塔克拉玛干沙漠地表发射率及分布变化特征

通过利用便携式傅立叶变换热红外光谱仪,对冷热黑体辐射和漫反射金板辐射校正,测量波长在8–14 μm的热红外大气窗口的地表辐射光谱,计算出地表的发射率光谱,再转换成地表的发射率值(ε)。为获得塔克拉玛干沙漠精确的ε,沿着沙漠公路,从南至北穿越沙漠,平均每50 km进行一次测量,获得了沙漠地表发射率的分布变化特征。结果表明：靠近绿洲的地表发射率值最高,达到0.93,绿洲与沙漠过渡带的值为0.91–0.92,沙漠其它地区的值为0.90–0.91,而沙漠中心区接近0.89。     

沙漠地区土壤质地对不同频点微波地表发射率反演和模拟的影响

首先运用先进微波扫描辐射仪(AMSR-E)资料反演了北非沙漠地区晴空条件下的地表微波发射率。然后根据不同的土壤类型,进一步分析了沙漠地表微波发射率频谱特性,并将增加土壤质地信息前、后的翁(Weng)氏微波地表发射率模型(2001)的模拟结果和反演结果进行了比较。结果表明,沙漠地表发射率与土壤质地密切相关,随土壤颗粒大小的不同变化明显。在沙漠土壤类型中,以大颗粒为主的土壤类型,其水平(垂直)极化的发射率通常随频率提高而增大(减小);而对于以较小粒子为主的沙漠土壤类型,地表发射率几乎为常数,或水平(垂直)极化的发射率随频率提高略有减小(增大)。并且,发射率的季节性特征明显,特别是以小颗粒组成的土壤,其水平极化的发射率比垂直极化的发射率表现出更强的季节性变化。以上这些发射率特征与翁氏模型模拟结果一致。此外,在翁氏模型的输入参数中增加土壤质地信息(土壤组分含量、粒径尺度)改善了翁氏模型在沙漠地区的模拟结果,特别是对于包含大量小粒子的沙漠土壤类型,如黏土和黏质壤土,模拟误差从6%9%降低至4%以下。由于翁氏模型是美国国家环境预报中心(NCEP)全球同化和预报系统的重要组成部分,对翁氏模型的改进将提高沙漠地区卫星资料的利用率并有望改进数值天气预报的准确度。     

Mineralogy,M-type tetrad effect and radioactivity of altered granites at the G. Abu Garadi shear zone,central Eastern Desert,Egypt

The G. Abu Garadi area is covered mainly by metasediments, alkali feldspar granites and stream sediments. The alkali feldspar granite is traversed by a major strike-slip fault trending in an N-S direction as well as two subordinate sets of faults trending NW to WNW for the first one and NE for the second one. These faults represent the shear zones affected by magmatic (syngenetic) as well as hydrothermal (epigenetic) activities causing alteration of the granitic rocks. The most common alteration features are albitization, greisenization and koalinitization. The mass balance calculations of the studied altered samples show enrichments in Zr, Y, Ni, U, Th and Ga and depletions in Zn, Sr, Nb, Ba, Pb, Cu and V. Only the greisenized samples exhibit a significant enrichment in Nb, ∑REE budget and pronounced lanthanide tetrad effect (M-type), especially TE1,4, while weakly expressed tetrad effects are for the other albitized and koalinitized samples. Mineralogically, the common accessory minerals in the altered samples include samarskite-(Y), betafite, uranothorite, zircon, fluorite and cassiterite. The greisenized granites contain high eU and eTh than the other altered types, where they are characterized by an assemblage of the radioactive minerals; samarskite-(Y), betafite, uranothorite in addition to zircon. The inter-element relationships between U and Th and also their ratios illustrate that the radioelement distribution in these granites is mainly governed by magmatic processes, in addition to post-magmatic ones. The distribution of chemical elements and the fractionation of some isovalents within the shear zone are largely controlled by the newly formed mineral phases. With respect to uranium mobilization, uranium migrated from the host alkali feldspar granites of G. Abu Garadi, while the shear zones acted as traps for the migrated uranium. Moreover, U migrated in the shear zone during greisenization and albitization, and migrated out during koalinitization.     

