Water Flows Toward Power: Socioecological Degradation of Lake Urmia,Iran

Water is an invaluable resource, and equitable access to it is a fundamental human right. Disenfranchised groups often lose access to water resources because their interests are not well represented by decision makers. Excluding these groups from resource management policy often results in myopic decisions that contribute to further ecosystem damage. We describe the ecological degradation of Lake Urmia in Iran, which has recently experienced increased salinity and declining water quantity. The lake is a UNESCO Biosphere Reserve and Ramsar site, and supports unique biodiversity in the region. The lake's decline is driven by the destruction of Zagros forests and the government's water policies, which diverted water to more politically connected agricultural land users, increasing social inequity and prompting more deforestation. The most straightforward restoration solution is to discontinue the diversions and allow critical inflows to recharge Lake Urmia, preserving the lake and wetlands for migratory birds, tourists, and local communities.     

基于组合楔形体原理的采动坡体稳定性研究

地下采煤通常会引起地表严重开裂,甚至发生滑坡、崩塌等地质灾害,采动坡体的稳定性研究一直是工程实际关心的问题。本文以贵州省都匀市煤洞坡采动坡体为例,在斜坡破坏机制分析基础上,采用组合楔形块体原理构建了采动坡体稳定性系数计算方程,并从实验、经验类比、采空率等方面对采动坡体的强度指标进行了综合取值,计算了采动坡体在天然、饱水及裂隙水作用下的安全系数。结果表明:煤洞坡山体是处于稳定状态的,这与坡体上的裂缝位移监测成果是相符的。但在长时间降雨或暴雨情况下,煤洞坡山体稳定性就会逐渐变差,甚至发生滑动; 坡体稳定性安全系数随内摩擦角的降低而降低,随裂隙水充水高度的增加而降低; 一旦后缘块体挤压前缘块体时,就会存在一个安全系数急剧降低的阀值。从裂缝水柱高度与降雨渗入裂缝的雨水量关系出发,建立了裂缝水柱高与降雨量之间关系式。经计算当降雨量(短时间内)超过192mm,斜坡就会失稳。     

Long-term Changes in the Saline Lake Qarun(Egypt)

正1 Introduction There is now ample evidence of the impacts of the recent climate change and anthropogenic activities on different saline lake ecosystems.All over the world salt lakes are threatened by climate change,water diversions upstream for agricultural purposes,watershed changes,introduction of aliens,etc.that result in catastrophic     

Stable Isotope and Element Geochemistry of Saline Springs in Evaporite-bearing Mengla Basin,South Yunnan,China

正1 Introduction Mengla Basin is a sub-basin in southern evaporitebearing Lanping-Simao Basin.There are many salt springs in the basin.In 2012,11 spring samples were collected for analyses of chemistry and boron,hydrogen and oxygen     

Wet and Dry Basalt Magma Evolution at Torishima Volcano, Izu Bonin Arc, Japan: the Possible Role of Phengite in the Downgoing Slab

The arc-front volcanoes of Sumisu (31·5°N, 140°E)and Torishima (30·5°N, 140·3°E) in thecentral Izu–Bonin arc are similar in size and rise asrelatively isolated edifices from the seafloor. Together theyprovide valuable along-arc information about magma generationprocesses. The volcanoes have erupted low-K basalts originatingfrom both wet and dry parental basaltic magmas (low-Zr basaltsand high-Zr basalts, respectively). Based on models involvingfluid-immobile incompatible element ratios (La/Sm), the parentalbasalts appear to result from different degrees of partial meltingof the same source mantle (20% and 10% for wet and dry basaltmagmas, respectively). Assuming that the wet basalts containgreater abundances of slab-derived components than their drycounterparts, geochemical comparison of these two basalt typespermits the identification of the specific elements involvedin fluid transport from the subducting slab. Using an extensiveset of new geochemical data from Torishima, where the top ofthe downgoing slab is about 100 km deep, we find that Cs, Pb,and Sr are variably enriched in the low-Zr basalts, which cannotbe accounted for by fractional crystallization or by differencesin the degree of mantle melting. These elements are interpretedto be selectively concentrated in slab-derived metasomatic fluids.Variations in K, high field strength element and rare earthelement concentrations are readily explained by variations inthe degree of melting between the low- and high-Zr basalts;these elements are not contained in the slab-derived fluids.Rb and Ba exhibit variable behaviour in the low-Zr basalts,ranging from immobile, similar to K, to mildly enriched in somelow-Zr basalts. We suggest that the K-rich mica, phengite, playsan important role in determining the composition of fluids releasedfrom the downgoing slab. In arc-front settings, where slab depthis 100 km, phengite is stable, and the fluids released fromthe slab contain little K. In back-arc settings, however, wherethe slab is at 100–140 km depth, phengite is unstable,and K-rich fluids are released. We conclude that cross-arc variationsin the K content of arc basalts are probably related to differingcompositions of released fluids or melts rather than the widelyheld view that such variations are controlled by the degreeof partial melting. KEY WORDS: arc volcano; degrees of melting; mantle wedge; water; wet and dry basalts     

