8块新发现的西北非球粒陨石的矿物岩石学特征

Petrology and Mineralogy of Eight Pieces of Chondrites Newly Founded in Northwest Africa

为了解不同种类小行星母体的起源与演化信息,选取8块近期在西北非地区发现的未经过详细研究的球粒陨石,利用扫描电子显微镜观察其显微结构,利用能谱仪及电子探针测试样品的成分。结果显示,NWA 7613与NWA 8340为CV3_（oxA）型陨石,另外5块普通球粒陨石的热变质程度变化更为广泛且球粒中橄榄石铁含量更高。NWA 7613（LL3）球粒中橄榄石CaO含量稍高（0.08%~0.24%）,高于平衡型普通球粒陨石（小于0.05%）。NWA 6468（R4）与普通球粒陨石具有相似的岩相结构,但不发育铁镍金属,且橄榄石铁含量（Fa_（35.9~42.1））及镍含量（平均含0.23%）更高,是强氧化环境下的产物。NWA 7251（Limpact melt）具有特殊的火成结构,是大规模灾难性撞击事件产物,橄榄石铁指数（Fa_（21.4~26.7））与L型球粒陨石的橄榄石成分一致,但CaO含量（0.16%~0.31%）高于平衡型普通球粒陨石。

In order to probe information about the origin and evolution of various kinds of asteroid parent bodies, petrolog- ic-mineralogical analyses of eight pieces of chondrites newly founded in Northwest Africa have been carried out by using scanning electron microscope, energy dispersive spectrometer and electron microprobe. Results show that NWA 7613 and NWA 8340 are CV3oxA chondrites. Other five pieces of ordinary chondrites have a wide range of thermal metamorphism in- tensities with higher contents of FeO in olivine grains in chondrules than those in carbonaceous chondrites. Olivine grains in chondrules of NWA 7613 （LL3）have higher contents of CaO （0. 08%-0.24% ）than those in equilibrated ordinary chon- drites（〈0.05%）. NWA 6468（R）has similar petrographical textures to those of the ordinary chondrites but without FeNi metal alloy. In addition, its olivine grains have high contents of Fe （Fa35.9-42 1）and Ni （average 0.23% ） , indicating they were formed under highly oxidized condition. NWA 7251 （L-impact melt） shows specific textures of igneous rocks. This in- dicates that it is a product of catastrophic impact event. Olivine grains in Sample NWA 7251 （ Fa21.4-26.7 ） contain similar FeO contents to those of the L chondrites but higher CaO contents（ 0. 16%-0.31% ）than those of the equilibrated ordinary chondrites.