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

Abstract：The origin of sillimanite-quartz aggregates in the early Precambrian Wanzhi 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 three types: (1) globular and nodular sillimanite-quartz aggregates, which form by anatexis 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 aggregates, 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 metamorphic origin and whose chemical composition are controlled by original rocks.