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1.
哈萨克斯坦北部Kumdy-Kol金刚石矿床地质与变质金刚石成因 总被引：1，自引：0，他引：1
Pavel NITSENKO 《地学前缘》2004,11(2):333-338
哈萨克斯坦北部Kokchetav地区的Kumdy Kol金刚石矿床是世界上惟一的变质金刚石矿床。对该金刚石矿床成因以及相关岩石的诸多研究成果不仅深化了对超高压变质岩的研究 ,而且推动了大陆动力学研究的进展。在该金刚石矿床中找到的岩相学证据证明 ,该金刚石矿床的主要含矿岩石大理岩曾经在俯冲带中循环到 >2 4 0km的深部。文章在介绍Kokchetav变质金刚石矿床的地质特征和大地构造背景的基础上 ,讨论了该变质金刚石矿床的形成过程以及变质金刚石的成因。Kokchetav变质金刚石主要表现出蜂窝状或草莓状的特征外形。这种蜂窝状或草莓状金刚石是快速生长条件下结晶的结果。结合最近的研究成果 ,笔者认为Kokchetav金刚石矿床中金刚石的形成与深俯冲大理岩中的白云石分解作用密切相关。白云石分解反应形成文石和菱镁矿组合 ,菱镁矿继续分解形成金刚石 (MgCO3 =金刚石 +MgO +O2 )。基于这个认识 ,Kokchetav金刚石矿床中碳 (金刚石和石墨 )的来源应该是碳酸盐岩 相似文献
2.
Jinfu Shu 《地学前缘(英文版)》2012,3(1):1-8
We have performed measurements of minerals based on the synchrotron source for single crystal and powder X-ray diffraction,inelastic scattering,spectroscopy and radiography by using diamond anvil cells.We investigated the properties of iron（Fe）,iron-magnesium oxides（Fe,Mg）O, silica（SiO2）,iron-magnesium silicates（Fe,Mg）SiO3 under simulated high pressure-high temperature extreme conditions of the Earth’s crust,upper mantle,low mantle,core-mantle boundary,outer core, and inner core.The results provide a new window on the investigation of the mineral properties at Earth’s conditions. 相似文献
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金刚石由于其独特的物理化学性质,在经济生产与科学研究中均具有重要价值.金刚石形成于地球大于150 km的深度范围内,是人类可以获得的来自地球深部地幔乃至核幔边界的最直接的样品,因此可以为研究地球深部物质组成和物理化学条件提供重要的素材.金刚石由碳元素组成,还含有微量的杂质元素（如氮、硼、氢、氧等）,其中氮和硼元素对于划分金刚石的晶体结构类型发挥着重要的作用.根据金刚石的产出类型,金刚石可以划分为幔源型、超高压变质型、陨石相关型以及蛇绿岩型金刚石.全球约百分之一的幔源型金刚石含有包裹体,对这些包裹体的研究显示,金刚石主要来源于地球150~200 km深度的岩石圈地幔.这些含有包裹体的金刚石中,仅有1%的金刚石来自于地球深部的软流圈、地幔过渡带、下地幔、甚至核幔边界.我国的金刚石产出类型多样,但是,目前仅山东蒙阴、辽宁复县的金伯利岩矿床以及湖南沅水的砂矿具有经济价值.蛇绿岩型金刚石是近年来金刚石研究领域取得的重要进展,该类型金刚石分布在全球多个造山带不同时代、不同构造属性的蛇绿岩地幔橄榄岩和铬铁矿中,被认为是一种新的金刚石的产出类型.相对于其他国家和地区的金刚石的研究,我国的金刚石领域的研究程度相对较低,缺乏对金刚石结构、化学组成以及包裹体组成的系统研究,制约了对我国金刚石成因的认识,限制了我国的金刚石的找矿工作.因此,亟需结合先进的分析手段对我国的金刚石及其围岩做进一步的研究,以期揭示金刚石的形成过程,为金刚石的找矿提供理论基础. 相似文献
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上天、入地、下海,进行极端条件下的矿物学研究,研究微矿物,发现新矿物。主要利用金刚石压机,结合使用国内外同步辐射X-光源、中子源,以及其他多种物理的、化学的、光学的测试手段(如岩石矿物化学分析,光薄片测定,电子探针,离子探针,扫描电镜,透射电镜,红外、紫外、拉曼光谱,激光加热等),对来自天外的陨石、陨石坑样品、地球深处地幔源矿物以及海底甲烷水合物进行了一些研究。模拟不同温度和压力下各种不同成分的矿物材料的晶体结构、物理和化学性质。文章着重研究从地球内核到地壳海底的各种不同组分在不同温度、压力极端环境下形成的各种各样的典型矿物:从金属固体内核和金属液体外核中的ε-Fe到核幔边界(CMB)地球D″层的后钙钛矿(Post-Perovskite)结构(ppv)镁铁硅酸盐(Mg,Fe)SiO3,从下地幔中的铁磁性钙钛矿(Perovskite)结构(pv)镁铁硅酸盐布里奇曼石(Bridgmanite)(Mg,Fe)SiO3、镁铁氧化物(Fe,Mg)O和后尖晶石(Post-Spinel)结构的含Fe3+毛河光矿(Maohokite)(HP-Mg$Fe^{3+}_{2}O_{4}$)到过渡带、上地幔和地壳中的镁铁硅酸盐、硅氧化物、铬铁氧化物和金刚石及其内含物以及甲烷水合物(CH4·H2O)等。进行高温高压极端条件下的矿物学研究,为探索地球结构性质、形成动力和发展历史提供了新的窗口。 相似文献
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S.A. Morse 《Geochimica et cosmochimica acta》2002,66(12):2155-2165
