中国大陆东部温泉流体来源解析与地震地球化学异常判识方法

Methods for Identification of Seismic Geochemical Precursors and Source Partitioning of Hot Spring Fluids in Eastern Chinese Mainland

统计分析已有研究中数千组大气化学、温泉流体化学、水-岩反应实验以及地幔包体气体同位素组成等数据,从流体组分来源解析的角度讨论了温泉水和气体的来源,提出了估算深部流体和地幔氦贡献量的模式以及温泉地震流体地球化学异常判识步骤方法。温泉水的δ^(18)O和δD数据表明,H_(2)O主要来源于大气降水,少量的(<1%)深部流体对温泉的离子和热能供给不容忽视。大气降水和空气颗粒物可溶离子数据统计结果表明,温泉水中海盐的贡献是可以忽略的。通过统计分析大量大气降水、空气颗粒物可溶盐、水-岩反应实验、深部流体和温泉水的离子浓度及其比值,建立了δ^(18)O-δD和Na^(+)-Cl^(-)浓度的离子来源判识模型。380多组中国东部新生代玄武岩地幔包体的^(3)He/^(4)He和δ^(13)C_(CO_(2))值统计结果表明其平均值或峰值能够代表本区上地幔的氦、碳同位素比值。在估算温泉气体中地幔氦的百分比时,用汉诺坝地幔包体的^(3)He/^(4)He均值(2.1 R_(A))代表嫩江—紫荆关断裂带以西造山带的上地幔端元值,选用地幔包体较高的^(3)He/^(4)He峰值(7 R_(A))代表断裂带以东上地幔端元^(3)He/^(4)He值,这有益于合理估算地幔供给温泉系统、地热田和地震孕育的能量。利用所建源解析模型,提出了从温泉地球化学观测数据中剔除海盐、气象和人为源的干扰,以及从时间序列中提取地震地球化学异常的步骤方法。在半径约为500 km的区域内,多个观测点地球化学指标一起或短时间内先后出现的异常变化可视为地震地球化学前兆。判断地震流体前兆和利用地震流体前兆预测地震必须结合其他学科的观测资料。

The origins of water and gas in hot springs in eastern China's mainland were discussed by means of source partitioning,and the models of assessing percentages of deep fluids and mantle-derived helium in hot spring fluids and methods of identifying seismic geochemical anomalies were proposed by statistically analyzing thousands of geochemical data of meteoritic water,hot spring fluids,experimental rock-water reactions and gaseous isotope compositions in mantle-derived xenoliths from the literatures.δ^(18) O andδD data of spring waters indicate H_(2)O of springs are predominantly originated from meteoric water,while ions and heat energy transported by small amount(<1%)of deep thermal fluids must be emphasized.The statistical results of data of meteoric water and soluble ions of air particles indicated that sea salt contribution to the hot spring water was usually negligible.The modelsδ^(18) O-δD and Na^(+)-Cl^(-) for source identification were proposed based on statistical analysis of plenty of chemical data of meteoric water,soluble ions of air particles and ion concentrations of deep thermal fluids and hot spring waters.The mean value or peak value of more than 3803He/4He ratios andδ^(13) C_(CO_(2)) values of mantle xenoliths in Cenozoic basalts in eastern China can be considered as the isotopic compositions of He and CO_(2) in the local upper mantle.The value of mantle end-member to estimate percentage of mantle-derived He in hot spring gases by using the two end-member model,therefore,average(2.1 R_(A))of 3He/4He of Hannuoba xenoliths should be employed in the orogenic belts in the west of the Nenjiang-Zijingguan fault,while higher peak value(7 R_(A))of 3He/4He of mantle xenoliths in eastern China should be used in the continental rift valley in the east of the fault,which favors reasonable assessment of heat energy supplied from the mantle to the hot spring system,geothermal fields and earthquake generation.The seismic geochemical anomalies could be identified in the time series of geochemically monitoring data of hot springs after ion contributions of sea salt,atmospheric and artificial sources to the spring waters were eliminated by using the proposed source partitioning models.The anomalies of multiple geochemical indicators occurred simultaneously or in short period in an area of 500 km radius could be considered as earthquake precursors.Additionally,the monitoring data from other disciplines should be combined to identify earthquake precursors and predict earthquake using geochemical data.