摘要
笔-铜碱性镁铁质火山岩体由碎屑岩和熔岩组成。熔岩的主要岩石类型有苦橄岩(富橄辉玄岩)和碱性玄武岩。所有样品都富集不相容元素,REE显示出高度分离的分配型式,其(La/Yb)_(ON)比值多数在15和20之间,而相容元素(Co、Cr和Ni)则明显亏损,计算表明,碱性镁铁质熔岩不可能由球粒陨石型地幔分离出的橄榄岩部分熔融产生,而可能是由交代地幔适度部分熔融产物。
Alkali mafic subvolcanic body occurring in Bijiashan-Tongdongwan con- sists of clastic rock and lava. The main rock types for the later are picrite (ankaratrite)and alkalibasalt. All samples show a typical enrichment in incompatible elements. In particular, the REE patterns exhibit a Strong fra- ctionation characterized by a(La/Yb)_(CN) ratio between 15 and 20. In the same way, the compatible elements(Co, Cr and Ni)show rather large dep- letion. Calculations suggest that the alkali mafic lava cannot be derived by direct partial melting from a peridotites which were fractionated from chondritic type mantle, and instead they could result by proper partial melting of the metasomatically enriched mantle.
