内蒙古东南部早三叠世花岗岩带岩石地球化学特征及其构造环境  

Petrological and Geochemical Characteristics of the Early Triassic Granite Belt in Southeastern Inner Mongolia and Its Tectonic Setting

作　　者：刘建峰[1,2] 李锦轶[1] 迟效国[2] 曲军峰[1] 胡兆初[3] 郭春丽[4] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]吉林大学地球科学学院,长春130061 [3]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [4]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2014年第9期1677-1690,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41102029);中国地质调查局国土资源调查项目(编号12120113096400);1212011121064)资助的成果

摘　　要：锆石U-Pb定年结果表明位于林西县北西的转山子岩体的形成时代为245.6±0.9Ma,该岩体与内蒙古东南部的龙头山和建设屯岩体共同构成一条大致平行于西拉木伦河蛇绿岩带的早三叠世花岗岩带。岩石学和地球化学分析表明,上述早三叠世岩体属于钙碱性和高钾钙碱性系列,铝饱和指数(ACNK)均小于1.1,属于偏铝质或弱过铝质的I型花岗岩。其中,转山子岩体轻重稀土分馏较弱,含有较低的Sr含量(<400×10-6),显示经典岛弧岩石的特征;建设屯岩体具有强烈的轻重稀土分馏以及较高的Sr含量(>400×10-6),显示埃达克岩的地球化学特征;龙头山岩体的轻重稀土分馏特征和Sr的含量总体介于前两者之间。锆石Hf同位素分析表明,上述三个岩体都具有正的εHf(t)值。岩石地球化学特征反映它们起源于不同深度的新生下地壳不同程度的部分熔融作用。综合考虑区域地层和岩浆岩资料,本文认为该花岗岩带与区域上同时代的镁铁质火山岩共同形成于西伯利亚和中朝古板块碰撞造山过程中与伸展有关的地球动力学环境,可能与向南俯冲的古亚洲洋板块在早三叠世的断离引起的软流圈上涌有关。Zircon U-Pb dating indicates that the age of the Zhuanshanzi pluton from northwest Linxi County is 245.6±0. 9 Ma. The pluton and the Longtoushan and Jianshetun plutons in southeast Inner Mongolia constitute an Early Triassic granite belt, which is approximately parallel with the Xar Moron river ophiolite belt. Petrological and geochemical studies indicate that all the plutons are calc-alkaline and high- K calc-alkaline granites and their aluminum saturation indexes （ACNK） are less than 1.1, so they belong to metaluminous or weak peraluminous I-type granite. The fractionation between light and heavy rare earth elements of Zhuanshanzi pluton is weak and the pluton has low Sr content （〈400 × 10^-6）, which are the characteristics of typical island arc magmatic rocks. The Jianshetun pluton has relatively stronger fractionation between light and heavy rare earth elements and higher Sr content （〉400 ×10^-6）, which are the characteristics of adakite. While the degree of fractionation between light and heavy rare earth elements and the Sr content of Longtoushan pluton are between those of the former two plutons. The zircons of all the three plutons have positive εHf （t） values. All the geochemical characteristics above indicate that the plutons originated from different degree partial melting of the juvenile lower crust under different depths.Considering regional stratigraphic and magmatic data, it is suggested that the early Triassic granite belt and coeval mafic volcanic rocks in southeast Inner Mongolia were formed in an extensional geodynamic setting during the collisional orogenic process between the Siberian and the Sino-Korean paleoplates, which might have relation with the upwelling of asthensophere caused by the break off of the southward subducting Paleo-Asian Ocean plate in early Triassic.

关 键 词：内蒙古 早三叠世 花岗岩 古亚洲洋 地球化学 

分 类 号：P588.121[天文地球—岩石学]