GEOMORPHIC FEATURES OF THE SHULE RIVER DRAINAGE BASIN IN QILIANSHAN AND ITS INSIGHT INTO TECTONIC IMPLICATIONS

Because of the strong uplift of the Qilian Shan since late Cenozoic,the drainage basins that are derived from the mountains have undergone strong tectonic deformation.So the typical geomorphology characteristics of these drainage basins may indicate the strong tectonic movement in the region.For example,the Shule River drainage basin,which originates from the western part of the Qilian Shan owns unique geomorphology characteristics which may indicate the neotectonic movement. Stream networks of the Shule drainage basin extracted from the DEM data based on GIS spatial analysis technology are graded into five levels using Strahler classification method.Four sub-catchments,numbered 1,2,3 and 4 are chosen for detailed analysis.Furthermore,the four sub-catchments,the hypsometric integral curves,Hack profiles,SL index and average slope of the Shule drainage basin are determined by GIS tools.In addition,we analyzed the slope spectrum of the Shule drainage basin. The average elevation of the Shule drainage basin is very high,however,the slope of the drainage basin is very low,the gentle slope occupies so large area proportion that the slope spectrum shows a unimodal pattern and a peak value is in low slope region (0°~5°),so tectonic movement has a strong influence on the drainage basin.Under the intensive impact of the tectonic movement of the active fault and regional uplift,the hypsometric integral curve is sigmoid,revealing that the Shule drainage basin is in the mature stage.The Hack profile is on a convex,the longitudinal profile is best fitted by linear fitting and the abnormal data of the SL index of the Shule River has a good fit with the section through which the active fault traverses,that means the tectonic movement of the active fault has strong influence on the river's SL index.It is worth noting that lithologic factors also have great impact on the river geomorphology in some sections. According to the above analysis,we recognize that in the interior of active orogen,the evolution of river geomorphology usually is influenced by tectonic movement and reveals the regional neotectonics in turn.     

GEOMORPHIC FEATURES OF EASTERN HIMALAYAN SYNTAXIS AND ITS TECTONIC IMPLICATIONS

The eastern Himalayan syntaxis is located on the leading edge of Indian-Eurasian plate collision, and the uplift rate of Namche Barwa area is higher than that of the peripheral zones, which is considered as the core position of the eastern Himalayan syntaxis(Uplift Center).It is indicated according to the recent regional earthquake observation results that, the seismic activity is poor in the area of Namche Barwa, but with strong seismic activity in its southeast region. In order to study the current geodynamical characteristics of the eastern Himalayan syntaxis, the elevation frequency distribution and hypsometry curve of Namche Barwa area, its northwest and southeast as well as the northeast Assam area is analyzed using DEM data. It is shown according to the result that, the Namche Barwa area is in the mature stage of erosion and the regional tectonic uplift and denudation are in the highly balanced status. Influenced by plateau-climate weather effect, the denudation of this area is relatively poor, which indicates that the uplift of the Namche Barwa area is relatively slow at present. The geomorphology in the northwest and southeast as well as in northeast Assam is in young evolutionary phase, belonging to erosive infancy, and the geomorphology of northeast Assam is closer to the early stage of infancy. The geomorphic evolution stage on northwest side reflects that the regional erosion is poor and it still belongs to plateau-climate area; Influenced by south subtropical monsoons, there is rich rainfall in the area from southeast Namche Barwa to Assam area, and this area still belongs to erosive infancy, even the geomorphic development degree of northeast Assam is lower as it suffers from strong erosion effect, which means that the tectonic uplift in east Namche Barwa is very intensive, and the northeast Assam has the highest uplift rate. It is considered according to the research that, under the mode that India Plate moves towards the north at present, the core position of the eastern Himalayan syntaxis(Uplift Center)moves towards the southeast, and the new core position may be located in northeast Assam, where there is intensive regional tectonic uplift with high potential of great earthquake.     

