86 (1.18)
0.88 (0.00) 0.91 (0.06) 0.99 (0.04) 0.85 (0.10)
18.45 (0.19) 18.53 (0.11) 17.69 (0.21) 17.60 (0.16)
0.00 (0.00) 0.06 (0.02) 0.00 (0.00) 0.01 (0.02)
6.92 (0.10) 6.01 (0.07) 4.99 (2.35) 5.63 (1.94)
0.14 (0.19) 0.22 (0.08) 0.22 (0.04) 0.17 (0.09)
6.66 (0.00) 7.02 (0.18) 7.38 (0.93) 7.50 (0.67)
8.20 (0.06) 8.68 (0.14) 9.75 (0.31) 9.68 (0.34)
3.29 (0.01) 3.93 (0.10) 2.90 (0.09) 2.78 (0.05)
1.84 (0.06) 1.88 (0.07) 1.65 (0.13) 1.57 (0.07)
98.71
100.81
98.92
99.65
1.67
10.87
27.84
30.14
8.62
7.90
11.67
51.98

1.88
9.75
24.54
30.38
14.51
14.08
3.79
55.32

1.61
9.28
23.52
30.91
13.85
14.85
4.61
56.78

Standard deviation in parentheses.

compositions of glasses at 1.0 GPa were also plotted
in Harker's diagram (Fig. 6) and compared with the

Fig. 7. Variations of SiO2, Al2O3, total Fe as FeO, MgO, CaO,
Na2O, and K2O of residual glasses versus temperature at 1.5 GPa.
KYBP] are the run numbers listed in Table 1.

527

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531
Table 8
Glass compositions in the runs at 2.0 GPa
Run no.
T (8C)
No. of analyses
Wt(%)
SiO2
TiO2
Al2O3
Cr2O3
tFeO
MnO
MgO
CaO
Na2O
K2O
Total
CIPW Norm
Il
Or
Ab
An
Di
Hy
Q
Ol
Mg ]
a

KYBP13
1340
4

KYBP9
1325
4

KYBP14
1280
3

KYBP16
1260
4

KYBP15
1220
3

52.74 (0.31)a
0.79 (0.01)
18.47 (0.25)
0.03 (0.01)
6.02 (1.06)
0.16 (0.00)
7.88 (0.22)
8.23 (0.65)
3.55 (0.15)
1.64 (0.24)
99.51

53.51 (0.18)
0.92 (0.05)
18.50 (0.12)
0.06 (0.02)
6.00 (0.06)
0.19 (0.10)
7.06 (0.16)
8.72 (0.14)
3.93 (0.08)
1.86 (0.06)
100.75

52.46
0.90
18.52
0.03
6.91
0.27
6.69
8.18
3.25
1.83

55.11 (0.33)
0.80 (0.12)
18.40 (0.15)
0.01 (0.04)
7.34 (0.04)
0.21 (0.03)
5.81 (0.05)
7.34 (0.05)
3.12 (0.03)
2.22 (0.03)
100.44

56.45
1.51
18.21
0.04
7.35
0.19
4.07
4.73
3.00
3.76

1.50
9.69
30.04
29.62
9.08
4.49
0.00
15.05
49.65

1.75
10.99
31.23
27.34
1.10
12.93
0.00
15.33
46.68

1.71
10.81
27.50
30.54
8.21
9.13
0.00
11.09
52.62

1.52
13.12
26.40
29.86
5.39
23.53
0.00
0.60
53.08

2.87
22.22
25.39
23.47
0.00
21.46
3.25
0.00
48.04

(0.56)
(0.03)
(0.18)
(0.03)
(0.08)
(0.02)
(0.05)
(0.05)
(0.06)
(0.05)
99.04

(2.67)
(0.03)
(0.29)
(0.08)
(0.79)
(0.17)
(1.21)
(0.15)
(0.29)
(0.55)
99.31

Standard deviation in parentheses.

range. This implies that fractionation of the Kuanyinshan volcanics cannot be modeled at 1.0 GPa.
3.5. 1.5 GPa

Na2O, and K2O as temperature decreases (Table 7 and
Fig. 7). The Ol-norm in glasses decreases with decreasing temperature. In Fig. 8, the liquid lines of descent
are compared to the Kuanyinshan fractionation trend.

The residual magmas at 1.5 GPa become enriched in
SiO2, MgO, and CaO and depleted in Al2O3, FeO,

Fig. 8. The di€erentiation trend of the residual liquids in Harker's
diagram at 1.5 GPa. Symbols: solid dots: the glass compositions at
1.5 GPa; open circles: the same as in Fig. 6.

Fig. 9. Variations of SiO2, Al2O3, total Fe as FeO, MgO, CaO,
Na2O, and K2O of residual glasses versus temperature at 2.0 GPa.
KYBP] are the run numbers listed in Table 1.

528

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

The glasses at 1.5 GPa also cluster between 53% and
about 54% SiO2.
3.6. 2.0 GPa
The compositions of residual liquids at 2.0 GPa are
plotted versus temperature in Fig. 9. As temperature
decreases, the residual liquids become enriched in
SiO2, FeO, and K2O and depleted in MgO, CaO, and
Na2O while Al2O3 changes very little (Table 8 and
Fig. 9). In the Harker's diagrams, the di€erentiation
trend of the residual liquids does not adequately duplicate that of the Kuanyinshan volcanics (Fig. 10).
3.7. AFM diagram

Fig. 10. The di€erentiation trend of the residual liquids in Harker's
diagram at 2.0 GPa. Symbols: solid dots: the glass compositions at
2.0 GPa; open circles: the same as in Fig. 6.

