Role of underthrust oceanic crust in the genesis of a Fijian calc-alkaline suite   总被引：2，自引：0，他引：2  

James B. Gill 《Contributions to Mineralogy and Petrology》1974,43(1):29-45

A test of the proposition that calc-alkaline magmas are direct partial melts of underthrust oceanic crust is presented. It involves numerical evaluations of whether or not the major and trace element and isotopic composition of a Fijian calc-alkaline rock suite is consistent with these rocks representing unfractionated partial melts of oceanic crust at high pressures. Experimental data for one of the samples constrain the calculations.When compositions of liquidus minerals at 27 kb are combined with compositions of the volcanic rocks, close approximations can be made to the composition of oceanic crust only if the degree of partial melting is between 20% (dacite) and 45% (basaltic-andesite), and if accessory minerals are refractory phases. Concentrations of elements such as K, Rb, Sr, Pb, Th, and U, and 87Sr/86Sr ratios in the Fijian suite can be satisfactorily explained only if the parental material consisted of altered rather than fresh ocean floor basalt. Sediments are not likely to have been involved. Concentrations of Na, Ni, Co, Cr, Sc, V, the REE, Y, Zr, Hf, and Nb cannot be explained unless, or in some cases even if, several accessory phases are partially refractory. Therefore, partial melting of underthrust lithosphere does not seem likely to produce magmas with the composition of at least one quite typical calc-alkaline suite.  相似文献   

Geochemical variations within a laminated evaporite deposit: evidence for brine composition during formation of the Permian Castile Formation, Texas and New Mexico, USA     

Alick B. Leslie  Gill M. Harwood  Alan C. Kendall 《Sedimentary Geology》1997,110(3-4):223-235

The Upper Permian Castile Formation of the Delaware Basin in northwest Texas and New Mexico consists of up to 600 m of evaporites and is subdivided into units of anhydrite overlain by halite. The Castile Formation has commonly been interpreted as a deep-water, deep-basin deposit in which sediments were laid down in several hundred metres of water or brine. Recent textural observations within anhydrite units, in which the thick-bedded anhydrite horizons have been interpreted as being of shallow-water origin, have challenged this assumption. This geochemical study of the oldest anhydrite unit in the Castile Formation (the Anhydrite 1 Member) attempts to resolve some of the problems regarding brine depth and evolution in the basin. The Anhydrite 1 Member has been subdivided into five major cycles on the basis of the distribution of stratigraphic units of thick-bedded anhydrite.

Stable isotopic analyses of sulphur from anhydrite, and oxygen and carbon from calcite show that the basin waters were chemically homogeneous during precipitation of anhydrite, and do not indicate any significant input of meteoric, continental-derived waters. Throughout the section studied progressive enrichment of ¹⁸O upwards within cored intervals indicates continuous evaporation of the water body. Carbon isotopes appear to indicate fluctuations in organic activity within the cycles. Trace elemental analyses of Fe, Mg, Sr, Mn, Al, Ba, Zn, Pb and Cu from the sulphate fraction of the samples show a very high variability. There is a distinct increase in trace elemental abundances at the tops of cycles which may indicate variations in precipitation kinetics. Analyses of texturally defined cycles show that up-core trends for many of the trace elements correlate with changes in δ¹⁸O, indicating a progressive increase in the influence of evaporation. In addition, cyclical variations in trace elemental composition indicate changes in basin conditions with around a 350-year cyclicity. These changes are independent of δ¹⁸O values. The geochemical data do not provide conclusive proof of water depth during deposition of the Castile Formation. The data are interpreted as reflecting small-scale changes in conditions of deposition, despite the fact that water input remained essentially constant in terms of chemical composition.  相似文献   

Placing cyberspace: processes of Americanization in British children's use of the Internet     

Sarah L. Holloway  & Gill Valentine 《Area》2001,33(2):153-160

This paper counters the notion that cyberspace is a placeless electronic sphere through an analysis of British children's use of the Internet. It demonstrates that rather than being accessible from everywhere but existing nowhere, cyberspace is shaped through place-routed cultures, and in particular through processes of Americanization.  相似文献   

Water-table rise due to infiltration from canals     

Mohammed Akram Gill 《Journal of Hydrology》1984,70(1-4):337-352

Analytical solutions are presented for transient water-table profiles in finite unconfined aquifers due to infiltration occurring from a single canal or more than one canal. The aquifer boundaries are assumed to be parallel to the alignment of the canal(s) and the lower impervious bottom is horizontal. Further, the aquifer is assumed to be homogeneous and isotropic. Losses such as evapotranspiration are ignored; likewise replenishment from other sources, for example, rainfall, is also neglected.  相似文献   

