Geological Characteristics, Emplacement Mechanisms and Timing of the Ophiolites in Solonker Zone, Inner Mongolia

Abstract

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

CLC Number:

P588.12

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.

Figures/Tables 9

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

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

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

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

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

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

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

Fig.7 Field photo of piedmont fault and sudden topographychange

Fig.8 Models of ophiolite emplacement mechanisms

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