摘要:
本研究基于青海囊谦盆地8个盐泉的元素组成和稳定同位素分析,研究了盆地中高浓度盐泉盐类物质的来源与形成条件。结果表明,青海囊谦盐泉的平均矿化度为254.6 g/L,在空间上矿化度从西到东逐渐升高,水化学类型为硫酸盐型, pH为中性,盐泉元素可分为三类—Na+-Cl--K+-Br-, B3+-Li+-SO2-4-HCO-3, Ca2+-Mg2+。盆地中高浓度盐泉的大面积出现,及盐泉元素地球化学分析均表明囊谦盆地地下有丰富的含盐地层。盐泉的成因类型为溶滤盐泉,溶滤的主要矿物为石盐,其次还有少量灰岩和石膏岩。盐泉的硼同位素研究结果表明,盐泉水δ11B值在+3.55‰~+35.49‰之间变化,分布范围较大,从北西向南东逐渐降低,结合盐泉的 Br 含量,指示该含盐地层应属陆相成因。此外,盐泉水硼含量与硼同位素呈反比关系,呈现出高B低δ11B值端元和低B高δ11B值端元,盐泉的pH值与硼同位素组成也呈一定的反比关系。通过对盐泉和区域地质的综合研究,我们认为多伦多盐泉地区出露的大量火山物质可能是盐泉硼的一个重要来源。综合对比研究认为囊谦盐泉的形成条件为:(1)盆地内的含盐地层为盐类物源;(2)稳定的降水为盐泉提供了持续的水源;(3)广布的断裂构造为盐泉的发育提供了通道;(4)地形高差大为其提供了水力梯度。
Abstract:
Based on element composition and stable isotope analysis of high salinity salt springs in the Nangqian basin, the paper mainly studies sources of salt materials and their formation conditions of the springs. The results show that the average salinity of the springs in the Nangqian Basin is 254.6 g/L, with a higher salinity in the east than in the west of the basin. The hydrochemical types of the springs are all sulfate type with neutral pH value. Chemical elements in the springs can be divided into three groups: Na+-Cl–-K+-Br-, B3+-Li+-SO2– 4-HCO– 3 and Ca2+-Mg2+. High salinity and element geochemical characteristics indicate that salt strata are under the Nangqian Basin, which can provide rich salt materials for the springs. We concluded that the salts in the springs come mainly from dissolution of underground halite and a small amount of limestone and gypsum rock. The boron isotopeδ11B values in the springs range from 3.55‰ to 35.49‰ with a gradual decrease from northwest to southeast, which shows that the underground salt strata had formed in continental environments combining with the data of Br content. There is an inverse relationship betweenδ11B values and boron content in springs with a two-end-members: high boron content versus lowδ11B value and low boron content versus highδ11B value, meanwhile, another inverse relationship betweenδ11B and pH values was also discovered. Regional geological studies lead to the conclusion that the large amount of igneous rocks exposed in the Duolunduo area may be an important source of the boron in the springs. According to the comprehensive and comparative study, the following four factors are essential conditions for salt-spring formation in the Nangqian Basin: 1) the saliferous strata are the source of salt materials in the springs; 2) stable rainfall offers sustained water source for the spring; 3) widely distributed faults supply channels for groundwater migration; 4) large topographic altitude differences provide a stronger hydraulic gradient for groundwater flow.
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