九州-帕劳脊南段基底玄武岩的单斜辉石矿物化学及成因意义  

Mineral chemistry and genetic significance of clinopyroxenes in the basement basalts from the southern Kyushu-Palau Ridge

作　　者：刘振轩 鄢全树 刘焱光 杨刚 石学法 Liu Zhenxuan;Yan Quanshu;Liu Yanguang;Yang Gang;Shi Xuefa(Key Laboratory of Marine Geology and Metallogeny,First Institute of Oceanography,Ministry of Natural Resources,Qingdao 266061,China;Laboratory of Marine Geology,Laoshan Laboratory,Qingdao 266061,China;Key Laboratory of Deep Sea Mineral Resources Development,Shandong(preparatory),Qingdao 266061,China)

机构地区：[1]自然资源部第一海洋研究所海洋地质与成矿作用重点实验室,山东青岛266061 [2]崂山实验室海洋地质与环境功能实验室,山东青岛266061 [3]山东省深海矿产资源开发重点实验室,山东青岛266061

出　　处：《海洋学报》2023年第6期75-92,共18页

基　　金：崂山实验室“十四五”重大项目(2022QNLM050201-3);国家重点研发计划(2017YFC1405502);国家自然科学基金(41322036);山东省泰山学者建设工程项目。

摘　　要：九州-帕劳脊是古伊豆-小笠原-马里亚纳弧的重要组成,对其上基底岩石开展矿物学和岩石学研究可为理解洋内岛弧演化早期的岩石成因和岩浆活动特点提供重要线索。本文对九州-帕劳脊南段基底玄武岩中的单斜辉石斑晶和微晶开展详细的岩相学和原位主微量元素分析,结果表明,单斜辉石斑晶与微晶整体上具有相似的化学组分,为普通辉石及透辉石等种属,且亏损轻稀土元素,Eu负异常不明显。多数单斜辉石斑晶具有环带结构,可划分为简单环带及韵律性环带两类;从辉石核部到边部,MgO、FeO、Al_(2)O_(3)、TiO_(2)含量与核部镁指数Mg#等呈现复杂的高低变化,指示了多期次的岩浆混合与补给事件。单斜辉石的结晶温度、压力分别为1151~1210℃和1.3×10^(8)~4.2×10^(8)Pa。通过单斜辉石组分反演获得的母岩浆含水量为0.8%~2.3%(以湿质量计)。最后,我们提出,形成于典型的洋内岛弧背景下的九州-帕劳脊南段熔岩的母岩浆为亚碱性岛弧拉斑玄武质熔体,具有高温、中压、高氧逸度的特征,岩浆房深度较浅并存在多期次原始岩浆的补给和混合。The Kyushu-Palau ridge(KPR)is an important part of the proto-Izu-Bonin-Mariana arc.The mineralogic-al and petrological studies of the arc basement rocks can provide significant insights for understanding the petrogen-esis and magmatism characteristics of the early stage of intra-oceanic island arc evolution.In this paper,we per-formed petrographic and detailed mineral geochemical analyses including in situ major-trace elements of clinopyroxene(Cpx)phenocrysts and microcrystals from the basement basalts from the southern KPR.The results show that clinopyroxenes are mainly augites and diopside,which generally have similar chemical components for the phenocrysts and microcrystals.These clinopyroxenes are depleted in light rare earth elements with weak Eu neg-ative anomalies.Most of the Cpx macrocrysts display zoning structures,which can be classified into basic and oscil-latory zoning.The MgO,FeO,Al_(2)O_(3),TiO_(2) and Mg#contents show complex high-low variations from the pyroxene core to the rim,indicating multi-period magma mixing and replenishment events.The crystallization temperature and pressure of Cpx phenocrysts are 1151-1210℃and 1.3×10^(8)-4.2×10^(8) Pa,respectively.In addition,the water content of parent magma obtained by the inversion calculated from Cpx components is 0.8%-2.3%(wet weight).Conclusively,we suggested that the parent magma of the southern KPR lavas that formed within a typical intra-oceanic island-arc setting is a sub-alkaline island-arc tholeiite basaltic melt with high temperature,medium pres-sure,and high oxygen fugacity.The magma chambers were shallow in depth and there existed multi-period replen-ishment and mixing of primitive magma.

关 键 词：单斜辉石 矿物化学 环带结构 岩浆过程 岛弧玄武岩 九州-帕劳脊 

分 类 号：P575.3[天文地球—矿物学] P581[天文地球—地质学]