Multiple,isotopically heterogeneous plagioclase populations in the Bushveld Complex suggest mush intrusion     

《Chemie der Erde / Geochemistry》2015,75(3):357-364

The Bushveld Complex and other layered intrusions show significant initial isotopic heterogeneity, both between and within co-existing cumulate minerals. Various processes have been proposed to account for this, including (i) intrusion of variably contaminated crystal mushes from deeper staging chambers, (ii) blending of semi-consolidated crystal mushes as a result of subsidence during cooling, (iii) variable infiltration of contaminants into a partially solidified crystal mush, (iv) density-driven mixing of minerals from isotopically distinct magma pulses, (v) contamination of crystals at the roof of the intrusion and mechanical incorporation of such contaminated crystals into the lower crystallisation front as a result of gravitational instability at the upper crystallisation front, and (vi) late-stage metasomatic processes. In order to assess the likely process(es) responsible for initial isotopic heterogeneities within the Bushveld Complex, we analysed core and rim domains of 12 plagioclase crystals from the Main and Upper zones of the Bushveld Complex for their Sr-isotopic compositions. The data show the presence of multiple, isotopically heterogeneous populations of plagioclase occurring within the same rocks. The data presented here are best explained through the intrusion of variably contaminated crystal mushes derived from a sub-compartmentalized, sub-Bushveld staging chamber that underwent different degrees of contamination with crustal rocks of the Kaapvaal craton.  相似文献   

Micro-textures in plagioclase from 1994–1995 eruption, Barren Island Volcano: Evidence of dynamic magma plumbing system in the Andaman subduction zone     

M.L.Renjith 《地学前缘(英文版)》2014,5(1):113-126

A systematic account of micro-textures and a few compositional profles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995,from Barren Island Volcano,NE India ocean,are presented for the frst time.The identifed micro-textures can be grouped into two categories:(i)Growth related textures in the form of coarse/fne-sieve morphology,fne-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fuctuated due to change in temperature or H2O or pressure or composition of the crystallizing melt;and(ii)morphological texture,like glomerocryst,synneusis,swallow-tailed crystal,microlite and broken crystals,formed by the infuence of dynamic behavior of the crystallizing magma(convection,turbulence,degassing,etc.).Each micro-texture has developed in a specifc magmatic environment,accordingly,a frst order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit.Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth.Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective selfmixing environment.Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit.Intermittent degassing and eruption related decompression have also played a major role in the fnal stage of crystallization dynamics.  相似文献   

枫丹白露砂土的环境箱蒸发试验          下载免费PDF全文

宋卫康  丁文其  崔玉军 《水科学进展》2014,25(1):69-76

为研究土壤水分的蒸发机理,自主开发了大型环境箱试验装置,并以枫丹白露砂土为研究对象,室内模拟土壤水分的蒸发过程。该试验在控制大气参数和保持土壤底部水位稳定的条件下,对蒸发过程中大气参数（空气温度、相对湿度和流量）和土壤参数（土壤温度、基质吸力和体积含水量）的变化,特别是土壤表面基质吸力的变化进行了研究。同时根据试验结果对蒸发速率及累积蒸发量进行了计算分析。研究结果表明:蒸发主要限制在土壤浅层区域,浅层土壤的体积含水量和温度的变化均较大;空气温度和土壤蒸发过程对土壤温度的变化具有较大的影响;土壤表面空气相对湿度与蒸发过程具有相关性;土壤基质吸力随着蒸发的进行逐渐增大; 实际蒸发速率呈现3个阶段。  相似文献   

The death spiral of coal in the U.S.: will changes in U.S. Policy turn the tide?     

