Migmatite formation at subsolidus conditions–an alternative to anatexis     

ANDERS LINDH  CARL-HENRIC WAHLGREN 《Journal of Metamorphic Geology》1985,3(1):1-12

Abstract This contribution discusses the formation of stromatic high-grade migmatites. Volume considerations require that most of the leucosome material is not added from outside the system. A segregation mechanism is necessary except in those cases where the protolith of the migmatite already had a banded structure. Although partial melting is most often advocated to provide the segregation mechanism, several arguments can be raised against high degrees of melting: mineral compositions and even zoning patterns are similar in both mesosomes and leucosomes; sufficient degrees of melting at reasonable temperatures require more than the available amounts of water; the leucosomes do not always approximate to a minimum melt composition; high degrees of melting cannot occur without an appreciable volume increase; etc. Diffusion works as a segregation mechanism at low temperatures. As diffusion rates increase exponentially with temperature diffusion must become still more important as a segregation mechanism at high temperatures. A model is suggested based on the diffusion of components in response to the gradient δσ/δx, where σ= 1/3∑³_i=1 σ_i is the mean pressure. In homogeneously strained rocks, σ₃ is larger in rock parts rich in incompetent phases than in rock parts depleted in incompetent phases. Accordingly, mechanically competent but chemically incompetent high-volume phases like quartz and feldspars stressed in micadominated parts of a rock (high σσ) migrate to parts of the rock that are depleted in mica (low σ¯). It is suggested that hornblende occurring in many leucosomes may be premigmatitic or early syn-migmatitic and due to its mechanical competency it initiates the segregation. Diffusion occurs along grain boundaries and is enhanced by small amounts of ‘intergranular fluid’;. At the best, semiquantitative estimates of diffusion rates and distances indicate that the process should work over geological times.  相似文献   

星系团的分层效应     

赵君亮 《天文学进展》2007,25(3):206-214

对星系团各类分层效应的有关问题做了概要的评述,包括成员星系在位置空间和(或)速度空间中的形态分层、光度(质量)分层和元素丰度分层的表现形式和探测途径,分层效应可能的形成机制及其对星系和星系团的结构和演化的影响。  相似文献   

A laboratory study on capillary sealing efficiency of Iranian shale and anhydrite caprocks     

《Marine and Petroleum Geology》2015

Caprock has the most important role in the long term safety of formation gas storage. The caprocks trap fluid accumulated beneath, contribute to lateral migration of this fluid and impede its upward migration. The rapid upward passage of invasive plumes due to buoyancy pressure is prevented by capillary pressure within these seal rocks. In the present study, two main seal rocks, from the Zagros basin in the southwest of Iran, a shale core sample of Asmari formation and an anhydrite core sample of Gachsaran formation, were provided. Absolute permeabilities of shale and anhydrite cores, considering the Klinkenberg effect, were measured as 6.09 × 10⁻¹⁸ and 0.89 × 10⁻¹⁸ m², respectively. Capillary sealing efficiency of the cores was investigated using gas breakthrough experiments. To do so, two distinct techniques including step by step and residual capillary pressure approaches were performed, using carbon dioxide, nitrogen and methane gases at temperatures of 70 and 90 °C, under confining pressures in the range 24.13–37.92 MPa. In the first technique, it was found that capillary breakthrough pressure of the cores varies in the range from 2.76 to 34.34 MPa. Moreover, the measurements indicated that after capillary breakthrough, gas effective permeabilities lie in range 1.85 × 10⁻²¹ – 1.66 × 10⁻¹⁹ m². In the second technique, the minimum capillary displacement pressure of shale varied from 0.66 to 1.45 MPa with the maximum effective permeability around 7.76 × 10⁻²¹ – 6.69 × 10⁻²⁰ m². The results indicate that anhydrite caprock of the Gachsaran formation provides proper capillary sealing efficacy, suitable for long term storage of the injected CO₂ plumes, due to its higher capillary breakthrough pressure and lower gas effective permeability.  相似文献   

国外商业绅士化研究进展及其对本土研究的启示   总被引：1，自引：0，他引：1  

孙洁  宋伟轩 《世界地理研究》2021,30(5):1096-1105

商业是城市中最活跃,并且对城市发展和空间重构产生重要影响的功能之一。近20年来,随着产业转型与城市更新实践,日益突出的商业绅士化现象愈发引起国外学术界关注。同时,多源数据和定量分析方法的利用,促进了商业绅士化专题研究逐渐增多。商业绅士化的发生背景、表现特征、推动主体与形成机制,以及商业绅士化导致阶层置换、加深种族隔离等社会空间效应是主要的研究内容。通过对国外商业绅士化研究文献的梳理,以期展示城市商业高档化重构的机理以及绅士化演进的复杂性。基于当前我国城市转型和消费转型的特征与趋势,尝试提出对商业绅士化本土研究方向和方法的启示。  相似文献   

