TEM正演响应计算的几种频时域转换方法对比

在瞬变电磁的一维正演响应模拟中,常用的方法是先在频率域中求解,之后将结果转换到时间域。但该方法在晚期的计算精度通常不高,因此,使用5种频-时域转换方法(正、余弦变换的数值滤波算法,G?S逆拉普拉斯算法、正、余弦变换的折线逼近法)进行了计算,与解析解对比,得出余弦变换的数值滤波算法在晚期计算中精度最高的结论,并对这五种转换方法产生误差问题的原因进行了讨论和分析。本研究有利于瞬变电磁一维正演响应的高精度计算,使其在多维计算中得到更好的应用。     

In situ TEM observations of plastic deformation in quartz crystals

With in situ nanocompression experiments in a transmission electron microscope, we investigated plastic deformation in natural quartz crystals and observed both dislocation plasticity as well as mechanical twinning. Through this experimental method, we are able to provide direct evidence of Dauphiné twin nucleation and could measure the intrinsic twinning stress. The twinning phenomena appear to include a memory effect, where the same twin can reappear upon successive loading and unloading events. The data provide insight into this twin generation mechanism and can be used as a benchmark for the use of twins in quartz for paleopiezometry. Together, the observation of room-temperature dislocation plasticity and reversible twinning adds new insight into the extensive field of quartz plasticity and demonstrates the usefulness of small-scale testing techniques for mineral physics.     

Surprises from the top of the mantle transition zone

Recent studies of chromite deposits from the mantle section of ophiolites have revealed a most unusual collection of minerals present as inclusions within the chromite. The initial discoveries were of diamonds from the Luobosa ophiolite in Tibet. Further work has shown that mantle chromitites from ophiolites in Tibet, the Russian Urals and Oman contain a range of crustal minerals including zircon, and a suite of highly reducing minerals including carbides, nitrides and metal alloys. Some of the minerals found represent very high pressure phases indicating that their likely minimum depth is close to the top of the mantle transition zone. These new results suggest that crustal materials may be subducted to mantle transition zone depths and subsequently exhumed during the initiation of new subduction zones—the most likely environment for the formation of their host ophiolites. The presence of highly reducing phases indicates that at mantle transition zone depths the Earth's mantle is ‘super’‐reducing.     

Photoelectric lunar-occultation observations of several close binary stars

The results of photoelectric lunar-occultation observations for several stars are presented. Some of these are obvious close binary systems, while others are suspected close binaries or multiple systems, or show evidence for the presence of complex structure of some other kind. It is expected that new, efficient interferometric systems will enable detailed studies of the structure of many “ordinary” stars with an angular resolutions of 10^?4–10^?5 arcsec.     

The rheology of olivine and spinel magnesium germanate (Mg2GeO4): TEM study of the defect microstructures

Synthetic polycrystals of α-Mg₂GeO₄ (with the olivine structure) and γ-Mg₂GeO₄ (with the spinel structure) deformed at high temperature and pressure in their respective stability fields were investigated by analytical transmission electron microscopy. Specimens with a mean grain size of 20–30 µm deform by dislocation glide and/or climb. The predominance of glide versus climb depends on stress and grain orientation. The defect microstructures of both polymorphs are very similar to those observed in their respective silicate analogues, α- and γ-(Mg,Fe)₂SiO₄, and, in the case of the spinel phase, very similar to those observed in magnesium aluminate spinels. These observations suggest that Mg₂GeO₄ is a good rheological analogue for the Earth’s upper mantle. A spinel specimen deformed under the same conditions of temperature and strain rate as an olivine specimen was approximately three times stronger than olivine. In specimens of both phases deformed at or above 1400 K, a thin amorphous film composed of Mg, Ge, and O was detected along some grain boundaries. Grains ≤10 µm diameter surrounded by a film of amorphous phase (>10 nm thick) exhibited low dislocation densities, and deformation appeared to have occurred by grain boundary sliding.     

