Compositional variation in pillow lavas from the Mid-Atlantic Ridge     

Fumiko Shido  Akiho Miyashiro  Maurice Ewing 《Marine Geology》1974,16(4):177-190

Five fresh, two weathered, and two metamorphosed basalt pillows with a presently or originally glassy outermost layer, together with a weathered and a metamorphosed basalt fragment without an originally glassy layer, all from the Mid-Atlantic Ridge, were investigated in detail. Fresh pillows usually show only very slight compositional heterogeneity, except for the glassy outermost layer where the total iron and MgO contents are higher and the K₂O content and the $\text{Fe}{}_2\text{O}{}_3\text{FeO}$ ratio are lower than the interior. In particular, the K₂O content of the glassy outermost layer is only about a half of that of the core in some pillows. In weathered pillows the surface layer shows higher total iron, TiO₂, P₂O₅ and H₂O contents and a higher $\text{Fe}{}_2\text{O}{}_3\text{FeO}$ ratio and a much lower CaO content than the interior. Most of the compositional heterogeneity observed in metamorphosed pillows may be ascribed to chemical migration during weathering, though metamorphism also may cause considerable heterogeneity.  相似文献   

A new approach to simulating disorder in crystals     

I. L. Jones  Volker Heine  Maurice Leslie  Geoffrey D. Price 《Physics and Chemistry of Minerals》1990,17(3):238-245

The technique of calculating lattice dissociation energies using static, minimum lattice energy, ionic models has been extended to allow for multiple occupancy of the ionic sites. A particular lattice site can have a fraction x of an ionic species A and a fraction y of an ionic species B, where the position of each can be relaxed separately along with the unit cell dimensions until an equilibrium is reached. Various degrees of long and short range order can be modelled. This technique has been applied to the mineral sillimanite, Al₂SiO₅, to calculate the effect on the lattice energy of (Al, Si) ordering over the tetrahedral sites. It is found using this method that (Al, Si) ordering with space group Pbmn stabilizes the material by 29.25 kcal/mol (Al^iv-O-Al^iv), with respect to the completely disordered material.  相似文献   

A review of dimethylsulfoxide in aquatic environments     

Peter A. Lee  Stephen J. de Mora  Maurice Levasseur 《大气与海洋》2013,51(4):439-456

Abstract

Dimethylsulfoxide (DMSO) is an ubiquitous, albeit poorly understood, component of the marine sulfur cycle. Conventionally, the accepted formation pathways are the photochemical and microbial oxidation of dimethylsulfide (DMS). The principal loss mechanism is thought to be via microbial transformation, either consumption or reduction to DMS. The interactions between DMSO and DMS are likely to be important in controlling sea surface concentrations of DMS, and thus DMSO could influence the role played by DMS in global climate regulation. This review examines current knowledge of the distribution of DMSO in aquatic environments and the possible link between DMSO, DMS and global climate control. Mechanisms for the formation and loss of DMSO are also considered in addition to some of the factors influencing these processes. The review also considers that DMSO may be biosynthesized by phytoplankton, representing a non‐DMS source for DMSO, and that DMSO can undergo photochemical oxidation, a potential loss mechanism for DMSO in the marine environment.  相似文献   

A note on the effects of virtual temperature: Research note     

Maurice Danard 《大气与海洋》2013,51(2):485-493

Abstract

The effects of virtual temperature on parcel buoyancy are investigated and the following results obtained. For descent or unsaturated ascent, the buoyancy acceleration is enhanced if the mixing ratio increases with pressure. However, for saturated ascent, the buoyancy acceleration is inhibited unless the lapse rate of mixing ratio exceeds a value slightly greater than that along a moist adiabat. This criterion is evaluated for several mean soundings. For the case of Oklahoma supercells, the mixing ratio lapse rate is clearly large enough. However, for other cases it often is not. Horizontal gradients in water vapour and condensed water can have a significant influence on the thermal wind.  相似文献   

Simplified analytical solution for point load acting behind a cantilever wall     

George Maurice Iskander 《国际地质力学数值与分析法杂志》2012,36(3):344-351

The analysis of earth pressure resulting from an applied point load behind a retaining wall is to be carried out in three dimensions as the earth pressure distribution varies both in vertical and horizontal directions. In this research, the semi‐empirical expressions developed by Terzaghi [Trans. ASCE 1954; 119 ] for earth pressure due to point load are integrated and a correction factor is introduced to develop equivalent equations for two‐dimensional analyses. A new parameter referred to as the design width, which is the horizontal distance retained by the individual vertical retaining element is introduced. The used procedure and the resulted equations are tested and verified by adopting different design width values covering the practical range. The resulted equations together with the semi‐empirical expressions of earth pressure due to line load developed by Terzaghi [Trans. ASCE 1954; 119 ] can be easily used for two‐dimensional analysis of the effect of point load. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Enriched crustal and mantle components and the role of the lithosphere in generating Paleoproterozoic dyke swarms of the Ungava Peninsula,Canada     

