Spectra and vegetation index variations in moss soil crust in different seasons,and in wet and dry conditions

Similar to vascular plants, non-vascular plant mosses have different periods of seasonal growth. There has been little research on the spectral variations of moss soil crust (MSC) over different growth periods. Few studies have paid attention to the difference in spectral characteristics between wet MSC that is photosynthesizing and dry MSC in suspended metabolism. The dissimilarity of MSC spectra in wet and dry conditions during different seasons needs further investigation. In this study, the spectral reflectance of wet MSC, dry MSC and the dominant vascular plant (Artemisia) were characterized in situ during the summer (July) and autumn (September). The variations in the normalized difference vegetation index (NDVI), biological soil crust index (BSCI) and CI (crust index) in different seasons and under different soil moisture conditions were also analyzed. It was found that (1) the spectral characteristics of both wet and dry MSCs varied seasonally; (2) the spectral features of wet MSC appear similar to those of the vascular plant, Artemisia, whether in summer or autumn; (3) both in summer and in autumn, much higher NDVI values were acquired for wet than for dry MSC (0.6 ∼ 0.7 vs. 0.3 ∼ 0.4 units), which may lead to misinterpretation of vegetation dynamics in the presence of MSC and with the variations in rainfall occurring in arid and semi-arid zones; and (4) the BSCI and CI values of wet MSC were close to that of Artemisia in both summer and autumn, indicating that BSCI and CI could barely differentiate between the wet MSC and Artemisia.     

岩溶夷平面演化与青藏高原隆升

文章以作者在青藏高原南部及东邻地区获得的资料为基础,就青藏高原地区夷平面的识别、整体坡降、时代以及夷平面对构造隆升的响应等问题进行讨论。区域对比与成因分析显示青藏高原石林等形态形成于土下环境,属覆盖型岩溶,而与其共存的红色风化壳(石灰土)具有脱硅富铝作用弱而粘化作用强的特征,与湿热气候条件下的夷平面环境是一致的。根据野外观察资料和岩溶作用对水动力条件的敏感性,岩溶区厚层连续的风化壳只能发育在接近地貌侵蚀基准的夷平面上。因此,厚层连续的风化壳及其壳下的覆盖型岩溶均可指示地貌发育的晚期阶段和夷平面的存在,这为利用覆盖型岩溶及共存的风化壳识别夷平面提供了理论依据。根据青藏高原东邻地区岩溶地貌发育的演化特征,作者认为在同等条件下,岩溶夷平可以在更短的时间里达到更低的夷平高度(相对常态夷平),初步估计岩溶夷平面整体坡降小于0.5‰。构造隆升使青藏高原进入不利于岩溶作用的寒冻圈,岩溶夷平面经刻蚀作用演变为刻蚀平原,而云贵高原刻蚀作用较弱,但受到“土壤丢失”等岩溶过程的破坏。这种差别主要是构造隆升幅度的不同造成的。为了解决夷平面的年代问题,作者对滇西表生锰氧化物40Ar39Ar测年适宜性作了研究,结果显示鹤庆等地表生锰矿具有较     

藏南冈底斯岩基东段中新世中酸性高Sr/Y比岩浆岩的地球化学特征及成因探讨

藏南冈底斯带广泛发育中新世中酸性高Sr/Y比岩浆岩,对该类型岩石的成因研究可为藏南后碰撞岩浆活动提供良好的记录和约束。通过对冈底斯带东段中酸性岩浆岩进行锆石U-Pb年代学研究表明,该中酸性岩浆岩形成于16～18Ma,为中新世时期;全岩地球化学数据表明岩浆岩具有高SiO_2含量( 64%),高钾富钠,高Sr、低Y和高Sr/Y比,轻稀土富集、重稀土亏损且较平坦的特征,显示出埃达克质岩的地球化学亲缘性;与冈底斯带中段～14Ma埃达克质闪长玢岩脉相比,冈底斯带东段的中新世岩浆岩具有更高的K含量;锆石Hf同位素分析结果表明,中新世中酸性岩浆岩具有正的且变化较大的εHf(t)值(+1. 2～+14. 4);全岩(La/Yb)N值对中新世地壳厚度的估算结果为77～84km,处于壳幔边界处。综合上述数据分析表明,冈底斯带东段中新世中酸性高Sr/Y岩浆岩的成因为拉萨地块加厚下地壳(占主体的新生下地壳+少量古老地壳)的部分熔融,并在源区残留了石榴子石和角闪石,造成熔融的热量来源可能为拉萨地体岩石圈根部拆沉导致的热扰动。     

