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151.
Selection of the wavenumbers k using an optimization method for the inverse Fourier transform in 2.5D electrical modelling 总被引:1,自引:0,他引:1
An optimization method is used to select the wavenumbers k for the inverse Fourier transform in 2.5D electrical modelling. The model tests show that with the wavenumbers k selected in this way the inverse Fourier transform performs with satisfactory accuracy. 相似文献
152.
Carlos Calcáneo-Roldán Ben Moore Joss Bland-Hawthorn David Malin Elaine M. Sadler 《Monthly notices of the Royal Astronomical Society》2000,314(2):324-333
Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m b ∼27–28 mag arcsec−2 , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709. 相似文献
153.
154.
黑龙江省伊春红星地区大地构造上位于布列亚-佳木斯地块和张广才岭造山带结合部位,区内出露晚三叠世碱性花岗岩,其岩石组合为正长花岗岩、碱长花岗岩、含钠闪石、霓石碱性花岗岩。地球化学上,该套岩石具有富硅、富碱,铁镁比值较高,CaO、MgO含量低,富含F、Zr、Nb、Ce、Ga、稀土元素(REE)、Y和Zn等元素,贫Sr、P、Ti,镓铝比值高,轻重稀土分馏显著,具有强的Eu负异常等特点。在花岗岩成因类型判别图解中,它们均投影在A型花岗岩区,结合岩石具有过碱和相对贫铝的化学组成特征,表明它们应属过碱性A型花岗岩。在微量元素蛛网图上,这套岩石表现出较明显的Ba、Sr、P、Ti的负异常,保留有先期“弧”岩浆作用的地球化学印记,其Y/Nb和Y/Ta比值也较高,分别为1.55—3.27和13.5~44.00,在A型花岗岩岩石学亚类判别图解中,它们均投影在产于后造山环境的A2花岗岩区。根据对岩石地球化学的组成及产出地质背景的分析,表明这套岩石应形成于造山期后的张性构造环境。 相似文献
155.
大别造山带毛屋岩体的解体及古地幔性质的厘定 总被引:1,自引:0,他引:1
根据详细的地球化学 (特别是稀土元素地球化学 )的研究资料 ,提出大别造山带毛屋岩体应该解体。毛屋岩体不是由多幕式镁铁 超镁铁质层状堆晶作用形成的一套岩石系列 ,而是由橄榄岩类、含石榴石方辉岩类、榴辉岩类和绿辉石岩类组成的一个混杂岩体。其中含石榴石方辉岩类与绿辉石岩类之间存在成因上的联系 ,含石榴石方辉岩类的原岩是本区原始地幔经约36 %的部分熔融后剩下的残余 ,而绿辉石岩的原岩是由该熔融体结晶的产物。根据含石榴石方辉岩与绿辉石岩之间的成分制约关系 ,对该区古地幔的稀土元素组成和地幔性质进行了反演 ,结果表明 ,该区原始地幔稀土元素成分与球粒陨石中的相似 ,为轻稀土略亏损的平坦型组成模式 ;该区原始地幔矿物成分为橄榄石 (72 8% )、单斜辉石 (12 4% )和石榴石 (14 8% ) ,属含单辉石榴橄榄岩的地幔。 相似文献
156.