The Himalayan Collisional Orogeny: A Metamorphic Perspective

This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core. The Himalayan orogeny was divided into three stages. Stage 60–40 Ma: The Himalayan crust thickened to ~40 km through Barrovian-type metamorphism (15–25 °C/km), and the Himalaya rose from <0 to ~1000 m. Stage 40–16 Ma: The crust gradually thickened to 60–70 km, resulting in abundant high-grade metamorphism and anatexis (peak-P, 15–25 °C/km; peak-T, >30 °C/km). The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust, High Himalayan thrust, and Main Central thrust, and the Himalaya rose to ≥5,000 m. Stage 16–0 Ma: the mountain roots underwent localized delamination, causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism (30–50 °C/km), and the Himalaya reached the present elevation of ~6,000 m. Underplating and imbricate thrusting dominated the Himalaya’ growth and topographic rise, conforming to the critical taper wedge model. Localized delamination of mountain roots facilitated further topographic rise. Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events, contact metamorphism and rare metal mineralization, metamorphic decarbonation and the carbon cycle in collisional belts.     

温度循环下压实粗粒盐渍土水盐迁移与变形响应

“一带一路”规划的高速铁路频繁穿梭于盐质荒漠区,沿线优质不含盐路基填料极其匮乏。为解决粗粒盐渍土填筑高速铁路路基面临的技术难题,结合伊朗德伊高铁建设,以现场粗粒盐渍土路基填料为对象,开展了温度循环下压实粗粒盐渍土水盐迁移与变形响应试验研究。结果表明,每次温度循环后温度波幅值由土层浅表向深层土体衰减传递,土体埋深越浅、恒温时间越长,温度波幅值越大;水盐均匀分布的压实粗粒盐渍土经历多次温度循环后逐渐演化成非均匀分布,水盐向土体表面迁移聚集,越靠近土体表面水盐增量越大;前5次温度循环中压实粗粒盐渍土产生了塑性盐胀或塑性融沉,随着温度循环次数增加,盐渍土塑性盐胀或塑性融沉显著减小甚至消失;盐渍土层上设置非盐渍土层具有迟滞盐分向上迁移和消能减胀作用,粗粒盐渍土构筑高速铁路路基宜采用结构分层技术,非盐渍土层设置厚度一般不宜小于当地温度辐射影响显著深度;粗粒盐渍土路基设计宜考虑多次温度循环后形成的水盐非均质分布及其可能诱发的盐胀与融沉增大效应,路基压实度不宜过高。研究成果将为盐渍土地区高速铁路路基工程建造起到示范参考作用。     

Petrogenesis of Late Ordovician intrusive rocks in the West Kunlun orogenic belt: Constraints on the subduction process of the Proto-Tethys OceanSCIEI北大核心CSCD

西昆仑造山带发育有大量的早古生代岩浆岩,它们的形成与原特提斯洋俯冲-碰撞密切相关,然而,对于这些岩浆岩的岩石成因和形成的构造背景仍然存在较大的争议。本文对西昆仑造山带早古生代阿喀孜二长岩和赛图拉石英闪长岩岩体开展了详细的矿物学、锆石U-Pb年代学、全岩地球化学和Sr-Nd-Hf-O同位素研究,以探讨这些侵入岩的岩浆源区与成因,揭示原特提斯洋在这一时期的构造演化过程。这两个岩体的LA-ICP-MS锆石U-Pb年龄分别为456±2Ma和452±2Ma,指示它们形成于晚奥陶世。阿喀孜二长岩具有富碱(K_(2)O+Na_(2)O=10.5%~11.8%)、富钾(K_(2)O/Na_(2)O=1.20~1.44)特征,相对低MgO(0.89%~0.97%)、TiO_(2)(0.42%~0.45%)含量,富集Rb、Th、U等大离子亲石元素,且具有较高的全岩锆饱和温度(T_(Zr)=814~862℃),属于钾质碱性岩石。该岩体具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.72057~0.72186),负的全岩ε_(Nd)(t)值(-5.1~-4.5)和负的锆石ε_(Hf)(t)值(-7.6~-3.4),以及较高的锆石δ^(18) O值(5.39‰~7.94‰),表明其源区可能为伸展环境下古老基性下地壳部分熔融。赛图拉石英闪长岩SiO_(2)含量为56.8%~58.6%,全碱(Na_(2)O+K_(2)O)含量为5.75%~6.39%,具有较低的铝饱和指数(A/CNK=0.85~0.89),相对高的MgO含量(2.93%~3.41%)以及Mg^(#)值(~45),为高钾钙碱性系列岩石。它们富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Nb、Ta、Ti),且具有微弱的Eu异常(δEu=0.72~0.77),类似于俯冲带岩浆岩地球化学特征。这些石英闪长岩具有相对高的(^(87)Sr/^(86)Sr)_(i)比值(0.71317~0.71322),负的全岩ε_(Nd)(t)值(-5.6~-5.1)和负的锆石ε_(Hf)(t)值(-7.8~-2.9),与同时期来源于富集地幔的基性岩同位素特征相似,表明赛图拉石英闪长岩岩浆可能是由俯冲板片流体交代的富集地幔楔部分熔融形成,并在岩浆演化的过程中经历了橄榄石、辉石、角闪石、磷灰石和Fe-Ti氧化物等矿物的分离结晶作用。结合同位素和数字模拟计算(Rhyolite-MELTS)结果表明,赛图拉石英闪长岩可能由塔里木克拉通南缘玄武质岩浆的分离结晶而成。综合前人研究,本文提出晚奥陶世阿喀孜二长岩和赛图拉石英闪长岩形成于原特提斯洋向北俯冲相关的活动大陆边缘环境,该时期原特提斯洋板片回撤,诱发软流圈地幔的上涌,从而产生了大量的弧岩浆岩。     

