Lower Temperature Terminations of the Three-phase Region Plagioclase-Alkali Feldspar-Liquid     

STEWART  D. B.; ROSEBOOM  E. H.  JR. 《Journal of Petrology》1962,3(3):280-315

Geological and experimental evidence indicate that the three-phasefield, plagioclase-alkalifeldspar-liquid, may terminate in severaldifferent ways. The possible terminations have been developedfrom Schreinemakers' rules governing the disappearance of three-phasefields. In igncous rocks, these different terminations may arisefrom variations in the relative amounts of additional componentsin magmas, or from changes of total pressure, or from structuralchanges that effect the extent of solid solution in feldspar. The three-phase region originates from the intersection of thesolidus and the feldspar solvus. The available evidence regardingthis intersection is reviewed, as is the evidence for the existenceand form of the boundary curve on the feldspar liquidus. Thedata are used to project a series of isobaric polythermal andisobaric isothermal diagrams for each possible termination.Subsequent discussions relate the theoretical arguments to thenatural evidence, suggest the more probable geological environmentsof some of the terminations, and indicate characteristic featuresof each termination. It may be possible to identify the type of termination involvedin the crystallization of some rocks. The necessary data arethe amounts and compositions of both kinds of coexisting feldsparsand of the feldspar components of the coexisting liquid at oneor more stages of the crystallization process. Volcanic rocksare most suitable for such studies. The terminations explain many of the compositional relationshipspossible between feldspar crystals and silicate melt under geologicaland experimental conditions. These compositional relationshipsare fundamental to understanding the crystallization of igneousrocks and the formation of melts by partial fusion. Other geologicalapplications include a simple explanation for some resorbedfeldspars, the separation, correlation, and comparison of porphyriticrock units, interpretation of compositional changes of successivezones of zoned feldspars, and mantling of one feldspar by another.With all types of termination, extensive fractionation yieldsa liquid rich in Or and Ab that may crystallize to alkali feldsparor feldspars.  相似文献   

智慧社会下的城市地理学研究——基于居民活动的视角   总被引：4，自引：1，他引：3  

王波  卢佩莹  甄峰 《地理研究》2018,37(10):2075-2086

智慧社会下,信息通信技术已经渗透到居民日常生活中各个方面的网络/实体活动经历,是理解智慧社会发展的核心。同时,虚拟—实体空间关系、网络—实体活动关系及其对城市地域空间重构与演化的影响一直得到城市地理学者的广泛关注。在综述已有居民活动时空间研究的基础上,指出智慧社会下居民网络—实体活动的关系已经超越简单的替代—促进二元关系,而承载网络与实体活动的虚拟与实体空间也相互交织影响,挑战对实体空间中地方与移动性的理解,并重构虚拟空间中的秩序和规律,丰富智慧社会下城市地理学的研究问题。超越技术决定论与基于技术决定论的虚实空间二元论的讨论范畴,更能反映城市地理学在智慧社会发展话语体系中的地位。与发达国家不同,中国同时经历着快速的信息化与城镇化,对居民网络/实体活动组织及虚拟—实体空间关系的研究不仅提供了新的案例与理论贡献,而且为城镇化的可持续发展提供实践策略。  相似文献   

Quantification of SEM microtextures useful in sedimentary environmental discrimination   总被引：1，自引：0，他引：1  

WILLIAM C. MAHANEY  REW STEWART  VOLLI KALM 《Boreas: An International Journal of Quaternary Research》2001,30(2):165-171

Scanning electron microscopic imagery is often used to identify and discriminate among environments of sedimentation with the main aim of identifying individual microfeatures, or suites of microtextures, that are considered indicative of a particular depositional environment or geologic process. Because few microtextures are considered to represent a single geologic process it is necessary to analyze a large number of quartz sands and other mineralic grains with the objective of determining the frequency of occurrence of a range of microtextures within a distinct sample suite. Using percent frequency of occurrence of different microtextures from suites of fluvial, glaciofluvial and glacial sands from sites in Estonia and Latvia, we invoked statistical comparison of different sample suites using Euclidean distances. These provide a quantitative means of measuring the differences among different sediments and processes that formed them and also a quantification tool useful in assessing microtextures as a recorder of sedimentary environments.  相似文献   

