大兴安岭北段斯木科流纹质碎斑熔岩特征及成因

CHARACTERISTICS AND GENESIS OF THE LIPARITIC MORTAR-LAVA IN SIMUKE AREA OF NORTHERN DAXINGANLING

摘要: 在大兴安岭北段斯木科地区发育一种具有独特结构特征的火山岩石类型——流纹质碎斑熔岩,其具有熔岩和熔结凝灰岩的双重结构.岩石富Si、碱,Na₂O/K₂O=0.61~0.82,轻稀土富集,Eu亏损强烈,富集Rb、Th,亏损Ba、K,与同期流纹岩的地球化学特征相同,其区别主要在岩相学上.二者均形成于造山后伸展环境,属于由于岩浆向上运移、定位过程的不同而形成的"同质异相体".

Abstract: A special kind of liparitic mortar-lava with the texture of both lava and ignimbrite is developed in Simuke area, Northern Daxinganling.The rock is characterized by enriched Si, alkaline and LREE, Na₂0/K₂0=0.61-0.82, with relatively great negative Eu anomaly, high Rb and Th content and low Ba and K.It geochemically resembles the liparite of the same period, but with significant different in their lithofacies.They were probably both originated in post-orogenic extension environment, and might be the polymorphs formed in different emplacement of magma.