Mineralogy and geochemistry of Nb-, Ta-, Sn-, U-, Th-, and Zr-bearing granitic rocks from Abu Rusheid shear zones,South Eastern Desert,Egypt

Granite-hosted,Nb-,Ta-,Sn-,U-,Th-,and Zr(Hf)-bearing mineralization from the Abu Rusheid shear zones occurs about 97 km southwest of the town of Marsa Alam,South Eastern Desert,Egypt.The SSE-trending brittle-ductile Abu Rusheid shear zones crosscut the peralkalic granitic gneisses and cataclastic to mylonitic rocks(mylonite,protomlyonite,and ultramylonite).The northern shear zone varies in width from 1 to 3 m with a strike length of >500 m,and the southern shear zone is 0.5 to 8 m wide and >1 km long.These shear zones locally host less altered lamprophyre and locally sheared granitic aplite-pegmatite dykes.The rare-metal minerals,identified from the peralkalic granitic gneisses and cataclastic to mylonitic rocks are associated with muscovite,chlorite,quartz,fluorite,pyrite,magnetite,and rare biotite that are restricted to the Abu Rusheid shear zones;these are columbite-tantalite and pyrochlore(var.betafite) in the northern shear zone and ferrocolumbite in the southern shear zone.Cassiterite occurs as inclusions in the columbite-tantalite minerals.U-and Th-minerals(uraninite,thorite,uranothorite,ishikawaite,and cheralite) and Hf-rich zircon coexist.Magmatic(?) zircon contains numerous inclusions of rutile,fluorite,U-Th and REE minerals,such as uranothorite,cheralite,monazite,and xenotime.Compositional variations in Ta/(Ta+Nb) and Mn/(Mn+Fe) in columbite range from 0.07-0.42 and 0.04-0.33,respectively,and Hf contents in zircon from 1.92-6.46 of the two mineralized shear zones reflect the extreme degree of magmatic fractionation.Four samples of peralkalic granitic gneisses and cataclastic to mylonitic rocks from the southern shear zone have very low TiO2(0.02 wt%-0.04 wt%),Sr [(15-20)×10-6],and Ba [(47-78)×10-6],with high Fe2O3T(0.94 wt%-1.99 wt%),CaO(0.14 wt%-1.16 wt%),alkalis(9.2 wt%-10.1 wt%),Rb [(369-805)×10-6],Zr [(1033-2261)×10-6],Nb [(371-913)×10-6],U [(51-108)×10-6],Th [(36-110)×10-6],Ta [(38-108)×10-6],Pb [(39-364)×10-6],Zn [(21-424)×10-6],Y [(8-304)×10-6],Hf [(29-157)×10-6],and ∑REE [(64-304)×10-6],especially HREE [(46-167)×10-6].Three samples from the northern shear zone also have very low TiO2(0.03 wt%),Sr [(11-16)×10-6],and Ba [(38-47)×10-6],with high Fe2O3T(1.97 wt%-2.91 wt%),CaO(0.49 wt%-1.01 wt%),alkalis(7.2 wt%-8.3 wt%),Rb [(932-978)×10-6],Zr [(1707-1953)×10-6],Nb [(853-981)×10-6],Ta [(100-112)×10-6],U [(120-752)×10-6],Th [(121-164)×10-6],Pb [(260-2198)×10-6],Zn [(483-1140)×10-6],Y [(8-304)×10-6],Hf [(67-106)×10-6],and ∑REE [(110-231)×10-6],especially HREE [(91-177)×10-6].The very high Rb/Sr(57.5-88.9),and low Zr/Hf(16.9-25.6),Nb/Ta(7.7-9.8),and Th/U(0.21-1.01) are consistent with very frac-tionated fluorine-bearing granitic rocks that were altered and sheared.The field evidence,textural relations,and compositions of the ore minerals suggest that the main mineralizing event was magmatic(629+/-5 Ma,CHIME monazite),with later hydrothermal alteration and local remobilization of the high-field-strength elements.     

振冲砂桩复合地基单桩最优桩间距的确定

通过现场振冲砂桩施工及标贯试验,围绕振冲砂桩复合地基砂桩的合理间距开展了试验研究.结果表明在本文各种试验工况中,1.4m工况的桩间距为振冲砂桩施工的最优间距.分析认为对于振冲砂桩施工法而言,当地层条件、振动力、振动频率及施工工艺一定时,实际密实效果主要与桩间距有关.在与本文试验场地条件相似的场地进行振冲砂桩复合地基施工...     