EXAMPLES OF RESOLUTION IMPROVEMENT IN GEOELECTRICAL SOUNDINGS APPLIED TO GROUNDWATER INVESTIGATIONS1     

STEWART K. SANDBERG 《Geophysical Prospecting》1993,41(2):207-227

One simulation and two field examples from New Jersey illustrate resolution improvement in geoelectrical soundings applied to groundwater exploration. Layered-earth parameter resolution is derived from data obtained with the commonly used methods of resistivity, induced polarization (IP) and transient electromagnetic (TEM) soundings. Resolution improvement is achieved by simultaneous inversion of two or more data sets and by constraining parameters of the inverse problem. A quantitative analysis showing the contribution of IP data to the resolution of geo-electric sections is presented. Simultaneous inversion of simple IP data with conventional resistivity and resistivity-TEM data sets resulted in improved parameter resolution. IP data improved resolution in three ways: (1) by decoupling correlated layered-earth parameters, (2) by adding information to a geological interpretation about a second physical property, namely chargeability, and (3) by increasing the electrical information available.  相似文献   

The history of oil exploration and development in the northern North Sea     

DAVID STEWART 《Geology Today》1988,4(4):130-137

Discovery of the southern North Sea gas fields and, by 1970, several billion-barrel oil fields in the central North Sea encouraged oil companies to explore in the deeper, less hospitable waters of the northern North Sea. There, seismic surveys revealed a pre-Cretaceous unconfmity with 'highs' forming potential oil traps. One of the largest of these buried 'highs' was drilled by ShelllEsso, and oil was found in quantity in Middle Jurassic deltaic sandstones. This led to the discovery of eight major oil fields with reserves in excess of 7500 million barrels. Detailed studies of the sandstone reservoirs of the Brent Delta are enabling petroleum geologists and engineers to maximize recovery from these northern fields.  相似文献   

A meander-belt sandstone of the Lower Cretaceous of Southern England     

D. J. STEWART 《Sedimentology》1981,28(1):1-20

The meander-belt deposit comprises a sandstone resting on an erosion surface and bounded above and below by massive varicoloured mudstones with rootlet traces. The sandstone unit is composed of six bodies separated from one another, horizontally, by erosion surfaces; together the bodies form a single multilateral sand body. Internally each body is composed of lateral accretion units inclined at up to 6° from the horizontal. Vertical sequences of facies show significant variations but the grain size generally fines upwards. The principal lithofacies within the sandstones are, in common ascending order, intraformational conglomerate, large-scale cross-bedded, horizontal bedded and small-scale cross-laminated sandstone, and alternate sandstones and mudstones. Current directions are normal to the true slope of accretion surfaces and show insignificant scatter within individual bodies but are very diverse overall. Five of the sand bodies are believed to represent individual point bars, and one body an abandoned channel. Together they comprise the meander belt. The river was subject to very variable discharges and carried high suspended loads. Analysis of vertical profiles indicates that grain size segregation along the length of the point bars caused differentiation of the bars into coarse-grained heads and sandy tails.  相似文献   

Guest Editorial: Geocomputation and GIS     

A STEWART FOTHERINGHAM  GRAHAM CLARKE  BOB ABRAHART 《Transactions in GIS》1997,2(3):199-200

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A Geographical Analysis of Potential Railway Load Centers in China*     

Becky P. Y. Loo  Kai Liu 《The Professional geographer》2005,57(4):558-579

Railway containerization is important to the development of an efficient inland‐port distribution (IPD) system in China. After reviewing the general transportation network evolution and local circumstances, a strategy of focusing the limited capital investment at a few railway stations with the highest potential to develop into land‐based load centers (LLCs) was proposed. The fifteen major railway stations designated in the 2002 Plan form the basis for an evaluation. With the application of geographic information systems (GIS), each station's potential to become a LLC is evaluated under infrastructural, economic, logistics, and capacity dimensions. The 250‐ and 500‐km hinterland scenarios are considered.  相似文献   

Neoliberalism in the oceans: “rationalization,” property rights, and the commons question     

Becky Mansfield 《Geoforum》2004,35(3):313-326

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中国客运交通的碳排放地理特征与展望   总被引：1，自引：0，他引：1  

李琳娜  BeckyP.Y.Loo 《地理研究》2016,35(7):1230-1242

围绕全国、省市和“一带一路”三个空间层面,对1990-2012年中国客运交通的碳排放进行了估算和分析。研究表明：① 在全国层面上,公路是碳排放总量最大的运输方式,其次是航空,而铁路和水运的碳排放较低且保持稳定;② 在省市层面上,交通碳排放呈现出从东部向中、西部递减的趋势,并且空间分布越来越集中在东部省份;③ “一带一路”的主要城市中,“丝绸之路经济带”（简称“一带”）的沿线城市表现出较低的交通碳排放,而“21世纪海上丝绸之路”（简称“一路”）沿线的港口城市的交通碳排放较高,而且都以公路碳排放为主。未来在满足和控制交通需求的同时,有必要发展以铁路和公共交通为主的低碳交通模式,替代目前以公路为主的交通模式。  相似文献