Depths of Partial Crystallization of H2O-bearing MORB: Phase Equilibria Simulations of Basalts at the MAR near Ascension Island (7 11{degrees}S)     

Almeev  Renat; Holtz  Francois; Koepke  Jurgen; Haase  Karsten; Devey  Colin 《Journal of Petrology》2008,49(1):25-45

Phase equilibria simulations were performed on naturally quenchedbasaltic glasses to determine crystallization conditions priorto eruption of magmas at the Mid-Atlantic Ridge (MAR) east ofAscension Island (7–11°S). The results indicate thatmid-ocean ridge basalt (MORB) magmas beneath different segmentsof the MAR have crystallized over a wide range of pressures(100–900 MPa). However, each segment seems to have a specificcrystallization history. Nearly isobaric crystallization conditions(100–300 MPa) were obtained for the geochemically enrichedMORB magmas of the central segments, whereas normal (N)-MORBmagmas of the bounding segments are characterized by polybariccrystallization conditions (200–900 MPa). In addition,our results demonstrate close to anhydrous crystallization conditionsof N-MORBs, whereas geochemically enriched MORBs were successfullymodeled in the presence of 0·4–1 wt% H₂O in theparental melts. These estimates are in agreement with direct(Fourier transform IR) measurements of H₂O abundances in basalticglasses and melt inclusions for selected samples. Water contentsdetermined in the parental melts are in the range 0·04–0·09and 0·30–0·55 wt% H₂O for depleted and enrichedMORBs, respectively. Our results are in general agreement (within±200 MPa) with previous approaches used to evaluate pressureestimates in MORB. However, the determination of pre-eruptiveconditions of MORBs, including temperature and water contentin addition to pressure, requires the improvement of magma crystallizationmodels to simulate liquid lines of descent in the presence ofsmall amounts of water. KEY WORDS: MORB; Mid-Atlantic Ridge; depth of crystallization; water abundances; phase equilibria calculations; cotectic crystallization; pressure estimates; polybaric fractionation  相似文献   

Drought and institutional adaptation in the Great Plains of Alberta and Saskatchewan, 1914–1939     

Gregory P. Marchildon  Suren Kulshreshtha  Elaine Wheaton  Dave Sauchyn 《Natural Hazards》2008,45(3):391-411

Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought. These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover, these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective institutional adaptation.  相似文献   

冀北万全寺银金矿床地质地球化学特征     

王宝德  牛树银  孙爱群  刘亚明  郭鹏志  孙双海 《地质与勘探》2008,44(1):15-20

万全寺银金矿床位于张宣幔枝构造东侧的侏罗纪断陷盆地中,成矿时限晚于133.33Ma～101.82 Ma.通过硫、铅、氢、氧、碳及稀有气体同位素研究认为,成矿物质应源自地球深部,在中生代冀西北幔枝构造演化过程中集中成矿.成矿热液以岩浆水为主并加入了部分天水.  相似文献   

实验研究不同盐离子对水分子拉曼效应的影响   总被引：3，自引：0，他引：3  

陈勇  周瑶琪  查明  王爱国 《地球化学》2008,37(1):22-26

对流体包裹体中常见的几种盐水溶液进行了拉曼光谱分析.采用了频移参数描述水分子拉曼峰的形变强度,并讨论了频移参数与盐度之间的关系.实验分析结果表明,盐度越大,频移参数越大,水分子拉曼峰形变越大.对频移参数曲线斜率分析显示,盐类对水分子拉曼峰偏移程度影响的强弱顺序为NaCl＞Na2SO4＞NaHCO3＞Na2CO3.讨论了不同阳离子和阴离子对水伸缩振动拉曼峰的影响,结果表明,高价阳离子的影响明显高于低价阳离子;而阴离子对水拉曼峰影响的强弱顺序初步确定为Cl-≈SO2-4-＞HCO-3＞CO2-3≈NO-3.  相似文献   

引水工程秦巴段隧洞地应力模拟及工程地质问题     

李东林  吴树仁  韩金良  刘景儒 《地质与勘探》2008,44(5):81-86

利用Ansys有限元软件对三峡引水工程秦巴段线路不同深度、不同截面形态隧洞围岩的应力重分布情况进行模拟计算,得到圆形隧洞、城门形隧洞和马蹄形隧洞围岩的应力数值和等值线图.利用库仑一纳维尔强度准则,对花岗岩区及灰岩区隧洞围岩的剪切破坏进行分析;利用三种岩爆应力判别指标,对岩爆进行初步预测;进而对不同深度、不同截面形态的隧洞围岩的稳定性进行分析;最后对引水工程隧洞设计中截面形态的选择给出了初步建议.  相似文献   

Environmental hydrogeology of the southern sector of the Samborombon Bay wetland,Argentina     

Eleonora Carol  Eduardo Kruse  Jorge Pousa 《Environmental Geology》2008,54(1):95-102

The Samborombon Bay wetland is located on the west margin of the Rio de la Plata estuary, in the Province of Buenos Aires, Argentina. This paper analyses the geological, geomorphologic, soil and vegetation characteristics of the southernmost sector of this wetland and their influence on surface water and groundwater. The study area presents three hydrologic units: coastal dunes, sand sheets and coastal plain. Coastal dunes and sand sheets are recharge zones of high permeability with well-drained, non-saline soils, and a few surface water flows. Changes in the water table are related to rainfall. Groundwater in coastal dunes is Ca–Mg–HCO₃ to Na–HCO₃, and of low salinity (590 mg/l). Groundwater in sand sheets is mainly Na–HCO₃ with a salinity of about 1,020 mg/l. The coastal plain exhibits medium to low permeability sediments, with submerged saline soils poorly drained. Groundwater is Na–Cl with a mean salinity of 16,502 mg/l. A surface hydrological network develops in the coastal plain. Surface water levels near the shoreline are affected by tidal fluctuations; far from the shoreline water accumulates because of poor drainage. Both sectors have Na–Cl water, but the former is more saline. Human intervention and sea level rise may affect the wetland severely.  相似文献   

