Transmission electron microscopic study of the fine-grained vein matrix in the Suizhou L6 meteorite

• Published in: Acta geochimica 2016-06, Vol.35 (2), p.105-110
• Main Authors: Xiande, Xie, Jianbo, Wang, Xiangping, Gu, Yi, Xiong, Shuangfeng, Jia
• Format: Article
• Language: English
• Subjects: Crystallization; Crystals; Earth and Environmental Science; Earth Sciences; Geochemistry; Iron sulfides; Meteors & meteorites; Mineralogy; Minerals; Original Article; Polycrystals; Transmission electron microscopy; Veins (geology); 基质; 石榴石晶体; 矿物学特征; 细粒; 透射电子显微镜; 透射电镜; 随州陨石; 静脉
• ISSN: 1000-9426; 2096-0956; 1993-0364; 2365-7499
• DOI: 10.1007/s11631-016-0093-7

The mineralogy of shock vein matrix in the Suizhou meteorite has been investigated by optical and transmission electron microscopy. It was revealed that the vein matrix is composed of majorite-pyrope garnet, mag- aesiowtistite, and ringwoodite, with FeNi-FeS inter- growths. The observation and character of ring-like selected electron diffraction （SAED） patterns indicate that Lhe idiomorphic garnet crystals in the vein matrix have different orientations. The polycrystalline nature of magnesiowtistite is also confirmed by a ring-like SAED pattern. Both garnet and magnesiowtistite crystals showed sharp Jiffraction spots, signifying the good crystallinity of these ：wo minerals. The SAED pattern of cryptocrystalline 5ngwoodite shows only diffuse concentric diffraction tings. FeNi metal and troilite （FeS）, which were molten during the shock event, occur in the matrix as fine eutectic FeNi-FeS intergrowths filling the interstices between garaet and magnesiowiistite grains. Based on the phase dia- gram of the Allende chondrite and the results of this TEM study, it is inferred that majorite-pyrope garnet first crystallized from the Suizhou chondritic melt at 22-26 GPa, Followed by crystallization of magnesiowtistite at 20-24 GPa, and then ringwoodite at 18-20 GPa. The eutectic intergrowths of FeNi-metal and troilite are proposed to have crystallized during meteorite cooling and solidified at the last stage of vein formation.