青藏高原古高速远程滑坡沉积学特征研究

doi:10.13745/j.esf.sf.2020.9.12

摘要/Abstract

摘要：

高速远程滑坡运动学机理是国际工程地质领域亟待解决的重大前沿性关键科学问题。为探索高速远程滑坡的运动学机理,以青藏高原不同构造背景下的三大高速远程滑坡为研究对象,通过现场工程地质调查与分析,详细探讨了滑坡运动路径上所揭露出的各种表面与剖面沉积学特征,结果显示:(1)沿滑坡运动路径上依次可见大型堆积平台、纵向脊、横向脊、堆积丘等表面沉积学地貌的规律性分布,根据各类地貌的空间分布特征,可将滑坡区自后向前划分为源区、流通区和堆积区;(2)剖面上则可见反粒序堆积结构的展布,自上而下依次可划分为硬壳层、主体层和基底层,在硬壳层和主体层中可见层序保留、拼贴构造等低扰动性沉积学特征分布,在基底层中则可见其与下伏原沟谷堆积层强相互作用形成的底辟构造、小型褶皱等剖面沉积学特征分布。基于高速远程滑坡运动路径上各类表面和剖面沉积学地貌的空间展布特征,初步提出青藏高原关键地带高速远程滑坡的运动与停积就位机制,即滑体自源区失稳后主体表现为一种快速的低扰动性的整体性剪切运动过程,其流通区以快速拉张运动为主,堆积区则以快速推挤运动为主;当滑体下伏层中含水量较高时,伴随着滑体底部摩阻力的迅速降低,滑体表现出明显的侧限扩离运动。

关键词: 青藏高原, 高速远程滑坡, 表面沉积学地貌, 剖面沉积学特征, 运动机理

Abstract:

Rock avalanche kinematics is a forefront major challenge in the field of engineering geology globally. To explore the kinematics of rock avalanches, three typical prehistoric cases occurring on the Tibetan Plateau were investigated in this study. Detailed field surveys and analyses of their surface and internal sedimentary structures revealed the following: (1) Obvious sequential distributions of toreva blocks, longitudinal/transverse ridges, and hummocks were observed, and the rock avalanches could be divided into three zones from rear to front: the source area, transition zone, and accumulation zone, according to the spatial distribution of these landforms. (2) Inverse grading was observed in the deposits, with tree facies, carapace facies, body facies, and basal facies, divided vertically from top to bottom. In the carapace and body facies distribute retained stratigraphic sequences, jigsaw structures, etc.; in the basal facies, diapiric structures, convoluted laminations, etc. can be observed, indicating an intensive interaction between the basal facies and substrate. Based on these observations, we propose a plausible mechanism for the emplancement and accumulation of rock avalanches as follows: As avalanche mass became detached from the source area, it underwent first a rapid laminar flow-like motion, then an extensional sliding motion in the transition zone, followed by an extensional sliding motion as it arrived at the accumulation zone; and if the water content of the substrate were high, a rapid radial spreading process could occur at its frontal edge due to the rapid decrease in basal friction.

Key words: Tibetan Plateau, rock avalanche, surface sedimentary landforms, internal sedimentary structures, transport chronology

中图分类号:

P694
P642

王玉峰, 程谦恭, 林棋文, 李坤, 史安文. 青藏高原古高速远程滑坡沉积学特征研究[J]. 地学前缘, 2021, 28(2): 106-124.

WANG Yufeng, CHENG Qiangong, LIN Qiwen, LI Kun, SHI Anwen. Observations on the sedimentary structure of prehistoric rock avalanches on the Tibetan Plateau, China[J]. Earth Science Frontiers, 2021, 28(2): 106-124.

图/表 14

图1 研究区构造图(a)及滑坡点平面图(b—塔合曼滑坡;c—尼续村滑坡;d—乱石包滑坡)(据中国地势图:审图号GS(2016)1609号)

Fig.1 Geological settings of the study area (a), and plan-views of the Tagarma rock avalanche (b), the Nyixoi Chongco rock avalanche (c) and the Luanshibao rock avalanche (d). Modified after Topographic Map of China, No. GS(2016)1609.

图2 塔合曼滑坡遥感影像图(a)与堆积区统计点巨石展布玫瑰花图(b)

Fig.2 Remote sensing image of the Tagarma rock avalanche (a), and rose diagrams of the counted sites of megablocks (b)

图3 流通区大型堆积平台(a)及其内部拼贴构造(b)与右侧侧缘脊(c)展布图

Fig.3 View of the toreva block (a) with an enlarged-view of the jigsaw structure (b), and view of the right lateral levee (c)

图4 堆积区横向脊表面块石展布特征图图中红色箭头代表滑体运动方向。

Fig.4 Exhibition of megablocks deposited on the top surface of the transverse ridges

图5 滑坡运动路径上巨石的定向排列特征

Fig.5 Directional arrangement of layered masses composed of megablocks (a) versus runout (b-g)

图6 滑坡堆积剖面图(a)及下伏层堆积特征放大图(b-e) 图中红色箭头代表滑体运动方向。c-e均位于a下游侧。

Fig.6 Vertical profile of the deposit (a) with an enlarged view of the substrate (b-e)

图7 尼续村滑坡遥感影像图(a)及堆积体表面堆积脊统计柱状图(b)和玫瑰花图(c) c图中数字代表堆积脊个数,红色箭头指代滑体的主运动方向。

Fig.7 Remote sensing image of the Nyixoi Chongco rock avalanche (a), and histograms (b) and rose diagrams (c) of the counted ridges

图8 尼续村滑坡流通区大型堆积平台(a,b)和纵向脊(c)及其前缘高陡堆积斜坡(d) 图中红色箭头代表滑体运动方向。

Fig.8 The toreva blocks (a, b), and longitudinal ridges (c) featured by steep frontal accumulation slope (d) of the Nyixoi Chongco rock avalanche

图9 尼续村滑坡堆积区各亚区地貌图 a—Ⅲ-1亚区;b-c—Ⅲ-2亚区;d—Ⅲ-3亚区;e—Ⅲ-4亚区。

Fig.9 Subzone surfacial landforms of the accumulation zone of the Nyixoi Chongco rock avalanche

图10 尼续村滑坡堆积体表面巨石展布特征 a,b—巨石定向排列规律;c,d—拼贴构造。图中红色箭头代表滑体运动方向。

Fig.10 Photos of megablocks deposited on the top surface of the Nyixoi Chongco rock avalanche

图11 尼续村滑坡堆积剖面图

Fig.11 Photos showing the internal structures of the Nyixoi Chongco rock avalanche

图12 乱石包滑坡遥感影像图

Fig.12 Remote sensing image of the Luanshibao rock avalanche

图13 乱石包滑坡流通区(a,b)和堆积区(c-e)地貌展布图及巨石堆积图(f)

Fig.13 Photos showing the surficial landforms of zones Ⅱ (a,b) and Ⅲ (c-e) and deposited structures of megablocks (f) of the Luanshibao rock avalanche

图14 乱石包滑坡堆积剖面图

Fig.14 Photos showing the internal structures of the Luanshibao rock avalanche

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