Convective mixing influenced by the capillary transition zone

Convective mixing of dissolved carbon dioxide (CO₂) with formation brine has been shown to be a significant factor for the rate of dissolution of CO₂ and thus for determining the viability of geological CO₂ storage sites. In most previous convection investigations, a no-flow boundary condition was used to represent the interface between an upper region with CO₂ and brine and the single-phase brine region beneath. However, due to interfacial tension between the phases, the water phase is partly mobile in the upper region and advection may occur. Based on linear stability analysis and numerical simulations, we show that advection across the interface leads to considerable destabilization of the system. In particular, the time of onset of instability is reduced by a factor of two and the rate of dissolution is enhanced by a factor of two for three of four formations we consider, and by 40 % for the fourth formation. It is found that exponential decay of the relative permeability away from the interface provides a useful approximation to the real system. In addition, the exponential decay also simplifies the linear stability analysis. Interestingly, formations with large absolute permeability and small porosity have the largest impact from the transition zone, despite the fact that the relative permeability decays quickly above the interface in these formations. This is because the length-scale of instability is smallest in these formations.     

断层带中假玄武玻璃成因机制及非稳态流变意义

假玄武玻璃呈玻璃质或隐晶质特性,常常与断层带相伴出现,其形成能有效地降低断层摩擦强度,被认为是古地震快速滑动的化石纪录。因此,对假玄武玻璃的研究对深入了解深部就位的断层变形和地震成因机制等具有重要意义。尽管国内外学者对假玄武玻璃开展了长期的研究,也积累了丰富的资料,然而,由于天然假玄武玻璃非常少见或零星地被报道,再加上其形成环境和过程的复杂性,对假玄武玻璃的构造特征、形成环境和成因机制仍然存在诸多争议及亟待解决的关键科学问题。研究表明,假玄武玻璃可以发育在大陆岩石圈不同深度范围内,即中下地壳乃至上地幔以糜棱岩为主的韧性变形领域（>60 km）,或中上地壳层次以碎裂岩为主的脆性变形域（<12 km）。越来越多证据也显示出在断层带的脆—韧性转换域中形成的假玄武玻璃跟浅源地震活动直接关联,也意味着中上地壳脆性变形和中下地壳塑性变形之间存在着更为复杂的耦合关联,同时对不同深部岩石强度和力学行为提出了挑战。对假玄武玻璃形成机制存在由断层面上的摩擦热导致的摩擦熔融体或仅仅是断层面岩石超碎裂粉碎作用认识的争议。而有研究认为干的环境有利于假玄武玻璃形成,因为流体的存在会降低断层面的有效正应力,不利于热量的积累以及摩擦熔融的进行;然而,另外一种观点认为流体的存在可以降低矿物熔融温度有利于断层摩擦熔融及形成假玄武玻璃。本文从假玄武玻璃的形成机制、形成深度、流体影响、形成后对断层强度的影响、以及保存与破坏机制几方面进行了最新总结,并对假玄武玻璃中非晶态物质的成因、脆—韧性转换带之下岩石的变形机制以及对陆壳强度的影响和非稳态流变意义进行探讨。     

In situ X-ray observations of the coesite-stishovite transition: reversed phase boundary and kinetics

Using a DIA-type, cubic-anvil, high-pressure apparatus (SAM-85) in conjunction with in situ X-ray diffraction, we have investigated phase relations between coesite and stishovite up to 12 GPa and 1530 °C using synthetic powders of the two phases as the starting materials. The phase transition between coesite and stishovite was identified by observing the first appearance of a phase that did not already exist or by a change in the relative intensity of the two patterns. In most experiments, the diffraction patterns on samples were collected within 10 minutes after reaching a pressure and temperature condition. On this time scale, two phase boundaries associated with the coesite-stishovite transition have been determined: (1) for the stishovite-to-coesite transition, observations were made in the temperature range of 950–1530 °C, and (2) for the coesite-to-stishovite transition from 500 to 1300 °C. These observations reveal that there exists a critical temperature of about 1000 °C to constrain the coesite-stishovite equilibrium phase boundary. Above this temperature, both boundaries are linear, have positive dP/dT slopes, and lie within a pressure interval of 0.4 GPa. Below this temperature, the dP/dT slope for the stishovite-to-coesite phase boundary becomes significantly larger and that for the coesite-tostishovite phase boundary changes from positive to negative. As a result, an equilibrium phase boundary can only be determined from the results above 1000 °C and is described by a linear equation P (GPa)=6.1 (4)+ 0.0026 (2) T (°C). This dP/dT slope is in good agreement with that of Zhang et al. (1993) but more than twice that of Yagi and Akimoto (1976). For the kinetics of the phase transition, preliminary rate data were obtained for the stishovite-to-coesite transition at 1160 and 1430 °C and are in agreement with the simple geometric transformation model of Avrami and Cahn.     