The compositions of Kuanyinshan volcanics and experimental liquids at each pressure are compared in
the Na2O+K2O-FeO+Fe2O3-MgO (AFM) diagram in
Fig. 11. The fractionation trend at atmospheric press-

Fig. 11. Na2O+K2OÿFeO+Fe2O3ÿMgO (AFM) diagrams (Wagner and Deer, 1939) illustrating the variation of Kuanyinshan volcanics (Chen,
1990) and the glasses at 1 atm (Liu et al., 1998) and at pressures from 1.0 to 2.0 GPa in this study. Open circles: the same as in Fig. 6. The
boundary line between tholeiitic series and calc-alkaline series was reproduced after Kuno (1950).

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

529

Fig. 12. The plagioclase saturated pseudoternary projection following the techniques of Walker et al. (1979) and Sack et al. (1987). Symbols are
the same as in Fig. 11.

ure is most similar to the di€erentiation trends of the
Kuanyinshan volcanics whereas fractionation trends at
higher pressures deviate signi®cantly. This is consistent
with the trends found in the Harker's diagrams of
Figs. 6, 8, and 10.
In the pseudoternary Di-Ol-Sil diagram (Fig. 12),
the compositions of Kuanyinshan volcanics and experimental liquids at pressures from 1 atm to 2.0 GPa
were all plotted for comparison. With increasing pressure, the liquid lines of descent shift toward the Ol-apex
which is consistent with previous studies (e.g. Presnall
et al., 1978; Elthon and Scarfe, 1984; Liu and Presnall,
1990). Comparatively speaking, the fractionation trend
of experimental liquids at atmospheric pressure most
closely follows the di€erentiation trend of the Kuanyinshan volcanics.
3.8. Historical evolution of magmas in Kuanyinshan
The biotite hornblende andesite, augite andesite, and
two-pyroxene andesite were dated as 0.63, 0.53 and
0.43 Ma respectively by Juang and Chen (1989) based
on the K±Ar method. Using the ages of the rocks and
experimental results, the history of magmatic evolution
in the Kuanyinshan volcanic group can be interpreted
as follows:

At 0.63 Ma, the basaltic magma intruded the crust
at pressures between 1 atm and 1.0 GPa and fractionated into an andesitic magma compositionally similar
to the biotite hornblende andesite which occurs as a
dyke in Kuanyinshan. At 0.53 Ma, another batch of
basaltic magma moved upward into the crust at pressures between 1 atm and 1.0 GPa. This basaltic magma
fractionated into an andesitic magma and erupted to
form the clinopyroxene andesite of Layer 1. At 0.43
Ma, another batch of basaltic magma moved into the
crust and fractionated into an andesitic magma, which
then erupted to form a two-pyroxene andesite as Layer
2.
The composition of the hypersthene hornblende
andesite in Layer 3 is beyond the range of fractionation in this study. It is proposed that the basaltic
magma could evolve into a hypersthene hornblende
andesite with additional fractionation.
Since the compositions of pyroxene and plagioclase
phenocrysts in the Wannienta basalt are similar to
those synthesized at high pressures, it is suggested that
the basaltic magma had crystallized at high pressure.
At 0.20 Ma, the basaltic magma containing high-pressure phenocrysts invaded the crust and erupted to form
the Wannienta basalt.

530

T.C. Liu et al. / Journal of Asian Earth Sciences 18 (2000) 519±531

4. Conclusions
The experimental results show that the liquidus and
solidus temperatures increase by 608C/GPa and 408C/
GPa, respectively. The liquidus mineral at 1.0 GPa is
orthopyroxene whereas the liquidus mineral is clinopyroxene at 1.5 and 2.0 GPa. At lower temperatures
and pressures between 1.0 and 2.0 GPa, the crystallized phases are clinopyroxene and plagioclase. Garnet
appears at 2.0 GPa near the solidus.
The evolution of the residual magma shows the following geochemical trend with decreasing temperature:
enrichment in aluminum, sodium, and potassium and
depletion in magnesium at 1.0 GPa; enrichment in silicon, iron, and potassium and depletion in magnesium,
calcium, and sodium at 2.0 GPa. The fractionation
trend of the Kuanyinshan volcanic series is similar to
that exhibited by residual magmas at pressures
between 1 atm and 1.0 GPa. This implies that the
depth of fractional crystallization of the Wannienta
basaltic magma to produce andesites could be modeled
at low pressure. The fractionates involved in the fractionation included iron-titanium oxides, olivine, plagioclase, and clinopyroxene.

Acknowledgements
We would like to thank Dr. Jennifer Lytwyn, University of Houston, for her revision to signi®cantly
improve the manuscript. Professor Cheng-Hong Chen
of National Taiwan University generously allowed us
access to his graphite-evaporator for carbon coating
on polished sections. This research was supported by
the National Science Council of the Republic of China
under grant NSC86-2116-M-003-007 to TCL.

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