RIVER GEOMORPHIC PARAMETERS OF THE HUASHAN PIEDMONT AND THEIR TECTONIC IMPLICATIONS

Based on DEM data and ArcGIS software, we extract the geomorphic parameters of drainage basins and rivers that flow through the Huashan piedmont, which include stream length-gradient index (SL), stream-power incision model normalized channel steepness index (k_sn), hypsometric integral (HI), valley floor width to valley height ratio (Vf)and mountain front sinuosity (Smf). Study shows that all parameter indexes have obviously different distributions roughly bounded by Huaxian and Huayin. In the Huaxian to Huayin section, the stream length-gradient index has extremely high abnormal values near the fault, the values of river mean SL, mean k_sn, HI, Vf and Smf are concentrated in 500~700, 120~140, 0.5~0.6, 0~0.1 and 1.0~1.1, respectively. Between Lantian and Huaxian and between Huayin and Lingbao, the parameter indexes distributional characteristics are largely the same, with the values in 300~500, 100~120, 0.4~0.5, 0.2~0.6 and 1.2~1.5, respectively. Comprehensive analysis suggests that tectonic activity is the primary factor responsible for these differences. We divide each geomorphic parameter into three classes (strong, medium, and low)and calculate the relative active tectonics (Iat)of the Huashan piedmont. The results show that the Iat values in Huaxian to Huayin section are in 1.0~1.5, those at other places are in 1.5~3.0, indicating that the tectonic activity from Huaxian to Huayin is most intense, while that of other places are relatively weak. Field geological investigations show that the Huashan piedmont fault can be divided into Lantian to Huaxian section, Huaxian to Huayin section and Huayin to Lingbao section. In Huaxian to Huayin section the fault has been active several times since Holocene indicative of strongest activity, while in Lantian to Huaxian section and Huayin to Lingbao section the fault was active only in the late Pleistocene and its activity was weaker as a whole. Tectonic activity of the Huashan piedmont derived from river geomorphic parameters is consistent with field geological investigations, indicating that geomorphic parameters of rivers can be used to characterize activity of faults on a regional scale.     

地貌参数指示的临潭-宕昌断裂带最新构造隆升差异与地震活动

2013年7月22日,甘肃岷县漳县MS6.6地震发生在青藏高原东北缘的临潭-宕昌断裂带上。为了研究该断裂的最新构造隆升的差异性,基于ASTER GDEM数字高程模型数据提取了流域盆地及水系,并以此为基础,计算了面积高程积分及河道坡度指数。2个地貌参数的分析结果表明,临潭-宕昌断裂不同部位的最新隆升呈现不均匀性。其中,断裂的最新逆冲活动在临潭以西及以岷县附近明显强于其他各段。上述地貌参数所指示的断裂抬升强度还与历史及现今地震发震位置较好地匹配,体现了定量化地貌分析对断裂活动强弱的指示作用。临潭-宕昌断裂受区域NE-SW向挤压构造应力作用影响,其活动的差异可能与晚第四纪以来巴颜喀拉块体NE向扩展背景下的局部应力集中有关。     

祁连山西段玉门断裂晚第四纪活动特征及相关问题的讨论

新的证据显示,位于祁连山西段酒西盆地南部的玉门断裂的最新活动时代为晚更新世末,并兼有一定的走滑分量.这一结果表明,酒西盆地块体周边断裂的活动具有同时性的特点,酒西盆地块体可能发生过顺时针旋转.     

