The Uplift In The Northeastern Margin Of The BaYan Har Block Since The Quaternary

Since Cenozoic, the Tibetan Plateau has risen in the Asian continent and become the world’smost magnificent plateau. With a significant impact on the formation of monsoon climate and theforepassed global change, its uplift is the primary cause for global cooling, northern hemisphereice changes and Asian monsoon formation in the late Cenozoic. Thus, the deformation of TibetanPlateau has become a focused topic of international geology, with debates on the timing,magnitude, forms, mechanisms, evolution process of the deformation and environmental effects.Being a secondary terrane, the Bayan Har block belongs to the northeast of Qinghai-Tibetsubplate, adjoining the Qinling-Qilian-Kulun block in north，Tangula block in south and Yangtzeblock in east. The northeast part of the Bayan Har block (hereinafter referred to as the study area)lies in the transition zone of three large blocks, located in the area of the Tibetan Plateau whichwas intensively uplift and outward extended, as an active area of new tectonic movement andstrong earthquake regions in China. The research of uplift amount of the study area since theQuaternary time helps to understand the mechanism of uplift in Quaternary and the uplift processand deformation mechanisms in the Tibetan Plateau, playing a great role in earthquake preventionand disaster mitigation.Since Quaternary, under the action of diverse internal and external forces, a variety oflandforms have been formed on the earth’s surface. These geomorphic types include a certainsense of layered landform caused by earth crust uplift. If there are a series of layered landforms inthe study area, the research can recognize the formation process of the landscape in this area,which would reflect the amount of surface uplift (hereinafter referred to as uplift amount).Geomorphic surface is divided into many kinds, such as planation surface, terrace, etc. related totectonic setting, which are deeply researched. In long-time uplift movement areas, the river is oneof the main geologic forces transforming the surface appearance and the river terrace is the maintype of quaternary geomorphologic in mountains. There are two main rivers in the study area, theYangtze and Yellow river systems, forming multistage terraces under the effects of tectonics andclimate. These planation surfaces and terraces are the main objects of this thesis. Their spaceparameters (height), reflecting the uplift amount of the study area, are the main basic data in theresearch process.From14C, ESR, and OSL chronology of gravel beds，DGPS measurements, DEM spatialanalys is and other technical means, this work includes block division, access to uplift amountmethod, sedimentary characteristics, space parameters and formation age of the landscape:(1) Thestudy area is divided into different activity blocks, each block shows the characteristics ofactivities different from others since the Cenozoic.(2) Using DGPS methods, combined with thehigh resolution image data, a study method is proposed to acquire the layered landscape spaceparameters. This method not only effectively saves the wild field work time, but also meets theprecision requirement and increases the work efficiency.(3) The difference capacity of uplift sinceQuaternary is obtained by comparative analysis of the standard layered landscape profile indifferent blocks by the method presented in(2).Combined with dating data and strata, uplift ratesof different blocks are discussed.(4) Discuss how the eastward movement of the Bayan Har blockconstrains the uplift process and deformation distribution of the northeast edge.The major research results of this thesis are presented below.（1）Division of activity block According to the division method of the active blocks, for example, using regional tectonicenvironment to identify the boundary zone of the exposed position of faults; using the regionalgeophysical field and crust structure characteristics to analyze the deep geophysical fieldparameters of the boundary faults zone, and then its deep structure; based on the distribution,mechanic characteristics of earthquakes, the nature and intensity of the fault activity wereresearched. GPS data were combined with the fault slip rates to determine the active fault zone.Based on these results, the study area was divided into four primary blocks and three secondaryblocks. The four primary level blocks include the Bayan Har strong uplift, the Longmenshan faultuplift, Sichuan weak uplift and Qinling fault uplift; The three secondary fault blocks are the Zoigestrong uplift, and the Minshan break, the Bikou transition zone.