沙漠微生物矿化覆膜及其稳定性的现场试验研究

将微生物诱导矿化技术应用于原位沙漠覆膜的形成,使得流动沙丘经结皮固定而成为半固定、固定沙丘,从根本上阻断沙尘暴的源头。在内蒙古乌兰布和沙漠腹地选择两个微生物矿化试验区域（TP1和TP3）,分别用于两种不同矿化菌种诱导生成碳酸钙覆膜。研究沙漠微生物矿化覆膜的现场试验方法及工艺,对原位矿化覆膜的强度及其在沙漠环境中的长期稳定性进行跟踪检测。采用沙漠土中自行提取的葡萄球菌和传统的巴氏芽孢杆菌两种不同的微生物矿化菌种,通过现场贯入试验检测7、14、28、60、210 d后矿化覆膜沿深度发展的贯入阻力,并将覆膜厚度为2 cm处的平均贯入阻力换算成覆膜层强度,总结覆膜强度随时间的发展变化规律。现场观测结果显示,不同微生物菌种诱导生成的矿化覆膜均在试验的第4天开始形成,到第7天覆膜层具有稳定的强度和厚度,现场检测覆膜的平均厚度为2.0～2.5 cm,经自源葡萄球菌诱导生成的矿化覆膜（TP1）的强度是巴氏芽孢杆菌诱导生成的矿化覆膜（TP3）强度的1.05倍。当经历冬春交替后覆膜层强度都有不同程度的降低,明显地TP3较TP1区域表面剥落更为严重,第210天检测TP3的平均厚度为0.7～1.0 cm,覆膜强度较第7天时降低19%,覆膜内碳酸钙含量较第7天检测时降低15%～30%。而TP1在第210天时的强度较第7天时强度降低仅2%。因此,微生物诱导矿化技术可以应用于沙漠原位覆膜的形成,且沙漠自源葡萄球菌经诱导生成的矿化覆膜层具有更好的强度表现和稳定性。     

Early Cretaceous Adakitic Rocks in the Northern Great Xing’an Range, NE China: Implications for the Final Closure of Mongol-Okhotsk Ocean and Regional Extensional Setting

A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr(686–930 ppm) and HREE contents, low Y(11.9–19.8 ppm) and Yb(1.08–1.52 ppm) contents, and they therefore have high Sr/Y(42–63) and La/Yb(24–36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K_2O/Na_2O ratios(0.57–0.81), low Mg O contents(0.77–3.06 wt%), low Mg# value(17–49) and negative εHf(t) values(-1.7 to-8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.     

阿尔金南缘阿克提山岩体锆石U- Pb定年、Hf同位素特征及构造意义

阿克提山花岗岩体位于阿尔金断裂南缘,其形成时代与区域内其他花岗岩体差异较大,该岩体走向明显地受阿尔金断裂带分支断裂控制。锆石LA-ICP-MS U-Pb年代学分析表明,该岩体结晶年龄约为262Ma,其形成可能与南阿尔金地区在华力西期-印支期发生的大规模线性构造运动有关。岩体的岩性主要为石英闪长岩、花岗闪长岩,其暗色矿物以角闪石、黑云母为主,岩石A/CNK值均小于1.1,显示准铝质—弱过铝质特征,属于高钾钙碱性系列;大离子亲石元素Rb、Th、K相对富集,高场强元素Nb、Ta、P、Sr、Ti明显呈负异常;稀土元素配分曲线具有中等负Eu异常,δEu的平均值为0.73,(La/Yb)_N平均值为14.57,说明该花岗岩体岩浆部分熔融程度较高。根据岩石学及地球化学特征可判断该岩体为I型花岗岩。锆石Lu-Hf同位素分析表明,锆石ε_(Hf)(t)值为+1.46～+9.14,均为正值,二阶段模式年龄的峰值平均为943Ma,表明其源岩主要为新元古代新生地壳物质的部分熔融。阿尔金断裂在印支期的走滑运动是从地壳深部的韧性变形开始的,随后在浅地表发生脆性断裂形成大规模走滑断裂带。阿克提山岩体的形成与地壳深部减压熔融有关。     

