Node Document

阿拉善沙漠风积砂重矿物组成及物源分析

Heavy Mineral Assemblages and Provenance Analysis of Eolian Sand in the Alashan Desert, Northwestern China

To avoid encountering 504 error when downloading big files,please take CAJ download or PDF download by chapter as your first priority.

【Author in Chinese】 张诚

【Supervisor】 李卓仑

【Author's Information】 兰州大学, 地理学·地球系统科学, 2020, 硕士

【Abstract in Chinese】 中国北方沙漠位于中纬度干旱区,作为北半球沙尘的主要源区,在地球表生作用过程中起到重要作用,确定风成沉积物来源对研究地球系统的沉积旋回是至关重要的。此外,风成沉积物是风沙地貌形成和发育的物质基础,其特征记录了沙漠形成和发育过程中的重要信息,确定沙漠的物质来源对于沙漠化防治和生态保护具有重要意义。阿拉善沙漠是中国北方沙漠的重要组成部分,该地区具有剧烈的风沙活动,是典型干旱区沙漠的代表,沙漠内部沉积环境和地貌类型极其复杂,沉积物类型多样。此外,阿拉善沙漠周围分布着大量的基岩山地、戈壁和河湖相沉积物,同时,沉积物受到流水和风力两种搬运作用的双重影响。因此阿拉善沙漠的物源非常复杂,导致了其物源到目前为止还没有统一的认识。研究其风积砂的来源和传输过程,不仅可以为区域和全球土地沙漠化与风沙地貌的形成过程提供进一步的认识和理解,而且对土地沙漠化控制与防沙治沙有重要的指导意义,还可以为地表各圈层的相互作用过程和机制提供新证据。本研究采集阿拉善沙漠风积砂、沙漠内部古湖相沉积物、沙漠外围戈壁与基岩风化碎屑样品以及沙漠周围河流沉积物样品共433个,通过鉴定重矿物类型、统计重矿物特征指数并结合风向数据与区域地质背景,对阿拉善沙漠风积砂的物源进行了研究。结果显示:(1)阿拉善沙漠风积砂样品的重矿物类型主要有不透明矿物、石榴石、角闪石、锆石、电气石、金红石、白钛石、磷灰石、辉石、绿帘石、榍石和独居石。不同的沙漠以及同一沙漠不同的位置重矿物的相对含量不同。稳定重矿物相对含量整体上从沙漠外围向腹地逐渐增加,弱稳定性重矿物具有相反的变化趋势,但是不同的沙漠其空间变化存在差异。并且风积砂的重矿物组成与沙漠周围基岩、沙漠外围荒漠、河湖相沉积物的重矿物组成具有很强的相似性。(2)ZTR指数(锆石-电气石-金红石指数)与稳定系数在不同的沙漠具有不同的变化规律。巴丹吉林沙漠风积砂的稳定系数与ZTR指数的空间变率相对较小,整体上呈现出从沙漠西北向沙漠东南逐渐增加的趋势,但是在沙漠西南部与沙漠南部靠近基岩及沙漠北部靠近戈壁的沙漠区域,稳定系数均具减小的趋势。腾格里沙漠风积砂稳定系数和ZTR指数的空间变率很小,呈现出从沙漠西北向沙漠东南逐渐增加的特点,沙漠西南部的稳定系数和ZTR指数比沙漠东北部的大,在沙漠东部靠近贺兰山与沙漠南部荒漠的地方,二者呈现出低值区。乌兰布和沙漠风积砂的ZTR指数与稳定系数从沙漠周边向沙漠腹地逐渐增大,但不同区域的空间变率存在差异。(3)阿拉善沙漠风积砂的GZi指数(石榴石-锆石比值)都很高,巴丹吉林沙漠风积砂与腾格里沙漠风积砂的GZi指数在沙漠范围内变化不大,但是乌兰布和沙漠风积砂的GZi指数由西北部和西部向东部逐渐减小和局部高值的分布特征。三个沙漠风积砂的ATi指数(磷灰石-锆石比值)都在沙漠边缘增大,沙漠腹地减小,表明沙漠边缘风积砂的风化程度较低,越深入腹地,风积砂风化程度越高。通过对上述结果系统和详细的分析,得出了以下结论:(1)阿拉善沙漠丰富的重矿物组成表明风积砂的物源不唯一。巴丹吉林沙漠风积砂的物源主要包括西部与西北方向的基岩、荒漠和河湖相沉积物,东南部基岩贡献较小;腾格里沙漠的风积砂主要来源于西部-北部-东北沿线的基岩与荒漠、巴丹吉林沙漠的流沙以及沙漠内部的古湖相沉积物,而南部的荒漠则对风积砂贡献微弱;乌兰布和沙漠的风积砂主要来源于沙漠西部与西北的基岩和荒漠及沙漠内部的古湖相沉积物,东部黄河河相沉积和南部贺兰山基岩对其贡献较小。(2)通过对比分析发现沙漠周围的基岩和河湖相沉积物、沙漠外围的荒漠、沙漠内部的古湖相沉积物都是风积砂的重要物源,但是上述源区分布在沙漠不同的位置,使不同的物源对风积砂的贡献存在差异。(3)阿拉善沙漠风积砂特征指数的分布表明,三个沙漠风积砂受到的搬运距离均相对较短,物源主要以近源物质为主。此外,风积砂物源除了具有来自沙漠周围近距离荒漠和基岩等物源外,还有可能富含石榴石母岩的共同的源区。

