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Melt Generation by Plumes: A Study of Hawaiian Volcanism 总被引：18，自引：9，他引：9
The mantle plume underlying the Hawaiian Swell has been modellednumerically using a stationary steady axisymmetric plume undera solid conducting lid. A method of calculating the rate ofmelt production from the plume has been developed, and the totalmelt production rate, the residual depth anomaly and the geoidanomaly have been used to constrain the model. The plume hasa central potential temperature of 1558 ?C and the mechanicalboundary layer is 72 km thick. An average of 6?6% melting occursin a melt-producing region which has a vertical extent of 55km and a radial extent of 130 km to produce 0?16 km3/y of melt.A parameterization of melt composition has been developed thatis consistent with laboratory experiments, with models of MORBgeneration, and with primitive Hawaiian tholeiites containing 16% MgO. There is no evidence that the major and minor elementconcentrations in the source region of Hawaiian tholeiites differfrom those in the source region of MORB. The model is consistentwith the REE contents of Kilauean tholeiites if the source regionhas primitive REE contents. The viscosity of the low-viscositylayer is constrained to be 1016m2/s. 相似文献
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Rare Earth Element Inversions and Percolation Models for Hawaii 总被引：2，自引：4，他引：2
A detailed study has been made of the evolution with time ofthe mantle source and degree of melting required to producea typical Hawaiian volcano. The preshield stage involves a changefrom a depleted to a primitive mantle source and an increasein the melt fraction. Important intra- and inter-volcano variationsoccur during the shield stage which may be related to melt transportprocesses. With time, Mauna Loa's lavas show depletion in increasinglycompatible elements, a result which is consistent with percolationprocesses. Postshield magmas are generated by very small degreesof melting of a depleted mantle source and may be importantin the development of posterosional volcanism. Posterosionallavas can be generated by variable degrees of melting of anamphibole-bearing source that has been enriched by postshieldmagma. A simple percolation model is consistent with the isotopic evolutionof Hawaiian volcanoes. All of the observed isotopic variationseen between Hawaiian volcanoes may be produced from only twomantle sources by small variations in the percolation processes.
* Present address: Department of Earth Sciences, Parks Road, Oxford OX1 3PR, UK. 相似文献
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This paper presents a study on Manasbal lake, which is one of the high altitude lakes in the Kashmir Valley, India. Eighteen
water samples were analysed for major ions and trace elements to assess the variability of water quality of the lake for various
purposes. Geostatistics, the theory of regionalized variables, was then used to enhance the dataset and estimate some missing
spatial values. Results indicated that the concentration of major ions in the water samples in winter was higher than in summer.
The scatter diagrams suggested the dominance of alkaline earths over the alkali elements. Three types of water were identified
in the lake that are referred to as Ca–HCO3, Mg–HCO3 and hybrid types. The lake water was found to be controlled by rock–water interaction with carbonate lithology as a dominant
source of the solutes. The major (Ca2 + , Mg2 + , Na + , K + , NO3 and HCO3-{\rm{HCO}}_{3}^{-}, CO3 and Cl) and trace elements of the lake water were within the World Health Organization standards, therefore the lake water
was considered chemically safe for drinking purposes. Although NO3 concentration (ranging from 1.72 to 2 mg/L), is within the permissible limit and not very alarming, the gradually increasing
trend is not acceptable. It is however, important to guard its spatio-temporal variability as the water is used for domestic
as well as agricultural purposes. This study is significant as hydrogeological information on such high altitude lakes in
India is scanty. 相似文献
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STEVE CARVER IAN HEYWOOD SARAH CORNELIUS DAVID SEAR 《International journal of geographical information science》2013,27(4):475-486
ABSTRACT This paper examines the potential of using GIS (Geographical Information Systems) in the field for environmental characterization, modelling and decision support particularly in isolated areas where data collection is difficult. Observations are based on experiences gained during two Anglo-Russian expeditions to the Altai Mountains of south central Siberia aimed at evaluating proposals for a new national park in the Katunsky Ridge area of the Belukha Massif. The use of GIS together with GPS (Global Positioning Systems) for primary data collection and verification/update of existing data is described and the use of field-based systems for on-the-spot environmental modelling and decision support is evaluated. 相似文献
