内蒙古锡林浩特毛登牧场早石炭世花岗岩锆石U-Pb年龄、地球化学特征及其地质意义

发布时间：2018-11-25 21:10

【摘要】：通过对内蒙古锡林浩特毛登牧场早石炭世花岗岩体进行野外观察、LA-ICP-MS锆石U-Pb测年以及地球化学测试,讨论其构造环境,进一步为研究古亚洲洋闭合时限提供依据。测年结果表明:花岗闪长岩为(330.6±1.8)Ma,二长花岗岩为(327.7±2.6)Ma,成岩时代为早石炭世。岩石地球化学分析表明:花岗闪长岩为强过铝质、钙碱性系列岩石,具有活动大陆边缘的亲缘性特征。微量元素特征指示花岗闪长岩具有典型下地壳来源特征并伴有部分幔源岩浆混合作用,为弧岩浆岩。二长花岗岩为具高硅、富碱、相对低铝特征的高钾钙碱性系列岩石。两类差异明显的岩石稀土配分曲线表明二长花岗岩具有下地壳岩浆重熔的演化特征。微量元素特征指示样品为大陆弧环境下壳源重熔的成熟弧花岗岩。构造判别图显示花岗闪长岩为代表活动大陆边缘环境的I型花岗岩,而二长花岗岩则为指示活动大陆边缘弧后伸展环境的A2型花岗岩,二者构成I-A型复合岩体,说明研究区在早石炭世仍存在古亚洲洋向西伯利亚板块的俯冲作用,推测古亚洲洋此时尚未闭合。
[Abstract]:Based on the field observation, LA-ICP-MS zircon U-Pb dating and geochemical tests of the early Carboniferous granites in Maodeng Ranch, Xilinhaote, Inner Mongolia, the tectonic environment is discussed, which provides a basis for the study of the time limit for the closure of the Paleo-Asian Ocean. The results show that the granodiorite is (330.6 卤1.8) Ma, monzogranite, and its diagenetic age is (327.7 卤2. 6) Ma, during the early Carboniferous. The petrogeochemical analysis shows that the granodiorite is a strong peraluminous, calc-alkaline series of rocks, and has the genetic characteristics of active continental margin. The trace element characteristics indicate that the granodiorite is characterized by typical lower crustal origin and partial mantle magma mixing, which is an arc magmatic rock. The monzogranite is a series of high potassium calc-alkaline rocks with high silicon, alkali-rich and relatively low aluminum. The REE partition curves of the two kinds of rocks show that the bifeldspar granites have the evolutional characteristics of lower crust magmatic remelting. The trace element characteristics indicate that the samples are mature arc granites with crust-source remelting in continental arc environment. The tectonic discriminant diagram shows that granodiorite is an I type granite representing the active continental margin environment, while the 2 feldspar granite is an A2 type granite indicating the active continental margin back-arc extension environment. It is suggested that the subduction of the paleo-Asian ocean to the Siberian plate still exists in the early Carboniferous, and the paleo-Asian ocean has not been closed at this time.
【作者单位】：中国地质大学(北京)地球科学与资源学院;中化地质矿山总局地质研究院;中化地质矿山总局化工地质调查总院;河北地质大学资源学院;
【基金】：中国地质调查局地质调查工作项目(1212011220449)
【分类号】：P588.121

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