The recognition of former melt flux through high‐strain zones          下载免费PDF全文

Catherine A. Stuart  Sandra Piazolo  Nathan R. Daczko 《Journal of Metamorphic Geology》2018,36(8):1049-1069

High‐strain zones are potential pathways of melt migration through the crust. However, the identification of melt‐present high‐strain deformation is commonly limited to cases where the interpreted volume of melt “frozen” within the high‐strain zone is high (>10%). In this contribution, we examine high‐strain zones in the Pembroke Granulite, an otherwise low‐strain outcrop of volcanic arc lower crust exposed in Fiordland, New Zealand. These high‐strain zones display compositional layering, flaser‐shaped mineral grains, and closely spaced foliation planes indicative of high‐strain deformation. Asymmetric leucosome surrounding peritectic garnet grains suggest deformation was synchronous with minor amounts of in situ partial melting. High‐strain zones lack typical mylonite microstructures and instead display typical equilibrium microstructures, such as straight grain boundaries, 120° triple junctions, and subhedral grain shapes. We identify five key microstructures indicative of the former presence of melt within the high‐strain zones: (a) small dihedral angles of interstitial phases; (b) elongate interstitial grains; (c) small aggregates of quartz grains with xenomorphic plagioclase grains connected in three dimensions; (d) fine‐grained, K‐feldspar bearing, multiphase aggregates with or without augite rims; and (e) mm‐ to cm‐scale felsic dykelets. Preservation of key microstructures indicates that deformation ceased as conditions crossed the solidus, breaking the positive feedback loop between deformation and the presence of melt. We propose that microstructures indicative of the former presence of melt, such as the five identified above, may be used as a tool for recognising rocks formed during melt‐present high‐strain deformation where low (<5%) volumes of leucosome are “frozen” within the high‐strain zone.  相似文献   

超慢速扩张环境下超镁铁质岩系统的热液硫化物成矿机理以及启示     

曹红  孙治雷  刘昌岭  姜学钧  何拥军  黄威  尚鲁宁  王利波  张喜林  耿威  施美娟  李东义 《海洋学报》2018,40(4):61-75

西南印度洋63.5°E热液区是在超慢速扩张洋脊发现的首个超镁铁质岩热液系统。对取自该区的热液硫化物样品进行了系统的矿物学和地球化学分析，矿物学分析结果表明:该热液区硫化物为富Fe型高温硫化物，且经历了较深程度的氧化蚀变，大量中间态的Fe氧化物充填在硫化物矿物间的孔隙及内部解理中；这些硫化物相以白铁矿为主，其次是等轴古巴矿和少量铜蓝，缺乏黄铁矿、闪锌矿。据推断，该区的热液成矿作用分为4个阶段:低温白铁矿阶段→高温等轴古巴矿阶段→自形白铁矿阶段→后期海底风化阶段（少量铜蓝以及大量的Fe的羟氧化物）。与之相对应，地球化学分析结果表明这些硫化物的Fe含量较高（31.57%~44.59%），Cu含量次之（0.16%~7.24%），而Zn含量普遍较低（0.01%~0.11%）；微量元素较为富集Co（328×10-6~2 400×10-6）和Mn（48.5×10-6~1 730×10-6）。该区硫化物中较高含量的Fe、Co与超镁铁质岩热液系统相似，明显高于镁铁质岩热液系统。独特的热液硫化物矿物学特征和元素组成可能与该区普遍出露的地幔岩、橄榄岩蛇纹石化作用以及拆离断层的广泛发育的环境有关。  相似文献   

豫西南泥湖地区辉长岩地球化学特征及其与成矿关系          下载免费PDF全文

刘辉 《山东国土资源》2018,34(3)

