Petrography and chronology of lunar meteorite Northwest Africa 6950
Petrography and chronology of lunar meteorite Northwest Africa 6950
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西北非洲 6950 月球陨石的岩相学和年代学
DOI：
10.1007/s11432-019-2809-3
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发表时间：
2020-03
期刊：
影响因子：
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通讯作者：
Wang Chen
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文献类型：
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作者：
Bao Zemin;Shi Yuruo;Anderson J. Lawford;Kennedy Allen;Ke Zuokai;Gu Xiangping;Wang Peizhi;Che Xiaochao;Kang Yuelan;Sun Huiyi;Wang Chen
西北非洲（NWA） 6950是一种橄榄辉长岩月球陨石，具有与其他月球玄武岩明显不同的岩石结构。在这篇文章中，我们报道了该月球陨石中坏辉石和磷酸盐的岩石学、矿物学和U-Pb年代学，并与其他NWA 773配对陨石进行了比较。NWA 6950主要由粗粒橄榄石、辉石和斜长石组成，少量有钛铁矿、铬铁矿、三辉石、坏辉石、带长石和磷灰石。丰富的圆形至自面体橄榄石的Fo值在68 ~ 69之间。辉石中既有辉石，也有鸽石，mg# =71 ~ 80范围较窄，组成分别为en46 - 52fs12 - 16wo32 - 41和En58-68Fs19-28Wo7-20。斜长石主要呈倒面体，与橄榄石和辉石的晶界一致。斜长石晶粒呈细长状，长度达几百微米。拉曼光谱显示斜长石已转变为低钠低钾（Ab4-9Or0.6-3.7）、高钙（An87-95）的斜长石。利用灵敏的高分辨率离子探针（SHRIMP II）测得的baddeleyite和磷酸盐的207pb /206Pb加权平均年龄分别为3119±16 Ma （n= 9, MSWD = 2.5）和3119±18 Ma (n= 15, MSWD = 2.1)，给出了陨石的结晶年龄。NWA 6950与NWA 773族镁质辉长岩具有相似的矿物组成、地球化学特征和几乎相同的结晶年龄。我们认为NWA 6950和NWA 773是一对陨石，结晶时间约为3119 Ma，代表了月球KREEP(富含钾（K)、稀土元素（REE）和磷(P)物质）区域的岩浆活动。
Northwest Africa (NWA) 6950 is an olivine-gabbro lunar meteorite that has a distinctly different petrographic texture from other lunar basalts. In this contribution, we report the petrography, mineralogy, and U-Pb geochronology of baddeleyite and phosphate in this lunar meteorite and make a comparison with other NWA 773 paired meteorites. NWA 6950 consists mainly of coarse-grained olivine, pyroxene, and plagioclase, with minor ilmenite, chromite, troilite, baddeleyite, taenite, and apatite. The abundant rounded to euhedral olivine has a limited Fo ranging from 68 to 69. Pyroxenes include both augite and pigeonite, with a narrow range of Mg#=71–80, and composition, respectively, En46–52Fs12–16Wo32–41and En58–68Fs19–28Wo7–20. Plagioclase is mainly anhedral, conforming to the crystal margins of olivine and pyroxene. The plagioclase grains are elongated and several hundreds of microns in length. Raman spectra shows that plagioclase has been transformed into maskelynite, which is very calcic (An87–95) with low sodium and very low potassium (Ab4–9Or0.6–3.7). The weighted mean207Pb/206Pb ages of baddeleyite and phosphate measured using a sensitive high resolution ion micro probe (SHRIMP II) are 3119 ± 16 Ma (n= 9, MSWD = 2.5) (mean squared weighted deviates, MSWD) and 3119 ± 18 Ma (n= 15, MSWD = 2.1), respectively, giving the crystallization age of the meteorite. NWA 6950 has similar mineral compositions, geochemical characteristics, and an almost identical age of crystallization to the magnesian gabbro of the NWA 773 clan. We conclude that NWA 6950 and NWA 773 are paired meteorites, which crystallize at ca. 3119 Ma, and represent magmatic activities in the KREEP (potassium (K), rare earth elements (REE) and phosphorus (P) rich lunar material) region of the Moon.
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DOI：
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发表时间：
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期刊：
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影响因子：
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