内蒙古索伦山地区蛇绿岩岩石单元地质特征、就位机制及时限
Geological Characteristics, Emplacement Mechanisms and Timing of the Ophiolites in Solonker Zone, Inner Mongolia

摘要： 内蒙古索伦山地区出露蛇绿岩，其研究对探讨古亚洲洋演化具有重要意义。对内蒙古索伦山地区蛇绿岩进行了系统的调查和研究，探讨了其就位机制与时限。 结合索伦山蛇绿岩地质特征和区域地质背景综合分析，认为研究区蛇绿岩组合包括地幔与洋壳组分。索伦山地区蛇绿岩存在较为完整的蛇绿岩组合模式，出露地幔岩石组合为蛇纹石化纯橄榄岩、蛇纹石化二辉-方辉橄榄岩、橄榄辉石岩和硅化碳酸盐化蚀变超基性岩(风化壳)等。蛇绿岩组合中洋壳组分为辉长岩、辉绿岩、玄武岩和硅质岩。蛇绿岩就位机制划分为4种，即碰撞仰冲型、增生底垫型、俯冲剥离型和角流型。其中，俯冲剥离型就位机制表现为岩石组合齐全完整的特征，产出形态为岩块、岩片，其中岩块、岩片与基质为构造断层接触；在俯冲带近大陆一侧常形成岛弧岩浆岩等特征。索伦山蛇绿岩地质特征与俯冲剥离型就位机制特征完全相符，故索伦山蛇绿岩就位机制大致为洋中脊俯冲剥离型。根据大洋岩石圈形成之后在10 Ma之内就位这一原则，结合索伦山地区辉长岩SHRIMP锆石UPb年龄为(2807±53) Ma，认为索伦山蛇绿岩就位时限在270 Ma左右。
Abstract: The ophiolites in Solonker zone, Inner Mongolia is of significance on evolution of the PaleoAsian Ocean. The ophiolites from the study area have been investigated and studied systematically on petrology. On that basis, emplacement mechanisms and timing of the Solonker zone ophiolites were discussed. Combined with analyses of the geological and tectonic characteristics of the ophiolites from Solonker,we concluded that the ophiolites consist of compositions of both mantle and oceanic crust. There are a relatively complete sequence of the ophiolite in Solonker zone.In Solonker zone, mantle rocks are composed of serpentinized dunite，serpentinized lherzolite, serpentinized harzburgite, olivine pyroxenite and silicified, carbonated metamorphic ultrabasic rock(weathering crust)and so on. Oceanic crust rocks are composed of gabbro, diabase, basalt and chert.The ophiolites occur in the form of tectonic slices and blocks. The contact relationship between the ophiolites and adjacent geological body rocks is fault contact. Based on different proeesses and characteristics,four mechanisms of ophiolite emplacement are mainly discussed:collisionobduction type, accretionunderplating type,subductionflake type, and corner flow type.Among the four mechanisms,the characteristics of subductionflake type ophiolite emplacement mechanisms are as the following: sequence in rock associations of ophiolite is complete; the ophiolites emerge in the form of tectonic slices and blocks；the contact relationship between tectonic slices,blocks and matrix is fault contact; arc magmatic rocks occur in the subducting belts next to continent and so on. Geological characteristics of the ophiolites from Solonker conform basically with the characteristics of subductionflake type ophiolite emplacement mechanisms. Emplacement mechanism of ophiolites in the Solonker zone is mainly subductionflake of midocean ridge type.Since ophiolites emplacement occur in 10 Ma after forming oceanic lithosphere and the SHRIMP UPb age dating of zircons from the gabbro of ophiolite is (2807±53) Ma, emplacement timing of