In a bimineralic eclogite xenolith (sample JJG41) from the Roberts Victor kimberlite, compositional gradients in clinopyroxene are related to garnet exsolution. Two principal reactions involving clinopyroxene and garnet occur: (i) The net-transfer Al2Si-1Mg-1 which is responsible for garnet growth according to the equation 2Di+Al2Si-1Mg-1=Grossular+MgCa-1 (reaction 1). This has created substantial compositional gradients in Al, Si and Mg within clinopyroxene. (ii) The exchange of Fe–Mg between garnet and clinopyroxene (reaction 2). During the stage of garnet growth (reaction 1) the lamellae crystallized sequentially as a result of a temperature decrease from around 1400 to 1200° C. This exsolution growth-stage was under the control of Al diffusion in clinopyroxene and at around 1200° C further growth of garnet lamellae became impeded by the sluggishness of Al diffusion in the clinopyroxene host. However, reaction 2 continued during further cooling down to about 1000° C; this temperature being inferred from the constant Fe–Mg partitioning at clinopyroxene-garnet interfaces for the whole set of lamellae. The initial clinopyroxene in JJG41 was probably formed by crystallization from a melt in Archaean time. The cessation of Fe–Mg exchange between garnet and clinopyroxene at about 1000° C may well predate the eruption of the eclogite in kimberlite at around 100 Ma. Kinetic models of reaction are examined for both reactions. Modelling of reaction 1, involving both diffusion and interface migration, allows several means of estimating the diffusion coefficient of Al in clinopyroxene; the estimates are in the range 10-16-10-20 cm2/s at 1200° C. These estimates bracket the experimentally determined data for Al diffusion in clinopyroxene, and from these experimental data a preferred cooling rate of about 300° C/Ma is obtained for the period of growth of garnet exsolution lamellae. A geospeedometry approach (Lasaga 1983) suitable for a pure-exchange process (reaction 2) is used to estimate the cooling rate in the later stages of the thermal history (after garnet growth); values 4–40° C/Ma are consistent with the shape of the Fe-diffusion gradients in the clinopyroxene. The extensive thermal history recorded by JJG41, including probable melt involvement at ca. 1400° C, demonstrates the complex evolution of rocks within the mantle. Whilst the notion of formation of mantle eclogites from subducted oceanic crust has become fashionable, it is clear that tracing eclogite geochemical and P-T characteristics backwards from their nature at the time of xenolith eruption, through high-temperature mantle events to the characteristics of the original subducted oceanic crust, will be very complex. 相似文献
157.
The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide(VHMS) deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead-sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered δ~(34)S_(CDT) values of 1.13‰-3.36‰, average 2.22‰, and show a tower-type distribution,implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides(~(206)Pb/~(204)Pb = 17.59225-18.56354, average 18.32020; ~(207)Pb/~(204)Pb =15.51770-15.69381, average 15.66217; ~(208)Pb/~(204)Pb= 37.99969-39.06953, average 38.52722) are close to the values of the volcanic host rocks(~(206)Pb/~(204)Pb= 18.10678-18.26293, average 18.21158; ~(207)Pb/~(204)Pb =15.63196-15.68188, average 15.65345; ~(208)Pb/~(204)Pb= 38.43676-38.56360, average 38.49171), thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo-Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit. 相似文献
158.
LEE Ben 《中国地球化学学报》2011,30(2):204-216
The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic. 相似文献
159.
利用中尺度模式MM5对1999年6月下旬发生在长江中下游地区的一次锋上西南低涡发展的梅雨锋暴雨过程进行了研究。通过敏感性试验, 探讨了低涡对锋强、 锋生的敏感性, 锋生、 锋消与低涡发展演变的时间空间上的联系等问题\.结果表明, 低涡对中层锋面强度的变化敏感, 中层锋强发生改变会导致整层涡度发生同位相的变化。中层系统对梅雨锋气旋的发展起主要作用, 中层锋面对低涡发展的影响比边界层锋更关键。中层锋面强度改变会激发出中低层的垂直次级环流, 低层的辐合上升运动发生改变, 最终影响到低涡强度的发展。敏感性试验证明, 锋面强度变化对低涡发展造成的影响有超前性, 中层锋面先发生变化, 6 h左右以后低涡强度发生改变。锋区强度和低涡强度发生变化的地理位置基本在同一经度上, 锋强变化的位置在涡强变化位置的北面。 相似文献
160.
利用新一代天气雷达资料分析了造成2011年6月18日湖北省江汉平原强降水涡旋状中尺度对流系统(MCS)发生发展过程的结构特征,联合常规观测、地面加密观测及雷达四维变分风场反演资料初步研究了MCS可能成因。结果表明:(1)成熟阶段的强降水涡旋状MCS回波表现为气旋性弯曲的多条螺旋对流回波带、周围被大片层状云回波所包裹的结构特征,后期因冷空气侵入演变出冷暖锋式结构。回波合并和旋转式列车效应是产生强降水的主要运动特征。(2)涡旋状MCS是在有利环境场下,主要由鄂西山地一江汉平原过渡带边界层中尺度涡旋系统强烈发展组织的结果。(3)中尺度涡旋系统形成发展与地面暖倒槽发展、西南低涡前侧降水和特殊地形作用有密切关系,来自不同方向气流形成的强烈辐合是其前期形成发展的主要机制,后期发展可能与潜热释放有关,涡旋环流向上发展到700 hPa。 相似文献