Petromineralogy, origin and impact metamorphism of a new lunar meteorite NWA 12279
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P185.83;P588.12+4

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    Abstract:

    NWA 12279 is a piece of anorthosite lunar meteorite newly discovered in 2016, consisting of 86% anorthite and 14% impact melt breccia. The anorthosite, has a poikilitic texture and is composed of plagioclase (70.6%), olivine (11.3%), pyroxene (10.0%) and magnesium-aluminum spinel (7.0%), with a small amount of quartz, chromite and ilmenite. The impact melt breccia is mainly composed of lithic clasts such as anorthosite, gabbro-troctolite-anorthosite, microporphyritic crystalline impact melt breccias and gabbro, and such mineral fragments as olivine, pyroxene, plagioclase and spinel, and glass as well as matrix. The anorthosite has the same mineral composition as the breccia:plagioclase (An92.9~98.4), hypersthenes (Fs15.5~32.2Wo2.98~4.22), pigeonite (Fs27.9~53.1Wo7.19~14.7), augite (Fs8.42~38.9Wo17.0~44.1), olivine (Fo53.7~89.4), and magnesium aluminum spinel (Mg4.97Fe0.86)5.83 (Al11.4Cr0.61)12.0O24. Based on mineral composition, clastic composition, mineral components, total rock composition and shock-metamosphism features of the meteorite, as well as a comparison with the discovered lunar anorthosite, the authors hold that the meteorite may originate from a new spinel-rich gabbro-troctolite-anorthosite highland. Anorthite and breccia of this meteorite have different shock metamorphic features. Planar fractures in olivine, maskelynite of plagioclase and impact melt veins containing unmelted pyroxene and olivine fragments were produced in the anorthite, and vitreous veins, impact melt-pockets and rock brecciation were developed in the breccia. The peak shock pressures in anorthosite and breccias are estimated to be~45 GPa and~78 GPa respectively, and the shock temperature peaks to be~1 100℃ and~1 890℃ respectively. The shock stage is S5~S6.

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周剑凯,陈宏毅,谢兰芳,缪秉魁,仲艳,2019,一块新发现的月球陨石NWA 12279的岩石矿物学、源区和冲击变质作用[J].岩石矿物学杂志,38(4):521~534. ZHOU Jian-kai, CHEN Hong-yi, XIE Lan-fang, MIAO Bing-kui, ZHONG Yan,2019,Petromineralogy, origin and impact metamorphism of a new lunar meteorite NWA 12279[J]. Acta Petrologica et Mineralogica,38(4):521~534.

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History
  • Received:March 07,2019
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  • Online: July 15,2019
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