Equatorial spread-F initiation: Post-sunset vortex, thermospheric winds, gravity waves     

Erhan Kudeki  Ahmed Akgiray  Marco Milla  Jorge L. Chau  David L. Hysell 《Journal of Atmospheric and Solar》2007,69(17-18):2416

We present experimental evidence and modeling results which indicate that eastward thermospheric wind is the primary controlling factor of equatorial spread-F initiation in the post-sunset ionosphere. Eastward wind-driven Pedersen currents are able to polarize F-region density perturbations with westward tilting wavefronts into rapidly growing modes to trigger the formation of spread-F bubbles. The described process is so rapid that seeding requirements of spread-F initiation by external factors such as gravity waves are effectively eliminated.  相似文献   

Chemical perturbations in the planetary boundary layer and their relevance for chemistry transport modelling     

Adolf Ebel  Michael Memmesheimer  Hermann J. Jakobs 《Boundary-Layer Meteorology》2007,125(2):265-278

The role of perturbations of reactive trace gas concentration distributions in turbulent flows in the planetary boundary layer (PBL) is discussed. The paper focuses on disturbances with larger spatial scales. Sequential nesting of a chemical transport model is applied to assess the effect of neglecting subgrid chemical perturbations on the formation and loss of ozone, NO _x , peroxyacetyl nitrate (PAN) and HNO₃ calculated with a highly complex chemical mechanism. The results point to characteristic differences regarding the process of mixing of chemically reactive species in the PBL and lower troposphere.  相似文献   

大比例尺地貌晕渲的几种制作方法及比较   总被引：1，自引：0，他引：1  

史保勇  李雪梅 《地理空间信息》2007,5(4):99-102

针对大比例尺地貌晕渲生成存在的问题,介绍了基于Atlas3D、基于Arc/Info、基于3DSMax三种制作大比例尺地貌晕渲的方法,并进行了比较。  相似文献   

Carbonate platform drowning caught in the act: The sedimentology of Saya de Malha Bank (Indian Ocean)     

Christian Betzler  Sebastian Lindhorst  John J. G. Reijmer  Juan Carlos Braga  Thomas Lüdmann  Or M. Bialik  Jesus Reolid  Anna-Lena Geßner  Dagmar Hainbucher  Dass Bissessur 《Sedimentology》2023,70(1):78-99

Mesophotic reefs, hardgrounds and current-controlled pelagic to hemipelagic carbonates are facies marking carbonate platform drowning successions, irrespective of the factors controlling this evolution. A modern analogue of a carbonate platform in a state of drowning, where these facies occur has not been properly reported on to date. In the present study, the sedimentary environments of the Saya de Malha Bank are characterized using a multi-disciplinary approach including sedimentology, hydroacoustics, seismics and oceanography. The Saya de Malha Bank edifice with a surface of 40 808 km² is located in the tropical Indian Ocean and lies in a water depth of 8 to 300 m extending from the surrounding more than 2000 m deep ocean floor, with no reef reaching the sea surface. Mesophotic coral and red algal facies co-exist with hemipelagic and bioclastic sands, together with a hardground. Ocean currents and internal waves are identified as major sedimentological controlling factors in the absence of elevated nutrient influx. Many features distributed along the present-day Saya de Malha Bank were described from studies presenting fossil examples of carbonate platform drowning. The results herein can therefore be applied to other drowning examples, in some cases allowing for more accurate interpretation of the stratigraphic record.  相似文献   

Late Cretaceous arc magma differentiation in southern Tibet: Evidence from zircon U-Pb chronology,mineralogy and geochemistrySCIEI北大核心CSCD     

