内蒙古中心屯地区晚侏罗世火山岩岩石地球化学特征及其成因意义

PETROCHEMISTRICAL CHARACTERISTICS AND THEIR GENETICSIGNIF ICANCE OF LATE JURASSIC VOLCANO ROCKS IN ZHONGXINTUN AREA OF NEIMENGGU

中心屯地区位于大兴安岭火山岩带中南段,区内岩浆活动强烈,发育有中生代不同时期的基性-酸性火山岩。在野外地质调查的基础上,通过研究晚侏罗世火山岩岩石学特征及岩石化学数据,发现区内晚侏罗世火山岩主要为中性-酸性岩石,属于钙碱性系列;稀土元素大都具有铕负异常,配分曲右倾,显示轻稀土元素富集、重稀土元素亏损的特点;微量元素的过渡元素Cr、Co、Ni含量较低,富集大离子亲石元素Rb、Ba、K等,亏损大离子亲石元素Sr,亏损Nb、Th、Ti、P等高场强元素。综合分析表明,晚侏罗世火山岩岩浆来源于地壳。其形成环境处于亚洲大陆边缘断陷带,受太平洋板块俯冲作用的影响。

The Zhongxintun erea is located in south section of volcanic belt of Dahingan Mountains, where the strong magma movement different stages of Mesozoic magmatic has formed basic to acidic rocks.Based on thefield geological investigation, geognosy characteristics of the Mesozoic volcanic rocks and rock chemical data shows that the Mesozoic volcanic rocks in the region are mainly of neutral - acid rocks that belong to calc-alkaline series; While the negative EU anomalies and rightward distribution curve owned by most REE demonstrate the characteristics of LREE enrichment and HREE loss; Trace elements of transition elements Cr, Co, Ni are low, enrichment of large ion lithophile elements Rb, Ba, K, loss of large ion lithophile elements Sr, Nb, Th, Ti, loss of P high strength element. Comprehensive analysis shows that the late Jurassic volcano magma source in the earth＇s crust. Its formation environment in the Asian continental margin rift belt by the subduction of the Pacific plate imnact.