雷琼火山现今幔源流体释放及气体源区温度研究  

Investigation on the present-day mantle-derived fluids release and gas source temperature of Leiqiong Volcanic Field,South China

作　　者：赵慈平 胡久常[3] 周艺颖[1,2,4] 郭明瑞 ZHAO Ciping;HU Jiuchang;ZHOU Yiying;GUO Mingrui(Kunming Institute of Earthquake Prediction,China Earthquake Administration,Kunming 650201,Yunnan;Yunnan Earthquake Agency,Kunming 650224,Yunnan;Hainan Earthquake Agency,Haikou 570203 Hainan;Hainan Geological Bureau(Hainan Marine Geological Survey),Haikou 570206,Hainan)

机构地区：[1]中国地震局昆明地震预报研究所,云南昆明650201 [2]云南省地震局,云南昆明650224 [3]海南省地震局,海南海口570203 [4]海南省地质局(海南省海洋地质调查局),海南海口570206

出　　处：《第四纪研究》2023年第2期458-472,共15页Quaternary Sciences

基　　金：云南省重点研发计划社会发展专项项目"云南重大地震灾害及其灾害链综合风险评估技术与应用"(批准号:202203AC100003)资助。

摘　　要：雷琼火山位于欧亚板块与巽他板块交界处附近,规模大、喷发活动期次多。地震层析成像结果表明,雷琼火山区附近存在地幔柱,但地幔柱中心与现今雷琼火山区的中心位置存在200km的错位。一种可能是地幔柱本身是倾斜的;另一种可能是,像夏威夷火山链那样,地幔柱没有发生位置变化,但地幔柱上方的岩石圈发生了漂移,从而火山喷发区与地幔柱发生了错位。为了探讨这两种可能性及其他可能的情景,本研究在雷琼火山及其邻近区域进行了地下水逸出气体氦氖碳同位素调查,共调查了雷州半岛及其东北邻近区域水文点(温泉、冷泉、自流井)62个(其中45个无逸出气体),获得并分析了主要位于雷州半岛东北邻近地区(海南地幔柱位置的正上方)17个温泉的逸出气体样品,而在雷琼火山区内(包括雷州半岛和琼北)则并未发现有逸出气体的水文点;雷琼火山区西南邻近地区海南岛中南部的14个温泉则直接利用前人数据。结果表明,雷琼火山邻区温泉逸出气主量化学成分主要来源于大气,微量化学成分主要是大气或大气饱和水与壳源或幔源气体不同程度混合的产物;He主要为壳幔来源,以壳源为主,幔源混入显著;幔源He比例呈双峰分布,分别是0.5%~5.0%和10.0%~20.0%;CO_(2)及CH_(4)多数为壳源,部分为幔源,少量为生物成因;视碳同位素温度普遍较低,5个泉点接近或大于400℃,最高863℃。从空间分布上看,不管是幔源He比例还是视碳同位素温度,均表现出从外围向雷琼火山区升高的总体趋势。样条函数插值预测,在雷琼火山区中心(雷州半岛)幔源He将达到50%,视碳同位素温度将达到1750℃,说明雷琼火山仍然是活动的,至少仍有幔源岩浆的补充;海南地幔柱的正上方有地幔柱源挥发份的少量渗漏。我们提出一个解释海南地幔柱和雷琼火山错位200km的现象的模型:海南地幔柱的主体(下部)位置是固定�Leiqiong Volcanic Field(LVF)is located near the boundary between Eurasian plate and Sunda plate,with large scale and many eruptive periods.The seismic tomography results show that there is a mantle plume near the LVF,but there is a 200km dislocation between the center of the mantle plume and that of the current LVF.One possibility is that the mantle plume itself is inclined;Another possibility is that,like the Hawaiian volcanic chain,the position of the mantle plume did not change,but the lithosphere above the mantle plume drifted,so that the volcanic eruption area and the mantle plume were dislocated.In order to explore these two possibilities and other possible scenarios,we have carried out a survey of helium,neon and carbon isotopes of the gas escaping from groundwater in LVF and its adjacent areas.We have investigated 62 hydrological points(hot springs,cold springs,artesian wells)in Leizhou Peninsula(LP)and its northeast vicinity,45 of which have no escaping gas,obtained and analyzed escaping gas samples of 17 hot springs which mainly located in the northeast vicinity of LP(directly above the position of Hainan mantle plume(HMP),while no hydrological points with escaping gas have been found inside LVF(including LP and the north part of Hainan Island(HI).We directly use the literature data of 14 hot springs in the south and central part of HI,adjacent to the southwest of LVF.The results show that the major components of the gas released from the hot springs in the adjacent areas of LVF are mainly from the air,and that the trace components are mainly mixture of the air or the air-saturated water and the gas from the crust or mantle to varying degrees;that He is mainly from crust,but mixed significantly by the mantle-derived;that the mantle-derived He ratio(MHR)presents a bimodal distribution:0.5%~5.0%and 10.0%~20.0%;that most CO_(2) and CH_(4) are crust-derived,some are mantle-derived,and a few are biogenic;and that the Apparent Carbon isotope Temperature(ACT)is generally low,and the five spring points are clos

关 键 词：氦氖碳同位素 视碳同位素温度 海南地幔柱 软流圈运动 雷琼火山 

分 类 号：P317.3[天文地球—固体地球物理学] P597.2[天文地球—地球物理学]