The formation of SiO<Subscript>2</Subscript>-rich melts within the deep oceanic crust by hydrous partial melting of gabbros   总被引：5，自引：0，他引：5  

Juergen Koepke  Jasper Berndt  Sandrin T. Feig  Francois Holtz 《Contributions to Mineralogy and Petrology》2007,153(1):67-84

Small amounts of felsic, evolved plutonic rocks, often called oceanic plagiogranites, always occur as veins or small stocks within the gabbroic section of the oceanic crust. Four major models are under debate to explain the formation of these rocks: (1) late-stage differentiation of a parental MORB melt, (2) partial melting of gabbroic rocks, (3) immiscibility in an evolved tholeiitic liquid, and (4) assimilation and partial melting of previously altered dikes. Recent experimental data in hydrous MORB-type systems are used to evaluate the petrogenesis of oceanic plagiogranites within the deep oceanic crust. Experiments show that TiO₂ is a key parameter for the discrimination between different processes: TiO₂ is relatively low in melts generated by anatexis of gabbros which is a consequence of the low TiO₂ contents of the protolith, due to the depleted nature of typical cumulate gabbros formed in the oceanic crust. On the other hand, TiO₂ is relatively high in those melts generated by MORB differentiation or liquid immiscibility. Since the TiO₂ content of many oceanic plagiogranites is far below that expected in case of a generation by simple MORB differentiation or immiscibility, these rocks may be regarded as products of anatexis. This may indicate that partial melting processes triggered by water-rich fluids are more common in the deep oceanic crust than believed up to now. At slow-spreading ridges, seawater may be transported via high-temperature shear zones deeply into the crust and thus made available for melting processes.  相似文献   

利用陆面岩石中生成的宇生同位素重建冰川漂砾运动历史的尝试   总被引：3，自引：0，他引：3       下载免费PDF全文

王建  FrancoisYiou  GrandRaisbeck  徐孝彬 《地质学报》2003,77(3):407-413

冰川漂砾的形成年代通常难以直接测定，并且漂砾形成以后是否被再次搬运或者移动过，更是无法知道。本文研究发现，通过测试砾石不同部位的宇生同位素，不仅可以测定砾石形成的时代，而且可以确定砾石再次被搬运或者被翻转的年代，从而恢复砾石运动的历史。本文以石英中生成的宇生同位素^10Be，对青藏高原东南部海子山的冰川漂砾进行了探讨，结果表明该砾石形成于倒数第二次冰期(186～128ka BP之间)，在末次冰期中再次被冰川搬运，使之反转。该方法不局限于^10Be和冰川漂砾，也适用于其他陆面岩石中生成的宇生同位素以及其他成因的石块或者砾石。因此为探讨冰川作用、泥石流活动、重力崩塌等过程提供了一种重要的方法和技术途径。  相似文献   

Using project food aid to help alleviate urban poverty - experience and issues     

John Shaw  Bruce Crawshaw  Francois Fortier 《GeoJournal》1994,34(3):305-313

As urban poverty in the Third World worsens, an increasing proportion of World Food Programme (WFP) food aid is being used to support poor urban dwellers. WFP food aid has typically been used in three main ways in urban areas: as free relief after disasters (such as floods or earthquakes) have struck urban centres; as part of institutional feeding projects; and as support to urban renewal. While there have been some creative approaches to using food aid to help overcome urban poverty, the benefits have usually only been temporary. It has proved difficult to design food aid interventions for the urban poor that help to overcome the causes of poverty in sustainable ways. The challenge is to use food aid to help make permanent as well as temporary improvements in the lives and livelihoods of the poor.  相似文献   

Hydrology of a spring complex, studied by geochemical time-series data, Acquarossa, Switzerland     

Emanuel Mazor  Francois D. Vuataz 《Applied Geochemistry》1990,5(5-6)

A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types: (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO₄, 700 mg/l HCO₃, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO₂, and with an isotopic composition of δD = − 73.0‰ and δ¹⁸ O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ¹⁸ O = −10.5‰ and tritium as in recent (post-bomb) precipitation.  相似文献   

Crystallization of quartz dioritic magmas at 2 and 1 kbar: experimental results     

Anna Pietranik  Francois Holtz  Jürgen Koepke  Jacek Puziewicz 《Mineralogy and Petrology》2009,97(1-2):1-21