THE LATE QUATERNARY TECTONIC DEFORMATION REVEALED BY THE TERRACES ON THE BAIYANG RIVER IN THE NORTHERN QILIAN MOUNTAINS

The Qilian Mountains, as a major orogenic belt in the northeastern margin of the Tibetan plateau, is the forefront of the expansion of the plateau to the northeast, where thrusts and folds dominate tectonic deformation. The Baiyang River starts from the inner Qilian Mountains, flowing northward across various structures, and finally into the Jiuxi Basin. This work focused on exhaustive investigations to the terraces on this river to characterize the Late Quaternary tectonic deformation in this region. The results show that (1)these river terraces on the Baiyang River are segmented, of which multiple levels developed at steep terrains and anticlines in the basin. Bounded by the Niutou Mountains, mainly 2-3 and 4-5 levels of terraces formed in the upper and lower reaches, respectively. (2)The longitudinal profiles along the river suggest a vertical motion rate of the Changma fault as (0.32±0.09)mm/a and crustal shortening rate (0.12±0.09)mm/a. There was no vertical activity since the formation of T₅ surface (13ka)on the Hanxia-Dahuanggou fault. At the terrace T₅ (9ka)on the Laojunmiao anticline, fold uplift amounts (6.55±0.5)m and shortening amounts (3.47±0.5)m, yielding uplift and shortening rates (1.23±0.81)mm/a and (0.67±0.44)mm/a, respectively. The Baiyang River anticline began to be active about 300ka with uplift and shortening rates (0.21±0.02)mm/a and (0.14±0.03)mm/a, respectively since 170ka. (3)In the Qilian Mountains, there were two different deformation characteristics in response to the expansion of the Tibetan plateau. Shear deformation dominates the inner Qilian Mountains, which is manifested as lateral extrusion of blocks. In the northern margin of Qilian Mountains and Jiuxi Basin, the deformation is dominated by compression, expressing crustal shortening and uplift, and the shortening within the basin accounts about half of the total deformation.     

GEOLOGICAL AND GEOMORPHIC EVIDENCE FOR DEXTRAL STRIKE SLIP OF THE HELAN SHAN WEST-PIEDMONT FAULT AND ITS TECTONIC IMPLICATIONS

The horizontal movement of the Helan Shan west-piedmont fault is important to determination of the present-day boundary between the Alashan and North China blocks as well as to the exploration of the extent of the northeastward expansion of the Tibetan plateau. Field geological surveys found that this fault cuts the west wing of the Neogene anticline, which right-laterally offset the geological boundary between Ganhegou and Qingshuiying Formations with displacement over 800m. The secondary tensional joints (fissures)intersected with the main faults developed on the Quaternary flood high platform near the fault, of which the acute angles indicate its dextral strike slip. The normal faults developed at the southern end of the Helan Shan west-piedmont fault show that the west wall of this fault moves northward, and the tensional adjustment zone formed at the end of the strike slip fault, which reflects that the horizontal movement of the main fault is dextral strike slip. The dextral dislocation occurred in the gully across the fault during different periods. Therefore, the Helan Shan west-piedmont fault is a dextral strike slip fault rather than a sinistral strike slip fault as previous work suggested. The relationship between the faulting and deformation of Cenozoic strata demonstrates that there were two stages of tectonic deformation near the Helan Shan west-piedmont fault since the late Cenozoic, namely early folding and late faulting. These two tectonic deformations are the result of the northeastward thrust on the Alashan block by the Tibet Plateau. The influence range of Tibetan plateau expansion has arrived in the Helan Shan west-piedmont area in the late Pliocene leading to the dextral strike slip of this fault as well as formation of the current boundary between the Alashan and North China blocks, which is also the youngest front of the Tibetan plateau.     

GEOMORPHOLOGY OF THE GYARING CO FAULT ZONAL DRAINAGE SYSTEM AND ITS STRUCTURAL IMPLICATIONS

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau. The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau. The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone. The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co. From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin. Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics. In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement. In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images (Landsat and GeoEye) and field work. We acquired basic geomorphic parameters of 153 sub-basin (such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve. Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault. Southern drainage basins' relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity. Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east. By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins. Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift. The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.     

