西金乌兰构造混杂岩带特征

西金乌兰构造混杂岩带为西金乌兰一金沙江缝合带的西端，由于以往研究程度低而认识较为模糊。通过1：25万区调系统研究表明．混杂岩带组成复杂。由基底岩块、海滩砂岩、辉长(辉绿)岩墙群、蛇绿岩、硅质岩、灰岩(海山)、复理石和磨拉石组成。蛇绿岩环境分析表明。部分为洋中脊环境。大部分为洋岛环境。明确了西金乌兰构造混杂岩带由一系列向南俯冲的逆冲断层分隔的岩块组成。初步总结了西金乌兰蛇绿构造混杂岩带的演化过程。     

HOH XIL PIGGYBACK BASINS:IMPLICATIONS FOR PALEOGENE SHORTENING OF THE TIBETAN PLATEAU

HOH XIL PIGGYBACK BASINS:IMPLICATIONS FOR PALEOGENE SHORTENING OF THE TIBETAN PLATEAU     

乌兰布和沙漠腹地古湖存在的沙嘴证据及环境意义

通过大范围的系统野外考察发现,在乌兰布和沙漠腹地存在众多干盐湖,其周围存在不同高度的湖岸堤.其中,贺日木西尼沙嘴最为典型.该沙嘴呈NW-SE走向,海拔高度从1052 m下降至1035 m,长达11 km.是古湖泊发育和存在的重要证据和标志.通过对湖滨沉积物的OSL年代测定,该沙嘴形成于全新世的8.6-7 ka BP阶段,与中国西部许多沙漠出现的相对湿润环境状况相一致.其主要由强劲的风力作用和吉兰泰古湖沿岸流以及丰富的松散物质传输堆积而成.依据该沙嘴的海拔高程和形成年代来推测,在乌兰布和沙漠腹地曾经发育面积巨大的古湖,其范围西到吉兰泰盆地,东延河套盆地西部,形成早全新世的吉兰泰古湖.之后,受区域构造运动和干旱气候的影响,古湖水位下降,水域面积缩小,古大湖解体,导致该沙漠腹地的古湖部分水体逐渐向西退缩,形成了吉兰泰盐湖.在古湖退缩过程中,乌兰布和沙漠腹地残留众多湖泊,随着气候干旱化和蒸发作用的加剧,这些湖泊逐渐演变成盐湖.在强劲的风力驱动下,古湖周围的松散物质被侵蚀、搬运、扩散、堆积成现在的乌兰布和沙漠.     

青海可可西里东部盐湖水化学及沉积特征初步研究

2008 a夏对可可西里地区东部4个新发现的盐湖,进行了卤水水化学组分、矿物组成及其石盐元素含量分析。结果表明,该区水体卤水矿化度高,湖表卤水富硼锂等组分。通过对化学组分及水化学特征系数的研究,卤水的水化学类型主要为硫酸镁亚型和硫酸钠亚型。卤水pH值随着矿化度的增加而降低。Na+、Cl-含量与总矿化度呈正相关,SO42-"与矿化度呈负相关。Li与Mg物源、迁移规律近似。本区盐类沉积物以石盐为主,石盐中Si、Al、Fe、Sr含量低,其间相关性好,物质来源可能为周围岩石风化。布查盐湖盐类沉积存在少量硬石膏、半水石膏和铁白云石,表明布查盐湖的盐类物质来源很可能与地下热水作用有关。     

Spatial-temporal variations of lake ice phenology in the Hoh Xil region from 2000 to 2011

Lake ice phenology, i.e. the timing of freeze-up and break-up and the duration of the ice cover, is regarded as an important indicator of changes in regional climate. Based on the boundary data of lakes, some moderate-high resolution remote sensing datasets including MODIS and Landsat TM/ETM+ images and the meteorological data, the spatial-temporal variations of lake ice phenology in the Hoh Xil region during the period 2000–2011 were analyzed by using RS and GIS technology. And the factors affecting the lake ice phenology were also identified. Some conclusions can be drawn as follows. (1) The time of freeze-up start (FUS) and freeze-up end (FUE) of lake ice appeared in the late October–early November, mid-November–early December, respectively. The duration of lake ice freeze-up was about half a month. The time of break-up start (BUS) and break-up end (BUE) of lake ice were relatively dispersed, and appeared in the early February–early June, early May–early June, respectively. The average ice duration (ID) and the complete ice duration (CID) of lakes were 196 days and 181 days, respectively. (2) The phenology of lake ice in the Hoh Xil region changed dramatically in the last 10 years. Specifically, the FUS and FUE time of lake ice showed an increasingly delaying trend. In contrast, the BUS and BUE time of lake ice presented an advance. This led to the reduction of the ID and CID of lake. The average rates of ID and CID were–2.21 d/a and–1.91 d/a, respectively. (3) The variations of phenology and evolution of lake ice were a result of local and climatic factors. The temperature, lake area, salinity and shape of the shoreline were the main factors affecting the phenology of lake ice. However, the other factors such as the thermal capacity and the geological structure of lake should not be ignored as well. (4) The spatial process of lake ice freeze-up was contrary to its break-up process. The type of lake ice extending from one side of lakeshore to the opposite side was the most in the Hoh Xil region.     