管琪  张敏杰  曹军林  史宏江  李增胜  王对兴 《岩石学报》2023,(5):1459-1483

造山带岩浆作用记录了从大洋俯冲消减到陆陆碰撞的一系列地质过程,同时也蕴含了关于大陆地壳生成、生长的重要信息,其中,与俯冲相关的弧岩浆作用被认为是大陆地壳生长的主要机制。本文通过对西藏南部拉萨地体曲水县至贡嘎县一带出露的黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩开展同位素年代学、矿物学和岩石地球化学研究,探讨了该岩石组合的成因和弧岩浆的分异演化过程。锆石U-Pb定年结果表明,这些岩石的形成时代为91~88Ma。其中,黑云母二长花岗岩属中钾钙碱性偏铝质岩石系列(A/CNK=0.77~0.99),具高SiO 2(68.90%~69.18%)和Al_(2)O_(3)(15.21%~15.48%),低MgO(1.15%~1.16%)和Mg#值(~44),高Sr/Y比值(60~82),其地球化学特征与埃达克质岩石相似;镁铁质微粒包体的SiO 2含量为54.75%~54.96%,具有较高MgO含量(3.92%~5.40%)和Mg#值(52~61),并具弱的负Eu异常(δEu=0.79~0.82)。石英闪长岩为中钾钙碱性偏铝质岩石(A/CNK=0.84~0.88),其SiO 2含量为58.55%~63.32%,具有较高的Mg#值(44~48)和弱的负Eu异常(δEu=0.68~0.81)。另外,所有黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩样品的Sr-Nd同位素和锆石εHf(t)值相近((87 Sr/86 Sr)i=0.703594~0.703939,εNd(t)=+4.6~+4.8,εHf(t)=+10.9~+15.6)。矿物成分分析表明,黑云母二长花岗岩和镁铁质微粒包体中发育环带的斜长石An值由中心向边部逐渐下降,未发育反环带结构;石英闪长岩中的辉石为单斜辉石,所分析角闪石均为钙质角闪石,黑云母为镁质黑云母。综合上述特征,本文认为黑云母二长花岗岩、镁铁质微粒包体以及同生石英闪长岩分别代表了源自亏损地幔的母岩浆通过分离结晶作用所派生的不同阶段的产物:其中,石英闪长岩最先由基性岩浆发生以辉石、Ti-Fe氧化物和磷灰石为主的分离结晶作用形成,继而作为母岩浆进一步分异演化;镁铁质微粒包体是岩浆早期结晶的堆晶产物;而黑云母二长花岗岩代表了包体形成后残余熔体的组分。本文的研究表明,冈底斯岩浆岩带晚白垩世发生了富水条件下的岩浆分离结晶和堆晶作用,俯冲带弧岩浆分异对于大陆地壳的形成和演化发挥着重要的作用。  相似文献   

大兴安岭牙克石地区新元古代与晚古生代两类岩石组合的构造属性及其地质意义   总被引：2，自引：2，他引：0  

董金龙  白志达  徐德兵  罗志波 《岩石学报》2018,34(6):1758-1774

在内蒙牙克石地区发育两种不同构造属性的岩石组合:一类为乌奴耳-头道桥蛇绿混杂岩,另一类为晚古生代弧属性侵入岩。乌奴耳-头道桥蛇绿混杂岩由辉长岩、辉长辉绿岩、辉绿玢岩(岩墙?)、变玄武岩和放射虫硅质岩组成;地球化学特征显示基性岩类属于拉斑玄武岩系列,具有相似的稀土和原始地幔标准化配分模式,与N-MORB的特征类似,不具有Nb-Ta负异常,Nb/Nb~*值平均1;构造环境判别图显示该蛇绿混杂岩可能形成于扩张脊。晚古生代弧属性侵入岩出露于白井山、乌尔其汗,由中基性单元(辉长岩、辉长闪长岩和石英闪长岩)和酸性单元(花岗闪长岩和二长花岗岩)组成;地球化学特征显示中基性单元和酸性单元属于钙碱性岩系列,富集LREEs和LILEs,具有Nb-Ta负异常,高Sr、Sr/Y值,低HREEs和Y,Eu异常不明显;酸性单元显示埃达克质岩的地球化学特征。乌奴耳-头道桥蛇绿混杂岩可能形成于新元古代,与头道桥蓝片岩、吉峰蛇绿混杂岩、新林蛇绿岩构成一条重要的缝合带,暗示本区古洋盆的存在。晚古生代弧属性侵入岩中,辉长岩的结晶年龄为326±1.9Ma,花岗闪长岩的结晶年龄为323.7±1.9Ma;微量元素的组成特征显示,中基性单元和酸性单元的形成与早石炭世洋壳板片的俯冲作用有关,暗示兴安地块和松嫩地块之间洋盆的萎缩。  相似文献   

基于扫描电镜技术电弧直读原子发射光谱载体缓冲剂的改进     

邱宏喜  赵刚  刘玖芬  李克勇  龙志武  李志雄  向懋笔  刘伟洪 《岩矿测试》2018,37(3):283-291

原子发射光谱粉末固体进样法由于样品处理方法简单,检出限低,环境污染小,被大量应用于痕量Ag、B、Sn等多种元素的同时测定,但显著的基体效应制约了方法的适用性。本文基于扫描电镜微区检测技术,对比分析了特定配方与不同样品、在不同时段反应产物的组成差异,结合蒸发曲线反推反应过程,研制了适用于不同基体类型地球化学样品的载体缓冲剂。在实现前人致力改善弧烧过程的基础上,研制的载体缓冲剂是以K2S2O7、Na F作为助熔剂,"催化"基体分解,与聚四氟乙烯、沉降S等协同促进待测元素以多种形式快速蒸发;缓冲剂在与样品基体作用过程中形成的Al_2O_3-SiO_2-CaO-BaO互熔体降低了Tammann温度,能够原位吸收Ca O、Si O等基体氧化物,抑制了其干扰。相比已有方法,灵敏度提高1.2倍以上,精密度、准确度、检出限等优于各类地球化学调查规范要求。  相似文献   