滇西地区地壳速度结构及其构造意义

使用2011年8月至2012年8月在南北地震带南段布设的密集流动地震台站记录的波形数据,采用绝对定位方法对滇西地区的1593个地震进行了初步定位,应用近震走时层析成像方法获得了滇西地区三维地壳P波速度结构。研究结果表明,攀枝花附近的高速异常从地表可一直延伸至中地壳,并在中下地壳深度与滇西北地区的高速异常形成大范围的高速块体。这一高速异常体对青藏高原物质向南逃逸起到一定的阻挡作用,可能是导致川滇活动块体北部次级块体快速抬升的重要因素。位于印度板块与欧亚板块俯冲边界的腾冲、保山地块在下地壳表现为明显的大范围低速异常,推测该低速异常与印度板块东向俯冲引起的地幔热物质上涌有关。金沙江-红河断裂带是川滇块体重要的南部边界,红河断裂带中段的弥渡至红河一带具有高速的地壳结构以及较弱的地震活动性,可能表明该区现阶段处于闭锁状态,是未来需要重点监测的地段之一。     

渭河流域河流下切速率及其构造意义

基于河流阶地高度和阶地形成年代数据,通过二者的线性拟合方法得到了渭河不同河段及其支流的下切速率,结果表明河流在陇西盆地的下切速率明显高于渭河盆地,可能反应了西秦岭北麓构造活动西高东低的特点。     

牛首山-罗山断裂带的变形特征及其构造意义

牛首山-罗山断裂带是青藏高原东北缘最外侧的一条断裂带,其空间分布、深部结构、运动学特征以及变形机制对研究青藏高原东北角弧形断裂系的形成与演化具有重要意义。文中通过对横穿牛首山-罗山的4条地震反射剖面的解释及断裂带部分地区大比例尺的构造地质填图,发现牛首山-罗山断裂带具有不连续性与分段性。断裂带南段罗山断裂以正花状构造为特征,显示断裂具有右旋走滑性质;中段牛首山东麓断裂可能并不存在,该区以强烈的褶皱变形为特征;北段三关口断裂则以左旋走滑为特征。牛首山-罗山断裂带的这种不连续性和分段性反映了断裂带的不同构造部位在青藏高原向NE方向扩展过程中具有不同的变形样式。     

祁连山东段石羊河流域河流纵剖面及其构造意义

石羊河流域位于祁连山东段,其河流体系记录了最新的构造信息和构造活动。提取石羊河流域的地貌信息,有助于揭示祁连山东段石羊河流域地貌对构造活动的响应,及系统探讨该区地貌发育特征及其所蕴含的构造意义。文中基于GIS空间分析技术,利用数字高程模型(DEM)、Matlab脚本提取了石羊河流域7条河流的纵剖面,并利用基岩河道水力侵蚀模型对其进行分析,获得了7条河流的陡峭系数、平均侵蚀量、凹曲度、裂点分布、高程、距河流出水口距离和流域面积等地貌信息。结果表明,石羊河流域的各条支流至少存在1个主裂点,裂点上、下河段具有不同的陡峭度(ks)与凹曲度(θ),说明河流纵剖面裂点的上、下河段具有不同的发育趋势。对河流纵剖面、裂点分布及岩性进行综合分析,结果表明,古浪河、金塔河、杂木河、西营河、东大河和西大河都具有"坡折式"裂点,处于瞬时状态。祁连山东段河流地貌演化主要与构造活动相关。利用本区晚第四纪活动断裂相关裂点上游河道的凹曲度指标拟合出整条河流,得到石羊河流域的平均侵蚀量约488m,发源于古浪推覆体的6条支流的平均侵蚀量为508. 5m。进一步计算研究区河网归一化的河流陡峭系数(ksn)并得到其空间分布,结合河流纵剖面和裂点分析结果对祁连山东段石羊河流域的构造特征进行了综合分析,ksn的结果显示下游段陡峭系数<60,中游明显大于下游。同时,位于构造结处的古浪推覆体其ksn值呈现高值,表明该区第四纪以来经历了明显的构造抬升过程。文中结果表明石羊河流域地貌演变处于非均衡状态,构造变形是祁连山东段地貌演化的主要影响因素,控制着该区现今的地貌发育及演化历史。     