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Magmatic Evolution of the Skye Igneous Centre, Western Scotland: Modelling of Assimilation, Recharge and Fractional Crystallization 总被引：3，自引：2，他引：1
The Skye igneous centre, forming part of the British Tertiarymagmatic province, developed over a 7 Myr period (61–54Ma) and is characterized by a complex suite of lavas, hypabyssaland intrusive rocks of picritic to granitic composition. Theintrusion of magma from mantle to crust at 2x10–3km3/yr(6 Mt/yr) advected magmatic heat of roughly 0·2 GW averagedover the period of magmatism supporting an ‘excess’heat flux of about 130 mW/m2, or about twice the present-dayaverage continental heat flow. The volume of new crust generatedat Skye (15000 km3) spread over the present-day area of Skyecorresponds to 9 km of new crust. The geochemical evolutionof the Skye magmatic system is constrained using the Energy-ConstrainedRecharge, Assimilation, and Fractional Crystallization (EC-RAFC)model to understand variations in the Sr- and Pb-isotopic andSr trace-element composition of the exposed magmatic rocks withtime. The character (composition and specific enthalpy) of bothassimilant and recharge magma appears to change systematicallyup-section, suggesting that the magma reservoirs migrated toprogressively shallower levels as the system matured. The modelof the magma transport system that emerges is one in which magmabatches are stored initially at lower-crustal levels, wherethey undergo RAFC evolution. Residual magma from this stagethen migrates to shallower levels, where mid-crustal wall rockis assimilated; the recharge magma at this level is characterizedby an increasingly crustal signature. For some of the stratigraphicallyyoungest rocks, the data suggest that the magma reservoirs ascendedinto, and interacted with, upper-crustal Torridonian metasediments. KEY WORDS: assimilation; EC-RAFC model; geochemical modelling; magma recharge; Skye magmatism 相似文献
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SARAH E. COULTER JONATHAN R. PILCHER VALERIE A. HALL GILL PLUNKETT SIWAN M. DAVIES 《Boreas: An International Journal of Quaternary Research》2010,39(1):163-169
Coulter, S. E., Pilcher, J. R., Hall, V. A., Plunkett, G. & Davies, S. M. 2009: Testing the reliability of the JEOL FEGSEM 6500F electron microprobe for quantitative major element analysis of glass shards from rhyolitic tephra. Boreas , 10.1111/j.1502-3885.2009.00113.x. ISSN 0300-9483.
Electronprobe microanalysis is now widely adopted in tephra studies as a technique for determining the major element geochemistry of individual glass shards. Accurate geochemical characterization is crucial for enabling robust tephra-based correlations; such information may also be used to link the tephra to a specific source and often to a particular eruption. In this article, we present major element analyses for rhyolitic natural glass standards analysed on three different microprobes and the new JEOL FEGSEM 6500F microprobe at Queen's University Belfast. Despite the scatter in some elements, good comparability is demonstrated among data yielded from this new system, the previous Belfast JEOL-733 Superprobe, the JEOL-8200 Superprobe (Copenhagen) and the existing long-established microprobe facility in Edinburgh. Importantly, our results show that major elements analysed using different microprobes and variable operating conditions allow two high-silica glasses to be discriminated accurately. 相似文献
Electronprobe microanalysis is now widely adopted in tephra studies as a technique for determining the major element geochemistry of individual glass shards. Accurate geochemical characterization is crucial for enabling robust tephra-based correlations; such information may also be used to link the tephra to a specific source and often to a particular eruption. In this article, we present major element analyses for rhyolitic natural glass standards analysed on three different microprobes and the new JEOL FEGSEM 6500F microprobe at Queen's University Belfast. Despite the scatter in some elements, good comparability is demonstrated among data yielded from this new system, the previous Belfast JEOL-733 Superprobe, the JEOL-8200 Superprobe (Copenhagen) and the existing long-established microprobe facility in Edinburgh. Importantly, our results show that major elements analysed using different microprobes and variable operating conditions allow two high-silica glasses to be discriminated accurately. 相似文献
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