Causal Understanding Of Tangbazi Klippen Belt At Central Longmenshan Mountains-gexianshan, Pengzhou County And Its Front Accumulation

Longmenshan Mountain, showing southwest-northeast spreading along boundaryof Qinghai-Tibet Plateau and Sichuan Basin, makes the geomorphic boundary ofeastern and western China at the same time (FU Xiaofang, HOU Liwei et al.,2011).Main body of Longmenshan Mountain located within Sichuan Province, it starts fromLuding County—Tianquan County down the south, extending via BaoxingCounty—Lushan County, Tianquan County, Dujiangyan City, Pengzhou City, ShifangCity, Mianzhu City, Anxian County, Beichuan County, Jiangyou City, QingchuanCounty, and Guangyuan City to the north until Mianxian County in Shaanxi Province,totaling500kilometers in length, with its width from east to west about50kilometersto60kilometers.About30klippen with different size and scale distributed on the front range ofLongmenshan tectonic belt, most of which lies in central section ofPengxian—Guanxian area. Klippen body size varies a great difference—from tens ofsquare meters to tens of square kilometers range, with a full set of type, togethermaking it a unique landscape. A single klippe body usually appear in shape ofelongated strip, with its long axis mostly north-east directing. All these long strippedklippen one after another, together make the NE-SW directing distribution alongLongmenshan front range corridor just like a consistent beaded belt, with the directionof extension the same as several major faults of Longmenshan tectonic belt, scatteredklippen covering an area of about180square kilometers.Recent years for decades, geologists have put forwarded further studies onLongmenshan thrust nappe tectonic belt, which enables deeper understanding ofrelevant theory. As the most characterized object, the research of klippen fromLongmenshan region has always been a hot issue. For the material sources anddeformation features of Klippen belt at front Longmenshan Mountains of Tangbazi atGexianshan Mountain, Pengxian County, there have been controversial with various mixed views, dominated by two schools of thought. That some scholars hold the viewthat Tangbazi Klippen were made by napping oregeny, such as LIU Zhaochang (1986),XU Zhiqin (1992), HOU Liwei, FU Xiaofang (2002) and MA Yongwang (2003);However on the other hand, scholars such as HAN Tonglin (1999) etc. view theTangbazi klippen as moved by Quaternary Glaciation as a whole GexianshanMountain.Based upon historical research, specific field investigation and in-housecombination study has been carried out in order to learn the origin of klippen and itsfront accumulation. A further analysis has been made to Tangbazi Klippen, and also tothe composition, sedimentary feature, deformation character and the cause ofTangbazi Klippen and its front accumulation. Recognition of the cause of klippenmeans a great deal to further reveal the cause of which in central part ofLongmenshan.The author of this paper holds the view that the formation of Tangbazi Klippenof Gexianshan Mountain at Pengxian County has experienced5phases development.They are namely: the phase of stable continental margin sedimentary stage before theLate Triassic Period, the phase of Indosinian stage thrusting, the phase of Yanshanstage general uplifting, the phase of Himalayan Epoch gliding and napping, and thephase of Early Pleistocene positioning at last. It is a result of multi-stage construction,which experienced multiple pressures, and step by step, formed the way it appears bynow.A suite of pressure breccias accumulation has been identified on the front andbottom of Tangbazi Klippen. Lithology comparison and paleontology comparisonshow the consistence of both lithology and geological age with klippe body. Therefore,the formation of the found accumulation should be a tectonic body gliding from NWto SE, influenced by stress, crushed along detachment fault zone; during gravitationaleffects in after ages, gliding has been made and thus in the front range corridor ofLongmenshan Mountain such suite of tensile breccias are formed. With varying sizes,the same composition and structure with klippen body, such breccias are dominatedby angular and sub-angular texture, and can be described as gliding structure tensilebreccia. Such type of breccia indicates to some degree, as one of those symbolicfeatures to tell the structure of front range gliding of nappe structure in orogenic zone.