稀有矿物天津蓟县锰方硼石振动光谱特征研究   总被引：2，自引：0，他引：2  

张然  许虹  李梅梅 《岩矿测试》2018,37(2):139-145

锰方硼石是一种罕见的锰氯硼酸盐矿物(Mn_3B_7O_(13)Cl),天津蓟县锰方硼石矿床是世界上唯一一个锰方硼石矿床,该地锰方硼石矿物粒度细小(50~300 nm),与美国锰方硼石存在明显差别。目前涉及我国锰方硼石的研究较少,为了探究稀有矿物蓟县锰方硼石矿物学和材料学特征,本文对其进行振动光谱和高温拉曼光谱研究。常温振动光谱结果表明,蓟县锰方硼石与美国锰方硼石各主要谱带归属一致,但峰位整体上表现为向高频方向偏移且谱峰宽、强度小。高温拉曼光谱显示,随着温度升高,谱带向低频方向偏移,位移距离随温度升高呈现先增大后减小的趋势,且在680~687K处位移距离出现转折。蓟县锰方硼石粒度细小是造成上述谱峰变化的主要原因。本文运用高温拉曼技术对粒度极为细小的锰方硼石进行测试分析,研究其谱峰变化与相变的关系,实验证明高温拉曼光谱可以作为研究矿物相变的一种有效手段。  相似文献   

电感耦合等离子体发射光谱法测定西藏矽卡岩型铜多金属富矿石中8种成矿元素     

王祝  邵蓓  柳诚  冯源强  刘高令  邬国栋  李明礼 《岩矿测试》2018,37(2):146-151

矽卡岩型铜多金属富矿石是西藏特有矿产,具有成矿元素多样且含量普遍较高的特点,矿物类型主要为硫化物型,成矿元素有Cu、Pb、Zn、Fe、Ag、Bi、Cd、Co等。采用湿法处理此类样品时常因银、铅等元素含量较高出现难溶解、易沉淀现象,导致测定结果偏低。本文采用盐酸预处理、硝酸-氢氟酸-高氯酸溶矿体系,能有效除去样品中的硫,样品分解效果好,选择稀释倍数为1000、溶液介质为10%盐酸,样品溶液不会产生沉淀,采用电感耦合等离子体发射光谱法测定各待测元素均可获得较好的准确度、精密度。方法测定范围为:Cu 0.0056%~20.0%,Pb 0.0087%~20.0%,Zn 0.0031%~20.0%,Fe 0.0090%~20.0%,Ag 5.40~3000μg/g,Bi 10.8~5000μg/g,Cd 0.69~5000μg/g,Co 2.09~5000μg/g。用国家标准物质进行验证,方法准确度小于5.40%,精密度(RSD,n=11)小于4.41%。该方法具有前处理流程简单、分析速度快、同时测定元素多、线性范围宽等优点,经实际样品测试与不同方法分析数据吻合。  相似文献   

Liassic age of an oceanic gabbro of the External Rif (Morocco): Implications for the Jurassic continent–ocean boundary of Northwest Africa     

《Comptes Rendus Geoscience》2018,350(6):299-309

This work concerns the northernmost limit of the West African Craton (WAC) and Variscan WAC-related terranes of NW Africa. Based on newly obtained radiometric age of an oceanic gabbro from the “Mesorif Suture Zone” of the External Rif Belt, we propose a revised interpretation of this puzzling lineament. We report on a 190 ± 2 Ma LA–ICP–MS U–Pb zircon age of a trondhjemite vein cross-cutting the Bou Adel gabbro, which is one of the largest oceanic units of the quoted suture zone. We previously interpreted the arcuate MSZ in terms of transported, hyper-extended margin of the Alpine Tethys, based on a K–Ar 166 ± 3 Ma age ascribed to the Bou Adel gabbro in the literature. The new, Early/Middle Liassic age coincides instead with the onset of oceanic floor formation in the Central Atlantic. We hypothesize that the Mesorif suture zone corresponds to the transported trace of the West African Atlantic margin surrounding the northwestern Moroccan Meseta promontory and connecting with the ENE-trending North African Transform North African transform. The latter zone sharply bounded the North Africa margin and connected the Central Atlantic with the Alpine Tethys. We propose that transported elements from the North African transform constitute the “Mesorif Basalt–Breccias” lineament parallel to and more external than the Mesorif suture zone. If correct, this new interpretation provides an opportunity to develop detailed field and laboratory studies of an exhumed segment of the up-to-now conceptual Jurassic North African transform.  相似文献