Microstructural development of fine-grained quartz aggregates by syntectonic recrystallization

Experimental study of syntectonic recrystallization of fine-grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition. Agate was axially compressed with a constant-strain-rate apparatus. Experiments were conducted at 4 kbar solid confining pressure, 700–1000°C and 10⁻⁴-10⁻⁶ sec⁻¹ to 10%–45% strain. In all runs, deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium.Two different types of microstructure were distinguished in the deformed specimens. One is P-type which is characterized by equant, equidimensional, and polygonal grains. The other is S-type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis. The P-type microstructure is developed at higher temperatures and slower strain rates, while the S-type developed at lower temperatures and faster strain rates. The transition between the S- and P-types is found to be very sharp.     

Flow behavior and microstructures of hydrous olivine aggregates at upper mantle pressures and temperatures

Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5–9.8 GPa, temperatures of 1223–1800 K, and strain rates ranging from 0.8 × 10^?5 to 7.5 × 10^?5 s^?1. The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 ± 6 cm³ mol^?1 and a stress exponent of 3.2 ± 0.6 at temperatures of 1323–1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323–1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633–1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 ± 7 cm³ mol^?1 assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol^?1 (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth’s upper mantle.     

闪锌矿40Ar/39Ar真空击碎与阶段加热定年技术

凡口铅锌矿闪锌矿样品40Ar/39Ar真空击碎实验释出较高的39Ark,电子探针分析证实了闪锌矿中含有丰富的钾矿物微晶,因此对该闪锌矿真空击碎分析后的固体粉末继续进行40Ar/39Ar阶段加热分析.真空击碎分析获得了两条明显分开的等时线,对应的等时线年龄～235 Ma和～270 Ma分别代表了次生、原生流体包裹体的形成年龄.固体粉末阶段加热分析获得了闪锌矿中钾矿物微晶的年龄为～271 Ma,与该闪锌矿原生包裹体年龄一致,代表了闪锌矿的成矿年龄.真空击碎和阶段加热实验得到截然不同的K/Ca比值,表明真空击碎法提取的气体主要来自流体包裹体,而加热法释出的气体则主要来自钾矿物微晶.闪锌矿40Ar/39At真空击碎与阶段加热分析技术将为探索铅锌矿床直接定年提供新的技术手段.     

来自蛇绿岩地幔的硫（砷）化物矿物组合

近来在西藏雅鲁藏布江蛇绿岩带的罗布莎蛇绿岩块的地幔豆荚状铬铁矿中发现一个包括金刚石、柯石英、自然元素、合金、氧化物以及硫(砷)化物组成的地幔矿物群。该矿物群的硫(砷)化物具有特殊化学成分并呈包裹体分布在贱金属(BM)和铂族元素(PGE)或它们的合金中,大量化学成分分析得知它们主要由下列元素组成:S、As、Te、Fe、Ni、Co、Cu、Pt、Pd、Ru、Rh、Os、Ir、Mn和Ti。根据化学成分可辨别出约30种硫(砷)化物矿物:FeS、NiS、(Ni,Fe)S、Fe3S2、Ni3S2、(Ru,Os,Ir)S2、Rh7As3、Rh5Ni(Cu)As4、Pd4Rh3As3、Pd8As2、Pd3TeAs、Pd7Te3、RuAs、PtAs2、Ni4Rh3As3、Rh(As,S)2、(Rh,Ir)(As,S)2、Ir(As,S)2、MnS、Ti7S3、Ti7N3、Rh3.5Se3.5CuS2、RhS、Ir2S3、(Ir,Cu)2、S3(Co,Ni,Fe)2(As,S)3、(Ir,Pt)(As,S)2、Ru3(As,S)7以及(BM)x(PGE)yS10-(x y)等,其中包括已定名和未定名的矿物。由于矿物粒度小(<25μm),缺乏X射线分析资料,有待进一步研究。     

锶掺杂的正铌酸镧超细粉体的合成与性能

采用溶胶低温燃烧法和高温固相反应法制备了锶掺杂的正铌酸镧（La0.95Sr0.05NbO4）超细陶瓷粉体。应用XRD、SEM和激光粒度分析仪等对陶瓷粉体的物相、粒度和粒度分布进行了表征,同时考察了两种方法制备的粉体的烧结性能。结果表明：采用溶胶低温燃烧法制备的La0.95Sr0.05NbO4（LSNb）为粒径〈100 nm、粒度分布范围窄的超细粉体;高温固相反应法制备的粒径为0.5-1.0μm、呈球形的LSNb超细陶瓷粉体。溶胶低温燃烧法制备的粉体在1 250℃烧结10 h形成致密的陶瓷片;高温固相反应法制备的粉体在1 400℃以上烧结10 h致密。两种LSNb致密膜均具有一定的透氢作用,900℃氢渗速率分别为1.96&#215;10^-3mL&#183;cm^-2&#183;min^-1和1.67&#215;10^-3mL&#183;cm^-2&#183;min^-1。     

