雅鲁藏布江中游全新世溃决洪水滞留沉积物粒度及微观结构特征分析  

GRAIN SIZE AND MICROSTRUCTURE CHARACTERISTICS OF HOLOCENE MEGAFLOOD SLACK WATER DEPOSITS IN THE MIDDLE REACHES OF THE YARLUNG TSANGPO RIVER

作　　者：徐博 王萍[1] 王慧颖 郭桥桥 石灵璠 石宇翔 XU Bo;WANG Ping;WANG Hui-ying;GUO Qiao-qiao;SHI Ling-fan;SHI Yu-xiang(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]成都理工大学,地球科学学院,成都610059

出　　处：《地震地质》2023年第2期305-320,共16页Seismology and Geology

基　　金：中国地震局地质研究所西藏拉萨地球物理国家野外科学观测研究站研究课题(NORSLS20-06);地震动力学国家重点实验室自主研究课题(LED2021A04);国家自然科学基金(42072214)共同资助。

摘　　要：青藏高原东南部的河谷中广泛分布堰塞湖、溃决洪水和风成沙等不同类型的沉积物,利用粒度和形貌指标识别沉积物类型的相关研究还处于探索阶段。为了解洪水沉积物的粒度特征、空间分异规律及颗粒表面的微形貌特征,我们在雅鲁藏布江中游加查峡谷出口—派镇长约350km范围内的全新世早期溃决洪水滞留沉积物中采集了33个样品,利用Malvern 3000型激光衍射粒度仪、 Zeiss Signma扫描电子显微镜进行测试,结合数字地貌(DEM)数据提取的河道宽度、陡峭系数,对粒度特征的空间分布规律进行分析,取得以下认识:溃决洪水滞留沉积粒度的总体特征为细—粉砂(2.57~5.18Φ),分选较差,呈正偏、窄峰态;通过端元建模得出2个端元模型:EM1端元可能代表高山峡谷区溃决洪水能量较高的冲积特征,EM2端元可用来指示溃决洪水滞留沉积的堆积过程。溃决洪水滞留沉积的石英颗粒表面的微观结构特征以机械成因的擦痕、贝壳状断口、上翻解理及解理台阶为主,化学成因的溶蚀孔洞较为少见。作为半湿润季风区河谷地带爬坡沙丘的典型代表,位于下游河段的丹娘佛掌沙丘与已知溃决洪水滞留沉积的粒度特征及石英颗粒表面的微形貌特征相似,我们认为佛掌沙丘的沙源主要来自溃决洪水沉积。The terrain in southeastern Tibet is steep and the valleys are crisscrossed.Since the Quaternary,glacial ice and debris have blocked the course of the Yarlung Tsangpo River and its tributary river valleys to form giant dammed lakes,and the huge flood deposits formed by the dammed lake outburst floods are often associated with moraines,ice water deposits,lacustrine deposits,aeolian sand or other running water sediments to form complex river valley accumulation landforms.Different types of sediments in alpine and canyon areas are similar in morphology,structure and fabric,and are difficult to distinguish.Grain size and morphological characteristics are the most important structural characteristics of sediment,and the distribution rules are controlled by many factors such as sedimentary environment,physical properties of detrital material,transporting medium and transporting mode,etc.,which is an important proxy index for restoring paleoclimate and inverting paleoenvironment.However,the relevant research on identifying sediment types in alpine valley area of southeast Tibet by grain size and morphology index is still in the exploratory stage.In order to understand the particle size characteristics and spatial differentiation laws of outburst flood sediments and the micromorphological characteristics of particle surfaces,we collected 33 samples of Holocene flood retention sediments preserved along the river within about 350km from the outlet of the Jiacha Gorge in the middle reaches of the Yarlung Tsangpo River to Pai Town,and measured them with Malvern 3000 laser diffraction particle size meter and Zeiss Signma scanning electron microscope,combined with digital geomorphology(DEM)data extracted river channel width and steepness coefficient.The features of spatial distribution law of particle size are analyzed,and the following understanding is obtained.The particle size of outburst flood retention deposits is characterized on the whole by fine-silty sand(2.57~5.18Φ)with poor sorting,positive skew and narrow peak sta

关 键 词：雅鲁藏布江 全新世溃决洪水 粒度特征 端元模拟 扫描电镜(SEM)微观结构 

分 类 号：P512[天文地球—地质学]