Journal of Taiwan Normal University: Mathematics, Science & Technology 1997, Vol. 42 (New Version), 53-59
A Preliminary Report on the Experimental Study
of the Two-pyroxene Andesite from Kuanyinshan
,
Northern Taiwan
Teh-Ching Liu, Bore-Sing Chen, Jan-Jee Pan,
Pei-Kai Chen
,
and Shan-Zon Wu Department of Ear也 sc區 DCesNatioDB.l TaiwaD Normal University
The high temperature furnace and the high pressure high temperature piston-cylinder apparatus were set up in the experimental petrological laboratory of Department of Earth Sciences, National Tai-wan Normal University. The thermal gradient in the high temperature furnace is smaller than 1 T per
10 cm in the uniform zone. The precisions for the pressure and temperaωre measurements of the pis-ton-cylinder apparatus are 0.3 kb and 50
C , respectively. The thermocouple used in the present experi-ments was calibrated and the temperature correction is -21.20
C . The liquidus temperatures of the Kuanyinshan andesite were determined to be 1210 oC , 12500
C , and 1290 oC at the atmospheric pressure,
10 kbar and 20 kbar, respectively. Near-liquidus minerals at atmospheric pressure are iron-titanium ox-ides and plagioclase. Plagioclas巴， however, is the near-liquidus rnineral at 10 kbar and 20 kbar. The slope of the liquidus curve of the andesitic meIt is about 400
C per 10 kbar.
Keywords: Andesite Liquidus Near-liquidus rnineral
Introduction
Taiwan is in the col1ision area between the Eurasian plate and the Philippine plate. Based on the seismic studies, the Philippine plate bends along Ryukyu trench at about latitude 24 0 N lati-tude and dips northward with about
45
0 beneath the Eurasian plate (Tasi, et a1., 1977; Kao and Wu,1996). The magma activity created the Tatun and
Kuanyinshan volcanoes may be related with the subduction after Pliocene. It is significant to study the petrogenesis of the Kuanyinshan volcanics for the special tectonic setting in this area.
Kuanyinshan volcano is situated in Taipei county
,
northern Taiwan. This volcano is mainly consisted of three successive andesitic lava flows. According to the mafic minerals of the rocks, two 叮'pes of basalt and six types of andesite were found in this area (Ichimura, 1950; Chen, 1982). Acaldera structure in the southeastern area was re-congnized by Chen and Hwang (1982) and Hwang
and Lo
(1
986). The eruptive sequences of the lavaflows were augite andesite lava, the first, two-pyroxene andesite lava
,
the second,
and hypers-thene andesite lava,
the third,
as determined by Hwang and Lo (1986).Based on the contact relationship between the volcanics and the surrounding sedimentary rocks,
Yen (1958) inferred that the age of the
Kuanyin-shan eruption was between Plio-Pleistocene and middle Pleistocene. Juang and Chen (1989) dated the Kuanyinshan volcanics between 0.63 and 0.20
Ma with the potassium-argon method. The volcanic activity was traced back to 1.1 Ma by Wang (1989)
with fission track method.