北大别造山后伸展期中-下地壳流动形式数值模拟研究

造山后伸展过程中,深部地壳的变形形式反映深部岩石圈的构造活动方式,是造山后伸展深部动力学研究的主要内容。本次工作以大别造山带造山后伸展变形构造为研究对象,在详细的构造观察和组构分析基础上,以实际变形组构为约束开展数值模拟,系统地研究伸展变形构造在垂向剖面上岩石变形机制的空间分布,进而揭示大别造山带造山后伸展过程中深部地壳的变形形式。野外观察表明,北大别穹隆边缘区域拉伸线理优选方位显著,而到穹隆中部拉伸线理定向性减弱,再到穹隆核部线理定向性有所增强。运动学上,北大别穹隆内呈现了一致的上盘向NW的剪切指向。以此为约束的数值模拟研究表明,大别造山带造山后伸展期中-下地壳流动方式总体上是介于透入性简单剪切形式与纯剪切形式之间的组合形式;垂直剖面上呈现为由上、下边界向中心简单剪切分量显著降低,中-下地壳流变带中部以纯剪切变形为主。我们用造山带加厚地壳的韧性垮塌和深俯冲的太平洋板块"后撤"来解释其动力学来源。     

海南岛新生代玄武质熔岩源区中再循环物质及其年龄的限定:来自Hf-Sr-Nd-Pb同位素的制约

再循环洋壳和沉积物在壳.幔循环过程中扮演着重要的角色。前人研究指出板片俯冲与海南地幔柱形成关系密切,然而地幔柱源区中是否存在再循环沉积物仍然不得而知。本文将首次报导海南岛新生代玄武质熔岩的Hf同位素,并将新的Sr-Nd-Pb同位素与前人数据相结合,限定再循环物质的组成及其年龄。与同位素地幔趋势相比,给定εNd时,海南岛玄武质熔岩的εHf值更低;而且Eu/Eu*>1、Sr/Sr*>1,与Al2O3、MgO都不存在相关性,说明Eu和Sr的正异常是继承了源区的特征,指示源区中存在再循环洋壳物质的参与。海南岛玄武质熔岩的Ce/Pb与εNd、εHf呈正相关关系,Nd/Pb与87Sr/86Sr呈负相关关系,它们都指向了沉积物端元。根据εHf-εNd模型和Pb同位素演化模型,推断源区中再循环洋壳和沉积物相对年轻,其年龄应小于1.0Ga。这些再循环洋壳和沉积物将进入深部地幔,并与地幔中的橄榄岩反应形成二阶段辉石岩,随着海南地幔柱不断上升而发生熔融,最终熔体喷发至地表形成海南岛玄武质熔岩。     

GEOCHEMISTRY

正20141357 Guo Tao(School of Mathematics and Science,Shijiazhuang University of Economics,Shijiazhuang 050031,China);Hu Jiawen Assessment on the New Pressure-Volume-Temperature(PVT) Data of Supercritical Water(Geological Journal of China Universities,ISSN1006-7493,CN32-1440/P,19(3),2013,p.447-455,9 illus.,3 tables,32 refs.)Key words:supercritical fluids     

Near‐surface hydraulic conductivity of northern hemisphere glaciers

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day^?1, with a mean of 0.185 ± 0.019 m day^?1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.