Oil prospects of the helez formation,southern hashephela region,Israel: Evaluation of the thoroughness of search achieved by past exploration     

D. Gill  R. Gabai 《Mathematical Geosciences》1983,15(1):211-215

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Substrate kinetics of DMSP-lyases in axenic cultures and mesocosm populations of <Emphasis Type="Italic">Emiliania huxleyi</Emphasis>     

Michael Steinke  Claire Evans  Gareth A. Lee  Gill Malin 《Aquatic Sciences - Research Across Boundaries》2007,69(3):352-359

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Extending the strain path method analogy for modelling penetrometer installation     

D. R. Gill  B. M. Lehane 《国际地质力学数值与分析法杂志》2000,24(5):477-489

The Strain Path Method (SPM) is an approximate framework for simulating the disturbance caused by piles or penetrometers in soil. The key conceptual assumption of the SPM is that the deformation and strain fields caused during these penetration processes are strongly kinematically constrained (especially during undrained penetration of clays) and can be estimated independently from the actual constitutive properties of the surrounding soil. Previous applications of SPM have estimated strain fields for a variety of penetrometer geometries using velocity fields of ideal inviscid fluids. This paper refines the strain field for penetrometers with 60° conical tips using numerically computed velocity fields in viscous fluids with a variety of boundary conditions imposed on the penetrometer shaft. Following a parametric study, a set of flow conditions is selected which provides a best fit between computed soil deformations and physical displacement measurements made in three separate experiments. The approach is simple and rapid and, while highlighting some of the inaccuracies associated with the existing SPM solution, may also be used for comparative purposes to assist the development of other approaches to the deep penetration problem. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Estimation of compaction in marine geological formations from engineering data commonly available     

E.D. Gill  J.G. Lang 《Marine Geology》1977,25(4):M1-M4

The compaction of Quaternary marine formations can be estimated (under the conditions stated in this paper) by comparing values of 1 + 2.7w, where w is the water content, a figure usually provided in engineering reports for bridges, harbours and such. The procedure is to compare values for an older formation with those for a younger one in the same area, or a past formation with present sediments.  相似文献   

Release and transformations of inorganic iodine by marine macroalgae     

Rosie Chance  Alex R. Baker  Frithjof C. Küpper  Claire Hughes  Bernard Kloareg  Gill Malin 《Estuarine, Coastal and Shelf Science》2009

A number of field and laboratory studies on the impact of marine macroalgae on dissolved inorganic iodine speciation are presented. Within tidally isolated rock pools, the brown macroalga Fucus serratus was found to both release stored iodide and to facilitate the reduction of iodate to iodide. In contrast, no discernible changes in iodine speciation were observed in rock pools containing green macroalgae of the genus Ulva. Incubation experiments confirmed that the macroalgae Laminaria digitata, F. serratus and Kallymenia antarctica release iodide, though the rate of release varied between species and between specimens of the same species. Application of oxidative stress by treatment with cell wall derived oligoguluronate elicitors increased the efflux of iodide by L. digitata approximately 20-fold. The release of iodide by macroalgae may impact upon the formation of volatile iodine species (molecular iodine and iodocarbons) that are of importance in the coastal atmosphere.  相似文献   

Ship board testing of a deoxygenation ballast water treatment   总被引：2，自引：1，他引：1  

McCollin T  Quilez-Badia G  Josefsen KD  Gill ME  Mesbahi E  Frid CL 《Marine pollution bulletin》2007,54(8):1170-1178

A ship board trial of a deoxygenation method for treating ballast water was carried out during a voyage from Southampton (United Kingdom) to Manzanillo (Panama). A nutrient solution added to two ballast tanks encouraged bacterial growth, resulting in a gradual change to an anoxic environment. Samples were taken from two treated tanks and two untreated tanks to assess changes in the abundance and viability of zooplankton, phytoplankton and bacteria. The work was carried out before the International Maritime Organization (IMO) standard was agreed so only a broad indication of whether the results achieved the standard was given. For the zooplankton, the standard would have been achieved within 5 or 7 days but the phytoplankton results were inconclusive. The biological efficacy was the result of the combination of several factors, including the treatment, pump damage and an increase in the water temperature during the voyage.  相似文献