宁强碳质球粒陨石岩石学及化学组成的研究

THE PETROLOGY AND CHEMICAL COMPOSITION OF NINGQIANG METEORITE

宁强碳质球粒陨石含有大量聚集的球粒(13.7体积％)和非常低的难熔包体丰度(～2±1体积％),属于异常的CV球粒陨石(氧化亚群)。相对于典型的CV3球粒陨石,宁强具有低的难熔包体和较高橄榄石集合体(8.2体积％)及聚集的球粒丰度,相对于CV3氧化亚群,宁强具有较多的金属Fe-Ni及磁铁矿,高的磁铁矿(3.3体积％)/金属Fe-Ni(0.5体积％)比值(6.6),并有作为主要金属相的镍铁矿(Ni_3Fe),表明宁强球粒陨石类似于CV3氧化亚群。

The Ningqiang is an anomalous CV chondrite (oxidized subgroup) containing a high abundance of aggregational chondrules (13.7 vol.%) and a very low abundance of refractory in-clusions (~2±1 vol.%). Granpblastic chondrules (which contain olivines forming 1200 triple junctures and little mesostasis) are rare (0.2. vol.%). Coarse-grained chondrule rims are scarce surrounding only ~5% of the Ningqiang chondrules. As a consequence of its deple-tion in refractory inclusions, the Ningqiang whole-rock has low abundances (~0.82×CV) of refractory lithophiles.Aggregational chondrules appear to have been formed by incipient melting of fine-grained aggregates in the solar nebula. Cementation occurred at relatively low temperatures, possibly by the same mechanism responsible for chondrule formation. Low nebular heating temperatures may also account for the relative scarcity of coarse-grained chondrule rims.Granoblastic chondrules were probably formed in the solar nebula by incomplete melting of precursor materials that were olivine normative and depleted in Si, Ca, Al, Fe and Na.Relative to typical CV3 chondrites, the Ningqiang has a very low abundance of refractory inclusions and high abundances of olivine aggregates (8.2vol %) and aggregational chondrules. Relative to oxidized CV3 chondrites, the Ningqiang has more metallic Fe-Ni (0.5 vol.%) and more magnetite (3.3 vol.%).