Mushy zones, assemblages of crystals and their pore-space liquids, have been invoked for both the upper and lower boundaries of the liquid outer core. The timescale of very slow accumulation compared with solidification at either of these interfaces militates against such zones, where instead hard ground should be expected to form by solidification at the interface. Such adcumulus growth involves isothermal, isocompositional solidification by successful exchange of evolving solute with fresh melt from an infinite reservoir. At both boundaries of the outer core, the removal of rejected material is significantly aided by compositional convection. The accumulation rates at the outer core boundaries are orders of magnitude slower than required for adcumulus growth, as calibrated both by field and experimental evidence in silicate melts. A conceptual phase diagram for the core-mantle boundary helps to visualize the relevant equilibria. Capture of core metal into the mantle has been suggested to occur via a mushy zone, to explain a high electrical conductivity there, as plausibly required by the secular behavior of the Earth’s nutation. One conjecture is that the rejected light elements from the freezing of the inner core might be able to congregate as a porous flotation sediment at the top of the core. The idea of porosity in such a mushy zone must be rejected from experience with solidification of cumulates from magmas.A high electrical conductivity might instead be caused by solution of core metal by mantle, followed by exsolution. The hottest part of the mantle lies in contact with the molten outer core, where the maximum solubility of Fe must occur in the major mantle phases. On leaving the core-mantle boundary, the mantle must cool and may exsolve metal on the metal-silicate solvus. If the iron-rich metal resides chiefly in the rheologically weaker metal oxide phase, which coats the deforming perovskite grains, it may furnish a short circuit for mantle conductivity in the basal mantle. At still cooler and higher levels, the mantle encounters more normal mantle redox conditions, and any exsolved Fe metal should oxidize to FeO in the metal oxide and perovskite phases, ceasing to be a conductor. 相似文献
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《Russian Geology and Geophysics》2016,57(8):1135-1142
A fluid model for the formation of mantle plumes is proposed. During the emission of gas from the Earth’s core, it accumulates as lenses at the core-mantle boundary. Reaching a critical size, the lenses burst out into the mantle and migrate to the surface. A relatively stationary transmantle fluid flow from the core-mantle boundary arises, which heats the mantle and the layer interacting with it. The flow stops in the base of the hard lithosphere and spreads laterally, causing its melting accompanied by the formation of magma chambers, which, reaching critical sizes, massively intrude and flow out. 相似文献
9.
Yusuke Seto Daisuke Hamane Takaya Nagai Kiyoshi Fujino 《Physics and Chemistry of Minerals》2008,35(4):223-229
We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K,
corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition
process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm.
With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO2 + perovskite via reactions with SiO2. Magnesite is not the only host phase for subducted carbon—solid CO2 also carries carbon in the lower mantle. Furthermore, CO2 itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for
diamond formation in the lower mantle. 相似文献
10.
