海南岛新生代玄武岩成因——来自橄榄石和尖晶石的制约  

Petrogenesis of Hainan Cenozoic basalts--Constrains from the compositions of olivines and spinels

作　　者：胡琪伟 任钟元[1] 张乐[1] HU Qiwei;REN Zhongyuan;ZHANG Le(State Key Laboratory of Deep Earth Processes and Resources,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,深地过程与战略矿产资源全国重点实验室,广东广州510640 [2]中国科学院大学,北京100049

出　　处：《地球化学》2025年第2期293-307,共15页Geochimica

基　　金：国家自然科学基金面上项目(41672057)资助。

摘　　要：海南岛北部出露大规模的新生代玄武岩,但其成因一直存在争议。橄榄石是基性岩浆中最早结晶的矿物之一,高Mg橄榄石可以记录原生岩浆在经历地壳混染和分离结晶之前与其成因相关的重要信息。本研究选取海南岛永兴、薄片和龙河3个地区的新生代玄武岩,对其中的橄榄石斑晶和橄榄石中的尖晶石包裹体进行元素化学分析,探讨橄榄石的结晶温度、母岩浆的氧化状态、含水量以及源区性质。结果显示,永兴橄榄石Fo值(82~84)和龙河橄榄石Fo值(79~81)变化范围较小,薄片橄榄石的Fo值变化较大(76~85)。海南岛橄榄石的结晶温度为1170~1256℃,氧逸度为ΔQFM=-0.33~0.57。其中,3个地区的橄榄石结晶温度没有明显变化,龙河和薄片岩浆的氧逸度(ΔQFM=-0.33~0.07)略低于永兴(ΔQFM=-0.08~0.57)。橄榄石-熔体CaO的分配系数显示,海南岛岩浆具有较低的含水量。3个地区的橄榄石均具有高的Ni含量、Fe/Mn和Zn/Fe值以及低的Mn、Ca含量和Mn/Zn值,指示海南岛地幔源区存在辉石岩组分。不同地区玄武岩中橄榄石在微量元素含量和氧逸度上的差别,以及海南岛玄武岩全岩和熔体包裹体成分的多样性,共同反映了海南岛具有不均一的地幔源区。Cenozoic basalts are widespread in the northern part of Hainan Island.However,the origins of these basalts are still debated.The bulk rock has experienced many geological processes during magma ascent,which has removed information about the origin of the magma.Olivine is the first crystallized silicate mineral in typical mantle-derived magmas,and high-Mg olivine can record important information about the origin of the primary melt prior to subsequent modification of crustal contamination and fractional crystallization.In this study,we analyzed the chemical compositions of olivine and spinel inclusions in olivine from three areas(Yongxing,Baopian,and Longhe)in North Hainan Island to investigate the olivine crystallizing temperature,oxygen fugacity,water contents of the parental magmas,and nature of their mantle source.The Fo of the olivines from Yongxing(82-84)was higher than that of Longhe(79-81),while the Fo of the olivines from Baopian(76-85)has a wide range.The olivine-spinel thermometer showed that the olivine-crystallizing temperature in Hainan Island is 1170-1256℃.The oxygen fugacity of the parental magmas in Hainan Island is ΔQFM=-0.33-0.57.Among them,there was no significant difference in the olivine crystallizing temperature in the three areas,while the oxygen fugacities of the Longhe and Baopian magmas(ΔQFM=-0.33-0.07)are slightly lower than that of Yongxing(ΔQFM=-0.08-0.57).The Calcium-in-Olivine Geohygrometer shows that there is a low magmatic water content in Hainan.The olivine of all three areas had high Ni contents and Fe/Mn and Zn/Fe ratios,and low Mn and Ca contents and Mn/Zn ratios,indicating that pyroxenite existed in the mantle source of Hainan Island.The differences in the trace element composition of olivine and the oxygen fugacity of parental magmas of different areas,as well as the diversified composition of the bulk-rock and melt inclusions in Hainan Island,reflect a heterogeneous mantle source in Hainan Island.

关 键 词：新生代玄武岩 橄榄石 尖晶石 源区不均一 海南岛 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学]