Factors controlling the spatial and temporal variability of dust emissions

New field measurement techniques are allowing researchers to better understand how surficial properties affect the temporal and spatial variability of dust emissions. In this paper we review the current understanding of the dust emission process and present new field measurements that examine how three surface properties： roughness, crust strength, and temporal changes of surface properties affect dust emissions. These data were collected using three unique measurement systems developed by our team. Roughness exerts considerable control on the entrainment threshold and emissions of dust from a surface. We have carried out a series of experiments designed to quantify roughness effects on aeolian sediment entrainment and transport in a shear stress partitioning framework. Our results show that the model of Raupach et al. （1993） provides very good agreement with available data to predict the amount of shearing stress on the intervening surface among roughness elements, relatively independent of their size and distribution. However, element size affects the aeolian sediment transport process beyond that attributable only to the reduction of surface shear stress caused by the roughness. Additional interactions of the elements with the saltation cloud appear to reduce the transport efficiency and potentially dust emissions as well. The effect of crust strength on dust emissions was assessed using a newly-developed pin penetrometer, which can measure crust strength in-situ. Previous researchers suggested that variation in crust strength even within a small area could lead to considerable spatial variability in dust emissions. Our measurements showed that crust strength is highly variable over a scale of centimeters. This variability may help to explain some of the observed scatter in field measurements of dust emissions for what appear to be homogeneous surfaces. Variability of dust emissions in time and space was also evaluated using a new instrument, the Portable In-Situ Wind Erosion Lab （PI-SWERL） developed to measure dust emissions from soil surfaces.     

Naturally acidic and metalliferous waters at unmined volcanogenic massive sulfide deposits in the Bonnifield mining district, Alaska Range, east-central Alaska

The Bonnifield district hosts 26 tmmined volcanogenic massive sulfide （VMS） occurrences. Environmental geochemical samples of water and stream sediment were collected at several occurrences, concentrating on the two best-exposed and largest deposits, Red Mountain （RM） and Sheep Creek （SC）. Limited samples were also collected at the poorly exposed WTF deposit. The deposits are Late Devonian to Early Mississippian, and are hosted by felsic metavolcanic and carbonaceous schist members of the Totatlanika Schist or Keevy Peak Fm. Spring and stream waters at RM and SC have pH values commonly 〈3.5 （as low as 2.4 at RM and 2.5 at SC）, high conductivity （up to 11000 μS/cm）, and very high （Is to 100s mg/L） dissolved contents of Al, Cd, Co, Cu, Fe, Ni, and Pb. Waters at RM are characterized by extremely high REE contents （summed REE median 3200 μg/L, n=33）. At both RM and SC, pyrite oxidation and dissolution produce low pH waters that interact with and dissolve bedrock minerals, resulting in acidic, metal-laden, naturally degraded streams that are mostly devoid of aquatic life. Ferricrete is common. In contrast, WTF barely produces a surficial environmental footprint, mostly due to topography and relief. RM and SC are well exposed in the areas of relatively high relief, and both exhibit extensive areas of quartz-sericite-pyrite-alteration. While WTF shares many of the same deposit-and alteration characteristics, it is concealed by tundra in a large, nearly flat area. Surface water at WTF is absent and outcrops are sparse. Even though WTF is roughly the same size as Red Mountain （both around 3 million tonnes） and has similar base- and precious-metal grades, the surficial geochemical manifestation of WTF is minimal. However, exposure through mining of the altered, mineralized rock at WTF potentially could initiate the same processes of pyrite oxidation, acid generation, and mineral dissolution that are observed naturally at RM and SC.     

青藏高原东缘龙门山晚新生代剥蚀厚度与弹性挠曲模拟

龙门山是青藏高原东缘边界山脉,具有青藏高原地貌、龙门山高山地貌和山前冲积平原三个一级地貌单元。利用数字高程模式图像和裂变径迹年代测定方法研究和计算龙门山晚新生代剥蚀厚度与剥蚀速率,结果表明:3.6 Ma以来龙门山的剥蚀厚度介于1.91-2.16 km之间,剥蚀速率介于0.53-0.60 mm/a之间。在此基础上,开展了该地区岩石圈的弹性挠曲模拟,结果表明龙门山的隆升机制具有以构造缩短隆升和剥蚀卸载隆升相叠合的特点。3.6 Ma之前,龙门山的隆升与逆冲推覆构造负载有关,以构造缩短驱动的构造隆升为特色;3.6 Ma之后,龙门山的隆升与剥蚀卸载驱动的抬升有关,并以剥蚀卸载隆升为特色,进而提出了龙门山晚新生代以来的隆升机制以剥蚀成山作用为主的认识。     

澳大利亚的第三纪及第三纪—第四纪过渡期(英文)