河西走廊和阿拉善东缘地区中寒武世古地磁研究的初步结果

用可西走廊和阿拉善地体东缘中寒武世15个采点107块定向岩芯样品,进行岩石磁学实验和古地磁学研究,结果表明,所采样品以磁铁矿为主要载磁矿物,高温特征分量B4组分在95%置信水平下通过了褶皱检验,其构造校正后的方向明显区别于华北地块及河西走廊和阿拉善地区志留纪以来的特征剩磁方向.这一组分对应的古地磁极位置(349.9°E,21.1°N,95%置信圆锥半顶角A95为14.9°)与华北地块同时期的极位置相近,表明河西走廊和阿拉善地体与华北地块主体之间,在中寒武世之后未发生明显的纬向相对运动;但在中寒武世-奥陶纪期间,河西走廊和阿拉善地体相对于华北地块主体仍可能发生15°左右的逆时针旋转.这一旋转作用可能代表了河西走廊和阿拉善地体与华北地块主体的增生过程,最终在晚寒武世形成统一的华北地块.     

河西走廊和阿拉善东缘地区中寒武世古地磁研究的初步结果

用河西走廊和阿拉善地体东缘中寒武世１５个采点１０７块定向岩芯样品,进行岩石 磁学实验和古地磁学研究,结果表明,所采样品以磁铁矿为主要载磁矿物,高温特征分量Ｂ４组 分在９５％置信水平下通过了褶皱检验,其构造校正后的方向明显区别于华北地块及河西走廊 和阿拉善地区志留纪以来的特征剩磁方向．这一组分对应的古地磁极位置(３４９．９°Ｅ,２１．１°Ｎ, ９５％置信圆锥半顶角Ａ_(９５)为１４．９°)与华北地块同时期的极位置相近;表明河西走廊和阿拉善 地体与华北地块主体之间,在中寒武世之后未发生明显的纬向相对运动;但在中寒武世－奥陶 纪期间,河西走廊和阿拉善地体相对于华北地块主体仍可能发生１５°左右的逆时针旋转．这 一旋转作用可能代表了河西走廊和阿拉善地体与华北地块主体的增生过程,最终在晚寒武世 形成统一的华北地块。     

阿尔金断裂带西段莫勒切河河口阶地的构造及气候意义

通过对阿尔金断裂带西段莫勒切河河口附近卫星影像解译、野外调查测量及地貌面样品年龄测定,利用宽谷阶地、堆积阶地获取构造隆升速率、构造变形方式及加积速率,并结合区域气候资料探讨该区阶地发育对气候变化的响应.莫勒切河出山口发育4级阶地(T<‘4>,T<‘3>,T<‘2>,T<‘1>),其中T<‘4>、T<‘3>为宽谷阶地,T...     

