Temporal stability of soil moisture in an oasis of northwestern China

Temporal stability of soil moisture has been widely used in hydrological monitoring since it emerged. However, the spatial analysis of temporal stability at the landscape scale is often limited because of insufficient sampling numbers. This work made an effort to investigate the spatial variations of temporal stability of soil moisture in an oasis landscape. The specific objectives of the study were to explore the spatial patterns of temporal stability and to determine the controlling factors of temporal stability in the desert oasis. A time series of soil moisture measurements were gathered on 23 occasions at 118 locations over 3 years in a rectangular transect of approximately 100 km². The nonparametric Spearman's rank correlation coefficient, standard deviation of relative difference (SDRD), and mean absolute bias error (MABE) were used to quantify the temporal stability of soil moisture. Results showed that the temporal stability of soil moisture was depth dependent and season dependent. The spatial pattern of soil moisture in a deep soil layer and between two same seasons generally had a high temporal stability. SDRD and MABE were spatially autocorrelated and exhibited strong spatial structures in the geographic space. The concept of temporal stability can be extended to describe the time‐stable areas of soil moisture with geostatistics. There were great differences between SDRD and MABE in describing the temporal stability of soil moisture and in identifying the controlling factors of temporal stability. In this case, MABE was a better alternative to estimate the areal mean soil moisture using representative locations than SDRD. Land use type, soil moisture condition, and soil particle composition were the dominant controls of temporal stability in the oasis. These insights could help to better understand the essence of temporal stability of soil moisture in arid regions.     

Impact of gneissic layering and localized incipient melting upon melt flow during experimental deformation of migmatites

In this study, we test experimentally the role of compositional layering as a key parameter for controlling melt flow in a natural migmatite during coaxial deformation. We performed in – situ pure-shear experiments on two natural gneisses. The first gneiss is weakly foliated with minerals homogenously distributed. The second gneiss shows a pronounced compositional layering of alternating quartz – feldspar – rich and biotite – muscovite – rich layers. Experimental conditions were selected to obtain homogeneous melt distribution in the homogeneous gneiss and heterogeneous melt distribution in the layered gneiss. Initial melt distribution is not modified by deformation in experiments on the homogeneous gneiss, implying that melting products did not migrate from their initiation sites. In contrast, melt flowed in shear zones or in inter-boudin positions during experimental deformation of the heterogeneous gneiss. These experiments attest to the strong influence of initial gneissic layering on melting pattern, melt segregation and flow during deformation of partially molten rocks.     