On the nature of mantle heterogeneities and discontinuities: evidence from a very dense wide-angle shot record

A seismic survey with a receiver spacing of 50 m provided one of the most densely sampled wide-angle seismic reflection images of the lithosphere. This unique data set, recorded by an 18-km-long spread, reveals that at wide-angles the shallow subcrustal mantle features high amplitude reflectivity which contrasts with a lack of reflectivity at latter travel times. This change in the seismic signature is located at approximately 120–150 km depth, which correlates with the depth estimates of the lithosphere–asthenosphere boundary (LAB) of previous DSS studies. This seismic signature can be simulated by two-layer mantle model. Both layers with similar average velocities differ in their degree of heterogeneity. The shallow heterogeneous layer and the deeper and more homogeneous one correlate with the lithosphere and the asthenosphere, respectively. Studies involving surface outcrops of ultramafic massifs and mantle xenoliths infer that the upper mantle is a heterogeneous mixture of ultramafic rocks (lherzolites, harzburgites, pyroxenites, peridotites, dunites, and small amounts of eclogites). Laboratory measurements of physical properties of these mantle rocks indicate that compositional variations alone can account for the wide-angle reflectivity. A temperature increase would homogenize the mixture, decreasing the seismic reflection properties due to melting processes. It is proposed that this would take place below 120–150 km (1200 °C, the LAB).     

Spatial correlation of deformation and mineral reaction in experimentally deformed plagioclase–olivine aggregates

Shear deformation of hot pressed plagioclase–olivine aggregates was studied in the presence and absence of mineral reaction. Experiments were performed at 900 °C, 1500 MPa, and a constant shear strain rate of 5×10⁻⁵ s⁻¹ in a solid medium apparatus. Whether the mineral reaction between plagioclase and olivine takes place or not is controlled by choosing the appropriate plagioclase composition; labradorite (An₆₀) does not react, anorthite (An₉₂) does. Labradorite–olivine aggregates deformed without reaction are very strong and show strain hardening throughout the experiment. Syndeformational reaction between olivine and anorthite causes a pronounced strain weakening. The reaction produces fine-grained opx–cpx–spinel aggregates, which accommodate a large fraction of the finite strain. Deformation and reaction are localised within a 0.5-mm-wide sample. Three representative samples were analysed for their fabric anisotropy R* and shape-preferred orientation α* (fabric angle with the shear plane) using the autocorrelation function (ACF). Fabric anisotropy can be calibrated to quantify strain variations across the sheared samples. In the deformed and reacted anorthite–olivine aggregate, there is a strong correlation between reaction progress and strain; regions of large shear strain correspond to regions of maximum reaction progress. Within the sample, the derived strain rate variations range up to almost one order of magnitude.     

Significance of inhomogeneous compression of mineral substance for explaining crystalline crust and uppermost mantle velocity profiles

Consideration of the Voronezh Crystalline Massif shows that three-layered seismic models and velocity profiles with a characteristic distribution of layer velocities and their gradients in each layer, reflect a crystalline crust and uppermost mantle structure formed through regional metamorphism and magmatism processes.Velocity and seismic parameter vertical gradients from the lithosphere profile are several times higher than those for homogeneous compression of minerals and rocks.For the identified layers the contribution of different factors for each seismic parameter gradient value is estimated. Anomalously high rates of increase with depth for V_p, V_s and ø are shown to be caused by the combined effects of structure-phase transformations and substance composition variations in lithospheric complex mineral parageneses.     

Osmium isotope and highly siderophile element geochemistry of mantle xenoliths from NW Turkey: implications for melt depletion and metasomatic history of the sub-continental lithospheric mantle

