四川鲜水河-安宁河断裂带温泉氢氧稳定同位素特征

温泉地下水同位素特征对确定断裂带地下水来源、循环过程和断裂带活动性至关重要。为了确定青藏高原东缘温泉的地下水同位素特征和流体来源本研究采集了鲜水河-安宁河断裂带上温泉水、冷泉水、河流和积雪融水等样品,进行了氢氧稳定同位素和水化学组分测定,并进行了同位素特征的对比研究。分析结果表明,温泉水体δ¹⁸O变化范围为-19.04%~-12.71‰,平均值为-16.42‰;δ²H变化范围为-144.07‰~-88.63‰,平均值为-122.37‰。河水的δ¹⁸O变化范围为-15.90‰~-10.85‰,平均值为-13.86‰;δ²H变化范围为-118.21‰~-71.12‰,平均值为-98.99‰。康定冷泉δ¹⁸O和δ²H分别为-13.66‰和-106.74‰。道孚积雪融水的δ¹⁸O和δ²H分别为-10.27‰和-65.41‰。不同类型水体样品氢氧稳定同位素组成主要分布在全球和区域大气降水线上表明了大气降水成因,缺少明显的氧同位素漂移特征。不同类型水体同位素值差异较大显示出温泉与河水、积雪融水之间补给来源的不一致性。温泉同位素值具有明显的同位素高程效应,鲜水河-安宁河断裂带上氧同位素高程效应为-0.23‰/100m,氢同位素高程效应为-1.95‰/100m。温泉氧同位素漂移与相关离子比值、Na-K-Mg三角图、Li和Sr元素等指标表明研究区域大部分温泉的水岩作用强度弱。氢氧稳定同位素特征、水岩作用特征和循环深度揭示出温泉的成因为远距离大气降水运移补给地下水,地下水在地下热储层加热后通过断裂上升到地表形成温泉,这为认识青藏高原东缘地热水循环、断裂带活动性与演化特征提供了依据。

Characteristics of hydrogen and oxygen stable isotopes of hot springs in Xianshuihe-Anninghe fault zone, Sichuan Province, China

Isotopic feature and recharge sources of hot springs are very important to monitor a fault zone activity.This study investigated the hydrogen and oxygen stable isotopes and hydrochemical compositions at hot springs,cold spring,rivers and snowmelt water in the Xianshuihe-Anninghe fault zone in the eastern margin of the Tibetan Plateau.The analytical results show theδ¹⁸O variation range from-19.04‰to-12.71‰with an average of-16.42‰,and the range ofδ²H from-144.07‰to-88.63‰with an average of-122.37‰in the hot springs.Theδ¹⁸O andδ²H values in river water change from-15.90‰to-10.85‰and from-118.21‰to-71.12‰with averages of-13.86‰and-98.99‰,respectively.Theδ¹⁸O andδ²H values of cold spring at Kangding are-13.66‰and-106.74‰,respectively.Theδ¹⁸O andδ²H values of snowmelt water at Daofu are-10.27‰and-65.4‰,respectively.The isotope ratios of hydrogen and oxygen are distributed around the global meteoric water line(GMWL)and local meteoric water line(LMWL),indicating that the water recharge sources are meteoric water with unobvious oxygen isotope shift.The isotopic ratios of different water types show wide variations,indicative of the inconsistency of recharge sources among hot springs,rivers and snowmelt water.The isotopic values of hot springs have clearly isotopic altitude effect.The altitude effect of oxygen isotope is-0.23‰/100 m and the hydrogen isotope is-1.95‰/100 m in the Xianshuihe-Anninghe fault zone.The oxygen isotope shift,the relevant ions ratios,a Na-K-Mg triangular diagram and Li and Sr concentrations indicate that most of the hot springs are with weak water-rock interactions.The isotopic characteristics,water-rock interaction and circulation depths suggest that the groundwater recharges are the long-distance migration meteoric water,and the groundwater are heated in underground thermal reservoirs and then rise to the surface along the faults.The investigative results are very important for understanding the characteristics of geothermal water circulation and fault activity and evolution in the eastern margin of the Tibetan Plateau.