Gerhard P. Brey Vadim Bulatov Andrei Girnis Jeff W. Harris Thomas Stachel 《Lithos》2004,77(1-4):655-663
Experiments on compositions along the join MgO–NaA3+Si2O6 (A=Al, Cr, Fe3+) show that sodium can be incorporated into ferropericlase at upper mantle pressures in amounts commonly found in natural diamond inclusions. These results, combined with the observed mineral parageneses of several diamond inclusion suites, establish firmly that ferropericlase exists in the upper mantle in regions with low silica activity. Such regions may be carbonated dunite or stalled and degassed carbonatitic melts. Ferropericlase as an inclusion in diamond on its own is not indicative of a lower mantle origin or of a deep mantle plume. Coexisting phases have to be taken into consideration to decide on the depth of origin. The composition of olivine will indicate an origin from the upper mantle or border of the transition zone to the lower mantle and whether it coexisted with ferropericlase in the upper mantle or as ringwoodite. The narrow and flat three phase loop at the border transition zone—lower mantle together with hybrid peridotite plus eclogite/sediments provides an explanation for the varying and Fe-rich nature of the diamond inclusion suite from Sao Luiz, Brazil. 相似文献
11.
Structure, mineralogy and dynamics of the lowermost mantle 总被引：1，自引：0，他引：1
Reidar G. Trønnes 《Mineralogy and Petrology》2010,99(3-4):243-261
The 2004-discovery of the post-perovskite transition initiated a vigorous effort in high-pressure, high-temperature mineralogy and mineral physics, seismology and geodynamics aimed at an improved understanding of the structure and dynamics of the D"-zone. The phase transitions in basaltic and peridotitic lithologies under pT-conditions of the lowermost mantle can explain a series of previously enigmatic seismic discontinuities. Some of the other seismic properties of the lowermost mantle are also consistent with the changes in physical properties related to the perovskite (pv) to post-perovskite (ppv) transition. After more than 25 years of seismic tomography, the lowermost mantle structure involving the sub-Pacific and sub-African Large Low Shear-Velocity Provinces (LLSVPs) has become a robust feature. The two large antipodal LLSVPs are surrounded by wide zones of high Vs under the regions characterized by Mesozoic to recent subduction. The D" is further characterized by a negative correlation between shear and bulk sound velocity which could be partly related to an uneven distribution of pv and ppv. Ppv has higher VS and lower $ V_{\Phi } $ (bulk sound speed) than pv and may be present in thicker layers in the colder regions of D". Seismic observations and geodynamic modelling indicate relatively steep and sharp boundaries of the 200-500 km thick LLSVPs. These features, as well as independent evidence for their long-term stability, indicate that they are intrinsically denser than the surrounding mantle. Mineral physics data demonstrate that basaltic lithologies are denser than peridotite throughout the lowermost mantle and undergo incremental densification due to the pvppv- transition at slightly shallower levels than peridotite. The density contrasts may facilitate the partial separation and accumulation of basaltic patches and slivers at the margins of the thermochemical piles (LLSVPs). The slopes of these relatively steep margins towards the adjacent horizontal core-mantle boundary (CMB) constitute a curved (concave) thermal boundary layer, favourable for the episodic generation of large mantle plumes. Reconstruction of the original positions of large igneous provinces formed during the last 300 Ma, using a paleomagnetic global reference frame, indicates that nearly all of them erupted above the margins of the LLSVPs. Fe/Mg-partitioning between pv, ppv and ferropericlase (fp) is important for the phase and density relations of the lower mantle. Electronic spin transition of Fe2+ and Fe3+ in the different phases may influence the Fe/Mg-partitioning and the radiative thermal conductivity in the lowermost mantle. The experimental determination of the $ {K_D}{^{Fe/Mg}_{pv/fp}}\left[ { = {{\left( {Fe/Mg} \right)}_{pv}}/{{\left( {Fe/Mg} \right)}_{fp}}} \right] $ and $ {K_D}{^{Fe/Mg}_{ppv/fp}} $ is technologically challenging. Most studies have found a $ {K_D}{^{Fe/Mg}_{pv/fp}} $ of 0.1-0.3 and a higher Fe/Mg-ratio in ppv than in pv. The experimental temperature is important, with the partitioning approaching unity with increasing temperature. Although charge-coupled substitutions of the trivalent cations Al and Fe3+ seem to be important in both pv and ppv (especially in basaltic compositions), the complicating crystal-chemistry effects of these cations are not fully clarified. The two anti-podal thermochemical piles as well as the thin ultra-low velocity zones next to the CMB may represent geochemically enriched reservoirs that have remained largely isolated from the convecting mantle through a major part of Earth history. The existence of such “hidden” reservoirs have previously been suggested in order to account for the imbalance between the inferred composition of the geochemically accessible convecting mantle and the observed heat flow from the Earth and chondritic models for the bulk Earth. 相似文献
12.
