四川盆地东部高褶带三叠系地层卤水和温泉的地球化学特征及成因

Characteristics of the Brines and Hot Springs in the Triassic Carbonates in the High and Steep Fold Zone of the Eastern Sichuan Basin

四川盆地是我国著名的大型沉积盆地,地下卤水资源丰富,在川东宣汉地区的川25井曾发现富钾卤水。本文对川东高陡褶皱带三叠系碳酸盐岩地下水的分布和富集进行分析,对川25井和卧57井深层卤水以及仙女山温泉和统景温泉的水化学特征进行总结并探讨其成因。认为当背斜核部的三叠系地层埋藏较深、封闭性较好时,有利于深层卤水的富集;在半开启-开启型背斜中,背斜核部受到强烈的风化侵蚀作用,三叠系地层裸露地表,接受大气降水入渗淋滤,不利于高TDS卤水保存。深层卤水的水化学类型均为Cl-Na型,富集Br^-、Li^-、Sr^2-、I^-、B^3＋等微量元素,是同生沉积卤水。其中川25井是少见的高TDS富钾卤水,其TDS达352.693g/L,已达到泻利盐沉积阶段,K^＋异常富集,达25.955g/L。仙女山温泉和统景温泉地下热水为SO4-Ca型,富集Sr^2＋、F^-、偏硅酸等。稳定性同位素δ^2 H、δ^18 O数据显示川东深层卤水均起源于古海水,仙女山温泉和统景温泉地下热水补给来源为大气降水。地下水在背斜核部三叠系裸露区接受大气降水的入渗补给,经历深循环获得加热后在地形较低的河谷处呈温泉出露。地下（热）水为溶滤围岩形成TDS不高（2-3g/L）的地下水,其总体趋势是朝着淡化的方向发展。

The Sichuan Basin is a well-known large-scale sedimentary basin in China with abundant subsurface brine resources.K-rick brines were found in the Chuan 25 well in the northeastern part of the basin.The occurrence and enrichment of groundwater in the Triassic carbonates in the high and steep fold zone in the eastern Sichuan Basin are examined in this paper,and hydrochemical characteristics and genesis of the deep formation brines in the Chuan 25 well and Wo 57 well and the Xiannvshan hot spring and Tongji hot spring are also discussed.The results show that if the Triassic formations in the core of the anticlines are deeply buried and are in a sealed state,the subsurface brines are found to be enriched,and high TDS brines are not preserved in the Triassic carbonates in the core of the open-semi-open anticlines,where the carbonates outcrop due to strong weathering and erosion and infiltration and lixiviation of precipitation occur.The subsurface brines,which are regarded as connate sedimentary brines,are of Cl-Na type and are rich in Br^-,Li^-,Sr^2-,I^-and B^3＋.The brines in the Chuan 25 well has high TDS of 352.693g/L（close to that of the Yellow Sea water and the South China Sea water when evaporated to the stage of epsomite precipitation）and high contents of K^＋of 25.955g/L.The Xiannvshan hot spring and the Tongji hot spring are of SO4-Ca type and have relatively high concentrations of Sr^2＋,F^-and H2SiO3.The stable isotopes ofδ^2 H andδ^18 O of the water samples suggest that the subsurface brines are of palaeo-marine origin and the hot springs were meteoric in origin.Groundwater were recharged from infiltration of precipitation in the outcropping areas in the cores of the anticlines and obtains heat when undergoing deep circulation and emerges as a hot spring in the low river valleys.The hot water has TDS of 2-3g/L and forms after lixiviation of groundwater in the carbonates.As a result,the hot water has a tendency of becoming fresh.