第三纪的板块运动驱动着澳大利亚的气候和植被进行演化。广布的湿润森林区是澳大利亚老第三纪的特征。一直到始新世 ,生物多样性都在不断地提高。毫无疑问 ,这是澳大利亚由高南纬区向北部中纬区运移的结果。从始新世到上新世 ,澳大利亚的气候总体上要比现在湿润 ,但降水量季节性变化的增强推动了中新世以后硬叶植物和旱生植物的发展。上新世晚期似乎与第四纪一样 ,都出现过周期性干旱。这种干旱与冰期条件有关 ,至少由南澳大利亚晚第四纪的记录可以认识到这一点 ,澳大利亚的这段历史与东亚的气候变迁是同步发生的。在东亚 ,印—澳板块的运动致使青藏高原抬升 ,从而引发了区内乃至全球气候的巨变。穿越赤道区的季风和信风的环流格局 ,致使新第三纪和第四纪中国与澳大利亚的气候系统的相关性更强。     

由兰德斯和赫克托矿地震的地震波触发的地震

加州1992年兰德斯7.3级地震和1999年赫克托矿7．1级地震的接近和相似允许人们对触发地震的假设进行检验，而这在以前是不可能的。赫克托矿地震证实了对兰德斯地震所提出的推断：瞬时、振荡的“动态”形变以地震波的形式辐射，能触发地震活动速率的增加(Hill，et al，1993；Anderson，et al，1994；Gomberg and Bodin，1994；Spudich，et al，1995；Gomberg，1996；Gomberg and Davis，1996)。在本文中，我们对地震活动速率的空间和时间变化(Matthews and Reasenberg，1988)进行了量化。在兰德斯地震的北部地震活动速率增加，而对赫克托矿地震这种增加主要发生在震中以南。我们认为破裂方向性分别使兰德斯和赫克托矿断层的北方和南方动态形变提高，这可以由地震波速度场的不对称性得到证明。对于触发作用，动态和静态应力变化都很重要，距离较远处动态应力变化起主要作用。峰值波速证明了动态触发闽值的存在，并约束了动态触发闽值的范围。在大多数地区，这个阈值依赖当地的条件，从零点几到几MPa变化，超过静态闽值一个量级以上。在某些地点触发过程直到动态形变平息了之后才开始。这些观测现象的物理机制可能与导致液化和循环疲劳的机理相似。     

三分向台阵数据的偏振分析

给出了一种三分向地震台阵数据偏振分析的技术，并应用于挪威南部NORESS台阵三分向拾震器记录到的一大组区域事件。仔细分析了区域震相Pn、Sn和Lg的偏振性质。该技术基于Flinn(1965)最先提出的一种时域算法，通过解协方差矩阵的本征值问题，在滑动时间窗内计算偏振椭圆，由运动椭圆导出表征质点运动的各种属性。通过对不同拾震器的协方差矩阵求平均，把上述方法扩展到了由多个三分向拾震器组成的台阵情况，这样，当噪声和地方散射效应不相关时，可使方差估计减小1／M(M为拾震器数)。此方法的一个重要特点是穿过台阵相干波前的相速度不需要有很高精度。数据分析的重要结果为：在整个短周期频带内，很好地确定了Pn和Sn的偏振；由Pn和Lg波动获得了源方位的估计及Sn和Lg波独特的偏振属性使得在多数情形下能把这些震相区别出来。     

岩石破裂实验研究中强震发生前主破裂形成时能量释放过程的分析

分析用方程Q（t)=Q(t1) A1-A2(tf-t)^m[1 ccos(2πlog(tf-t)/p-φ)]来模拟强震前地震能量释放过程的一些条件，式中的Q（t)是在时间t以前所累积的“贝尼奥夫”总应变，tf是主震的时间，A1，A2，c,m,p,ψ都是模型的参数，Q（t1)是已知量（t1≤tf时）。表明在一定假定条件下幂指数m=α（2-d) 1。这里d是主震周围地震潜在震源群震中的尺寸，参数α决定着幂律。根据这个规律，地震时释放的地震能量和总能量的比值随地震的震级而变化。模型可用于分析实验研究岩石破裂释放声能的动力学，也适用于对堪察加一些强震前地震活动性的回溯性分析。     

塔里木地台西南缘皮山煌斑岩的^40Ar／^39Ar年龄及其地质意义

塔里木地台西南缘皮山县煌斑岩脉群为超钾系列的煌斑岩,侵位于元古宇角门片岩中。经~(40)Ar/~(39)Ar法测定,煌斑岩中金云母的等时线年龄为(231.7±0.3)Ma,全岩等时线年龄为(228.5±0.3)Ma。地球化学数据指示其源区为受俯冲     

SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane: Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton

The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane const     

全球气候变化及其影响

全球气候变化及其对社会与自然系统产生的影响已日益受到全世界各国政府与广大民众的关注。与天气和气候有关的灾害给人类生命财产造成的损失日益增大,社会与生态系统似乎变得日趋脆弱。人们关心刚刚过去的20世纪的天气与气候发生了什么变化,更希望了解未来的21世纪,人类居住的地球会出现什么样的气候情景。根据一些国家和地区的观测记录、研究成果以及科学家们对气候变化的评估与预测展望,对全球气候变化问题进行概括。首先阐明20世纪地区性气候变化的事实;并根据政府间气候变化委员会(IPCC)科学技术报告中关于20世纪全球气候变化进行的总结性评估以及对21世纪全球气候变化的预测,作为阐述过去与未来全球气候变化的主要依据。同时,还介绍了一些科学家对IPCC关于全球气候变化的结论所持的不同观点或质疑。还就气候变化对社会与自然系统可能产生的影响略作论述。