地幔转换带:地球深部研究的重要方向

地幔转换带是联系上下地幔的纽带,对于认识整个地幔的组成和演化、地幔对流、岩石圈深俯冲及深源地震等地球深部动力学问题具有重要意义。一般认为,转换带地震不连续面主要与橄榄石的高压相变密切相关。最新的高温高压实验研究表明,地幔中非橄榄石组分的相变,如辉石和石榴子石的相变,对不连续面的深度和宽度以及转换带内的波速和密度梯度也起到很大的影响。另外地幔全岩成分、端员组分、温度和水也对相变和不连续面具有重要影响,这些精细的实验研究成果更好地解释了转换带地震不连续面一些相对局部的性质和变化,促进了我们对地球深部性质和动力学过程的了解。因为缺少直接来自地球深部的样品,而地球物理和地球化学研究也有它们的相对局限性,所以高温高压实验仍然是我们了解地球深部成分和性质的重要手段之一。     

Structural assemblies of the Vladimir-Vyatka dislocation zone and the position of the Puchezh-Katunki Crater,East European Platform

The Puchezh-Katunki (PK) structural unit is situated in the Middle Volga region of the central East European Platform (EEP). It is expressed as a system of complex dislocations and a meteoritic crater with a central uplift. Based on the results of structural study, the attributes of its long evolution have been revealed. Four deformation stages have been established: Hercynian (1) fold-nappe and (2) trancpressional deformations, (3) formation of the Early Jurassic impact crater and the related system of radial-concentric faults, and (4) low-amplitude tectonic reactivation of Hercynian faults during the Kimmerian-Alpine stage of evolution. In general, the PK structural unit is localized in the most strained segment of the Vladimir-Vyatka Dislocation Zone, which separates the largest structural domains of the EEP. This is a long-lived zone, which developed cyclically beginning from Paleoproterozoic collisional events and up to the Kimmerian-Alpine stage of reactivation. Such a direct impact to the cluster of concentrated deformations in one of the largest tectonic zones of the EEP seems unlikely. Nevertheless, available evidence, including the estimated stress related to the impact effect (up to 50 GPa) and its decrease with depth, does not rule out the meteoritic origin of the PK structural unit.     

Kankan diamonds (Guinea) I: from the lithosphere down to the transition zone

Peridotitic inclusions in alluvial diamonds from the Kankan region of Guinea in West Africa are mainly of lherzolitic paragenesis. Nevertheless, extreme Cr₂O₃ contents (max. 17 wt%) in some of the exclusively lherzolitic garnets document that the diamond source experienced a previous stage of melt extraction in the spinel stability field. This initial depletion was followed by at least two metasomatic stages: (1) enrichment of LREE and Sr and (2) introduction mainly of MREE–HREE and other HFSE (Ti, Y, Zr, Hf). The Ti- and HFSE-poor character of stage (1) points towards a CHO-rich fluid or carbonatitic melt, the high HFSE in stage (2) favour silicate melts as enriching agent. Eclogitic inclusions are derived from a large depth interval ranging from the lithosphere through the asthenosphere into the transition zone. The occurrence of negative Eu anomalies in garnet and clinopyroxene from both lithosphere and transition zone suggests a possible relationship to subducted oceanic crust. Lithospheric eclogitic inclusions are derived from heterogeneous sources, that may broadly be divided into a low-Ca group with LREE depleted trace element patterns and a high-Ca group representing a source with negative LREE–HREE slope that is moderately enriched in incompatible elements relative to primitive mantle. High-Ca inclusions of majoritic paragenesis are significantly more enriched in incompatible elements, such as in Sr and LREE. Calculated whole rock compositions require metasomatic enrichment even if a derivation from MORB is assumed. Received: 26 January 2000 / Accepted: 18 May 2000     

