云南勐海县勐阿街温泉水化学和同位素特征及成因

Hydrochemical and isotopic characteristics and formation of the Mengajie hot spring in Menghai county of Yunnan

勐阿街温泉地处云南西南部勐阿盆地,现主要有4个温泉出露点,在澜沧江断裂带西侧沿NW向小型断裂磨刀河—曼懂断裂带出露。地下热储带分布于华力西期—印支期的中酸性侵入岩中,热水富集在花岗岩断裂破碎带及断裂交汇位置。温泉近20年来主要成分未发生较大变化,温泉矿化度较低(0. 31～0. 34 g/L),水化学类型为HCO_3—Na型,为中低温、弱碱性温泉。热水中F-含量为12. 8～13. 2 mg/L,H_2SiO_3含量为52. 5～67. 6 mg/L,含有锂、锶、钨等微量元素。温泉水化学类型成因为含CO_2的地下水对花岗岩体发生溶滤作用而形成,F-含量高可能是由于溶解了花岗岩中含氟的黑云母,H_2SiO_3含量较高的原因是温泉水与含硅酸盐岩的岩石发生大面积接触溶滤作用。氢氧稳定同位素组成表明勐阿街温泉的补给水源为大气降水,并具有轻微的18O漂移现象,表明水与围岩的氧同位素交换程度较高,热储温度较高。用同位素方法估算温泉的补给区高程在1 200 m左右,补给温度约为10℃,推测温泉水源主要来自勐阿街盆地周围山地的大气降水,计算得热储温度为93～104℃。勐阿街温泉成因为其周围山区大气降水入渗补给后,经历深循环受大地热流加热后,沿断裂带上升出露成泉。热水在上升途中与浅部冷水相遇,冷水混合比例52%～76%,热水循环深度为3 000～3 360 m。

The Mengajie hot spring is located in the Menga basin in the western Yunnan.The hot spring emerges along the NW-trending Modaohe-Mandong fault to the west of the Lancangjiang Fault.The subsurface geothermal zone occurs in the neutral-acid intrusive rocks of the Hercynian-indosinian Period.TDS of the hot spring is low(0.31-0.34 g/L),and the hydrochemical type of the hot water is of HCO3—Na type.The hot spring is of low to moderate temperature and is weak alkaline.The F-concentration of the hot spring ranges from 12.8 to 13.2 mg/L,and the H2 SiO3 concentration,from 52.5 to 67.6 mg/L.Li,Sr and W are relatively abundant in the hot water.The stable2 H and18 O contents of the spring water indicate that the Mengajie hot spring is of meteoric in origin.The elevation of the hot spring’s recharge area is estimated as about 1 200 m,the temperature of recharge area,approximately 10℃,and the temperature of the geothermal reservoir,from 93 to 104℃.During deep circulation the hot water is heated and rises along the fault zone after the infiltration of precipitation in the surrounding mountain area.The hot water mixes with the shallow cold water when it rises to the land surface.The proportion of mixing cold water is about 52%-76%,and the circulation depth of hot water is estimated as 3 000-3 360 m.