Structure and petrology of the Tregonning—Godolphin granite,Cornwall     

Maurice Stone 《Proceedings of the Geologists' Association. Geologists' Association》1975,86(2):155-170

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The ages of fractures in the Eye-Dashwa pluton,Atikokan, Canada     

D. Choudari Kamineni  Denver Stone 《Contributions to Mineralogy and Petrology》1983,83(3-4):237-246

Ages of fractures in the Eye-Dashwa granite pluton north of Atikokan, Ontario, are estimated from analyses of their filling materials (pegmatite, aplite, hornblendeporphyry, epidote, chlorite, gypsum, diabase, iron oxides, carbonate and clays). The analyses include radiometric age determinations of filling materials, comparison of crystallization temperatures of filling materials with the expected temperature of the pluton through time, and paragenetic relations derived from textures. The major fractures (primarily epidote and chlorite-filled) were produced by penetrative deformation during cooling immediately after intrusion of the pluton. From 2.6 Ga to 2.4 Ga they transected the pluton and largely defined the present overall fracture network. Less severe penetrative deformation occurred about 1.1 Ga, when a few diabase dikes and small gypsum fractures developed. A second source of fracturing appears to have existed through most of geological time, and it reopened segments of old fractures within about 400 m of the present erosional surface. It is unknown whether the near-surface, or supergene, fractures formed more or less continuously through time or in distinct episodes, such as during glacial periods. Open fractures, which are most common in the near-surface layer, tend to transmit groundwater, but fracture sealing due to the accumulation of filling materials seems to occur with time. Underground excavations such as nuclear fuel waste disposal vaults, would be less susceptible to the incursion of groundwater, if they were located below the near-surface layer.  相似文献   

Textural evolution of lithium mica granites in the Cornubian batholith     

Maurice Stone 《Proceedings of the Geologists' Association. Geologists' Association》1984,95(1):29-41

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Light-rare earth element-rich minerals associated with platinum-group element mineralization in the Archean Boston Creek Flow,Ontario     

W. E. Stone  J. H. Crockett  M. E. Fleet 《Mineralogy and Petrology》1994,51(1):85-109

Summary A variety of LREE-rich minerals are associated with late magmatic-stage platinum-group element (PGE) mineralization [(PGE + Au) = 300 ppb) in unsheared clinopyroxenite and gabbro proximal to sheared amphibolite in the Boston Creek Flow (BCF) Al-depleted komatiitic basalt, Archean Abitibi greenstone belt, Ontario. The LREE-rich minerals are LREE-rich apatite (La₂O₃ + Ce₂O₃ 1.5 wt%), LREE-rich epidote (Ce, La: 12 wt% REE), and bastnaesite [(Ce,La)(CO₃)(F,OH)]. The LREE-rich apatite forms rare zones in altered apatite grains and discrete, multifaceted micrometric-sized grains. LREE-rich epidote forms large (up to 100 ,m), compositionally zones grains in amphibolitized plagioclase. Bastnaesite forms areas marginal to and veinlets within the LREE-rich epidote and analyses are characterized by up to 0.4 wt% Cl. Compared to other unsheared rocks from the flow, the REE-rich mineral host rocks contain: intermediate REE contents (REE = 38 to 71 ppm), Ba contents (up to 240 ppm), and U/Th values (0.3 to 7.2); variable Cl contents (21 to 60 ppm); and slightly elevated ³⁴S values (up to 3.3). In contrast, the sheared amphibolite is characterized by low contents of REE (REE = 25 ppm), Cl (15 ppm), Ba (20 ppm), U (0.5 ppm), and Th (0.4 ppm), and a distinctive chondrite-normalized whole-rock REE pattern profile [(La/Sm)_n = <2 and (Tb/Yb)_n = < 1).The restricted occurrence, textures and chemical compositions of the LREE-rich minerals are interpreted as the result of mobilization and localized concentration of the LREE by hydrothermal fluids during greenschist facies contact metamorphism. LREE-rich epidote represents LREE redistribution accompanying the breakdown of plagioclase during abnormally intense amphibolitization and shear deformation within the flow at the peak of greenschist facies contact metamorphism. LREE-rich apatite and bastnaesite represent LREE mobilization and very localized reprecipitation during later stage, retrogressive amphibolitization. The low chlorine contents of the LREE-rich minerals and their host rocks suggest that complexing with Cl was only of minor importance in the concentration of LREE.The spatial association of the LREE-rich minerals with the PGE mineralization reflects concentration of shear deformation and amphibolitization at this stratigraphic level within the flow. The attendant hydrothermal fluid activity induced limited mobilization and reconcentration of PGE in veinlets and fractures within the mineralization. The low Cl suggests that complexing with Cl was not of importance in the PGE mobilization, nor in the late magmatic-stage mineralization process.