地幔转换带中的水及其地球动力学意义

综述了近20年国际上地幔转换带中水的研究进展。前人研究表明,地球深部的水主要以OH-(hy-droxyl)形式存储在名义上无水矿物(NAMs)中。高温高压实验研究表明,地幔转换带中的主要矿物均具有较高的储水能力,且在转换带的温压条件下,其储水能力随着温度的升高而降低,其中瓦兹利石(β-Ol)和林伍德石(γ-Ol)的储水能力为2%～3%,超硅石榴子石(Mj)的储水能力为0.1%左右,据此估算地幔转换带的储水能力约为1.2%～1.91%,是地表水总量的3.9～6.2倍;而转换带除外的上地幔和下地幔主要矿物的含水量或储水能力均小于0.1%,因此与上、下地幔相比,地幔转换带可能是地幔的主要储水库。尽管地幔转换带具有较强的储水能力,但对地幔转换带的实际含水量还存在干、湿两方面的地质和地球物理证据和争议。地幔转换带中的水会对转换带中一系列的过程产生重要影响,当水含量增加时,橄榄石(Ol)向β-Ol、γ-Ol分解以及超硅石榴石的分解反应分别向低压、高压和低压方向迁移,从而由橄榄石向β-Ol和γ-Ol分解两个相变反应界定的转换带宽度也会增加;水还会使地幔深部的部分熔融温度降低,熔体的密度降低;同时,水的加入可以很好地解释地幔岩"pyrolite"模型在410km不连续面处产生的与地震波测量不相符突变,也可以解决全地幔对流模式所不能解释的地幔成分分层问题。因此,深入研究和探讨转换带中的水对地球深部动力学过程的影响,包括中国东部地区受太平洋板块深俯冲作用的影响,均具有重要的约束和研究意义。     

Water transportation from the subducting slab into the mantle transition zone

Using a recently developed petrogenetic grid for MORB + H₂O, we propose a new model for the transportation of water from the subducting slab into the mantle transition zone. Depending on the geothermal gradient, two contrasting water-transportation mechanisms operate at depth in a subduction zone. If the geothermal gradient is low, lawsonite carries H₂O into mantle depths of 300 km; with further subduction down to the mantle transition depth (approximately 400 km) lawsonite is no longer stable and thereafter H₂O is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection. At this depth, hydrous β-phase olivine is stable and plays a role as a huge water reservoir. In contrast, if the geothermal gradient is high, the subducted slab may melt at 700–900 °C at depths shallower than 80 km to form felsic melt, into which water is dissolved. In this case, H₂O cannot be transported into the mantle below 80 km. Between these two end-member mechanisms, two intermediate types are present. In the high-pressure intermediate type, the hydrous phase A plays an important role to carry water into the mantle transition zone. Water liberated by the lawsonite-consuming continuous reaction moves upward to form hydrous phase A in the hanging wall, which transports water into deeper mantle. This is due to a unique character of the reaction, because Phase A can become stable through the hydration reaction of olivine. In the case of low-pressure intermediate type, the presence of a dry mantle wedge below 100 km acts as a barrier to prevent H₂O from entering into deeper mantle.     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and west-dipping, N–S to N20°–30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacılar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of left-lateral oblique slip of approximately 4.1 mm·year^–1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period.     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

Abstract

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and westdipping, N-S to N20°-30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacilar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of leftlateral oblique slip of approximately 4.1 mm?year^?1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

Emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures, conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones. Much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock-mechanics-based yield criteria for the inelastic deformations at the top and base. At mid-plate depths, stresses are likely to be supported elastically because bending strains and elastic stresses are low. The collisional tectonic regime, however, is far more complex because very large permanent strains are sustained at mid-plate depths and this requires us to include the broad transition between brittle and ductile flow. Moreover, important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid-plate depths.Two specific contributions of laboratory rock rheology research are considered in this paper. First, the high-temperature steady-state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks. Rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere. The thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm T_c above which (at geologic strain rates) the high-temperature ductile strength falls below some arbitrary strength isobar (e.g., 100 MPa). For olivine T_c is about 700°–800°C but for other crustal silicates, T_c may be as low as 400°–600°C, suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the Moho, as suggested by a number of workers on independent grounds. Put another way, the Moho is a rheological discontinuity. A second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere.     