Ultramafic xenoliths entrained in the late Miocene alkali basalts and basanites from NW Turkey include refractory spinel-harzburgites and dunites accompanied by subordinate spinel-lherzolites. Whole-rock major and trace element characteristics indicate that the xenoliths are mostly the solid residues of varying degrees of partial melting (～4–～15%), but some have geochemical signatures reflecting the processes of melt/rock interaction. Mantle-normalized trace element patterns for the peridotites vary from LREE-depleted to strongly LREE-enriched, reflecting multistage mantle processes from simple melt extraction to metasomatic enrichment. Rhenium and platinum group element (PGE) abundances and ¹⁸⁷Os/¹⁸⁸Os systematics of peridotites were examined in order to identify the nature of the mantle source and the processes effective during variable stages of melt extraction within the sub-continental lithospheric mantle (SCLM). The peridotites are characterized by chondritic Os/Ir and Pt/Ir ratios and slightly supra-chondritic Pd/Ir and Rh/Ir ratios, representing a mantle region similar in composition to the primitive mantle (PM). Moderate enrichment in PPGE (Pd–Pt–Rh)/IPGE (Ir–Os–Ru) ratios with respect to the PM composition in the metasomatized samples, however, reflects compositional modification by sulphide addition during possible post-melting processes. The ¹⁸⁷Os/¹⁸⁸Os ratios of the peridotites range from 0.11801 to 0.12657. Highly unradiogenic Os isotope compositions (γOs at 10 Ma from –7.0 to –3.2) in the chemically undisturbed mantle residues are accompanied by depletion in Re/Os ratios, suggesting long-term differentiation of SCLM by continuous melt extraction. For the metasomatized peridotites, however, systematic enrichments in PPGE and Re abundances, and the observed positive covariance between ¹⁸⁷Re/¹⁸⁸Os and γOs can most likely be explained by interaction of solid residues with basaltic melts produced by melting of relatively more radiogenic components in the mantle. Significantly, the wide range of ¹⁸⁷Os/¹⁸⁸Os ratios characterizing the entire xenolith suite seems to be consistent with multistage evolution of SCLM and suggests that parts of the lithospheric mantle contain materials that have experienced ancient melt removal (～1.3 Ga) which created time-integrated depletion in Re/Os ratios; in contrast, some other parts display evidence indicative of recent perturbation in the Re–Os system by sulphide addition during interaction with metasomatizing melts.     

The thermodynamics of substances at very high pressures and temperatures and some mineral reactions in the earth's mantle

The thermodynamic properties of 25 substances (elements, compounds, modifications) are calculated on the basis of an extrapolation of their caloric values and compressibilities into the region of pressures up to 2mbar and temperatures up to 4,000K. The extrapolation methods are described. The ratio of molar volumes is used to predict the thermodynamic properties of the high pressure modifications. It is inferred that water vapour and oxides of Mg, Fe, and Si ought to be stable in the entire mantle. In the lower mantle garnet should be more stable than the perovskite-type phase of MgSiO₃ (in presence of Al₂O₃ or Fe₂O₃). ‘Perovskite’ phase plus MgO are more stable here than forsterite, Mg₂SiO₄. Pyrrhotite, FeS, reveals astonishing stability in the entire mantle and in the outer core as well. Carbon dioxide, CO₂, may exist only in the upper mantle, whereas methane, CH₄, remains stable in the entire mantle.     

Effects of melt percolation on highly siderophile elements and Os isotopes in subcontinental lithospheric mantle: A study of the upper mantle profile beneath Central Europe

The effects of melt percolation on highly siderophile element (HSE) concentrations and Re-Os isotopic systematics of subcontinental lithospheric mantle are examined for a suite of spinel peridotite xenoliths from the 4 Ma Kozákov volcano, Bohemian Massif, Czech Republic. The xenoliths have previously been estimated to originate from depths ranging from ∼32 to 70 km and represent a layered upper mantle profile. Prior petrographic and lithophile trace element data for the xenoliths indicate that they were variably modified via metasomatism resulting from the percolation of basaltic melt derived from the asthenosphere. Chemical and isotopic data suggest that lower sections of the upper mantle profile interacted with melt characterized by a primitive, S-undersaturated composition at high melt/rock ratios. The middle and upper layers of the profile were modified by more evolved melt at moderate to low melt/rock ratios. This profile permits an unusual opportunity to examine the effects of variable melt percolation on HSE abundances and Os isotopes.Most HSE concentrations in the studied rocks are significantly depleted compared to estimates for the primitive upper mantle. The depletions, which are most pronounced for Os, Ir and Ru in the lower sections of the mantle profile, are coupled with strong HSE fractionations (e.g., Os_N/Ir_N ratios ranging from 0.3 to 2.4). Platinum appears to have been removed from some rocks, and enriched in others. This enrichment is coupled with lithophile element evidence for the degree of percolating melt fractionation (i.e., Ce/Tb ratio).Osmium isotopic compositions vary considerably from subchondritic to approximately chondritic (γ_Os at 5 Ma from -6.9 to +2.1). The absence of correlations between ¹⁸⁷Os/¹⁸⁸Os and indicators of fertility, as is common in many lithospheric mantle suites, may suggest significant perturbation of the Os isotopic compositions of some of these rocks, but more likely reflect the normal range of isotopic compositions found in the modern convecting mantle. Osmium isotopic compositions correspondingly yield model Re-depletion (T_RD) ages that range from essentially modern to ∼1.3 Ga.Our data provide evidence for large-scale incompatible behavior of HSE during melt percolation as a result of sulfide dissolution, consistent with observations of prior studies. The degree of incompatibility evidently depended on melt/rock ratios and the degree of S-saturation of the percolating melt. The high Pt contents of some of these rocks suggest that the Pt present in this pervasively metasomatized mantle was controlled by a phase unique to the other HSE. Further, high Os concentrations in several samples suggest deposition of Os in a minority of the samples by melt percolation. In these rocks, the mobilized Os was characterized by similar to the ¹⁸⁷Os/¹⁸⁸Os ratios in the ambient rocks. There is no evidence for either the addition of Os with a strongly depleted isotopic composition, or Os with suprachondritic isotopic composition, as is commonly observed under such circumstances.     