干旱生态环境及水资源对全球气候变暖响应的研究进展   总被引：7，自引：5，他引：2  

邓振镛  张强  辛吉武  赵鸿  王全福  王鹤龄 《冰川冻土》2008,30(1):57-63

西北地区现代气候变化基本特征是冬暖夏干,采用脆弱度和影响指数方法定量评价了生态环境对全球气候变暖响应,重点阐述了西北现代气候变化对干旱生态环境和水资源这两个领域的影响.结果表明: 由于现代气候变干变暖的自然和人为因素的共同作用,导致我国西北地区的黄土高原、黑河流域、石羊河流域、甘南高原和黄河首曲的地域生态环境有不断退化的趋势.气候变干使渭河上游、黄河上游(洮河和大夏河)以及黄土高原中部7条主要河流的径流量呈明显下降趋势,引起水资源短缺.  相似文献   

陆面过程中稳定水同位素逐日变化的数学模拟——引入稳定同位素效应的CLM实例分析     

章新平  王晓云  牛国跃  杨宗良  黄一民  张剑明 《冰川冻土》2008,30(1):100-107

将稳定同位素效应引入CLM(Community Land Model),并对巴西马瑙斯站在平衡年的稳定水同位素的逐日变化进行模拟和分析.结果表明: 降水、水汽和地表径流中δ18O存在明显的季节变化,并与相应的水量存在显著的负相关关系,但凝结物中δ18O与地面凝结量存在显著的正相关关系,蒸发水汽中δ18O与蒸发量之间无显著的相关关系.受土壤贮水削峰功能的影响,表层土壤和根区水中δ18O的季节变化全无.植被层蒸发水汽中稳定同位素的丰度与大气的干湿程度存在密切联系: 当降水量少时,大气干燥,植被层的蒸发较少,植被蒸发中δ18O较高;当降水量较大时,空气湿润,植被层的蒸发量较大,蒸发中δ18O则较低.植被蒸腾中δ18O的变化与源区水体中δ18O的变化保持一致,尤其是与根区水中的δ18O.由于地下径流直接源自根区水的补充,因此,地下径流中δ18O等于根区水中的δ18O.模拟结果还显示,降水MWL (大气水线)的梯度项和常数项均比全球平均MWL略偏小.尽管主要来自降水的贡献,但地表径流和植被层水体的MWLs与降水MWL存在较大的差异,这一方面与两类水体在蒸发过程中的稳定同位素的富集作用有关,另一方面与CLM模拟的水量有关.大气水汽线与降水的MWL的梯度值相近,说明大气水汽与降水近似处于稳定同位素平衡状态.另外,模拟的地面的凝结线与植被层的凝结线均与全球大气水线相近,且具有非常高相关程度,说明CLM的模拟是合理的.  相似文献   

渤海新近系浅水三角洲沉积体系与大型油气田勘探   总被引：32，自引：8，他引：24  

朱伟林  李建平  周心怀  郭永华 《沉积学报》2008,26(4):575-582

新近纪渤海具有构造稳定、沉降缓慢、湖泊水域范围大、内部无分割、地形平缓、坡度小等特点,广泛发育浅水三角洲,从而形成渤海海域新近系良好的储盖组合和优越的油气成藏条件。浅水三角洲砂岩储层由于受河流作用的控制,砂体具有明显的方向性,存在明显的分叉现象,与曲流河相比,砂体连通性较好,砂体等厚图呈典型的朵叶状。湖相厚层泥岩普遍发育,与浅水三角洲砂体组成多套垂向优质储盖组合。浅水三角洲发育于渤海新近纪至今处于生烃的峰期主力富烃凹陷的有利区带,新构造运动造成新近纪以来凹陷主力源岩生烃峰期与新构造运动的同步耦合,为渤海大型浅水三角洲成因的优质储层油气成藏创造了优越条件,可以形成大型油气田。因此,重视并充分挖掘渤海浅水三角洲储层类型油气藏的勘探潜力将是追求浅层优质油藏、进一步增储上产的方向所在。  相似文献   

新疆北部晚古生代以来中基性岩脉的年代学、岩石学、地球化学研究   总被引：13，自引：7，他引：6  

徐芹芹  季建清  韩宝福  朱美妃  储著银  周晶 《岩石学报》2008,24(5)

新疆北部中基性岩脉K-Ar表观年龄为187～271Ma,岩性以辉长、辉绿岩以及闪长、闪长玢岩为主,属于亚碱性系列.主量元素、稀土元素以及微量元素分析表明,中基性岩脉经历了源区地壳物质的混合以及侵位过程中的分离结晶作用,并在区域分布特点上受部分熔融程度的影响,而且由于结晶分异和部分熔融的不同,还出现了中基性岩脉系列的成分变异.排除上述岩浆作用的干扰,有证据显示岩脉起源于亏损地幔,由于Nd同位素模式年龄tDM集中在363～769Ma,反映源区是一个古生代时期的新生岩石圈地幔,该地幔源区属于大洋岩石圈地幔.新疆北部广泛出露的中基性岩脉在时间和空间上具有多样性,但是在产状、岩性组合和同位素特征上具有相似的特点,指示研究区在古生代以来具有一个相对统一和完整的源区,推测这个源区与北疆地区古生代以来长期存在的残余洋盆及其相关岩石圈有关.  相似文献