西藏羊八井地热水的氢、氧稳定同位素组成及氚含量

HYDROGEN AND OXYGEN STABLE ISOTOPIC COMPOSITION AND TRITIUM CONTENT OF WATERS FROM YANGBAJAIN GEOTHERMAL AREA,XIZANG, CHINA

Isotopic data on drill hole water and surface water samples from the Yengbajain geothermal area as well as an ice sample from the glacial amphitheater in the Mt. Nyainqintanglha to the northwest of the Yangbajain basin are presented in this paper. In consideration of isotopic fractionation during steam separation, the hydrogen and oxygen isotopic ratios for thermal waters collected at the mouths of drill holes have been calibrated. The D/H ratio of thermal waters is similar to that of local precipitation, indicating their meteoric origin. The δ D and δ^18O values of the thermal waters of --150--160 and -17-20‰, respectively are the lowest among those well-known geothermal fields in the world.The recharge area of the geothermal system is at elevation of about 4,800--5,000 m. Drill holes along the axis of a tongueshaped zone where loose Quaternary sediments have been cemented by siliceous material show greater δ D and δ^18O values and discharge tritiumfree thermal waters. It is suggested that the thermal waters may be derived from superhcated water and steam which find their way upwards along the tectonic fractures within the granitic base overlain by Quaternary sediments. The classification of drill hole geothermal waters have been made in accordance with their δ D and δ^18O values and chloride contents. The “oxygen shift” of the thermal waters seems to be 2‰, due to isotopic exchange reactions between geothermal waters and reservoir

Isotopic data on drill hole water and surface water samples from the Yangbajain geo-thermal area as well as an ice sample from the glacial amphitheater in the Mt. Nyainqintan-glha to the northwest of the Yangbajain basin are presented in this paper. In considerationof isotopic fractionation during steam separation, the hydrogen and oxygen isotopic ratiosfor thermal waters collected at the mouths of drill holes have been calibrated. The D/Hratio of thermal waters is similar to that of local precipitation, indicating their meteoric or-igin. The δD and δ^(18)O values of the thermal waters of -150- -160 and -17--20‰ respectively are the lowest among those well-known geothermal fields in the world.The recharge area of the geothermal system is at elevation of about 4,800-5,000 m. Drillholes along the axis of a tongueshaped zone where loose Quaternary sediments have beencemented by siliceous material show greater δD and δ^(18)O values and discharge tritium-free thermal waters. It is suggested that the thermal waters may be derived from superhe-ated water and steam which find their way upwards along the tectonic fractures within thegranitic base overlain by Quaternary sediments. The classification of drill hole geothermalwaters have been made in accordance with their δD and δ^(18)O values and chloridecontents. The 'oxygen shift' of the thermal waters seems to be 2‰ due to isotopic exchangereactions between geothermal waters and reservoir rocks.