岚皋绿色辉石捕虏体矿物学及其地质意义

Minera logy and GeoIogical Implication of Green-pyroxenite Xenoliths from Langao County, Shanxi Province

产于扬子板块北缘岚皋县境内的早古生代镁铁－超镁铁质煌斑杂岩中的绿色辉石捕虏晶及捕虏体，按其岩相学及化学成分可分成三种类型，它们是同一种岩浆在不同深度结晶分异的结果。绿色辉石岩系列是早古生代大陆边缘裂谷中超碱质基性岩浆活动的产物。同寄主煌斑杂岩的初始岩浆（煌斑岩浆）一样，是于裂谷作用不同阶段由交代富集的亏损地幔部分熔融所形成。

Green-pyroxenite xenoliths(inciuding green- pyroxene xenocrysts)that occur in the Early paleozoic alkaline mafic-ultramafic subvolcanic lamproph-yric complex within Langao County on the northern margin of Yantze plate might be classified into threo groups according to their potrotocrraphlcal facles and geochemical composition-All the green- pyroxenos in this area are green or pale,green colored,and can be easily distinguished from colorless pyroxenes.According to geochomical characterisics,most green-pyroxenes can be aseigned to Ca-Mg-Fe pyroenes rich in Na,while a fetw might be regarded as aeglrine-augite.Green-pyroxenes in the first group are rich in Mg and Ca but defi-cient in Fe and Na,while those in the second and the third group are rich in Fe and Na but deficient in Mg and Ca. Goochemical characteristics of all groen-pyroxenes change regularly,indicating that all green-pyroxenes crystal-lized from the same magma but at different depths:those in the socond group were formed under higher pressure than those in the first and the third group,Compared with those in the other two groups,the green-pyroxenes in the first group were crystallized at the later stage of the samo magmati evo-lutionary process.A study of the green-pyroxenite xenoliths shows that there existed ano-ther kind of magma-peralkaline basic magma derived from the small degree of partial melting of the metasomatized mantle at the early stage of the conti-nental rifting in Early Paleozoic,An investigation into peralkaline basic ma-gma would reveal more information about the tectonic movement of the conti-nental rift in North Daba Mountain and the evolution of lithosphere in South Qinling Mouptains.