【Abstract】 Deserts in northern China are located in the mid-latitude arid region and play an important role in shaping terrestrial hypergene processes.Furthermore,these deserts are the main source of dust in eastern Asia and even throughout the Northern Hemisphere.Therefore,accurate identification of the provenance of eolian sand in deserts is essential to studying sedimentation processes in the earth system.Eolian sediment is the material basis for the formation and development of aeolian geomorphology.Its characteristics record significant information in the formation and development of the desert.Thus,determination of the sedimentary environment and material provenances of the desert have great significance for desertification control and ecological construction.The Alashan Desert is an important part of the deserts of northern China with strong sandstorm activity.It is the representative of the typical arid desert with various landforms inside the desert and the sedimentary environment and sediment types is complex and varied.In addition,the Alashan Desert is surrounded by bedrocks,wilderness,fluvial sediment and lacustrine sediment and affected by both fluvial and eolian effects,which leads to quite complex provenances of the Alashan Desert and no unified understanding.Studies of the provenance and transportation processes of eolian sand can not only provide further understanding for the regional and global land desertification and the formation of aolian geomorphology,but also have important guiding significance for land desertification control.And it can provide new evidence for the interaction process and mechanism of various earth surface layers.Hence,in this study,we selected the Alashan Desert in northern China as the study area,and a total of 433 samples were collected throughout the desert and nearby regions to study the provenance of the eolian sand based on their heavy mineral assemblages and contents and combined with wind direction datum and regional geological background.The results show as follows:(1)The heavy mineral assemblages of eolian sand in the Alashan Desert is dominated by magnetite,hematite,garnet,amphibole,zircon,tourmaline,rutile,ilmenite,pyroxene,epidote,apatite,titanite and monazite.However,different deserts and different locations of the same desert have different relative content of heavy minerals.The relative content of stable heavy minerals gradually increases from the periphery of the desert to the hinterland on the whole,and the unstable heavy minerals have opposite trends,but the spatial changes of different deserts are different.Additionally,the heavy mineral assemblages of eolian sand is very similar to that in the bedrock,wildness and the fluvial-lacustrine sediments around the desert.(2)ZTR index and stability coefficient have different changes in different deserts.the spatial variability of the ZTR index and the stability coefficient of the eolian sand in the Badain Jaran Desert and the Tengger Desert are relatively small.That gradually increases from the northwest to the southeast of the desert on the whole.However,the stability coefficient tends to decrease in the areas near the northern Gobi and the bedrocks in the southwestern and the southern desert.The spatial variability of the stability coefficient and ZTR index in the Tengger Desert show a gradually increasing trend from the northwest to the southeast of the desert.And the low value appears in the areas closed to the Helan Mountains and the wildness in the southern of the desert.The ZTR index and stability coefficient of eolian sand in the Ulan Buh Desert gradually increased from the periphery of the desert to the desert hinterland,but the spatial variability in different regions was different.(3)The GZi index of eolian sand in the Alashan Desert are all very high.The GZi index have not changed much in the Badain Jara Desert and the Tengger Desert,while the GZi index in the Ulan Buh Desert have gradually decreasing trend from the northwest and west to the east of the desert with local high values.The ATi index of the eolian sand in the three major deserts is large at the edge of the desert and small in the desert hinterland,indicating that the weathering degree of the eolian sand at the edge of the desert is lower and the desert hinterland is higher.Through systematic and detailed analyses of the above results,the following conclusions are reached:(1)The rich and conplex heavy mineral assemblage of the Alashan Desert indicates that the provenance of eolian sand was not sourced from a single source rock.The sources of the eolian sand in the Badain Jaran Desert mainly include bedrock,gobi,fluvial-lacustrine sediments in the west and northwest of the desert,and the contribution of bedrock in the southeast was less.The eolian sand of the Tengger Desert mainly comes from bedrock and gobi along the west-north-northeast route,the quicksand of the Badain Jaran Desert and the paleolake sediments inside the desert,while the contribution of the gobi in the south of the desert was little for the eolian sand.The main provenances of eolian sand in the Ulan Buh Desert include the bedrock in the northwest of the desert,gobi to the west of the desert,and the exposed bedrock and paleolacustrine deposits in the desert hinterlands.The fluvial deposits in the Yellow River near the desert and bedrock in the Helan Mountains contributed little to the eolian sand in the Ulan Buh Desert.(2)It is found that the bedrocks,fluvial and lacustrine sediments around the desert,the wildness surrounding the desert,and the paleolacustrine sediments inside the desert were important provenances for eolian sand through heavy mineral analysis.But the above provenances are distributed in different locations in the desert,making every provenance have different contributions to eolian sand.(3)The characteristic index distribution of eolian sand in the Alashan Desert shows that the eolian sand in three desert were transported shortly,and the provenance was mainly near-source.In addition,the provenances of eolian sand were not only the gobi and bedrock around the desert,but also has common source where has rich-garnet bedrock.

【Keywords in Chinese】 物源重矿物干旱区风成沉积沙漠
【Key words】 ProvenanceHeavy mineralsArid regionEolian sedimentsSand sea
Snapshot search of full-text: 

Knowledge network:

Citation network of current document
网页聊天
live chat
在线营销
live chat