全球冥古宙的研究进展和存在问题

冥古宙是地球上最老的一个地质历史时期,由于缺少可靠的岩石记录一直没有得到国际地学界的重视和承认,到2004年才在建议的国际地层表中使用了冥古宙这一术语,定义从地球形成到出现地球最老岩石这段地球历史。但冥古宙与太古宙没有明确的地质界线,一些研究者提出了不同的年代界线(3.85Ga,4.0Ga,4.03Ga),目前还存在较大分歧。目前已知残存的冥古宙岩石只有两处,一处是加拿大的阿卡斯塔片麻岩(Acasta gneiss)中两个英云闪长岩和一个变质花岗闪长岩。前者锆石U-Pb年龄为4002±4Ma和4012±6Ma,后者为4031±1Ma。另一处是东南极索尼山(Mount Sones)的麻粒岩相英云闪长质片麻岩,已获得U-Pb年龄为3927±10Ma。世界上最老的表壳岩(≥3870Ma)出露在格陵兰。冥古宙年代久远,地球形成最初的600~700Ma的初始岩石经历了陨石撞击、地壳再循环、重熔等改造,甚至再循环到地幔,几乎已经消失殆尽。目前主要以年轻岩石中的碎屑锆石或继承锆石作为桥梁,来追索这些古老锆石原来母岩的类型、特征及成因。3800Ma的碎屑锆石已在全球十多个地区发现,而以西澳伊尔岗克拉通的杰克山最多最全,从3800Ma到4404Ma都有,在3840Ma,3900~3920Ma,4000~4200Ma,4260~4300Ma和4404Ma显示峰值,其中以3900~4200Ma最为发育,4404Ma是目前世界公认的最老碎屑锆石。此外在北美克拉通、南非克拉通、华北克拉通等古老克拉通以及一些年轻造山带中都发现有冥古宙的碎屑锆石,这些锆石是追索冥古宙地质事件的重要桥梁。通过对冥古宙碎屑锆石的研究提出了很多值得重视和进一步研究的课题和内容。包括早期地壳的性质,一些锆石具有与太古宙之后岩浆锆石特征相似的环带结构,因此这些碎屑锆石的母岩大部分被认为相当花岗质,来自老地壳的重熔。冥古宙碎屑锆石的Hf同位素等综合分析表明这些碎屑锆石来源于中性熔岩的结晶,或许表明早期地壳具有中性成分特征。冥古宙锆石的成因也是一个重要的课题,根据锆石中钛的含量、锆石Ti饱和温度计计算的温度以及锆石的一些结构特征,有的研究者提出冥古宙相当一部分碎屑锆石是陨石撞击导致的岩石熔融结晶产生的,是追溯地球早期撞击事件的重要手段。在4300Ma的碎屑锆石中包裹有金刚石和石墨晶体,前者表明锆石的母岩曾处于高压条件,而后者石墨的碳同位素接近有机碳,有人认为可能为生命起源的迹象。多个地区的碎屑锆石的边部Th/U比值低,U-Pb年龄为4000Ma左右,属于变质作用的产物,表明当时地壳已具有一定厚度。冥古宙碎屑锆石的研究提出了很多重要的问题,但是由于资料有限,有些认识还存在矛盾,还需要获得更多实际资料,才能对冥古宙的地质事件过程取得更可靠的科学认识。因此今后应加强可能赋存古老碎屑锆石地区的寻找,并发现更多古老碎屑锆石。对现有的古老碎屑锆石加强综合研究以及各地区的对比研究。     

青藏高原片麻岩穹窿与找矿前景

片麻岩穹窿是研究俯冲-折返和碰撞-折返造山过程的重要窗口。已查明的大量青藏高原片麻岩穹窿(群)分布在古特提斯和新特提斯大洋俯冲-折返以及地体碰撞-折返过程中。松潘-甘孜造山带中雅江甲基卡片(麻)岩穹窿的三叠纪变质片岩的含矿伟晶岩脉中发现了超大型锂矿床,揭示片(麻)岩穹窿构造与同构造花岗岩、含矿伟晶岩脉以及大型印支滑脱带在时空和成因上有天然联系,为片麻岩穹窿的找矿前景提供了范例。     

广义残差地形模型及其在局部重力场逼近中的应用

研究了残差地形模型中的非调和性问题,比较了基于棱柱体和球冠体的积分模型,提出了基于球冠体积分的广义残差地形模型。以泊松小波径向基函数为构造基函数,结合广义残差地形模型,融合多源实测重力数据构建了局部区域重力场模型。研究结果表明:基于棱柱体积分的残差地形模型精度较低,在山区可能引入毫伽级以上的误差,建议采用更为接近真实地形表面的球冠体积分模型。相比于原始的残差地形模型,基于球冠体积分的广义残差地形模型能更为精确地逼近局部重力场模型中地形因素引起的高频效应。     

基于规则格网的DEM插值实验

通过地形建模,将6个地形隶属函数按照101×101,112×112,126×126,144×144,168×168,201×201,257×257 7种格网密度生成6种局部地形单元的规则格网DEM;使用反距离加权(IDW)等7种插值算法,将前6种格网密度下的DEM插值成257×257规格;从原始257×257DEM中随机抽取检查点计算残差,并对残差中误差进行分析。通过分组插值实验,运用控制变量法、方差分析等方法研究地貌类型、采样密度和插值算法对DEM插值精度的影响。     