南海北部神狐海域细粒储层矿物组分对天然气水合物储集赋存的影响

为了探明矿物类型对于天然气水合物成藏的影响,笔者等利用南海北部神狐海域W07站位样品及其水合物饱和度数据,进行XRD全岩和黏土矿物测试分析、比表面积分析以及束缚水能力综合分析。结果表明,海床下110~127 m（即110~127 mbsf,meters below sea floor, 海床以下深度）为水合物储层段,海床下127~156 m为非水合物储层段。通过XRD分析可知,高石英及长石含量,低伊蒙混层含量的层段,比表面积与束缚水能力较低,说明其具有相对较好的孔渗条件,为水合物的运移与储集提供了良好的空间条件,因此形成水合物储层段;而在高伊蒙混层的层段中,比表面积较大,束缚水能力较强,其对甲烷气体及流体的吸附和束缚能力较强,对水合物成藏起到潜在的封隔作用,成为非储层段,储层与非储层段纵向叠置序列有利于优质水合物储层的形成。本次研究总结了矿物组分与优质水合物储层之间的关系,并揭示两者存在的潜在成因联系,以期丰富水合物富集成藏的基础理论,对未来南海北部天然气水合物的商业化开发提供支持。     

A physical model for the transport and sorting of fine-grained sediment by turbidity currents

Turbidite muds in cores from the outer Scotian continental margin, off eastern Canada, contain abundant thin silt laminae. Graded laminated units are recognized in parts of this sequence. These represent single depositional events, and show a regular decrease in modal grain size and thickness of the silt laminae through the unit. A similar fining trend is shown by both silt and mud layers over hundreds of kilometres downslope. Textural analysis of individual laminae allows the construction of a dynamically consistent physical model for transport and sorting in muddy turbidity currents. Hydraulic sorting aggregates finer material to the top and tail regions of a large turbidity flow which then overspills its channel banks. Downslope lateral sorting occurs with preferential deposition of coarser silt grains and larger mud flocs. Depositional sorting by increased shear in the boundary layer separates clay flocs from silt grains and results in a regular mud/silt lamination. Estimates can be made of the physical parameters of the turbidity flows involved. They are a minimum of several hundreds of metres thick, have low concentrations (of the order of 10^?3 or 2500 mg 1^?1), and move downslope at velocities of 10-20 cm s^?1. A 5 mm thick, coarse silt lamina takes about 10 h to deposit, and the subsequent mud layer ‘blankets’ very rapidly over this. A complete unit is deposited in 2-6 days which is the time it takes for the turbidity flow to pass a particular point. These thick, dilute, low-velocity flows are significantly different from the ‘classical’ turbidity current. However, there is mounting evidence in support of the new concept from laboratory observations and direct field measurements.     

稀有矿物锰方硼石的合成及其矿床地质意义

锰方硼石为稀有的锰氯硼酸盐(Mn3B7O13Cl)矿物, 首次发现于美国德克萨斯州钱伯斯郡盐丘回收的卤水中, 中国天津市蓟县赋存有世界上独一无二的锰方硼石矿床。采用五水平三因素(L25(53))的25组正交试验, 利用焙烧法人工合成锰方硼石, 得到锰方硼石的形成温度为250~400 ℃,弱酸性,高氯环境。实验条件下,最佳形成条件为400 ℃、C氯离子/C锰离子=2.5、pH=6。3种影响反应的因素中, 温度为主要因素。采用水热法在最优合成条件下得到了晶形比较完好的锰方硼石,平均粒度为600 nm。通过对钱伯斯郡盐丘和天津蓟县锰方硼石矿床的地质特征的分析讨论,认为蓟县锰方硼石矿床是海底热液成因,成矿温度低于400 ℃,并提出成矿模型。     

