河北平山湾子群夕线石英集合体的地质地球化学特征及成因

Genetic diversity of sillimanite-quartz aggregates in the Wanzhi Group and r elated rocks at Pingshan,Hebei---Geological and geochemical constraints

河北平山地区早前寒武纪湾子群及相关岩石中夕线石英集合体成因存在长期争论。根据地质地球化学研究,本文将它们划分为3种不同类型。(1)球状和团块状夕线石英集合体,其形成与钾长浅粒岩的深熔作用有关。(2)面状夕线石英集合体,与钾长浅粒岩在应力状态下的变质分异作用有关。两者地球化学组成及与相邻浅色体关系受母岩和作用过程双重因素制约。(3)层状夕线石英集合体,为变质沉积成因,地球化学上反映了变质原岩的组成特征。

The origin of sillimanite-quartz aggregates in the early Precambrian Wanzh i Group and related rocks in the Pingshan area,Hebei,has long been controversial .According to the geological and geochemical studies they may be divided into th ree types:(1)globular and nodular sillimanite-quartz aggregates,which form by an atexis of K-feldspar leucogranulitite and are lower in large-ion lithophile(LIL) elements and higher in rare earth elements(REE)and have stronger negative Eu and Ba anomalies than nearby anatectic derivatives;(2)planar sillimanite-quartz agg regates,which form by metamorphic differentiation of K-feldspar leucogranulitite under stresses and show depletion in LIL elements and strong negative Eu and Ba anomalies but no obvious variation in REE and Th contents compared with nearby leucocratic material;and(3)bedded sillimanite-quartz aggregates,which are of met amorphic origin and whose chemical composition are controlled by original rocks.