Optimized running conditions and sensitivity for direction sensitive detectors of WIMP dark matter     

J. Tatarowicz  C.J. Martoff 《Astroparticle Physics》2011,35(5):235-241

Optimum fill pressures for direction-sensitive dark matter detectors based on tracking in gases are considered. Given the minimum resolvable track length and the gas fill, the Lindhard–Scharf stopping model leads to the existence of an optimum pressure which maximizes the specific event rate R (event rate per unit detector volume). In addition, maximizing the detectibility of the recoil nucleus diurnal asymmetry is considered. Optimum fill pressures are calculated for Ar, CF₄, CS₂ and Xe gas fills, as a function of the WIMP mass and the minimum resolvable track length. The associated minimum target volumes required to achieve currently competitive WIMP-nucleon cross-section sensitivity are also calculated. The standard isothermal sphere model of the galactic WIMP halo is used throughout, but the method could be extended to use any desired WIMP distribution function.  相似文献   

Marine hydrocarbon source rocks of the Upper Permian Longtan Formation and their contribution to gas accumulation in the northeastern Sichuan Basin,southwest China     

《Marine and Petroleum Geology》2014

Identification of the main hydrocarbon source rocks of the large Puguang gas field (northeastern Sichuan Basin, southwest China) has been the subject of much discussion in recent years. A key aspect has been the lack of a comprehensive understanding of the development of hydrocarbon source rocks of the Upper Permian Longtan Formation, which had been thought to contain mainly coal seams and thick carbonate layers. In this paper, based on geological data from more than ten wells and outcrops and their related mineralogy and geochemistry, we investigated the depositional environment and main factors controlling organic matter enrichment in the Longtan Formation. We propose a model which combines information on the geological environment and biological changes over time. In the model, organic matter from prolific phytoplankton blooms was deposited in quiescent platform interior sags with rising sea-levels. During the Longtan period, the area from Bazhong to Dazhou was a platform interior sag with relatively deep water and a closed environment, which was controlled by multiple factors including syngenetic fault settling, isolation of submarine uplifts and rising sea-levels leading to water column stratification. Although the bottom water was anoxic, the phytoplankton were able to bloom in the well-lit upper euphotic zone thus giving rise to a set of sapropelic black shales and marlstones containing mostly algal organic matter with minor terrestrial contributions. As a consequence, these rocks have a high hydrocarbon generation potentials and can be classified as high-quality source rocks. The area from Bazhong to Dazhou is a center of hydrocarbon generation, being the main source of reservoired paleo-oils and presently discovered as pyrobitumen in the Puguang gas field. The identification of these source rocks is very important to guide future petroleum exploration in the northeastern Sichuan Basin.  相似文献   

Gas hydrate identified in sand-rich inferred sedimentary section using downhole logging and seismic data in Shenhu area,South China Sea     

《Marine and Petroleum Geology》2014

Downhole wireline log (DWL) data was acquired from eight drill sites during China's first gas hydrate drilling expedition (GMGS-1) in 2007. Initial analyses of the acquired well log data suggested that there were no significant gas hydrate occurrences at Site SH4. However, the re-examination of the DWL data from Site SH4 indicated that there are two intervals of high resistivity, which could be indicative of gas hydrate. One interval of high resistivity at depth of 171–175 m below seafloor (mbsf) is associated with a high compressional- wave (P-wave) velocities and low gamma ray log values, which suggests the presence of gas hydrate in a potentially sand-rich (low clay content) sedimentary section. The second high resistivity interval at depth of 175–180 mbsf is associated with low P-wave velocities and low gamma values, which suggests the presence of free gas in a potentially sand-rich (low clay content) sedimentary section. Because the occurrence of free gas is much shallower than the expected from the regional depth of the bottom simulating reflector (BSR), the free gas could be from the dissociation of gas hydrate during drilling or there may be a local anomaly in the depth to the base of the gas hydrate stability zone. In order to determine whether the low P-wave velocity with high resistivity is caused by in-situ free gas or dissociated free gas from the gas hydrate, the surface seismic data were also used in this analysis. The log analysis incorporating the surface seismic data through the construction of synthetic seismograms using various models indicated the presence of free gas directly in contact with an overlying gas hydrate-bearing section. The occurrence of the anomalous base of gas hydrate stability at Site SH4 could be caused by a local heat flow conditions. This paper documents the first observation of gas hydrate in what is believed to be a sand-rich sediment in Shenhu area of the South China Sea.  相似文献   

