内蒙古北山地区月牙山蛇绿质构造混杂岩带地质特征、形成时代及大地构造意义  

Geological characteristics, formation epoch and geotectonic significance of the Yueyashan ophiolitic tectonic mélange in Beishan area, Inner Mongolia

作　　者：胡新茁 赵国春[1] 胡新悦 廖云峰[2] 程海峰[2] 

机构地区：[1]中国地质大学(北京),北京100083 [2]河北省区域地质矿产调查研究所,河北廊坊065000

出　　处：《地质通报》2015年第2期425-436,共12页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:12120112220464)

摘　　要：月牙山蛇绿质构造混杂岩带位于红柳河—洗肠井蛇绿岩带东部的月牙山一带。月牙山蛇绿岩套出露较完整，自下而上由超基性杂岩、辉长岩、层状玄武岩、枕状玄武岩及放射虫硅质岩组成。蛇绿岩套北侧发生了强烈的构造混杂作用，形成蛇绿质构造混杂岩带，由强糜棱岩化、强蛇纹石化的辉橄岩、玄武岩基质和辉石岩、堆晶辉长岩、斜长花岗岩、橄榄岩、橄辉岩、角闪石岩、白云岩、放射虫硅质岩、蚀变玄武岩等岩块组成。通过对蛇绿岩套中辉石岩、辉长岩、斜长花岗岩、辉长闪长岩及蛇绿岩套北侧斜山——东七一山火山弧中的安山岩、花岗闪长岩等开展锆石U-Pb同位素测年研究，确定月牙山蛇绿岩套形成时代约为530Ma，相当于早寒武世；洋盆发生大规模自南向北俯冲作用的时间为421.0±15~442.4±1.5Ma，相当于志留纪。通过对蛇绿岩带两侧地层形成环境及蛇绿岩带对两侧地层单位的限定意义等研究认为，红柳河—洗肠井蛇绿岩带是代表古大洋闭合的板块缝合带，以该带为界，北侧为哈萨克斯坦板块，南侧为塔里木板块。The Yueyashan ophiolite tectonic melange belt is located in the Hongliuhe-Xichangjing ophiolite belt of eastern Yueyas-han area. Yueyashan ophiolite suite is exposed completely, composed from the bottom upward of ultrabasic complex, gabbro, lay-ered basalt and pillow basalt as well as radiolarian siliceous rocks. On the northern side of the ophiolite suite there happened intense tectonic melange activity, forming the ophiolite tectonic melange belt composed mainly of strongly mylonitized and serpentinized pyroxene peridotite, basalt matrix, pyroxenite, cumulate gabbro, plagioclase granite, peridotite, olivine gabbro, hornblendite, dolo-mite, radiolarian siliceous rocks, and altered basalt. The authors carried out zircon U-Pb isotopic dating of ophiolite suite pyroxe-nite, gabbro, plagioclase granite and gabbro diorite. In addition, the authors conducted U-Pb isotope experiments on andesite and granodiorite derived from the Xieshan-Dongqiyishan volcanic arc on the northern side of the ophiolite suite. The isotope dating confirmed that the Yueyashan ophiolite suite was formed at about 530Ma, corresponding to early Cambrian. It is also concluded that the large-scale ocean basin subduction from the south to the north occurred in the period of 421.0±15-442.4±1.5Ma, suggest-ing Silurian. Based on the study of stratigraphic formation environment on both sides of the ophiolite belt and its significance for the＆nbsp;limit of stratigraphic unit, the authors hold that the Hongliuhe-Xichangjing ophiolite belt represents the ancient ocean closed plate suture zone. With this zone as the boundary, the northern side is the Kazakhstan plate and the south side is the Tarim plate.

关 键 词：蛇绿岩 蛇绿质构造混杂岩 地质特征 形成时代 大地构造意义 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学]