CRUSTAL ANISOTROPY AND ITS TECTONIC IMPLICATIONS IN THE CHONGQING REGION

The receiver function which carries the information of crustal materials is often used to study the shear-wave velocity of the crust as well as the crustal anisotropy. However, because of the low signal-to-noise ratio in Pms(P-to-S converted phase from the Moho), the crustal anisotropy obtained by shear-wave splitting technique for a single receiver function usually has large errors in general. Recent advance in the analysis method based on Pms arrival time varying with the back-azimuth change can effectively overcome the above defects. Thus in this paper, we utilize the azimuth variations of the Pms to study the crustal anisotropy in Chongqing region for the first time. According to the earthquake catalogue provided by USGS, seismic waveform of earthquakes with magnitude larger than 5.5 and epicenter distance range of 30°~90° between January 2015 and December 2016 are collected from 14 broadband seismic stations of Chongqing seismic network. We carry out the bootstrap resampling to test the reliability of the radial maximum energy method for the observation data. In addition, we also applied the receiver function H-Kappa analysis in this paper to study the crustal thickness and Poisson's ratio. Our results show the crustal thickness ranges from 40~50km, and there is a thin and thick crust in the southern and northern Chongqing, respectively. The crustal average Poisson's ratio ranges from 0.23~0.31, the Poisson's ratio reaches the maximum value in the central part of Chongqing, while the Poisson's ratio in the northern and southern parts of Chongqing is obviously low. We obtain the crustal anisotropy from 9 stations in total. The delay time of crustal anisotropy distributes between 0.08s and 0.48s, with the average value of 0.22s. Among them, the CHS, QIJ and WAZ stations in central Chongqing have relatively large crustal delay time(>0.3s), followed by ROC station in the western Chongqing(0.25s), while the delay time in CHK station in northern Chongqing and WAS station in southern Chongqing are 0.08s, showing relatively weak crustal anisotropy. The fast polarization directions(FPDs)also change obviously from south to north. In southern Chongqing, FPDs are dominant in NNE-SSW and NEE-SWW, while the FPDs in WAZ station change to NWW-SEE, and the FPDs appear to be NW-SE in CHK in the northern Chongqing. In general, the FPDs are sub-parallel to the strikes of faults in most areas of Chongqing areas. Combined with other results from GPS observations, tectonic stress field and XKS splitting measurements, the main conclusions can be suggested as following:The cracks preferred orientation in the upper crust is not the main source of crustal anisotropy in Chongqing area. The crust and lithospheric upper mantle in the eastern Sichuan fold belt(ESFB)and Sichuan-Guizhou fault fold belt(SGFFB)are decoupled, and the deformation characteristics in the north and south parts of ESFB and SGFFB is different. The complex tectonic deformation may exist beneath the mountain-basin boundary, causing the fast directions of crustal anisotropy different from that in other areas of ESFB and SGFFB. The faults with different strikes may weaken the strength of average crustal anisotropy in some areas. The crustal deformation in southern Dabashan nappe belt(DNB)may be mainly controlled by the fault structure.     

西太平洋俯冲带的研究及其动力学意义

讨论了西太平洋俯冲带的分布及特征、西太平洋Ｗａｄａｔｉ－Ｂｅｎｉｏｆｆ带的形态及俯冲带上的应力状态及太平洋板块、菲律宾海板块与欧亚板块之间的相互作用；总结了地震层析成像结果；计算了俯冲板块在地幔中引起的Ｐ波速度异常，提出了俯冲板块与６６０ｋｍ间断面相互作用的４种可能；研究了俯冲板块物理性质的变化、俯冲板块产生的负浮力及其影响因素；提出需要开展俯冲带对东亚大陆构造运动和演化的影响、俯冲带相互关系及演化的研究．     

西太平洋俯冲带的研究及其动力学意义

讨论了西太平洋俯冲带的分布及特征、西太平洋Ｗａｄａｔｉ－Ｂｅｎｉｏｆｆ带的形态及俯冲带上的应力状态及太平洋板块、菲律宾海板块与欧亚板块之间的相互作用;总结了地震层析成像结果;计算了俯冲板块在地幔中引起的Ｐ波速度异常,提出了俯冲板块与６６０ｋｍ间断面相互作用的４种可能;研究了俯冲板块物理性质的变化、俯冲板块产生的负浮力及其影响因素;提出需要开展俯冲带对东亚大陆构造运动和演化的影响、俯冲带相互关系及演化的研究．     

滇西地区及邻区构造单元划分及其特征

依据板块构造学说划分大地构造单元的原则和构造亲缘关系,将滇西及邻区划分为８个一级构造单元Ｉ印度板块、Ⅱ冈底斯中间板块、Ⅲ拉萨地块、Ⅳ顷甸板块、Ⅴ滇顷泰板块Ⅵ印度板块、Ⅶ杨子板块、Ⅷ松潘一甘孜活动带。并且对其主要构造单元的地质特征进行阐述。