Charles Maurice  Don Francis 《Lithos》2010,114(1-2):95-108

Paleoproterozoic mafic dyke swarms (2.5–2.0 Ga) of the Ungava Peninsula can be divided in three chemical groups. The main group has a wide range of Fe (10–18 wt.% Fe₂O₃) and Ti (0.8–2.0 wt.% TiO₂) contents, and the most magnesian samples have compositions consistent with melting of a fertile lherzolitic mantle at ~ 1.5 GPa. Dykes of a low-LREE (light rare earth element) subgroup (La/Yb ≤ 4) display decreasing Zr/Nb with increasing La/Yb ratios and positive εNd_2.0 Ga values (+ 3.9 to + 0.2) that trend from primitive mantle towards the composition of Paleoproterozoic alkaline rocks. In contrast, dykes of a high-LREE subgroup (La/Yb ≥4) display increasing Zr/Nb ratios and negative εNd_2.0 Ga values (? 2.3 to ? 6.4) that trend towards the composition of Archean crust. A low Fe–Ti group has low Fe (< 11 wt.% Fe₂O₃), Ti (< 0.8 wt.% TiO₂), high field strength elements (HFSE; < 6 ppm Nb) and heavy rare earth elements (HREE; < 2 ppm Yb) contents, but are enriched in large ion lithophile elements (LILE; K/Ti = 0.7–3) and LREE (La/Yb > 4). These dykes are interpreted as melts of a depleted harzburgitic mantle that has experienced metasomatic enrichment. A positive correlation of Zr/Nb ratio and La/Yb ratio, negative εNd_2.0 Ga values (? 14 to ? 6), and the presence of inherited Archean zircons further suggest the incorporation of a crustal component. A high Fe–Ti group has high Fe (> 14 wt.% Fe₂O₃) and Ti (> 1.4 wt.% TiO₂) contents, along with higher Na contents relative to the main group dykes. Dykes of a high-Al subgroup (> 12 wt.% Al₂O₃) share Fe contents, εNd_2.0 Ga values (? 2.3 to ? 3.4), La/Yb and Th/Nb ratios with Archean ferropicrites, and may represent evolved ferropicrite melts. A low-Al subgroup (< 12 wt.% Al₂O₃) has relatively lower Yb contents (< 2 ppm) and fractionated HREE patterns that indicate the presence of garnet in their melting residue. A comparison with ~ 5 GPa experimentally-derived melts suggests that these dykes may be derived from garnet-bearing pyroxenite or peridotite. The εNd_2.0 Ga values (? 0.3 to ? 2.0) of these dykes lie between the compositions of Archean granitoids and Paleoproterozoic alkaline rocks, signifying their petrogenesis involved both crustal and mantle components.Paleoproterozoic dykes containing a crustal component occur within, or close to, an isotopically enriched Archean terrane (T_DM 4.3–3.1 Ga), whereas dykes without this component occur in an isotopically juvenile terrane (T_DM < 3.1 Ga). The lack of a crustal component and the positive εNd_2.0 Ga values of dykes intruding the latter suggest that the crust they intruded was either too cold to be assimilated, or that its lower crust and/or lithosphere were Paleoproterozoic in age. In contrast, the ubiquitous presence of a crustal component and the diversity of mantle sources for dykes intruding the enriched terrane (lherzolite, harzburgite, pyroxenite) suggest a warmer crust with underlying heterogeneous lithospheric mantle.  相似文献   

Using 87Sr/86Sr, δ18O and δ2H isotopes along with major chemical composition to assess groundwater salinization in lower Shire valley,Malawi     

Maurice Monjerezi  Rolf D. Vogt  Per Aagaard  Asfaw Gebretsadik Gebru  John D.K. Saka 《Applied Geochemistry》2011,26(12):2201-2214