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Seltene Erd-Minerale in Assoziation mit Platinvererzung im Archaischen Boston Creek Flow, Ontario

Zusammenfassung Verschiedene LSEE-reiche Minerale kommen zusammen mit spätmagmatischer Platinvererzung (PGE + Au = 300 ppb) in Klinopyroxeniten und Gabbro, in engster Nachbarschaft mit zerschertem Amphibolit im Al-verarmten, komatiitischen Basalt des Boston Creek Flow (BCF), im archaischen Abitibi Grünstein-Gürtel, Ontario, vor. Die LSEE- reichen Minerale sind LSEE-reicher Apatit (La₂O₃ + Ce₂O₃ > 1.5 Gew.%), LSEE-reicher Epidot (Ce, La: 12 Gew.% SEE), und Bastnaesit ((Ce, La) (CO₃)(F, OH)). Der LSEE-reiche Apatit bildet Zonen in umgewandelten Apatitkörnern und auch individuelle, flächenreiche Körner, die einige Mikron groß sind. LSEE-reicher Epidot bildet große (bis zu 100 m) Körner mit zonierter Zusammensetzung in amphibolitisierten Plagioklasen. Bastnaesit bildet randliche Bereiche von, und Gängchen in LSEE-reichem Epidot. Analysen zeigen bis zu 0.4 Gew.%. Cl. Verglichen mit anderen unzerscherten Gesteinen aus dem BCF, enthalten die Wirtsgesteine der SEE-reichen Minerale: intermediäre SEE-Gehalte (SEE = 38 bis 71 ppm), Ba-Gehalte von bis zu 240 ppm und U/Th-Werte von 0.3 bis 7.2. Wechselnde Cl-Gehalte (21 bis 60 ppm) und etwas erhöhte ³⁴S-Werte (bis zu 3.3). Im Gegensatz dazu zeigt der zerscherte Amphibolit niedrige Gehalte von SEE (SSE = 25 ppm), Cl (15 ppm), Ba (20 ppm), U(0.5 ppm), und Th (0.4 ppm), sowie charakteristische Chondrit-normalisierte SEE-Verteilungsmuster ((La/Sm)_n = <2 und (Tb/Yb)_n = < 1).Das beschränkte Vorkommen, die Texturen und die chemische Zusammensetzung der LSEE-reichen Minerale werden als Ergebnis der Mobilisierung und örtlichen Konzentration von LSEE durch hydrothermale Fluide während einer Kontaktmetamorphose unter Bedingungen der Grünschiefer-Fazies interpretiert. LSEE-reicher Epidot ist das Ergebnis von LSEE Umverteilung im Zusammenhang mit dem Zerfall von Plagioklas während besonders intensiver Amphibolitisierung und Scherungsdeformation innerhalb des Basalt-Ergusses zum Höhepunkt der Kontaktmetamorphose. LSEE-reicher Apatit und Bastnaesit gehen auf LSEE-Mobilisierung und sehr lokale Wiederausfällung während retrograder Amphibolitisierung während eines späteren Entwicklungsstadiums zurück. Die niedrigen Chlorgehalte der LSEE-reichen Minerale und ihrer Wirtsgesteine weisen darauf hin, daß die Bildung von Chlorid-Komplexen bei der Konzentration von LSEE nur eine geringe Rolle gespielt hat.Die räumliche Verbindung von LSEE-reichen Mineralen mit der PGE-Vererzung dürfte auf die Verbindung von Scher-Deformationen und Amphibolitisierung in diesem stratigraphischen Niveau innerhalb des Basaltes zurückgehen. Die begleitende hydrothermale Fluid-Aktivität führt zu beschränkter Mobilisierung und Anreicherung von PGE in Gängen und Sprüngen innerhalb der Vererzung. Die niedrigen Chlorgehalte weisen darauf hin, daß Chlorid-Komplexe weder bei der PGE-Mobilisierung, noch bei der spätmagmatischen Vererzung von Bedeutung gewesen sind.

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With 4 Figures  相似文献   

Geographical Aspects of the “Limits to Growth” Concepts*     

Kirk H. Stone 《The Professional geographer》1976,28(4):336-340

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Earth system models of intermediate complexity: closing the gap in the spectrum of climate system models   总被引：10，自引：7，他引：10  

M. Claussen  L. Mysak  A. Weaver  M. Crucifix  T. Fichefet  M.-F. Loutre  S. Weber  J. Alcamo  V. Alexeev  A. Berger  R. Calov  A. Ganopolski  H. Goosse  G. Lohmann  F. Lunkeit  I. Mokhov  V. Petoukhov  P. Stone  Z. Wang 《Climate Dynamics》2002,18(7):579-586

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Creating and sustaining Islamic financial centers: Bahrain in the wake of financial and political crises     

