藏南地区新生代多阶段构造演化及其动力学的探讨

doi:10.13745/j.esf.sf.2019.11.29

摘要/Abstract

摘要：

开合构造是一种全球构造假说,该假说基础为地球上的一切物质和地质体都存在开合表现;可以用开合构造观解释一些板块构造理论登陆后不能合理解释的地质现象。文章在结合前人基础地质资料基础上,分析藏南地区基本的构造单元划分;强调动态构造单元划分,提出了被重力拆离断层改造叠加的逆断层区以及被拆离断层改造的正断层区。在主流观点提出碰撞挤压造山形成青藏高原时,野外科学考察发现了绒布寺伸展正断层的存在。文章认为绒布寺伸展正断层与主中央逆冲断层形成时间比藏南拆离系要早,两者构成了藏南挤出构造的两个边界;而藏南拆离系是晚期形成的,局部叠加在主中央逆冲断层之上,并且珠峰北追踪了早期绒布寺正断层呈相对高角度产出。3条断裂构造系统是不同时期、不同构造背景下的产物。藏南由前人所划分的飞来峰、构造窗等逆冲推覆构造系统中的构造单元,往往挤压逆冲特征表现不明显,却表现出由新的地层覆盖在老地层之上而显示地层柱缺失的特征。文章认为这些是滑覆构造的表现,是藏南地区晚期重力滑覆作用的产物。用开合构造理论将该地区新生代构造演化划分为由开转换为合;然后由合转换为开,构成一个完整开合演化历史,在这多阶段构造演化过程中,地球深部的热能、地球内部的重力势能以及构造引起的附加应力能起到关键作用。

关键词: 藏南, 地质结构, 新生代构造演化, 开合构造

Abstract:

Opening-closing tectonics is a hypothesis about the whole earth based on the theory that every tectonic movement on earth is opening-closing movement. It can explain some geological phenomena developing on the continents which can not be explained by plate theory. In this paper, using opening-closing theory, we analyzed the characteristics of tectonic units in South Tibet, and proposed that South Tibet can be divided into the gravitational detachment fault reformed thrust and normal faults. The field scientific investigation team found the Rongbusi normal fault when the mainstream opinion believed that the Tibetan plateau was formed by collision-compression orogenesis in 1970s. We consider that the Rongbusi normal fault and the Main Central Thrust developed before the South Tibet detachment fault, and that the former two faults are the two boundaries of the South Tibet extrusion structure. The South Tibet detachment fault partially superimposes on the Main Central Thrust and manifests high angle following the Rongbusi normal fault in the north of Chomolangma. We believe that the three fault systems developed in different tectonic backgrounds and periods. The structural units such as klippes and windows, which were identified by previous researchers in southern Tibet, belong to thrust fault system but usually have no obvious features of extrusion or thrust; however, they have the characteristics of missing strata column as younger strata overlaying on the older ones. We consider the klippes and windows the results of later gravitational decollement and having clear characteristics of extension and slippery. Based on opening-closing theory, we believe that since Cenozoic, the study area had undergone multiple developmental stages such as oceanic crust expansion (opening) and subduction (closing), continental collision (closing) and intra-continental extension (opening). Geothermal energy from deep earth, gravitational potential energy from Earth's interior, and stress energy from tectonic movements, played a key role in the multi-stage development.

Key words: South Tibet, geological structure, cenozoic tectonic evolution, opening-closing tectonics

中图分类号:

P541

刘德民, 杨巍然, 郭铁鹰. 藏南地区新生代多阶段构造演化及其动力学的探讨[J]. 地学前缘, 2020, 27(1): 194-203.

LIU Demin, YANG Weiran, GUO Tieying. Discussion on Cenozoic tectonic development and dynamics in South Tibet[J]. Earth Science Frontiers, 2020, 27(1): 194-203.