Groundwater resources in some parts of the lower section of Shire River valley, Malawi, are not useable for rural domestic water supply due to high salinity. In this study, a combined assessment of isotopic (⁸⁷Sr/⁸⁶Sr, δ¹⁸O and δ²H) and major ion composition was conducted in order to identify the hydro-geochemical evolution of the groundwater and thereby the causes of salinity. Three major end-members (representing fresh- and saline groundwater, and evaporated recharge) were identified based on major ion and isotopic composition. The saline groundwater is inferred to result from dissolution of evaporitic salts (halite) and the fresh groundwater shows influence of silicate weathering. Conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end-members. Hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater. On the other hand, the groundwater with low TDS, found at some distance from areas of high salinity, is influenced by mixing of evaporated recharge and fresh groundwater only. Close to the Shire marshes, where there is shallow groundwater, composition of stable isotopes of water indicates that evaporation may also be an important factor.  相似文献   

The influence of variable depth on steady zonal barotropic flow   总被引：1，自引：0，他引：1  

Gene H. Porter  Maurice Rattray Jr. 《Ocean Dynamics》1964,17(4):164-174

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Ferromanganese nodules from the devonian of the montagne noire (S. France) and West Germany     

Dr. Maurice E. Tucker 《International Journal of Earth Sciences》1973,62(1):137-153

Ferromanganese nodules (equivalent to Recent manganese nodules) are described from the Upper Devonian griotte (red pelagic limestone) of the Montagne Noire (S. France) and the Cephalopodenkalk of the Rheinisches Schiefergebirge, West Germany. They occur as encrustations, commonly exhibiting colloform structures, around skeletal material and limestone clasts. The nodules are associated with encrusting foraminifera and a development in the sublittoral environment is envisaged. Chemically, the ferromanganese nodules are depleted in manganese relative to iron, compared with Recent nodules, a loss which is attributed to diagenetic migration of manganese. Electron probe studies show that manganese covaries positively with calcium, but negatively with iron and silicon. Diagenetic enrichment of hematite occurs in the griotte at hardground horizons where two periods of mineralization can be established. The Devonian ferromanganese nodules show that solution of nodules has not occurred on burial.

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Zusammenfassung Es werden Eisenmanganknollen (als Äquivalent zu den rezenten Manganknollen) aus dem oberdevonischen Griotte (rote pelagische Kalke) der Montagne Noir und den Cephalopoden-Kalken des Rheinischen Schiefergebirges beschrieben. Sie treten als Umkrustungen von Skeletten und Kalksteinbruchstückchen auf und zeigen gewöhnlich Kolloform-Strukturen. Die Knollen sind vergesellschaftet mit umkrusteten Foraminiferen, und es wird deshalb sublitorales Bildungsmilieu angenommen. Verglichen mit rezenten sind die oberdevonischen Knollen durch Auslaugung von Mangan relativ Eisen-angereichert, was auf diagenetische Mobilisation zurückzuführen ist. Untersuchungen mit der Mikrosonde haben gezeigt, daß Mangan und Calcium gleichläufig, Mangan und Eisen und Kieselsäure gegenläufig sind. Diagenetische Hämatit-Anreicherungen gibt es im Griotte an hardground-Horizonten; es wurden zwei Mineralisationsphasen festgestellt. Die oberdevonischen Eisenmangan-Knollen zeigen, im Gegensatz zur allgemein verbreiteten Meinung, daß sich die Knollen bei Überlagerung nicht unbedingt auflösen.

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Résumé Les nodules de ferromanganèse (équivalents des nodules de manganèse de la période holocène) décrits ici proviennent de la griotte du Dévonien Supérieur (calcaire pélagique rouge) de la Montagne Noire (Sud de la France) et du calcaire à Céphalopodes du Massif Schisteux Rhénan, (Allemagne de l'Ouest). Ils se présentent comme des incrustations exhibant communément des structures colloformes autour de débris de squelettes et de matériaux clastiques calcaire. Les nodules sont associés à des foraminifères qui s'y incrustent; leur développement est conçu dans un milieu sous-littoral. Chimiquement les nodules de ferromanganèse, comparés aux nodules du manganèse de l'époque récente, sont de faible teneur en manganèse par rapport au fer, perte que l'on attribute à la migration diagénétique du manganèse. Des expériences faites à la sonde électronique montrent que le manganèse réagit positivement avec le calcium, mais négativement avec le fer et le silicium. L'enrichissement diagénétique de l'hématite se produit dans la griotte dans des zones de «hardgrounds», où deux périodes de minéralisation peuvent être constatées. Les nodules de ferromanganèse dévoniens montrent, contrairement à une opinion généralement répandue, que les nodules ne se dissolvent pas nécessairement par l'accumulation des sédiments.

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— — Griotte ( ) Montagne Noir . . ; , . , . , , , . Griotte ; . , , .

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A note on estimating the height of the constant flux layer     

Maurice Danard 《Boundary-Layer Meteorology》1981,20(3):397-398

A method is presented for estimating the height of the constant flux layer.  相似文献