安齐火山岩带的玄武岩岩石学特征及其地质意义

安齐火山岩带中玄武岩呈NE向断续带状分布于哈图断裂带与安齐断裂带之间的广大地区,岩石由橄榄拉斑玄武岩和石英拉斑玄武岩组成,均属亚碱性系列、钠质和普通质亚系列岩石。从对它们的岩石学、矿物学和微量元素研究表明,玄武岩类为地幔橄榄岩15％-25％部分熔融产物。玄武岩类共存“过渡的”洋中脊拉斑玄武岩和岛弧拉斑玄武岩两种特点,前者表明玄武岩形成于张应力较强的构造环境中,后者则进一步说明玄武岩形成于岛弧内的张应力较强的构造部位,即以洋壳为底的弧后海盆中,故其产物为大洋岛弧拉斑玄武岩范畴。

The Petrological Characteristics and Geological Singnificance in Anqi Volcanic rock Belt

The basalts lying between Hatu fault and Anqi fault Present intermitted strip-like distribution Theywere the Product of magma activity in the Early-Hercynian, and have a lenth of more than 100 km. The rocks mainly consist of olivine tholeiite and quhz tholeiite, belonging to Sub- alkaline series and sodic or general low-potasium tholeiite sub-series. Their main forming-rockmineralsare rich-calcium augite and plageoclase. The trasitional metal distribution of basalt, compared with that of original mantle, is higher in Sc, Ti, V, much iower in Cr, Co, Ni and a bit higher in Fe,Mn. then REE separation has a flat curve, and the ratio of (La/Lu) cn is less thsn or equal to l The research in petrology, mineralogy and trance elements of the basalts shows that basalts result from the parcial melting product of mantle peridotlte, in the rate af 15~-20% with characters of transitional MORB and arc-island tholeiite. The foemeu shows that basalt was formed in tectonic environment where extension was strong. The latter further shows that basalt was formed in extension stagein environment of arc-island. Through the study of geological cvolutional history, we consider that basalts were formed in are-back basin where their bottom was ocean crust, and belonged to ocean are-island tholeiite.