新疆二红洼镁铁—超镁铁岩体橄榄石成因及其对硫化物熔离的指示     

孙涛  钱壮志  张瑞  张江江  姜超  杨素红  王若梅 《地质学报》2014,88(8):1494-1503

二红洼岩体位于新疆东天山黄山镁铁—超镁铁岩带的西段,地表由南、北两个小岩体组成,北岩体出露面积约1.42km2,呈北东—南西向展布;南岩体在呈椭圆形,出露面积约为6.25km2。岩体可分为两个侵入期次:第一侵入期次岩性为(含长)二辉橄榄岩和橄榄辉长岩,第二侵入期次岩性为辉长苏长岩和淡色辉长岩,辉长苏长岩侵入于第一期次形成的含长二辉橄榄岩和橄榄辉长岩中。岩体橄榄石Fo值在80.9~89.7之间,为贵橄榄石;Ni含量变化范围较大,主要集中在102.19×10-6~4319.66×10-6之间。岩体母岩浆MgO含量为10.3%,FeO含量为10.8%;回归计算结果显示二红洼岩体的原始岩浆中MgO含量为15.73%,FeO含量为10.71%。在橄榄石的结晶过程中母岩浆达到硫饱和,并发生有硫化物的熔离作用;橄榄石与硫化物的晶出质量比(橄榄石:硫化物)为50~100∶1。通过岩石学、矿物学特征以及模拟计算结果表明,二红洼岩体具有形成铜镍矿床的基本条件,但是岩体在深部岩浆房已经达到硫饱和并发生了硫化物的熔离作用,导致母岩浆中亏损Ni、Cu等成矿元素,未能形成工业矿体;在以后找矿勘探中,需要寻找早期硫化物熔离所形成的那部分硫化物熔体,并进一步寻找成矿富集的有利地段。  相似文献   

常顶瓦斯油吸附法脱除微量氯的实验研究     

李玉明  伦会荣 《山东国土资源》2006,(Z1)

炼油厂将常压塔顶油和减一线油作为重整原料,但由于氯含量过高(30×10-6)无法利用,传统方法是将其中的有机氯转化为无机氯化氢后脱除,但其对加氢催化剂有毒害,采用常顶瓦斯油吸附法可直接脱除微量氯。  相似文献   

Contact Partial Melting of Granitic Country Rock, Melt Segregation, and Re-injection as Dikes into Ferrar Dolerite Sills, McMurdo Dry Valleys, Antarctica     

Hersum  Taber G.; Marsh  Bruce D.; Simon  Adam C. 《Journal of Petrology》2007,48(11):2125-2148

Numerous, interconnected, granitic dikes (<30 cm in widthand hundeds of meters in length) cut Ferrar dolerite sills ofthe McMurdo Dry Valleys, Antarctica. The source of the graniticdikes is partial melting of granitic country rock, which tookplace in the crust at a depth of about 2–3 km adjacentto contacts with dolerite sills. Sustained flow of doleriticmagma through the sill generated a partial melting front thatpropagated into the granitic country rock. Granitic partialmelts segregated and collected at the contact in a melt-rich,nearly crystal-free reservoir adjacent to the initial doleritechilled margin. This dolerite chilled margin was subsequentlyfractured open in the fashion of a trapdoor by the graniticmelt, evacuating the reservoir to form an extensive complexof granitic dikes within the dolerite sills. At the time ofdike injection the dolerite was nearly solidified. Unusuallycomplete exposures allow the full physical and chemical processesof partial melting, segregation, and dike formation to be examinedin great detail. The compositions of the granitic dikes andthe textures of partially melted granitic wall rock suggestthat partial melting was characterized by disequilibrium mineraldissolution of dominantly quartz and alkali feldspar ratherthan by equilibrium melting. It is also unlikely that meltingoccurred under water-saturated conditions. The protolith granitecontains only 7 vol.% biotite and estimated contact temperaturesof 900–950°C suggest that melting was possible ina dry system. Granite partial melting, under closed conditions,extended tens of meters away from the dolerite sill, yet meltsegregation occurred only over less than one-half a meter fromthe dolerite chilled margin where the degree of partial meltingwas of the order of 50 vol.%. This segregation distance is consistentwith calculated length scales expected in a compaction-drivenprocess. We suggest that the driving force for compaction wasdifferential stress generated by a combination of volume expansionas a result of granite partial melting, contraction during doleritesolidification, and relaxation of the overpressure driving doleriteemplacement. On a purely chemical basis, the extent of meltsegregation necessary under fractional and batch melting tomatch the Rb concentrations between melt and parent rock isa maximum of 48 and 83 vol.% melt, respectively. KEY WORDS: Antarctica; dike injection; disequilibrium; granite partial melting; silicic melt segregation  相似文献