西秦岭下三叠统华日组火山岩地球化学特征及构造环境分析

Geochemical Characteristics and Tectonic Significance of the Volcanic Rocks from Lower Triassic Huari Formation in West Qinling

摘要: 西秦岭合作一带华日组岩性以中酸性火山岩为主,岩性为英安岩、安山岩、火山角砾岩和凝灰岩.通过对其岩石地球化学研究,表明华日组火山岩属钙碱性系列,具高K、高AI和低碱、低Ti的特点;微量元素地球化学组成与典型火山岛弧环境的地球化学组成一致;稀土总量为61.91×10^-6~185.58×10^-6,平均含量为128.04×10^-6,显示出轻稀土富集,重稀土亏损的特点,具有弱的Eu负异常(平均为0.98);结合西秦岭造山带的构造演化特征,认为下三叠统华日组火山岩形成于岛弧环境.

Abstract: The Huari Formation, located in Hezuo region of West Qinling, are mainly consist of neutral to acidic volcanic rocks, including dacite, andesite, volcanic breccia and tuff. The rock geochemical results show that, these rocks belong to calc-alkaline series, with the characteristics of high potassium and alumina, low alkali and titanium. Moreover, the geochemical features of these rocks on trace elements are similar with the ones of typical volcanic island arc. The total rare earth elements are 61.91×10^-6~185.58×10^-6, with an average of 128.04×10^-6, showing LREE enrichment, HREE depletion with weak negative Eu anomalies (average is 0.98). Combined with the tectonic evolution of western Qinling orogenic belt, it's suggested that lower Triassic Huari Formation was formed in island arc setting.