山西吕梁群早元古代双峰式火山岩地球化学特征及成因

Geochemical Characteristics and Petrogenesis of the Early Proterozoic Bimodal Volcanic Rocks from Luliang Group, Shanxi Province

山西吕梁山区中部的吕梁群形成于早元古代（～２．１Ｇａ），其上部由变质玄武岩和变质流纹岩组成。流纹岩富集ＬＩＬ和ＨＦＳ元素且具高的Ｒｂ／Ｓｒ和Ｇａ／Ａｌ比值，显示出与Ａ型花岗质岩石的相似性。玄武岩具有低ＴｉＯ２和Ｐ２Ｏ５含量且富集ＬＩＬ和ＬＲＥＥ元素。地球化学研究表明吕梁群玄武岩和流纹岩形成于大陆边缘的裂谷环境。玄武岩的母岩浆起源于亏损程度较低的地幔，并经历了结晶分异和地壳混染作用。

Luliang Group in Central Luliang Mountain, Shanxi was deposited in Early Proterozoic(～2.1Ga). Its upper part comprises meta basalt and meta rhyolite (bimodal volcanism). The rhyolites are characterized by high LIL and HFS elements and large Rb/Sr and Ga/Al ratios, similar with A type granitoid rocks. The basalts have low TiO 2 and P 2O 5 content and are enriched in LIL and LREE. Geochemical studies indicate that the volcanic rocks of Luliang Group were erupted in rift type tectonic setting on continental margin. The parental magma of the basalts was derived from lower depleted mantle source and underwent fractional crystallization and contamination. The rhyolites originated from the partial melting of lower crustal granulites, triggered by high heat fluid and basaltic magma emplacement in the rift environment.