Crystallization experiments were performed on quartz diorite (~55 wt.% SiO₂, 3.1–8.4 wt.% MgO) from the G?siniec Intrusion (Bohemian Massif, SW Poland) at 1?2 kbar, 750–850°C, various mole fractions of water and with fO₂ buffered by the NNO buffer. The two natural quartz diorites (leucocratic poikilitic quartz diorite - ‘LPD’ and melanocratic quartz diorite - ‘MD’) differ in whole rock and mineral composition with MD being richer in MgO and poorer in CaO than LPD, probably due to accumulation of mafic minerals or melt removal in MD. LPD represents melt composition and is used to reconstruct crystallization conditions in the G?siniec Intrusion. The crystallization history of LPD magma, deduced from experimental and natural mineral compositions, includes a higher pressure stage probably followed by emplacement at ~2 kbar of partly crystallized magma at temperatures ~850?800°C and quick cooling. The mineral assemblage present in LPD requires water contents in the magma of at least 5 wt% and oxygen fugacity below that controlled by the NNO buffer. The compositions of mafic minerals in the MD composition were equilibrated at temperatures below 775°C and at subsolidus conditions. The equilibration was probably due to the reaction between water-rich, oxidizing residual melt and the cumulatic-restitic mineral assemblage. MD is characterized by occurrence of the euhedral cummingtonite and increasing anorthite content in the rims of plagioclase. A similar reaction was reproduced experimentally in both LPD and MD compositions indicating that cummingtonite may be a late magmatic phase in quartz dioritic systems, crystallizing very close to solidus and only from water saturated magma.  相似文献   

Subarctic Pacific evidence for a glacial deepening of the oceanic respired carbon pool     

S.L. Jaccard  E.D. Galbraith  D.M. Sigman  G.H. Haug  R. Francois  T.F. Pedersen  P. Dulski  H.R. Thierstein 《Earth and Planetary Science Letters》2009,277(1-2):156-165

Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial–interglacial change in deep North Pacific phosphate (PO₄) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation – and thus respired carbon storage – over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO₂) by sequestering CO₂ away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO₂.  相似文献   

Analysis of the northern South China Sea counter-wind current in winter using a data assimilation model   总被引：1，自引：1，他引：0  

Jiping Xie  Jiang Zhu  Laurent Bertino  Francois Counillon 《Ocean Dynamics》2015,65(4):523-538

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Marcel Bertrand et „l'orogenèse programmée“     

Professeur Francois Ellenberger 《International Journal of Earth Sciences》1982,71(2):463-474

Résumé Marcel Bertrand (1847–1907) est surtout connu pour avoir été le promoteur de la tectonique des grandes nappes alpines. Le présent article entend attirer l'attention sur un aspect moins souvent abordé de son oeuvre. En passant en revue et comparant, de façon à la fois méthodique et empirique, les données alors disponibles, il découvre une homologie frappante entre les suites d'évènements qui ont abouti à la formation des grandes chaînes de montagnes successives de l'Europe. Chacune a ses gneiss, son «Flysch fin» précoce, son «Flysch grossier» tardif externe et enfin ses grès rouges (molasses); de même, pour l'histoire magmatique et même métallogénique (roches vertes précoces, puis granite, «porphyres» et enfin laves basiques post-tectoniques). Il est donc clair que Marcel Bertrand a été le véritable initiateur (se gardant de tout dogmatisme), du modèle «programmé» de l'orogenèse, en général attribué à Hans Stille et ses é mules. D'un point de vue historique, on peut voir dans sa conception de l'orogenèse une synthèse réconciliant plusieurs théories jusque là antagonistes: l'étagement des grandes formations universelles de Werner devient le produit régionalement hétérochrone des cycles de transformation de Hutton; et les soulèvements successifs catastrophiques d'Elie de Beaumont sont retraduits en termes lyelliens, processus lents et graduels, néanmoins récurrents et ordonnés.