豫西南泥湖钼矿集区是以花岗斑岩体为中心的钼多金属矿床系列,区内出露大面积加里东期变辉长岩和燕山期辉长岩。通过分析区内辉长岩的岩石学、年代学、地球化学和成矿元素等方面特征,研究其在成岩成矿过程中的作用。区内加里东期变辉长岩和燕山期辉长岩成矿元素总稀土含量低,稀土元素球粒陨石标准化曲线右倾平缓,具有明显的Eu,Tm元素的异常;同比世界基性岩,自晚元古代上地幔主要成矿元素(除钨元素以外)基本没有明显的富集,主成矿元素钼含量呈明显的亏损,预示燕山期成矿花岗质岩浆没有从上地幔获得主要成矿物质。初步认为大规模的钼多金属成矿带的形成与基性岩浆的底垫作用相关,基性岩浆的底垫作用为下地壳部分熔融形成岩浆房提供了热源。  相似文献   

滇西北地区近年来应力场的数值模拟研究     

武永彩  李昂  唐红涛 《大地测量与地球动力学》2018,38(12):1238-1240

建立滇西北地区三维有限元地质模型，将2009~2016年GPS速度场数据作为数值模拟的位移边界条件，模拟获取该地区的构造应力场。结果表明，在楚雄至滇西北地区整体显示张性应力区；出现由“洱源鹤庆断裂-红河断裂-程海断裂”圈起的低值张性区，区域内部张性应力明显低于外部，这种张应力低值区尤其在区域四周断裂边界处，往往是地壳断裂活动的频发区；曲江断裂北端及元谋-绿汁江断裂南端出现张性应力集中区，是今后重点关注的断裂结点。  相似文献   

三亚海域浮游病毒与细菌丰度的时空变化规律以及相关环境因子*     

荆红梅  韦誉  郑丽平  许秋彤  张玥  朱文达 《热带海洋学报》2018,37(2):36-46

在三亚海域设置3个站位, 分别于各站位连续采集12个月表层水样。利用流式细胞仪进行浮游病毒及浮游细菌丰度的测定, 并对两者及其与环境因子之间的相关性进行研究, 同时对不同站位之间进行差异性分析。结果表明, 调查海域浮游病毒丰度(平均7.63×10⁶viruses·mL^-1)高于浮游细菌丰度(平均1.52×10⁶cells·mL^-1)。浮游病毒及浮游细菌丰度在三亚河口最高, 且有明显的季节变化, 冬春季高于夏秋季, 并且其与鹿回头半岛西侧、小东海之间均有极显著差异(P<0.01), 不同类群病毒代表的宿主类群也有所不同。调查海域总体水平浮游病毒丰度与浮游细菌丰度显著正相关(r=0.800, P<0.01); 叶绿素(Chl a)和氮盐(NO- 2、NO- 2+NO- 3、NH+ 4)是影响两者的关键因子。  相似文献   

南海IODP 349航次基底玄武岩中碳酸盐岩脉的岩石学特征*     

许佳锐  陈毅凤  王宝云 《热带海洋学报》2018,37(6):63-73

国际大洋发现计划(International Ocean Discovery Program, IODP)349航次在南海东部次海盆和西南次海盆残留扩张脊附近的U1431和U1433站位首次钻取基底玄武岩, 通过对16块基底玄武岩内的碳酸盐岩脉薄片镜下观察以及激光拉曼光谱分析, 揭示碳酸盐矿物为方解石和文石, 为典型的洋壳低温热液蚀变次生矿物。U1431站位碳酸盐岩脉为独立的方解石脉、文石脉交替出现; 而U1433站位则存在方解石脉、文石脉和方解石-文石共生脉三种情况。此外, U1431站位在基底~42.1m处出现了平行的方解石脉和文石脉, 揭示U1431存在不同来源热液的多期活动, 即可能存在多次或多阶段不同的热液注入。U1431和U1433站位的碳酸岩脉中, 文石的矿物集合体形状基本一致, 呈块状、纤维状和放射纤维状; 而方解石存在差异, U1431的方解石以斑块状、块状、粒状和纤维状出现, 而U1433的方解石仅出现块状。U1431站位的碳酸盐岩脉的丰度明显高于U1433站位。这些均揭示U1431站位的低温热液活动强, 而U1433站位则相对弱。两个站位的热液活动不同很可能是由于区域地质环境的差异造成——U1431附近的巨大海山为其提供了热液补给, 而U1433远离热液的补给/渗漏点。  相似文献   

