Seismochemical studies on a geothermal area in south China
Grant-in-Aid for international Scientific Research
|Allocation Type||Single-year Grants|
|Research Institution||University of Tokyo|
WAKITA Hiroshi Univ. of Tokyo. Faculty of Science. Professor, 理学部, 教授 (40011689)
CHEN Jianfa Lanzhou Inst. of Geology. Researcher, 蘭州地質研究所, 研究員
徐 永昌 中国科学院, 蘭州地質研究所, 教授
王 先彬 中国科学院, 蘭州地質研究所, 教授
IGARASHI Joji Hiroshima Univ.. Faculty of Science. Associate Professor, 理学部, 助教授 (00202854)
NAKAI Shun'ichi Univ. of Tokyo. Faculty of Science. Research Associate, 理学部, 助手 (50188869)
WANG Xianbin Lanzhou Inst. of Geology. Professor
XU Yongchang Lanzhou Inst. of Geology. Professor
|Project Period (FY)
Completed(Fiscal Year 1993)
|Budget Amount *help
¥4,000,000 (Direct Cost : ¥4,000,000)
Fiscal Year 1993 : ¥4,000,000 (Direct Cost : ¥4,000,000)
|Keywords||Helium Isotope / Subcontinental Mantle / China / Natural Gas / Hotspring Gas / Geothermal System / Heat Source / Rift Zone|
This International Scientific Research Program aimed at revealing heat source of a geothermal system in south China and chemical characteristics of the subcontinental mantle beneath China. Main research field was Tengchong geothermal area in western Yunnan. In addition, samples of hotspring gas and natural gas have been collected in northeastern area of China.
The Tengchong area located on the Indo-Eurasian plate collision belt is characterized by topographic features of circular structures clearly apparent in aerial photographs. The most active geothermal areas are distributed around the largest circular structure located to the south of Tengchong town.
The ^3He/^4He ratios in the range from 0.208 to 5.16Ra indicate the presence of mantle-derived helium in all the samples. The samples with high ^3He/^4He ratio concentrate near Tengchong area, while hot spring gases in the distant area from central Tengchong contain radiogenic helium. The distribution pattern of the helium isotopic ratio seems to suggest the presence of a magma supplying mantle volatiles beneath a circular structure near Tengchong. Our results are consistent with the implication of a molten body beneath central Tengchong area by a seismic reflection profiling study.
The ^3He/^4He ratio of the sample from the central Tengchong at 5.16 Ra is the highest value reported to date for mainland China, however, the value is lower than that of typical subduction magmatism. Our helium isotopic results suggests that the subcontinental mantle beneath the area have been metasomatized by subduction and/or collision event.
Samples of natural gases from northeast China contain helium with mantle origin. Samples with high ^3He/^4He(>2Ra) are distributed along the Tan-Lu rift zone. It has been revealed that the samples have hardly been contaminated by air component and they will be good samples for heavy noble gas studies. They will be processed for the study soon.
Research Output (2results)