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Marcel Bertrand (1847–1907) is best known for his trail-blazing recognition of the great nappes. The present paper draws attention to a lesser known side of his work: through a methodical, empirical review of the available data, Marcel Bertrand brought to light a striking similarity in the sequence of events which led to the formation of each of the successive mountain chains of Europe. Each has its own gneisses, early fine Flysch, later coarse external Flysch, and late red sandstone; and also the same magmatic (and even metallogenic) suite (early greenstones, then granite, porphyries, and finally post-tectonic basic lavas). Thus it appears that Marcel Bertrand was the real originator (avoiding any dogmatization) of the programmed model of orogeny commonly ascribed to Hans Stille and his followers. From a historical point of view, one may see in this conception of mountain building a conciliatory synthesis between some major antagonistic theories: the Wernerian universal formations become heterochronous products of the Huttonian cycle; and the catastrophic successive orogenies of Elie de Beaumont actually amount to slow, gradual, Lyellian processes, nonetheless orderly and recurrent.

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Zusammenfassung Marcel Bertrand ist besonders als der Entdecker der großen Alpinen Überschiebungen bekannt. Hier wird eine weniger bekannte Seite seines Werkes erwähnt: er hat klargemacht, daß die verschiedenen europäischen Gebirgsketten eine parallele und strukturierte Geschichte haben (sedimentär, magamatisch, metallogenisch). Eine objektive Zusammenstellung der tatsächlichen Kenntnisse zeigt, daß jedes Orogen seine Gneise, seinen feinen Flysch in dem zentralen Trog, seinen groben Flysch am Rand und sein Rotliegendes als Späterscheinung hat. In jedem Fall erkennt man die Anwesenheit von basischen Gesteinen als Früherscheinungen, von Graniten, dann von Porphyren und am Ende von posttektonischen, basischen Gesteinen. Hier kann man das von H. Stille und seinen Nachfolgern entwickelte Schema erkennen, das aber hier bei M. Bertrand rein empirisch bleibt. Vom historischen Standpunkt her ist es möglich, das Werk von M. Bertrand als die Synthese, die Zusammenfassung verschiedener, bis dahin antagonistisch gestellter Strömungen zu betrachten: der Wernersche, stufenartige, theoretische Bau wird zur heterochronen Folge des Huttonschen Zyklus; die nacheinander sich entwikkelnden katastrophalen Orogenesen von Elie de Beaumont werden, wie bei Lyell, langsam aber dennoch strukturiert und wiederkehrend.

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Technetium-99 content in some marine organisms collected near La Hague,France     

Lucien Jeanmaire  Michel Masson  Francois Patti  Pierre Germain  Liliane Cappellini 《Marine pollution bulletin》1981,12(1):29-32

Analyses for ⁹⁹Tc in some marine biological samples taken near the outlet of the low level radioactive effluent pipeline of the nuclear reprocessing plant of La Hague, France, gave positive results. From 500 to 3500 pCi kg^?1 wet weight of ⁹⁹Tc were observed in brown algae; Fucus sp. appeared to be a good indicator of this long-lived radionuclide in a marine environment.  相似文献   

The bi-decadal rainfall cycle,Southern Annular Mode and tropical cyclones over the Limpopo River Basin,southern Africa     

Johan Malherbe  Willem A. Landman  Francois A. Engelbrecht 《Climate Dynamics》2014,42(11-12):3121-3138

The association between bi-decadal rainfall variability over southern Africa and the rainfall contributed by tropical cyclonic systems from the Southwest Indian Ocean (SWIO) provides a potential means towards understanding decadal-scale variability over parts of the region. A multi-decadal period is considered, focusing on the anomalous tropospheric patterns that induced a particularly wet 8-year long sub-period over the Limpopo River Basin. The wet sub-period was also characterized by a larger contribution to rainfall by tropical cyclones and depressions. The findings suggest that a broadening of the Hadley circulation underpinned by an anomalous anticyclonic pattern to the east of southern Africa altered tropospheric steering flow, relative vorticity and moisture contents spatially during the sub-period of 8 years. These circulation modulations induced enhanced potential for tropical systems from the SWIO to cause precipitation over the Limpopo River Basin. The same patterns are also conducive to increasing rainfall over the larger subcontinent, therefore explaining the positive association in the bi-decadal rainfall cycle and rainfall contributed by tropical cyclonic systems from the SWIO. An overview of regional circulation anomlies during alternating near-decadal wet and dry epochs is given. The regional circulation anomalies are also explained in hemispheric context, specifically in relation to the Southern Annular Mode, towards understanding variation over other parts of the Southern Hemisphere at this time scale.  相似文献