Geomorphological evolution revealed by aeolian sedimentary structure in Badain Jaran Desert on Alxa Plateau, Northwest China

The Badain Jaran Desert,located in the Alxa Plateau,Northwest China,features mega-dunes and a unique dune-lake alternation landscape.This paper presented the aeolian sediment structures of three representative dunes in the Badain Jaran Desert using ground-penetrating radar (GPR).We processed and analyzed the GPR data and investigated the feasibility of using integrated GPR and sedimentological data to reconstruct dunes structure,sedimentary environment and geomorphological evolution.The results show that the internal structures of star dune and transverse dune represent various stages of mega-dune evolution: the main deposition processes of mega-dune are similar to those of transverse dunes but have a more complicated mechanism of sand transport and deposition because of the superimposition of dunes;the upper section of the mega-dune has a structure similar to that of star dune,with vertical aggradations on top.Diffraction hyperbolae in the GPR profile indicates that the presence of ancient dunes characterized by calcareous cementation layers is involved in the maintenance of mega-dunes,and water levels,shown by continuous,sub-horizontal GPR reflections,are supposed to be closely related to mega-dunes and the interdune lakes.Outcrop of wet sand and horizontal stratifications on the GPR image indicate moisture potentials with different levels inside mega-dunes.The multiplex geomorphology in the Badain Jaran Desert is the result of global climatic undulation,the unique geographical location,the geological structural features,etc.     

Are ferns in arid environments underestimated? Contribution from the Saharan Mountains

Although ferns are able to colonize dry regions through specific adaptations, they are suggested to be rare in arid environments. By comparing recent observations in the South-Saharan Mountains with existing data from the whole Sahara, we re-evaluated the distribution of the understudied Saharan fern diversity. Observations in the Aïr Mountains (Niger) from 2003 to 2006 identified six ferns species, among which three were new records for the Aïr and for Niger. A total of 17 species are currently known from the Sahara. The desiccation tolerant Actiniopteris radiata and Cheilanthes coriacea were located in habitats with abiotic refuges providing shade, whereas the drought avoiding Ophioglossum polyphyllum was found in a sandy highland plain. All were growing in isolated populations at elevations above 1600 m. These results, combined with data from the Hoggar and the Tibesti mountains, indicate that ferns are more frequent than initially thought in arid environments thanks to efficient dispersal, elevation refuges, physiological adaptations, and the presence of local abiotic refuges. The three newly recorded species most likely radiated from the Ethiopian highlands. Their deep isolation, their rarity, and their successful adaptation to drought suggest that their conservation status might be particularly high.     

巴丹吉林沙漠湖泊水化学空间分带性与湖泊面积的等级关系

依据Q-型系统聚类分析方法,选取巴丹吉林沙漠湖泊水化学离子为变量,将研究区划分为A、B、C三个分带（区）。同时,利用遥感影像资料提取相应湖泊的面积信息,并进行等级划分,与湖泊水化学特性作对比分析,以探究二者的关系。结果表明：位于沙漠东南边缘的A类湖泊沿东北-西南向呈带状分布,以淡水湖和微咸水湖为主,湖泊面积极小;B类湖...     

巴丹吉林沙漠典型高大沙山迎风坡粒度特征

风沙地貌形态与地表风动力的互馈机制研究是近年来风沙地貌学研究的热点问题.以巴丹吉林沙漠高大沙山为研究对象,选取巴丹吉林沙漠东南部苏木巴润吉林以西高度约400 m的高大沙山,对其迎风坡沉积物粒度特征进行系统采样分析,研究了高大沙山迎风坡沙物质粒度由坡脚至丘顶以及表层和下层的变化规律.结果表明,沙山迎风坡表层沉积物的粒度组...     

塔克拉玛干沙漠腹地塔中地区风沙流输沙特征研究

利用多种积沙仪,通过野外实时输沙观测,对塔克拉玛干沙漠腹地塔中的地表风沙流特征进行了分析,结论如下:(1)100 cm高度范围内,总输沙量的63.1%分布在20 cm高度内,72.4%分布在30 cm高度内,随高度的增加,输沙量呈负指数函数下降;由此可见,该地区的风沙活动主要集中在近地面20～30 cm高度范围内;(2...