Michael C. Ewers  Ryan Dicce  Jesse P.H. Poon  Jeffery Chow  Justin Gengler 《Urban geography》2018,39(1):3-25

Although primarily concentrated in countries with Muslim majorities, Islamic finance has become a global industry representing both a decentering of the global financial architecture and the emergence of an urban network that resides beyond the confines of traditional world city literature. While geographers have identified the “Mecca’s” of the Islamic finance industry – one of which is Bahrain – there remains a need to identify the factors necessary to create and sustain centers of Islamic finance. This paper examines these factors through a firm-level survey of foreign and local Islamic financial institutions in Bahrain, in conjunction with key informant interviews with representatives of these firms. We find that while Bahrain’s entrenched institutional advantages have preserved its role as a center in the Islamic financial landscape, ongoing political instability and the increasing attractiveness of new and emerging centers are threatening this role. As the country navigates the current social and political unrest, questions are raised as to what it takes to be an Islamic financial center.  相似文献   

Velocities of shallow overland flow on semiarid hillslopes          下载免费PDF全文

Viktor Polyakov  Mark A. Nearing  Jeffry Stone 《地球表面变化过程与地形》2018,43(12):2578-2583

A series of 188 rainfall plot simulations was conducted on grass, shrub, oak savanna, and juniper sites in Arizona and Nevada. A total of 897 flow velocity measurements were obtained on 3.6% to 39.6% slopes with values ranging from 0.007 m s^‐1 to 0.115 m s^‐1. The experimental data showed that shallow flow velocity on rangelands was related to discharge and ground litter cover and was largely independent of slope gradient or soil characteristics. A power model was proposed to express this relationship. These findings support the slope–velocity equilibrium hypothesis. Namely, eroding soil surfaces evolve such that steeper areas develop greater hydraulic roughness. As a result overland flow velocity becomes independent of the slope gradient over time. Our findings have implications for soil erosion modeling suggesting that hydraulic friction is a dynamic, slope and discharge dependent property. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Platinum-group element contents of chromites from mafic–ultramafic layered flows, Abitibi greenstone belt, Ontario: implications for geochemical fractionation and mineral exploration     

W. E. Stone  J. H. Crocket 《Mineralogy and Petrology》2003,78(1-2):139-147

Summary ?The PGE contents of chromite separated from peridotite layers of Archaean mafic–ultramafic flows, Abitibi belt (Canada), indicate enrichment in Os–Ir–Ru (600 ppb) relative to Pd–Au (<5 ppb). Evidently, chromite was a sink for Ir–Os–Ru during melt-chromite fractionation in each of the flows. However, an additional phase, probably olivine, is required to explain the bulk Ir content of the sulphide-poor peridotites. In contrast, the chromite Pt contents range from <10 ppb to 400 ppb, with large variation in Pt/Ru (0.02–2.76) and Pt/Pd (5–400) ratios. The Pt enrichment may be related to the presence of Pt spinel structure compounds in oxidised melt, reflecting Fe–Ti spinel-related mineralisation in higher pyroxenite-gabbro layers. Received December 5, 2002; revised version accepted January 7, 2003  相似文献   

Testing the Clausius–Clapeyron constraint on changes in extreme precipitation under CO<Subscript>2</Subscript> warming     

P. Pall  M. R. Allen  D. A. Stone 《Climate Dynamics》2007,28(4):351-363

Increases in extreme precipitation greater than in the mean under increased greenhouse gases have been reported in many climate models both on global and regional scales. It has been proposed in a previous study that whereas global-mean precipitation change is primarily constrained by the global energy budget, the heaviest events can be expected when effectively all the moisture in a volume of air is precipitated out, suggesting the intensity of these events increases with availability of moisture, and significantly faster than the global mean. Thus under conditions of constant relative humidity one might expect the Clausius–Clapeyron relation to give a constraint on changes in the uppermost quantiles of precipitation distributions. This study examines if the phenomenon manifests on regional and seasonal scales also. Zonal analysis of daily precipitation in the HadCM3 model under a transient CO₂ forcing scenario shows increased extreme precipitation in the tropics accompanied by increased drying at lower percentiles. At mid- to high-latitudes there is increased precipitation over all percentiles. The greatest agreement with Clausius–Clapeyron predicted change occurs at mid-latitudes. This pattern is consistent with other climate model projections, and suggests that regions in which the nature of the ambient flows change little give the greatest agreement with Clausius–Clapeyron prediction. This is borne out by repeating the analyses at gridbox level and over season. Furthermore, it is found that Clausius–Clapeyron predicted change in extreme precipitation is a better predictor than directly using the change in mean precipitation, particularly between 60°N and 60°S. This could explain why extreme precipitation changes may be more detectable then mean changes.  相似文献