江西萍乐坳陷区东部中二叠世火山岩地质特征与构造环境

在萍乐坳陷区东段的鸣山地区发现中二叠世火山岩, 岩石类型主要为碱性玄武岩、亚碱性玄武岩及安山玄武岩，故将其命名为鸣山玄武岩。该套火山岩呈似层状夹于中二叠统鸣山组薄层状硅质岩与硅质页岩之间，可见气孔构造及大量杏仁体，厚约15m。火山岩具有贫硅、富铁、高铝、低镁的特点，Mg#介于4.08~19.48之间，高场强元素Nb、Ta、Zr、Hf相对富集，U、Th及轻稀土元素明显富集，(La/Yb)N=3.58~72.53, Eu弱亏损 (δEu=0.42~0.85)，稀土元素配分曲线呈右缓倾。初步研究认为，鸣山玄武岩可能形成于板内陆缘裂谷环境, 是轻稀土矿有利的矿源层，也是东吴运动在华南地区引发海底火山喷溢活动的证据。关键词：中二叠世；火山岩；萍乐坳陷区东部；东吴运动；江西

Geological characteristics and tectonic environment of Middle Permian volcanic rocks in eastern Pingle depression,Jiangxi Province

Middle Permian volcanic rocks were discovered in the Mingshan area of eastern Pingle depression, and the rock type is mainly composed of alkali basalt, sub-alkaline basalts and andesitic basalt, called Mingshan basalt. The volcanic rocks are sandwiched between Mingshan Formation thin siliceous rocks and siliceous shale, with vesicular structure and a large number of amygdales, about 15m in thickness. The volcanic rocks are characterized by poor silicon, rich iron, high aluminum, low magnesium, Mg# content ranging from 4.08 to 19.48, relative enrichment of high field strength elements Nb, Ta, Zr, Hf, significant enrichment of U, Th and light rare earth elements (LREE), and (La/Yb)N content ranging from 3.58 to 72.53, with insignificant Eu depletion (δEu=0.42~0.85) and slightly rightly-oblique REE distribution patterns. Researches show that Mingshan basalt was probably formed in an active continental margin rift basin environment with light rare earth ore source bed; nevertheless, there also exists the evidence arguing that the Dongwu Movement caused the submarine volcanic eruption in South China.