核—幔相互作用及其地球动力学意义 总被引：1，自引：0，他引：1
核－幔边界是地球内部反差最大的一个边界,也是最重要的边界,界区的核－幔相互作用过程在整个地球动力学系统中起着重要的作用。本文在概述了该－边界基本特征的基础上,系统地总结了有关核幔物质的化学反应和Ｄ”层的形成,核－幔间的质量传递及其对地幔对流之贡献,核－幔耦合与动量传递等的研究成果及有关问题。 相似文献
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《Russian Geology and Geophysics》2015,56(9):1322-1331
Experimental data on Fe-CaCO3 interaction at 6 GPa and 1273–1873 K are presented. The system models the hypothetical redox interaction in subducting slabs at the contact with the reduced mantle and a putative process at the core-mantle boundary. The reaction is accompanied by carbonatite melt formation. It also produces Fe3C and calcium wustite, which form solid or liquid phases depending on experimental conditions. In iron-containing systems at 6 GPa, calcium carbonate melts in the range 1473–1573 K, which is consistent with aragonite disappearance from complex carbonate systems. The composition of calcium carbonate liquid is not influenced by metallic Fe. It corresponds to nearly pure CaCO3. Along the mantle adiabat or at slightly higher temperatures, nearly pure CaCO3 coexists with metallic iron or calcium wustite. This hypothesis explains the coexistence of metallic iron and carbonate inclusions in lithospheric and superdeep diamonds. 相似文献
14.
Liquid Fe metal-liquid silicate partition coefficients for the lithophile and weakly-siderophile elements Ta, Nb, V, Cr, Si, Mn, Ga, In and Zn have been measured in multianvil experiments performed from 2 to 24 GPa, 2023-2873 K and at oxygen fugacities of −1.3 to −4.2 log units relative to the iron-wüstite buffer. Compositional effects of light elements dissolved in the metal liquid (S, C) have been examined and experiments were performed in both graphite and MgO capsules, specifically to address the effect of C solubility in Fe-metal on siderophile element partitioning. The results were used to examine whether there is categorical evidence that a significant portion of metal-silicate equilibration occurred under very high pressures during core-mantle fractionation on Earth. Although the depletion of V from the mantle due to core formation is significantly greater than that of Nb, our results indicate that both elements have similar siderophile tendencies under reducing conditions at low pressures. With increasing pressure, however, Nb becomes less siderophile than V, implying that average metal-silicate equilibration pressures of at least 10-40 GPa are required to explain the Nb/V ratio of the mantle. Similarly the moderately-siderophile, volatile element ratios Ga/Mn and In/Zn are chondritic in the mantle but both volatility and core-mantle equilibration at low pressure would render these ratios strongly sub-chondritic. Our results indicate that pressures of metal-silicate partitioning exceeding 30-60 GPa would be required to render these element ratios chondritic in the mantle. These observations strongly indicate that metal-silicate equilibration must have occurred at high pressures, and therefore support core-formation models that involve deep magma oceans. Moreover, our results allow us to exclude models that envisage primarily low-pressure (<1 GPa) equilibration in relatively small planetary bodies. We also argue that the core cannot contain significant U as this would require metal-silicate equilibration at oxygen fugacities low enough for significant amounts of Ta to have also been extracted from the mantle. Likewise, as In is more siderophile than Pb but similarly volatile and also quite chalcophile it would have been difficult for Pb to enter the core without reversing the relative depletions of these elements in the mantle unless metal-silicate equilibration occurred at high pressures >20 GPa. 相似文献
15.
根据体波层析成像技术,利用大量走时数据,做出0°～180°E,30°S～90°S范围内0～2889km深的三维速度分布图像,得到欧亚地区局部区域岩石圈及地幔的高分辨率速度结构,并从地球动力学角度出发对这些成像结果做进一步解释。 相似文献
16.
I. I. Fedorov A. I. Chepurov V. M. Sonin A. A. Chepurov A. M. Logvinova 《Geochemistry International》2008,46(4):340-350
Silicate inclusions are widespread in natural diamonds, which also may contain rare inclusions of native iron. This suggests that some natural diamonds crystallized in metal-silicate-carbon systems. We experimentally studied the crystallization of diamond and silicate phases from the starting composition Fe0.36Ni0.64 + silicate glass + graphite and calculated the Fe mole fractions of the silicate phases crystallizing under these conditions. The silicates synthesized together with diamond had low Fe mole fractions [Fe/(Fe + Mg + Ca)] in spite of strong Fe predominance in the system. The Fe mole fractions of the silicates decreased in the sequence garnet-pyroxene-olivine, which is consistent with the results of our thermodynamic calculations. The Fe mole fraction of silicates under various redox conditions under which metal-carbon melts are stable drastically decreases with decreasing fo2. The low Fe mole fractions of silicate inclusions in diamond from the Earth’s mantle can be explained by the highly reducing crystallization conditions, under which Fe was concentrated as a metallic phase of the magmatic melts and could be only insignificantly incorporated in the structures of silicates. 相似文献
17.