基于随机森林模型的云南元阳梯田地形因子分析

为探究地形因子对梯田空间分布的影响,以云南元阳梯田坝达流域为研究区,运用GeoEye-1遥感卫星数据(2010年,1 m分辨率)和数字高程模型(20 m分辨率),提取梯田空间分布信息以及海拔高程、地形坡度、地形坡向、地面曲率、高程变异系数、地形起伏度、地面粗糙度、地表切割度、到水系距离9个地形因子。采用随机森林(Random Forest)方法建模,结合ROC曲线和AUC值对模型进行精度评价,根据随机置换残差均方减少量和因子作用曲线,探讨地形因子对梯田分布的影响规律。研究结果表明:该流域内梯田总面积1 158395 hm2,模型AUC值为0.947,海拔高度因子的随机置换残差均方减少量为38814,到水系距离因子为199.77,地面坡向因子为80.26,三者占总值的73.45%。由此可见,元阳梯田的空间分布主要受海拔高度、到水系距离、地面坡向3类地形因子的影响,其因子曲线表明梯田分布与地形因子间呈非线性关系。     

架子台沟低品位铅锌矿原生晕地球化学特征及深部矿产预测

对架子台沟一带1:50 000化探异常检查中,地表发现有铅锌矿化显示,经对激电测深异常深部钻探验证发现有低品位锌矿(化)体。通过系统采集0号勘探线上的2个钻孔中岩石、矿石样品,进行原生晕特征研究分析表明:矿体近矿元素为Ag、Pb、Zn、Cd,尾矿元素为W、Sn、Bi;轴向分带序列由上至下为:Pb-Au-Ag-Mo-Bi-Sn-Cu-Cd-W-Zn。对成矿元素与相关金属元素进行聚类分析、因子分析,并结合激电测深结果,认为在矿体的侧部、深部仍可能有盲矿体。     

北京平原区地质剖面的初步建立——太古宙结晶基底和元古宙地层

北京平原目前尚未建立系统的地质剖面。1867年庞培莱将北京西山分为3大系,1871年李希霍芬提出震旦系、划分12层。1922年葛利普将震旦系限定在前寒武系,1923年田奇镌将南口剖面划分为7个岩组,1934年高振西将震旦系3分(南口群、蓟县群、青白口群)。1976年乔秀夫3分青白口群(下马岭组、龙山组和景儿峪组),1980年汪长庆等将十三陵剖面分为4系12组,1991版《北京市区域地质志》将十三陵剖面分为3系12组。本文初步建立平原区地层表,详细描述太古宙结晶基底和元古宙地层剖面,在京南大兴区的榆垡(兴热-1井)和安定(兴热-2井)发现太古宙片麻岩,在京热-70井、京热-59井、京热-71井和京热-75井编录蓟县纪地层,利用亦庄小学钻孔厘定待建系下马岭组、青白口纪龙山组和景儿峪组。     

Underwater Navigation Based on Real-Time Simultaneous Sound Speed Profile Correction

Precise sound speed profile (SSP) information is critical when using sonar for underwater terrain navigation. Nevertheless, acquiring SSP information in real-time is difficult, especially in underwater navigation environment. To account for this problem, this paper presents an underwater navigation method that applies real-time SSP correction to the terrain measurements. The method uses a probe to measure the surface sound speed simultaneously. Meanwhile, redundancy of topographic measurement data is exploited to derive the equivalent SSP information. The acquired equivalent SSP is updated continuously with particle filter algorithm. The terrain measurements can be corrected in real-time with the equivalent SSP to improve the performance of underwater terrain navigation. By removing the impact of inaccurate SSP from the terrain measurements, the proposed method can achieve precise and robust underwater navigation result without using an underway-profiling instrument. Simulated results confirm the good performance of the proposed method.