普通球粒陨石NWA15004岩石矿物学特征及球粒类型研究  

STUDY ON PETROLOGICAL AND MINERALOGICAL CHARACTERISTICS AND CHONDRULES TYPES OF NWA 15004 ORDINARY CHONDRITE

作　　者：林书宇 陈燕 陈洪 张川统 张兆峰 LIN Shuyu;CHEN Yan;CHEN Hong;ZHANG Chuantong;ZHANG Zhaofeng(International Center for Planetary Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Institution of Meteorites and Planetary Materials Research,Key Laboratory of Planetary Geological Evolution at Universities of Guangri Province,Guilin University of Technology,Guilin,Guangxi 541006,China)

机构地区：[1]成都理工大学地球科学学院行星科学国际研究中心,四川成都610059 [2]桂林理工大学、行星地质演化广西高校重点实验室、陨石与行星物质研究中心,广西桂林541006

出　　处：《矿物岩石》2023年第1期1-14,共14页Mineralogy and Petrology

基　　金：中科院先导B项目(编号:XDB41000000);民用航天“十三五”技术预先研究项目(编号:D020205)。

摘　　要：普通球粒陨石是目前发现数量最多的陨石,对认识早期太阳星云演化和太阳系物质成分具有重要的意义。Northwest Africa(NWA)15004是一块非洲西北部新发现的普通球粒陨石。本次研究使用光学显微镜、电子探针以及扫描电镜等分析仪器对该陨石进行详细的岩石学、矿物学及球粒特征研究。结果表明该陨石球粒轮廓较为模糊,基质重结晶明显,橄榄石平均Fa值为25.4 mol%(PMD为2.65%),低钙辉石的平均Fs值21.3 mol%(PMD为3.95%),硅酸盐矿物化学成分较为均一,根据岩相学及矿物学特征将其划分为L5型普通球粒陨石。橄榄石和辉石颗粒发育波状消光和面状破裂,且观察到有熔融囊的出现,表明该陨石受到S3以上的冲击变质作用。球粒的成因和形成的星云环境需要准确的球粒类型划分,球粒按结构类型分类较多,但其化学成分均一,该陨石所有球粒的橄榄石辉石的Mg^(#)约为74.5,均为Ⅱ型富铁球粒,结合“CIPW标准”计算基质化学成分均为A5型球粒。利用共生单斜辉石和斜方辉石矿物对成分特征计算得到NWA 15004陨石热变质平衡温度为814℃,说明该陨石母体经历了较高程度热变质过程。利用镍纹石中心镍浓度和镍纹石的带宽计算得到平均冷却速率约为10℃/Myr,说明该陨石在母体阶段还经历了较快速的冷却历史。To understand the evolution of the early solar nebula and the material composition of the solar system,newly discovered ordinary chondrite 15004 from Northwest Africa(NWA)was analyzed using op-tical microscopes,electron probes and scanning electron microscopy(SEM)to examine its petrographic,mineralogical and chondrite characteristics.The results show that the chondrules of the meteorite have a vague outline with obvious matrix recrystallization.The average Fa value of olivine is 25.4 mol%(PMD-2.65%),and the average Fs value of low-calcium pyroxene is 21.3 mol%(PMD=3.95%),with a rela-tively uniform chemical composition of silicate minerals.According to the petrographic and mineralogical characteristics,it can be classified as L5 ordinary chondrite.The olivine and pyroxene grains in the chon-drites developed wavy extinction and faceted fracture,and the presence of a fusion capsule indicates that the meteorite was subjected to shock metamorphism above S3.The Mg^(#)of all the olivine and pyroxene chondrules of the meteorite is about 74.5 and belongs to type II iron-rich chondrules.According to the CIPW standard,the chemical composition of the matrix is type A5 chondrules.By calculating composition characteristics of paragenetic clinopyroxene and orthopyroxene mineral pairs,the thermal metamorphic equilibrium temperature of NWA 15004 meteorites is 814℃,indicating that the meteorite parent body has experienced a high degree of thermal metamorphism.The calculation of nickel concentration in the center of the taenite and the bandwidth of the taenite show that the average cooling rate of NWA 15004 meteorites is about 1o C/Myr,indicating that the meteorite has also experienced a relatively rapid cooling history in the parent stage.

关 键 词：NWA 15004陨石 L群普通球粒陨石 球粒 岩石学 矿物学 M-FeO-CaO分类 

分 类 号：P185.83[天文地球—天文学]