Yu. V. Bataleva Yu. N. Palyanov Yu. M. Borzdov O. A. Bayukov N. V. Sobolev 《Doklady Earth Sciences》2016,466(1):88-91
Experimental studies of the Fe0–(Mg, Ca)CO3–S system were carried out during 18–20 h at 6.3 GPa, 900–1400°C. It is shown that the major processes resulting in the formation of free carbon include reduction of carbonates upon redox interaction with Fe0 (or Fe3C), extraction of carbon from iron carbide upon interaction with a sulfur melt/fluid, and reduction of the carbonate melt by Fe–S and Fe?S–C melts. Reconstruction of the processes of graphite formation indicates that carbonates and iron carbide may be potential sources of carbon under the conditions of subduction, and participation of the sulfur melt/fluid may result in the formation of mantle sulfides. 相似文献
18.
地幔柱大辩论及如何验证地幔柱假说 总被引：20，自引：1，他引：20
目前关于地幔柱存在与否的争论主要集中在地幔柱学说的三个假设上:(1)起源于地球核幔边界缓慢上升的细长柱状热物质流;(2)热点下具有异常高温地幔;(3)地幔柱是相对静止的。这三个方面的验证需要今后深部地球物理探测、岩石学和古地磁等学科的综合运用和进一步的工作。文中认为,地幔柱学说依然能合理地解释地球上一级地质现象,反对地幔柱的学者过分强调了一些小尺度的与地幔柱理论不符的细节,而小尺度地壳特征显然还受到其他许多因素的影响。可以从以下5个方面来鉴别老地幔柱:(1)大规模火山作用前的地壳抬升;(2)放射状岩墙群;(3)火山作用的物理特征;(4)火山链的年代学变化;(5)地幔柱产出岩浆的化学组成。研究表明,峨眉山大火成岩省满足其中的3到4个指标,因此地幔柱是形成峨眉山玄武岩的主要动力学机制。 相似文献
19.
核幔边界层在地球演化过程中扮演着极为重要的作用,是人们认识地球的主要研究对象之一。文中综述了近十多年来对核幔边界D″区开展地震学研究的主要方法及成果,内容涵盖了核幔边界D″区上部间断面、不均匀性、各向异性和超低速层等4个主要研究对象。结合多个相关学科的研究进展,从对热-化学-动力学三方面的耦合作用的分析,来探讨形成D″区各种观测现象的原因和机制,以及在此基础上提出的动力学演化模型。最后简要叙述了有关核幔边界研究的地震学、矿物实验、理论分析及计算科学的发展方向和挑战。随着对D″区认识的不断更新,逐步揭示地表观测到的可能受核幔边界因素控制的多种地质及地球物理现象。 相似文献
20.
Cathodoluminescence (CL) imaging of polished sections of a diamond from the Guaniamo region of Venezuela suggests a history of the diamond involving two periods of growth separated by a period of resorption and possibly brittle deformation. In situ electron probe analysis of multiple eclogitic garnet inclusions reveals a correlation between garnet composition and location in the stone. An early-formed garnet in the diamond core has higher Ca/(Ca+Mg) and lower Mg/(Mg+Fe) values than later garnets associated with the second period of diamond growth. This variation conforms to an extensive trend of variation in the suite of eclogitic garnets extracted from Venezuelan diamonds. The diamond is zoned in carbon isotope composition (in situ secondary ion mass spectrometry, SIMS, data). The core compositions (δ13C PDB), corresponding to the first stage of growth, average −17.7‰. The second period of growth is apparently in two sub-sets of CL zones with mean values of −13.0‰ and −7.9‰. Nitrogen contents of diamond are low (30–300 atomic ppm) and do not correlate with carbon isotope composition. Oxygen isotope ratios of the garnet inclusions are elevated substantially above those expected for “common mantle”; δ18O VSMOW of early garnet is approximately +10.5‰ and two late garnets average +8.8‰. The evolutionary trend of magnesium enrichment in garnet is unlikely to represent igneous fractionation. The stable isotope data are consistent with diamond formation in subducted meta-basic rocks that had interacted with sea water at low temperatures at or near the sea floor and contained a substantial biogenic carbon component. During or following subduction, diamonds continued to form in an evolving system that was progressively modified by interaction with mantle material. 相似文献