Determination of undrained strength of fine-grained soils by means of SPT and its application in Turkey

The Standard Penetration Test (SPT) is one of the oldest and the most common in situ test used in soil explorations. In the recent years with the advent of new technology and techniques in determining the drawbacks in SPT, several researchers have attempted to correlate corrected field measured values with several soil properties. In this context, corrections applied to field values have become critical. In this study a questionnaire including the performance of the standard penetration test and equipment used in practice in Turkey is circulated in order to determine the relevant correction factors. Thus the appropriate corrections are used in acquiring corrected SPT-N values. The relationships between SPT-N and the undrained shear strength (S_u) are examined from the statistical point of view by taking the test types and SPT corrections into consideration, and comparison is made with previous studies. It is observed that SPT corrections play an important role on the obtained correlation equations. In addition, the importance of the effects of test types on the correlations is also emphasized. The Standard Penetration Test is found to be sufficient for reliable assessment of S_u.     

Dual aspects of mantle convection through time: Changes in global upper mantle temperature, Earth’s rotation, and global plate motion acceleration induced by mantle avalanches

The mean depth of the mantle transition zone depends on the global mantle temperature through the Clapeyron slope. Numerical models of mantle convection with endothermic phase change at 670 km are characterized by quiet periods of partial layering alternating with catastrophic events. During an avalanche, global thermal anomalies, reaching several tens of degrees, and lasting several tens of million years occur that induce a global deepening of the mantle transition zone. The resulting inertia tensor perturbations lead to acceleration of the Earth’s rotation. The bottom heat fluxes remains strong as a consequence of the steep thermal gradient at the CMB level; whereas it decreases to a low level during quiet periods. The upper surface heat flux displays a more complex behavior due to the re-heating of upper mantle by plumes generated at the transition zone and at the CMB. Following these numerical results, two significantly different regimes of mantle convection may have alternated several times during the Earth’s history. The avalanche periods are also associated with a global increase of plate tectonic activity (ridge accretion and continental break-up) due to an increase of the surface velocity during the avalanche process. This work shows the richness of the behavior in surfaces and bottom heat fluxes that arises from the alternation of quiet periods of partial layering with catastrophic avalanche events. Complexities in the real Earth displays are surprisingly simular to those caused by the consequences of mantle avalanches.     

Residual platinum-group minerals from highly depleted harzburgites of the Lherz massif (France) and their role in HSE fractionation of the mantle

In order to constrain the highly siderophile elements (HSE: Re and platinum group elements (PGE: Os, Ir, Ru, Pt and Pd)) host mineral(s) in refractory, base metal sulfide-free mantle residues, four very depleted spinel-harzburgites from the Lherz massif (France) have been analyzed for HSE in whole-rock and in major mineral separates (olivine, orthopyroxene, clinopyroxene and spinel) by isotope dilution. In addition, HSE host minerals have been separated and analyzed with a scanning electron microscope. Olivine and spinel show the highest HSE concentration especially for Os, Ir, Ru and Pt (up to 10 ppb) among the modally-major minerals, while the pyroxenes are 1-2 orders of magnitude poorer in HSE. The major minerals account for less than 30% of the whole-rock platinum group element budget. On the other hand, rare, micron to submicron platinum group minerals (PGM), such as Ru-Os ± Ir sulfides and Pt-Ir ± Os alloys, likely located in the intergranular spaces of the refractory depleted harzburgite, account for 50-100% of the HSE budget. The PGM grains are interpreted to be residual, having formed in response to the complete consumption of the base-metal sulfides by the high degree of partial melting (i.e. 23-24%) experienced by these samples. As they sequester the compatible platinum group elements (Os, Ir, Ru and Pt) in the mantle residue, these PGM provide key constraints for the modelling of PGE contents in terrestrial basalts (e.g. the solid/liquid partition coefficients needed to account for the compatible behavior of these elements in the mantle residue) and for understanding the long-lived Os isotope heterogeneities of the upper mantle, especially the old Re-Os ages found in young oceanic mantle. In fact, because of their Os-rich compositions and high melting temperatures, these microphases are likely to preserve their initial Os isotopic compositions unmodified over multiple events of mantle melting and mixing, and therefore generate, through recycling, heterogeneous Os isotopic signatures at different scales in the convecting mantle.