Formation mechanism of central-type structures in the West Pacific continent-ocean transition zone

The rotary formation mechanism of various central-type geological structures functioning in the strike-slip fault systems of the West Pacific continent-ocean transition zone is considered. This mechanism explains many tectonomagmatic processes and is confirmed by geological, geophysical, and geomorphological studies. At the same time, it is not the only possible mechanism. Examples of magmatogenic central-type ring and vortical structures in the Japan Sea segment of the West Pacific continent-ocean transition zone are given. In our opinion, the proposed geodynamic model is inscribed into the paradigm of tectonic delamination of the lithosphere developed by Yu.M. Pushcharovsky.     

Geochemistry of the Archean low- to high-grade transition zone,Southern India

The transition zone between Archean low- and high-grade rocks in southern India represents eroded crustal levels representative of 15–20 km. It is comprised chiefly of tonalitic gneisses with some varieties showing incipient charnockitization and of minor amounts of granitic gneiss and charnockite, both of which appear to have developed from the tonalitic gneisses.Tonalitic gneisses and charnockites are similar in major and trace elements composition while granitic gneisses are relatively enriched in Rb, K, Th, Ba and light rare earth element (REE) and depleted in Cr and Sc. All three rock types exhibit enriched light REE patterns with variable positive Eu anomalies. Total REE content decreases with increasing Eu/Eu and SiO₂ and with decreasing Fe₂O_3T and MgO in the tonalitic gneisses and charnockites.An internally consistent model for the production of the tonalitic gneisses involves partial melting of an enriched mafic source with variable ratios of hornblende to clinopyroxene. This source, in turn, is derived from an ultramafic mantle relatively enriched in incompatible elements. Granitic gneisses form from tonalitic gneisses by alkali metasomatism from chloride-bearing fluids with high H₂O/CO₂ ratios purged from the lower crust by CO₂, and charnockites are produced from tonalitic gneisses (and granitic gneisses) by ischochemical CO₂ metamorphism following the alkali metasomatism.     

新疆阿合奇地区木兹杜克过渡带的薄皮构造

新疆阿合奇地区木兹杜克过渡带位于塔里木西北边缘的柯坪前陆盆地,是典型的薄皮构造,其主滑脱面为寒武纪阿瓦塔格组膏泥层,盖层变形强烈。该薄皮构造带是长期、多期、至今仍在活动的产物,受区域构造影响,木兹杜克过渡带的变形由北向南发展,盖层中存在不整合面和多个次级滑脱面,具有横向分带垂向分层的特点。     

Ripple/dune to upper stage plane bed transition: Some observations from the ancient record

In two Proterozoic sandstones, of the Indian shield cross-stratification and cross-lamination are observed to grade continuously into parallel-laminations often bearing parting lineations. These are interpreted as having resulted from a gradual transition from ripple/dune to upper stage plane bed structures. During the transition the inclination of the cross-strata diminishes and their shape changes from concave-up to sigmoidal. The sigmoidal cross-strata are characterized by well defined topsets, foresets and toesets and the topsets bear parting lineations. In the course of the transition sigmoidal cross-strata may give way either to horizontal parallel-lamination or inclined parallel-lamination. In the former the toesets of the successive sigmoidal cross-strata thicken and the thickness of the cross-strata beyond the brink point (the junction between the topset and foreset) tends to become uniform until a plane-bed state is reached and horizontal parallel-laminations are formed. In the latter the topset of the successive sigmoidal cross-strata increases in length at the expense of the foreset and toeset until the brink point ceases to exist so that only the topset laminations prevail and appear as inclined parallel-laminations. These transitions presumably result from a gradual increase in flow intensity beyond the stability limits of ripples/dunes. The progressive morphological changes of the cross-stratification over the transition are attributed to changing fallout patterns on the lee face of the bedforms in response to increasing flow intensity. Preservation of the records of such transitions suggests an abundant supply of sand grade sediments from suspension during the transition, shaping the sediment concentration profile over the bedforms and facilitating turbulence suppression. The variation in the pattern of transition from sigmoidal cross-stratification to parallel-lamination may be the result of different rates of sediment feed from the prevailing suspended sediment load in the two instances.