不同变形速率下前陆褶皱冲断带的发育特征——基于砂箱物理模拟实验研究

构造模拟实验是研究和模拟自然界地质构造现象、变形特征、成因机制和动力学过程的一种物理实验方法。本文基于砂箱构造物理模型高、中、低速7组不同单向挤压速度的构造模拟实验,揭示不同变形速率下砂箱物质变形的几何学、运动学及其演化特征,探讨不同变形速度(尤其是不同量级速度)对前陆褶皱冲断构造变形的重要性。高速单向挤压变形过程中(0.4~0.1mm/s),砂箱模型中石英砂体后缘构造加积强烈,砂体变形主要以楔形体向前扩展变形为主,其构造样式主要表现为前展式叠瓦冲断构造。中速挤压变形过程中(0.05~0.005mm/s),砂体后缘加积相对较弱,构造变形样式主要为砂箱楔形体前缘先形成(前展式为主)逆冲断层,当达到临界楔形体后,反冲断层发育并与前展式逆冲断层构成冲起构造,构造样式上表现为叠瓦构造与冲起构造的无序叠加。低速挤压变形过程中(0.002mm/s),砂箱物质构造样式以典型冲起带为主。由于砂箱模拟过程的时效性,即如何在最有效时间内获得最全面而复杂的演变过程,通过本次系列实验,我们建议将此有效挤压速度设定为0.05~0.005mm/s范围内,可以先后清晰而全面的获得高速和低速挤压下砂体的变形过程和构造样式。     

我国西北夏季风边界千年尺度变化的证据--来自盐池和猪野泽盐类矿物分析结果

我国夏季风西北缘是响应长尺度气候变化最为敏感的区域之一, 但夏季风边界变化与千年尺度气候变化之间的关系尚不明确, 相关研究仍缺乏足够证据。夏季风西北缘湖泊沉积物中盐类矿物种类与含量的时空变化, 有助于推测气候变化特征。盐池和猪野泽分别位于祁连山北麓的河西走廊中段和东段, 是研究长时间尺度亚洲夏季风影响区西北边界变化的关键区域。研究全新世千年尺度下, 夏季风西北边界的变化对夏季风西北缘气候变化过程的影响, 对明确季风边缘区千年尺度季风变化机制, 预测未来长尺度气候变化有重要意义。因此, 本文选择盐池古湖泊盐池剖面(YC), 猪野泽青土湖01、02剖面(QTH01、QTH02)等三个剖面, 开展全新世千年尺度下, 亚洲季风西北边界地区湖泊沉积物盐类矿物时空变化对比研究。结果显示:QTH01、QTH02剖面盐类矿物以碳酸盐为主, 硫酸盐类矿物仅零星出现, 而YC剖面硫酸盐类矿物含量相对较高, 同时出现了氯化物型矿物, 全新世气候特征整体较猪野泽更为干旱。末次冰期和早全新世, 三个剖面受季风输送水汽影响明显, 碳酸盐类矿物能较好沉积, 季风边界在这一时期向北扩张, 推进到祁连山中段地区;中全新世QTH01、QTH02剖面受夏季风影响减弱, 湖泊退缩, 碳酸盐类矿物含量达到峰值, YC剖面则表现出极端干旱的气候特征, 硫酸盐类矿物因“盐效应”含量下降, 此时夏季风西北部水汽输送边界位于石羊河流域和盐池流域之间;晚全新世盐池和猪野泽均以风成沉积为主, 气候干旱, 碳酸盐类矿物难以保存, 硫酸盐和氯化物矿物含量出现高值, 说明夏季风西北边界进一步向南迁移。综上所述, 盐类矿物含量变化能良好反应夏季风西北缘全新世气候变化特征, 同时证明, 在全新世千年尺度上, 夏季风西北边界在盐池流域和石羊河流域之间存在变化。