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

摘要/Abstract

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。

关键词: 蛇绿岩, 就位机制, 就位时限, 内蒙古索伦山

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 the ophiolites in Solonker zone is 270 Ma or so.

Key words: ophiolite, emplacement mechanism, emplacement timing, Solonker, Inner Mongolia

中图分类号:

P588.12

薛建平, 苏尚国, 李成元, 侯万荣, 董明明, 刘永新, 梁月升. 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[J]. 现代地质, 2017, 31(03): 498-507.

XUE Jianping, SU Shangguo, LI Chengyuan, HOU Wanrong, DONG Mingming, LIU Yongxin, LIANG Yuesheng. Geological Characteristics, Emplacement Mechanisms and Timing of the Ophiolites in Solonker Zone, Inner Mongolia[J]. Geoscience, 2017, 31(03): 498-507.

图/表 9

图1 标准蛇绿岩序列剖面(据王国强[24]修改)

Fig.1 Standard ophiolite sequence profile (Modified from Wang[24])

图2 蛇绿岩研究发展历史进程示意图(据MOORES[23]修改)

Fig.2 The sketch map of advances and histories of ophiolites

表1 索伦山蛇绿岩岩石组合序列对比

Table 1 The contrast of sequence in rock associations of ophiolite in Solonker zone

序列号	理想序列蛇绿岩	索伦山蛇绿岩
1	深海沉积	硅质岩
2	A枕状熔岩;2B席状岩墙	玄武岩、辉长岩、辉绿岩
3	A层状岩石;3B堆晶岩	堆晶辉长岩、辉石岩
4	上地幔构造岩-变超镁铁、镁铁质岩	蛇纹石化二辉-方辉橄榄岩、纯橄榄岩

图3 索伦山地区蛇绿岩分布图

Fig.3 The map of distribution about ophiolites in Solonker zone

图4 蛇绿岩野外宏观特征与矿物显微特征

Fig.4 The field macroscopic and mineral microscopic characteristics of the ophiolites

图5 索伦山地区局部大比例尺构造-岩性图

Fig.5 The large scale structural-lithologic map of part in Solonker zone

图6 岩性突变、存在明显的断层面的野外照片

Fig.6 Field photos of lithologic sudden shifts and obvious fault plane

图7 山前断裂、地势突变的野外照片

Fig.7 Field photo of piedmont fault and sudden topographychange

图8 蛇绿岩就位机制模型(据文献[25,27,34?-36]修改)

Fig.8 Models of ophiolite emplacement mechanisms

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