Roman Mendelevitch  Christian Hauenstein  Franziska Holz 《Climate Policy》2013,13(10):1310-1324

ABSTRACT

The administration of U.S. President Donald Trump has promised to stop the ongoing spiralling down of the U.S. coal industry. We discuss the origins of the decline and assess the effects of policy interventions by the Trump administration. We find that, with fierce competition from natural gas and renewables, a further decrease of coal consumption must be expected by the old and inefficient U.S. coal-fired electricity generation fleet. By contrast, we consider the overly optimistic (for coal producers) view of the U.S. Energy Information Agency, and test whether the tide for the U.S. coal industry could turn as a result of three potential support measures: (i) revoking the Clean Power Plan (CPP); (ii) facilitating access to the booming Asian market; and (iii) enhanced support for Carbon Capture, Transport and Storage (CCTS) technology. We investigate the short-term and long-term effects on U.S. coal production using a comprehensive partial equilibrium model of the world steam coal market, COALMOD-World (Holz, Haftendorn, Mendelevitch, & von Hirschhausen, 2016). We find that revoking the CPP could stop the downward trend of steam coal consumption in the U.S., but even allowing for additional exports, will not lead to a return of U.S. coal production to the levels of the 2000s, that is, over 900?Mt per year. When global steam coal use is aligned with the 2°C climate target, U.S. steam coal production drops to around 100?Mt per year by 2030 and below 50?Mt by 2050, even if CCTS is available and exports via the U.S. West Coast is possible.

Key policy insights

• Declining U.S. coal use is primarily caused by competition from natural gas and renewables not by environmental regulation of the coal sector.

• Without substantial policy support, U.S. coal-fired generation capacity will continue to decline rapidly.

• Revoking the Clean Power Plan will lead to about one eighth higher U.S. coal production in the next years.

• Carbon Capture, Transport and Storage does not prevent the rapid decline of coal use required under stringent climate policy.

• Even in the most extreme pro-coal scenarios with additional export possibilities, U.S. coal production will not return to its pre-2010 levels.

  相似文献   

AEC-Ⅰ型自动排气控制仪的研制及其应用          下载免费PDF全文

张清秀  林木金  尤宇星  杨鼎鸿  陈莹  陈彩虹  曹淑贞 《地震工程学报》2013,35(S1):135-138

AEC-Ⅰ型自动排气控制仪(Automatic Exhaust Control)可与真空果配套使用排除水氡观测闪烁室内的残留氡气。该仪器性能稳定、操作简单,能够对闪烁室自动按"排气-抽真空-再排气-再抽真空"顺序循环操作,还可以根据需要调节"排气-抽真空"状态的循环时间,提高排气效率,排气后的闪烁室本底达到《规范》要求,并在面板上实现了排气时间可视化。在该仪器试运行期间,对仪器的稳定性、真空时间和排气时间对排气效果的影响、仪器连续使用时间对排气效果的影响、与手动排气结果对比等方面进行测试分析,结果认为:AEC-I型自动排气控制仪控制精度高,性能稳定,对闪烁室的排气效果达到规范要求,可以作为水氡观测辅助设备用于闪烁室的排气工作。  相似文献   

云南腾冲火山构造区马站—固东岩浆囊的地球物理模式   总被引：7，自引：0，他引：7  

姜枚  谭捍东  张聿文  彭淼  李庆庆  张立树  许乐红  王伟 《地球学报》2012,33(5):731-739

位于青藏高原东南边缘的云南腾冲火山构造区岩浆活动频繁强烈,火山活动规模宏大。为配合国家深部探测专项科学钻探选址,在腾冲盆地北部马站到固东、曲石乡一带进行了大地电磁测深、可控源音频大地电磁测深、反射地震和重磁测量的工作。本文依据电磁法取得的成果划分出了盆地地壳内的2个低阻低速层,其中浅部的低阻层由含水(热水)的火山岩下部、花岗岩上部与花岗砂砾岩组成,构成了腾冲盆地的地热资源的热储层,其主要层位在300到1500m范围内;深部的低阻体是作为热源的岩浆囊,位于马站—固东—曲石乡三镇的深12～30km,东西宽25km以上,向南可能与腾冲北的岩浆囊相连。小空山、大空山和黑空山火山口具有典型的火山口重磁场特征,特别是由于喷发造成物质亏损形成的重力负异常与火山地形呈清晰的镜像对应关系。  相似文献   