可可西里盆地早渐新世雅西措群爬升沙纹层理及其沉积环境意义

可可西里盆地早渐新世雅西措群砂岩极其发育爬升沙纹层理,形成于沉积物来源供给太快太多而不能随流体一起迁移,从而产生向上的加积。雅西措群砂岩主要包括迎水坡侵蚀的A型和迎水坡沉积的B1型两种,其中,A型沙纹层理单个层系厚一般约为2cm,爬升角小于7°;B1型沙纹层单个层系厚一般为4cm,爬升角介于10o～20o之间。这两种爬升沙纹层形成于变速流、非稳定流或变速非稳定流,主要归于砂质碎屑流和底流,平均流速在11～60cm/s之间,堆积速度可以达到0.1g/cm2s,发育于浅湖环境的三角洲前缘沉积。雅西措群爬升沙纹层理发育于青藏高原的早渐新世快速隆升作用和全球变冷变干气候条件下。     

Paleoclimate Changes during the Early Oligocene in the Hoh Xil Region, Northern Tibetan Plateau

Sedimentological, cyclic-stratigraphic, paleomagnetic, and clay-mineralogical studies on the early Oligocene Yaxicuo Group in the Hoh Xil Basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan Plateau, provide abundant information of paleoclimate changes. A 350-m thick section in the middle-lower Yaxicuo Group was analyzed to reveal the climatic history that occurred in the Hoh Xil region during the early Oligocene interval 31.30-30.35 Ma, dated with the paleomagnetic chronostratigraphy. The results indicate that arid and cold climate dominated the Hoh Xil region during the early Oligocene in general, being related to the global cooling and drying events that occurred in the earliest Oligocene. Within this period, relatively warm and wet climate accompanied by strong tectonic activity occurred in the 31.05-30.75 Ma interval; while arid and cold climate and relatively inactive tectonics occurred in the 31.30-31.05 and 30.75-30.35 Ma intervals. Furthermore, spectral analyses of hig     

藏北可可西里盆地老第三纪沉积物源区分析及其高原隆升意义

可可西里盆地位于昆仑山和唐古拉山之间 ,是青藏高原腹地最大的第三纪沉积盆地 ,对于研究青藏高原早期隆升和地壳短缩过程具有重要作用 .盆地保存的始新世—渐新世早期风火山群和雅西措群主要由碎屑岩和泥岩组成 ,厚度为 5 45 2 .8m .碎屑岩的物源区分析表明 ,风火山群主要来自于南部的唐古拉造山带二叠—三叠纪地层 ,而雅西措群主要来自于南部的唐古拉、白日榨加和黑石山 -高山造山带 ,剥蚀深度加大至石炭—二叠纪地层 .它们的沉积演化过程是盆地南部造山带老第三纪构造隆升持续加强的结果 ,表明在雅西措群沉积时期青藏高原北部已经隆升至一定的高度 .     

可可西里东部地区的夷平面与火山年代

青藏高原夷平面及其年代是高原隆升、时代和幅度研究中的一个关键问题。可可西里东部地区通过1∶100000航测地形图所示的山顶面形态特征分析表明,本区广泛分布的山顶平坦地形面为青藏高原主夷平面的一部分,其海拔高度大多在4900～5200m。本区平坦顶面的熔岩方山常与夷平面交叉分布,也为高原主夷平面一部分,其同位素年代19.6～6.95MaB.P.之间的有39个(9.9～6.95MaB.P.有17个)。又据本区相邻的山间盆地内的火山地貌年龄推论,夷平面形成于9.9～6.95MaB.P.之后,3MaB.P.之前已形成     

Spatial-temporal characteristics of lake area variations in Hoh Xil region from 1970 to 2011

As one of the areas with numerous lakes on the Tibetan Plateau, the Hoh Xil region plays an extremely important role in the fragile plateau eco-environment. Based on topographic maps in the 1970s and Landsat TM/ETM+ remote sensing images in the 1990s and the period from 2000 to 2011, the data of 83 lakes with an area above 10 km² each were obtained by digitization method and artificial visual interpretation technology, and the causes for lake variations were also analyzed. Some conclusions can be drawn as follows. (1) From the 1970s to 2011, the lakes in the Hoh Xil region firstly shrank and then expanded. In particular, the area of lakes generally decreased during the 1970s–1990s. Then the lakes expanded from the 1990s to 2000 and the area was slightly higher than that in the 1970s. The area of lakes dramatically increased after 2000. (2) From 2000 to 2011, the lakes with different area ranks in the Hoh Xil region showed an overall expansion trend. Meanwhile, some regional differences were also discovered. Most of the lakes expanded and were widely distributed in the northern, central and western parts of the region. Some lakes were merged together or overflowed due to their rapid expansion. A small number of lakes with the trend of area decrease or strong fluctuation were scattered in the central and southern parts of the study area. And their variations were related to their own supply conditions or hydraulic connection with the downstream lakes or rivers. (3) The increase in precipitation was the dominant factor resulting in the expansion of lakes in the Hoh Xil region. The secondary factor was the increase in meltwater from glaciers and frozen soil due to climate warming.