汝城拉张盆地基性火山碎屑岩建造

汝城拉张盆地中发育的侏罗系基性火山碎屑岩,与大致顺层侵入的辉绿岩及呈层状产出的玄武岩共同组成了一套基性火山岩系。该区基性火山碎屑岩建造属正常火山碎屑岩与正常沉积岩之间的过渡性岩类,包含沉积火山碎屑岩和火山碎屑沉积岩两个亚类。从北东向南西由厚(543 m)变薄(0.6 m)。具有快速堆积的逆向粒序构造特征。玄武岩角砾的化学成份在全碱-SiO_2相关图上投影点属拉斑玄武岩,其氧化系数(0.63)表明为近地表氧化环境形成。稀土元素模式与辉绿岩近于重合,表明两者同源。钾-氩法同位素年龄为145.6Ma。

THE BASIC PYROCLASTIC ROCK FORMATION IN RUCHENG TENSIONAL BASIN

The Jurassic basic pyroclastic rocks occurred in the inland tensional basin in Rucheng, and the diabase intruded roughly along the beds as well as the stratified basalt compose a set of basic volcanic rock series. The basic pyroclastic rocks in this area belong to the transitional type between normal pyroclastic rock and norma 1 sedimentary rock including two subtypes: sedimentary pyroclastic rock and pyroclastic sedimentary rock. Its thickness is becoming thinner from northeast (543m) to south-west (0.6m). It is characteristic of rapid sediment reverse graded structure. The chemical composition of the basalt breccia is projected into the scope of tholeiite in the Total Alkaline-SiO_2 correlogram, and its oxidation index (0.63) indicate its epigenetic origin in oxidizing milieu. Its rare earth element pattern approximately coincide with that of diabase, indicating their common source. Their K-Ar isotope age is 146.6 Ma.