A comparative study of isotopic hydrogeochemistry of geothermal fluids of sedimentary basin type and volcanic type
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摘要: 地热资源按地质构造及成因的不同可划分为火山型及沉积盆地型两种类型。国内外许多学者对沉积型地热系统的同位素水文地球化学研究较多，而火山型地热系统研究不足，且沉积型和火山型地热流体的同位素水文地球化学对比研究还有待进一步深入。文章以关中盆地腹部沉积型地热系统及腾冲火山地热系统为代表，应用同位素水文地球化学方法对不同类型地热流体的地质构造、地热流体起源及成因、热储开放程度等进行系统对比研究，进而揭示其异同之处，为我国不同类型地热资源的可持续开发利用提供科学依据。关中盆地与腾冲热海地热系统在热储空间、构造条件、热源方面均存在较大差异，前者热储更为封闭，热储层更厚，后者热储通道更为畅通，热源更为丰富；腾冲热海地热系统热储温度高，埋藏更浅，热水循环更快，更易于开发利用。关中盆地与腾冲热海地热系统均存在比较明显的δ18O富集现象，关中盆地地热流体滞留时间更长是δ18O富集的主控因素，腾冲较高的热储温度是δ18O富集的主控因素；关中盆地腹部为沉积-半封闭型、封闭型，腾冲热海地热系统为火山-半封闭型；在漫长的地质历史时期，水岩反应的程度是决定热储流体水化学类型的主控因素。Abstract: Geothermal resources can be divided into volcanic type and sedimentary basin type according to the different geological structures and geneses. Many scholars at home and abroad have done many researches on isotopic hydrogeochemistry of geothermal systems of sedimentary basin type. However, the study of volcanic geothermal systems is insufficient, and the comparative study of isotopic hydrogeochemistry between sedimentary and volcanic geothermal fluids needs to be further carried out. The geothermal system in the abdomen of the Guanzhong Basin and the Tengchong volcanic geothermal system are selected as representative geothermal systems. Isotopic hydrogeochemical methods are used to geological structures of different types of geothermal fluid origin and formation, thermal storage, geothermal fluid openness, and so on. The comparative studies of the similarities and differences may provide a scientific basis of different types of the sustainable development and utilization of geothermal resources in China. The Guanzhong Basin and the Tengchong Rehaia geothermal systems have large differences in thermal storage space, structural conditions and heat sources. The former has a more closed heat storage and a thicker thermal reservoir. The latter has a smoother heat storage channel and a richer heat source. The Tengchong Rehai geothermal system has a high heat storage temperature, shallower burial, faster hot water circulation, and easier development and utilization. Both the Guanzhong Basin and the Tengchong rehai geothermal systems have obvious δ18O enrichment. The longer geothermal fluid retention time is the main controlling factor of δ18O enrichment for the Guanzhong Basin geothermal fluids, and the higher thermal storage temperature is responsible for the δ18O enrichment in the Rehai geothermal fluids. The main controlling factors include: (1) the abdomen of the Guanzhong Basin is a semi-closed and closed sedimentary basin, and the Tengchong Rehai geothermal system is of semi-closed volcanic type. The degree of water-rock reaction during a long geological history is often the main controlling factor determining the hydrochemical type of the hot-storage fluids.
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Key words:
- Guanzhong Basin /
- Tengchong Rehai /
- hydrogeochemical /
- isotope /
- geothermal fluid /
- henetic formation
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