山东蓬莱地区侯格庄金矿床流体包裹体特征          下载免费PDF全文

王勇军  沈立军  朱裕振  黄鑫  徐昌  田明禛 《山东国土资源》2018,34(3)

侯格庄金矿床位于胶东栖(霞)-蓬(莱)金成矿带大柳行金矿田东南部。该文采用包裹体显微测温方法对金矿石中石英矿物内残留的流体包裹体进行研究,总结了金矿石石英矿物中的流体包裹体特征,并对该矿床成矿流体来源、矿床成因进行了研究。研究表明,该矿床石英矿物中流体包裹体以纯液包裹体为主,次为H_2O-CO_2气液两相包裹体及H_2O-CO_2三相包裹体,未见含子矿物包裹体。均一温度在109~396℃,盐度在2.9~22.44wt%NaCl,密度在0.64~1.06g/cm~3之间,估算成矿压力为128~340MPa,成矿深度约4.4~11.6km。该矿床至少经历了2个矿化期次,成矿流体为中低温、低盐度、低密度流体,流体来源于天水与岩浆水的混合产物,属中低温、中浅成热液矿床。  相似文献   

Time–space fractional governing equations of transient groundwater flow in confined aquifers: Numerical investigation          下载免费PDF全文

Tongbi Tu  Ali Ercan  M. Levent Kavvas 《水文研究》2018,32(10):1406-1419

In order to model non‐Fickian transport behaviour in groundwater aquifers, various forms of the time–space fractional advection–dispersion equation have been developed and used by several researchers in the last decade. The solute transport in groundwater aquifers in fractional time–space takes place by means of an underlying groundwater flow field. However, the governing equations for such groundwater flow in fractional time–space are yet to be developed in a comprehensive framework. In this study, a finite difference numerical scheme based on Caputo fractional derivative is proposed to investigate the properties of a newly developed time–space fractional governing equations of transient groundwater flow in confined aquifers in terms of the time–space fractional mass conservation equation and the time–space fractional water flux equation. Here, we apply these time–space fractional governing equations numerically to transient groundwater flow in a confined aquifer for different boundary conditions to explore their behaviour in modelling groundwater flow in fractional time–space. The numerical results demonstrate that the proposed time–space fractional governing equation for groundwater flow in confined aquifers may provide a new perspective on modelling groundwater flow and on interpreting the dynamics of groundwater level fluctuations. Additionally, the numerical results may imply that the newly derived fractional groundwater governing equation may help explain the observed heavy‐tailed solute transport behaviour in groundwater flow by incorporating nonlocal or long‐range dependence of the underlying groundwater flow field.  相似文献   

Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law          下载免费PDF全文

Ahmad Hajjar  Luc Scholtès  Constantin Oltéan  Michel Antoine Buès 《水文研究》2018,32(16):2510-2525

Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls.  相似文献   

“一带一路”沿线国家石油资源流动类型演变     

孙琪  赵媛  张新林  夏四友 《世界地理研究》2020,29(2):337-345

综合运用石油自给率、流动比率等方法，以“一带一路”沿线国家为研究对象，对1995—2014年各国石油资源流动类型时空演变进行研究。结果表明：1）1995—2014年石油净补给型国家数量较为稳定，无产型或低产型国家的石油贸易倾向变化相对较小；基本自给型国家数量占比最大，1995年占比1/2，其余四个年份占比稳定在1/3；净支出型国家数量显著增加，至2014年其中有5个国家保持不变，表明这些国家的石油产量具有较大的优势。2）1995年和2014年汇地国家均为39个国家，其中有34个国家一直保持汇地职能，空间分布上呈东多西少，南多北少，东西分化以西亚、中亚、东欧为界；有14个国家一直保持源地职能，其空间分布格局与汇地相应，西多东少，南多北少，主要分布于西亚、东欧及中亚；交流地数量较少，呈分散分布，且分布地不稳定。3）从数量变化来看，研究期内汇地略有增加，源地略有减少，交流地略有增加；“一带一路”源地总出口量与汇地总进口量的比呈逐年降低趋势。  相似文献