川东北元坝地区长兴组钠长石的发现及地质意义

The Genesis and Geological Significance of Albite Discovered in the Changxing Formation of the Yuanba Area in Northeastern Sichuan,China

为探讨川东北元坝地区长兴组岩石中钠长石矿物的成因,对其进行了利用电子显微镜、能谱仪及稀土元素测定等分析测试。结果表明,显微镜下钠长石主要呈分散状分布,明显的聚片双晶现象,交代早期成岩矿物;钠长石与石英、黄铁矿伴生;稀土元素总量较低,分布曲线较缓,轻稀土相对富集、重稀土元素相对亏损,正Eu异常。研究认为,钠长石的成因与深部热液活动有关。根据川东北地区晚二叠世拉张构造背景,推测其是在二叠世晚期峨眉地裂运动玄武岩喷发的构造背景下生成的,钠长石的发现为研究该区长兴期构造、岩浆活动、"热事件"等研究具有重要的地质意义。

In order to discuss the genesis of albite discovered in rocks of the Changxing Formation in the Yuanba area,al-bite has been studied by using electron microscope,energy spectrometer and rare earth element determination method.Re-sults show that albite,which has obvious polysynthetic twins,is mainly disseminated in association with quartz and pyrite in carbonates of the Changxing Formation.It replaced the early diagenetic minerals.It contains low contents of rare earth elements,with gently right-declined REE distribution patterns,relatively enriched LREE and depleted HREE,and typical positive Eu anomalies.It is believed that the albite was formed in association with the hydrothermal fluid in depth.Based on the extensional tectonic background of the Northeastern Sichuan in Late Permian,it is inferred that the albite was formed during the Emeishan basalt eruption in Late Permian.The discovery of albite has important geological significances for studying the structure,magmatic activity and the “thermal event”of the Changxing Formation in the area.