地下洞室围岩稳定性分析方法简述   总被引：3，自引：0，他引：3  

邓声君 《地质与勘探》2013,49(3):541-547

随着可持续发展战略的提出,地下工程的开发和利用显得尤为重要。地下洞室围岩稳定性是整个工程中的关键问题,现今对地下洞室围岩稳定性研究的分析方法有很多,为了明确各种研究方法的优缺点以及适用范围,本文对现有地下洞室围岩稳定性分析方法进行了分类总结,用系统性的方法从定性、定量、可靠度等方面考虑,主要包括洞室的整体稳定性分析和洞室局部块体的稳定性分析,研究结果对地下洞室围岩稳定性设计及计算有重要的意义,最后对相关研究的现状和发展趋势做了简述。  相似文献   

加筋黏性土挡墙长期工作性能的试验研究     

肖成志  刘波  李雨润  孙建诚 《岩土力学》2012,33(1):109-114

基于加筋黏性土挡墙的长期工作性能试验,综合分析加筋土挡墙在回填、加载过程及加载后各阶段对格栅应变、面板变形及墙后土压力的影响,以及格栅应变受模型槽尺寸效应的影响。试验结果表明：顶部加载完成后格栅应变随时间增加而逐渐增大,约6个月后增加趋势变缓并趋于稳定;随着距面板距离的增大,筋材应变先增大后减少,随着时间增长,黏性土中格栅应变沿全长发展并均有相应增长;受模型槽挡板与填料间的摩擦以及加载板与模型槽间存在间隙的影响,靠近两侧挡板筋材的应变值要比中间测点小些;相同位置处挡墙后最大水平土压力监测值约为朗肯主动土压力计算值的2倍;竖向土压力最大值仅为考虑顶部载荷和自重后应力总和的1/3左右,表明格栅加筋使挡墙填土中应力得以重新分布。  相似文献   

沙尘天气过程对沈阳大气冰核浓度与尺度分布的影响     

周德平  洪也  王扬锋  刘宁微  张云海  李丽光 《中国沙漠》2016,36(6):1672-1678

为研究沙尘天气对大气冰核浓度及尺度分布的影响,2010-2012年春季用FA-3型安德森采样器在沈阳地区开展了大气冰核观测,采样后的滤膜在中国气象科学研究院的静力扩散云室中进行统一检测分析。针对2011年5月11-12日一次典型沙尘天气过程,分析了沙尘过程前后大气冰核浓度和尺度分布与变化特征。结果表明：沈阳地区春季大气冰核的本底浓度较高,约为0.8个·L^-1（活化温度为-20℃）;沙尘天气出现时可使大气冰核浓度突增10倍以上。约2/3的大气冰核集中在>4.7μm粒径段;有沙尘影响时,2.11～5.80 μm粒径段的大气冰核浓度增加最明显。大气冰核浓度的粒子尺度谱近似服从幂指数n（D）=A·D^B分布,其中A和B的数值在沙尘日明显大于非沙尘日。根据观测,建议在沈阳乃至中国北方地区春季有沙尘天气影响时应慎重选择人工影响天气作业方案。  相似文献   

The P-wave velocity structure of Deception Island,Antarctica, from two-dimensional seismic tomography     

Tami Ben-Zvi  William S.D. Wilcock  Andrew H. Barclay  Daria Zandomeneghi  Jesús M. Ibáñez  Javier Almendros 《Journal of Volcanology and Geothermal Research》2009

Deception Island is a volcanic island with a flooded caldera that has a complex geological setting in Bransfield Strait, Antarctica. We use P-wave arrivals recorded on land and seafloor seismometers from airgun shots within the caldera and around the island to invert for the P-wave velocity structure along two orthogonal profiles. The results show that there is a sharp increase in velocity to the north of the caldera which coincides with a regional normal fault that defines the northwestern boundary of the Bransfield Strait backarc basin. There is a low-velocity region beneath the caldera extending from the seafloor to > 4 km depth with a maximum negative anomaly of 1 km/s. Refracted arrivals are consistent with a 1.2-km-thick layer of low-velocity sediments and pyroclastites infilling the caldera. Synthetic inversions show that this layer accounts for only a small portion of the velocity anomaly, implying that there is a significant region of low velocities at greater depths. Further synthetic inversions and melt fraction calculations are consistent with, but do not require, the presence of an extensive magma chamber beneath the caldera that extends downwards from ≤ 2 km depth.  相似文献