Geochemical characteristics of geothermal gases and their geological implications in Tibet

	Geochemical characteristics of geothermal gases and their geological implications in Tibet
	Zhao, P ; Xie, EJ ; Dor, J ; Jin, J ; Hu, XC ; Du, SP ; Yao, ZH
刊名	ACTA PETROLOGICA SINICA
	2002-10-01
卷号	18 期号:4 页码:539-550
关键词	geothermal gases carbon isotope hydrothermal activities genesis Tibet
ISSN号	1000-0569
文献子类	Article
英文摘要	Geothermal resources are abundant in the Tibetan Plateau. Two types of geothermal gases can be distinguished in the region, i.e. CO2- and N-2-rich gases. In most cases, CO2 is a dominant component of gases, usually higher than. 80% in volume and coexists with Cl-Na or HCO3-Na water. Cl-Na water generally appears in high-temperature geothermal systems associated with magma intrusions. HCO3-Na water presents in low- to medium-temperature geothermal systems warmed by high regional heat flow through meteoric water circulating at deep faults. In case of caverns appearance under sinter layers, CO2-rich gases will present pseudo-N-2-rich gases after fluid boiling, degassing and long-distance lateral movement under the layers. There are a few hot springs with N-2-rich dissolved gases in Tibet, in which N-2 content is more than 90% in volume. N-2-rich gases pre related to low-temperature geothermal systems and only coexist with HCO3-Na water. He content of gas samples is in a wide range, from under detection limit of instrument to 1.5% in volume. There is no relation found among He content, sampling temperature and genesis of hydrothermal systems. He-Ar-N-2 triangular diagram shows that nearly all of helium is generated by the decay of U and Th in the crust. N-2 and Ar are mostly of atmospheric origin. Low N-2/Ar ratio of the samples eliminates the possibility of N-2 and Ar escaping from mantle intrusions. On the basis of helium isotope ratios at well ZK4001 of the Yangbajain and at Gulu hot springs, it is inferred that there is about 3% of mantle component in partial melting layer of the crust in the region. Except the Yangbajain geothermal field and a few other hot springs most of CO2 originates from marine carbonates mixing with a little organic sediment. The relative abundances of geothermal gases can be applied to calculation of temperature in reservoirs. There are two H-2/Ar geothermometers proposed by different authors. When Log (H-2/Ar) value is in the range of -0.8 to 0.3, estimated temperatures from these ones are accordant with each other and close to the measured ones. However, if there is radioactive Ar adding in primordial gases or H-2 degassing during fluids' ascent, deviation of calculated temperature will increase. It is reasonable that H-2/Ar geothermometers can't be applicable for low temperature geothermal systems. In Tibet, the hydrothermal activities are mainly situated on the south side of the Banggong-Nujian suture. Only a few hot springs are located on the north side of this suture. Boiling, hydrothermal eruption and silica deposit manifestations associated with high-temperature geothermal systems are only distributed along the Yarlu-Zangbo suture and S-N striking Nagqu-Yangbajain-Yadong normal faults. On the Tibetan plateau, it is first time to detect the helium of mantle origin at Moincer hot spring. Therefore it indicates mantle component emplacement at the shallow part of the crust.
WOS关键词	FIELD ; FRACTIONATION ; CHEMISTRY ; PLATEAU ; CARBON ; SYSTEM
WOS研究方向	Geology
语种	英语
出版者	SCIENCE PRESS
WOS记录号	WOS:000179484500013
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/77673]
专题	中国科学院地质与地球物理研究所
通讯作者	Zhao, P
作者单位	1.Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China 2.Geothermal Geol Team Tibet, Lhasa 850000, Peoples R China
推荐引用方式 GB/T 7714	Zhao, P,Xie, EJ,Dor, J,et al. Geochemical characteristics of geothermal gases and their geological implications in Tibet[J]. ACTA PETROLOGICA SINICA,2002,18(4):539-550.
APA	Zhao, P.,Xie, EJ.,Dor, J.,Jin, J.,Hu, XC.,...&Yao, ZH.(2002).Geochemical characteristics of geothermal gases and their geological implications in Tibet.ACTA PETROLOGICA SINICA,18(4),539-550.
MLA	Zhao, P,et al."Geochemical characteristics of geothermal gases and their geological implications in Tibet".ACTA PETROLOGICA SINICA 18.4(2002):539-550.