图/表 8

图1 青藏高原南部地质构造(据文献[3,4]修改) 1—全新统;2—新生界;3—古近系;4—白垩系:5—中生界;6—石炭系—二叠系(盖层3);7—前泥盆系(盖层2);8—新元古界—寒武系(盖层1);9—新元古界(盖层1);10—中元古界(基底);11—蛇绿混杂岩;12—闪长岩;13—新近纪二长花岗岩;14—新近纪花岗岩;15—古近纪花岗闪长岩;16—古近纪花岗岩;17—奥陶纪二长花岗岩;18—奥陶纪花岗岩;19—新元古代二长花岗岩;20—元古宙花岗岩;21—正断裂;22—性质不明断裂;23—走滑断裂;24—逆冲断裂;25—拆离断裂;26—受拆离断层叠加改造的正断裂;27—受拆离断层叠加改造的逆冲断裂;28—隐伏逆冲断裂;29—隐伏拆离断裂;30—冈底斯构造带;31—雅鲁藏布构造缝合带;32—特提斯喜马拉雅构造带;33—高喜马拉雅构造带;34—低喜马拉雅构造带;35—次喜马拉雅构造带;36—主边缘逆冲断层;37—主中央逆冲断层;38—藏南拆离系;39—定日岗巴逆冲断层;40—札达—邛多江逆冲断层;41—雅鲁藏布江南逆冲断层。ITSZ—雅鲁藏布江构造带;THM—特提斯喜马拉雅构造带;GHM—高喜马拉雅构造带;LHM—低喜马拉雅构造带;SHM—次喜马拉雅构造带。

Fig.1 Tectonic sketch map of southern Tibet. Modified from [3-4].

图2 藏南拆离系构造位置示意图(据文献[6]) HST—喜马拉雅底部逆冲断裂;MCT—主中央逆冲断裂;MBT—主边界逆冲断裂;MFT—主前锋逆冲断裂;STDS—藏南拆离系。

Fig.2 Tectonic sketch map of the Himalayan region, showing the location of the STD structure. Adapted from [6].

图3 喜马拉雅造山带构造剖面图(据文献[7]) MHT—主喜马拉雅冲断裂;MCT—主中央逆冲断裂;MBT—主边界逆冲断裂;MFT—主前锋逆冲断裂;IYSZ—印度—雅鲁藏布缝合带;GDS—冈底斯构造带。

Fig.3 Tectonic profile of the Himalayan orogenic belt. Adapted from [7].

图4 藏南构造演化模式图(据文献[11]) 1—北喜马拉雅穹隆; 2—特提斯沉积岩系;3—上喜马拉雅结晶岩系; 4—下喜马拉雅结晶岩系; 5—低喜马拉雅构造带; 6—西瓦利克沉积岩系; 7—中新世磨拉石; 8—冈底斯岩基; 9—蛇绿岩;YTS—雅鲁藏布缝合带;GCT—大反向逆冲断层。

Fig.4 Tectonic evolutionary pattern of South Tibet. Adapted from [11].

表1 滑覆构造与推覆构造的区别

Table 1 Discrimination of nappe and slipe tectonics

对比特征		推覆构造(飞来峰)	滑覆构造(滑来峰)
对比特征		推覆构造(飞来峰)	伸展滑覆	重力滑动
构造体制		挤压体制	伸展体制	隆起背景下的重力作用
构造体的变形	断层组合	逆断层	正断层	兼而有之,其前缘更似推覆构造,根部则具伸展构造特征
	褶皱特点	倒转-平卧背斜为主, 倒转翼变薄拉断	下翼成倒转翼保存完好
	杏仁等变形	长轴直立,短轴水平, 常成直立椭球状	与之相反,常为平躺的椭球状
	变形序列	老地层推覆于新地层之上, 常地层重复	与之相反,常地层缺失
	变形结构	水平缩短,垂向相厚	水平拉长,垂向变薄
构造面之下变形		多经受挤压缩短	伸展变形微弱	有时有明显伸展变形

图5 珠峰近景照(a)(新华社官天一摄,1974)及地质剖面示意图(b)(引自郭铁鹰1974年野簿)

Fig.5 Close photo of Chomolangma (a) and geological profile (b) of Chomolangma

图6 珠峰一带地质简图 1—冰川覆盖区;2—第四系;3—二叠系;4—泥盆系—石炭系;5—志留系—泥盆系;6—奥陶系;7—新元古界—寒武系;8—新—中元古界;9—新近纪花岗岩;10—断层/被冰雪覆盖断层。

Fig.6 Sketch map of the Chomolangma area

图7 过珠穆朗玛峰构造剖面图(a)及高喜马拉雅构造带垂向挤出的数值模拟(b)(b据文献[24]) YZZ—雅鲁藏布江缝合带;LVS—拉轨岗日构造带;STDS—藏南拆离断层;RNF—绒布寺正断层;GHM—高喜马拉雅构造带;MCT—主中央逆冲断层;MBT—主边界逆冲断层;MFT—主前锋逆冲断层。

Fig.7 (a) Cross-section of the Chomolangma area. (b) Finite element modeling of the vertical extrusion of the Higher Himalayan Zone ((b)adapted from [24])

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