(2) Acquisition of space parameters of layered landformIn recent years, with the development of quantitative neotectonics, qualitative orquantitative research has been required to evaluate faulting, folding activities, vertical upliftmovement in neotectonics period, and so on. In order to solve these problems, some new methodsand means are tried and applied. Based on application examples, the system of layered landformdata acquisition method is proposed. A research method was proposed to apply the DGPS method,DGPS and SPOT-5across-track stereo images to obtain layered landform data and discuss thelayered geomorphic surfaces morphology on the large scale DEM section and geomorphicsignificance in the gridding DEM profile. In uniform uplift areas inside the block, firstlytraditional measurement methods were used to get space parameters of layered landform in mainterrace and analysis made to the space parameters of the typical layered landform. Secondly, basedon DEM data, this work analyzed planation surface and denudation surface level, distributionrange and elevation data， perfects space parameters of layered landform by contrasting,complementing and validation. In evident differential movement areas, the secondary units werefirstly divided by differential movement, and then the units were measured and analyzedaccording to the methods above.（3）Uplift amount of layered landform in each block in thestudy areaDistribution and characteristics of layered landform (including the cause, type, distribution,structure, series, and the late tectonic deformation, etc.) in the Tibetan Plateau edge are one of themain problems. Based on field investigation and measurements on distribution and characteristicsof layered landform, including the area of Heihe river, Baihe river, belonging to the Yellow Rivertributaries, and Bailong river, Minjiang river, FuJiang river, belonging to the Yangtze rivertributaries, combining DEM data, space parameters of layered landform in the study area wereobtained and the uplift amount was established in different blocks since the Quaternary. The Zoigestrong uplift can be subdivided into8level layered landforms and the planation surface shows anuplift amount of1400~1650m; Minshan fault uplift12level layered landforms, with the upliftamount of1700~1900m showed by the planation surface; Bikou transition zone11level layeredlandforms, with the uplift amount of1350m.（4）Uplift rateof layered landform in each block in thestudy areaLack of accurate dating and profile of dating data is another main problem. By collectingdating data of layered landform in the study area, combined with sedimentary characteristicsanalys is and correlation of strata, the formation time of all level layered landform was discussed.Based on the space parameters of layered landform in different blocks gained in (3), relevantlayered landform scales were built for different blocks and the uplift rates were discussed. The Zoige strong uplift, Minshan fault uplift and Bikou transition zone have strongly risen since theTibetan movement. Multilevel planation surfaces and terraces have been formed. The three blocksrose at different rates, the Minshan fault block uplifts at the largest rate, followed by the Zoigestrong uplift, with Bikou transition zone the slowest. The differential uplift has continued topresent day.（5）TheBayan Har block eastward migration impact on northeast edgeThe Bayan Har block borders the eastern part of the Kunlun fault zone to the north, theLongmenshan fault zone and the South China block to the east. The west Gansu block, borderingthe Kunlun Mountains to the north, and its frontal arc beam area began to react and graduallyuplifted at the end of the Tibetan movement. The movement accelerated at the end of Kunhuangmovement, with a rate lower than that of the Zoige strong uplift, Minshan fault lung and Bikoutransition area, equal to or higher than the rate of the latter three blocks uplift after GongheMovement. During the period of Tibetan movement, the Sichuan basin, bordering Longmenshanto the west, presented foreland deposition as a result of an obvious uplift movement. SinceGonghe movement, the Sichuan basin has rapidly uplifted. Bounded by the East Kunlun fault zoneand Longmenshan fault zone, the blocks on both sides uplifted differently, with the differenceabsorbed by faults. The study indicates that the movement shows a feature of the escape modeland block uplift model.（6）Since the Gonghe movement, accelerating uplift processes converge on differentblocks that have bigger differences from early. So this study speculated that the active rate of thisphase didn’t reflect the activities of the previous rate. If this speculation is correct, today’s motionstate of the Tibetan Plateau reflected by GPS also cannot be simply extended to the Tibetanmovement period, and even the Gonghe movement period.