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DOUCET SONIA; WEIS DOMINIQUE; SCOATES JAMES S.; NICOLAYSEN KIRSTEN; FREY FREDERICK A.; GIRET ANDRE 《Journal of Petrology》2002,43(7):1341-1366
A geochemical study of 28 Ma tholeiitic to transitional basaltsfrom the Kerguelen Archipelago (Mont des Ruches and Mont Fontaine)indicates that three distinct magma types erupted within 相似文献
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MATTIELLI NADINE; WEIS DOMINIQUE; BLICHERT-TOFT JANNE; ALBAREDE FRANCIS 《Journal of Petrology》2002,43(7):1327-1339
We report high-precision multiple collector inductively coupledplasma mass spectrometry (MC-ICP-MS) analyses of Hf isotopiccompositions for 39 Kerguelen Archipelago volcanic rocks thatadd a new perspective to the temporal evolution of the Kerguelenmantle plume. Samples cover the entire range of chemical andSr, Nd and Pb isotopic variations reported for the archipelago,and vary in age from 29 to 0·1 Ma. Their Hf isotopiccompositions show the largest variation for an individual oceanicisland and 相似文献
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DAMASCENO DIMITRI; SCOATES JAMES S.; WEIS DOMINIQUE; FREY FREDERICK A.; GIRET ANDRE 《Journal of Petrology》2002,43(7):1389-1413
Phenocryst compositions and mineral–melt equilibria inthe mildly alkalic basalts from the 25 Ma Mont Crozier sectionon the Kerguelen Archipelago are used to estimate the depthsat which magmas stalled and crystallized and to constrain therole of crustal structure in the evolution of magmas producedby the Kerguelen mantle plume. The Crozier section, of nearly1000 m height, consists of variably porphyritic flows (up to21 vol. % phenocrysts), dominated by plagioclase ± clinopyroxene± olivine ± Fe–Ti oxides. Feldspars showan extreme range of compositions from high-Ca plagioclase (An88)to sanidine and variable textures that are related to extensivefractionation, degassing, and mixing in relatively low-pressure(sub-volcanic) magma chambers. Although clinopyroxene is a minorphenocryst type (0–3 vol. %), its non-quadrilateral components,principally Al (1·9–8·6 wt % Al2O3), varywidely. The results of clinopyroxene–liquid thermobarometryand clinopyroxene structural barometry indicate that the Croziermagmas crystallized at pressures ranging from 相似文献
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This comment addresses the interpretation of oxygen fugacitydata for spinel peridotite xenoliths from five Mexican volcanicfields presented by Luhr & Aranda-Gomez (Journal of Petrology,38, 1075–1112, 1997). The postulated east–west increaseof the FMQ (‘relative oxygen fugacity’, where FMQis fayalite–magnetite–quartz) values is inherentto the method and therefore of questionable geological significance.Increases in FMQ do not necessarily mirror oxidation processesin the mantle controlled by subduction-related fluids. KEY WORDS: mantle metasomatism; Mexico; peridotite xenoliths; relative oxygen fugacity 相似文献
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Several papers presented at the last SEG Convention in Houston by Schneider, Backus et al have shown how important and fruitful it was to obtain a continuous knowledge of the velocity functions and they have solved their problem by a Dynamic Correlation Analysis. Our purpose is to introduce here a method based on the best summation of a set of traces instead of the best correlation. Practically, this approach has several advantages: 1) Two traces only can be correlated at each step whereas the summation can bear on any number of them; 2) Optimizing the summation is actually what we are looking for since, at the long end, the success of the improvement is evaluated from the compositing of several traces either weighted or not. On the other hand, an advantage of correlation is the possibility of adding correlations obtained at several places in a same neighbourhood in order to improve the results. With the summation method this is feasible only when dips are inexistent: we shall see that the difficulty due to the dip effect can be turned around. The basic principle of the method can be summed up as follows: traces relating to a same reflection point are considered; several composites are made, each after applying different move out corrections ranging widely around an estimated adequate velocity function. At each time coordinate, the best adapted velocity function, i.e. the one that yields the best phase relation between reflected events, corresponds to the composite trace the average amplitude of which is the largest. This way, the velocity function corresponding to primary reflections as well as those corresponding to multiple reflections can be established accurately. Some examples are shown. 相似文献
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Involvement of Continental Crust in the Formation of the Cretaceous Kerguelen Plateau: New Perspectives from ODP Leg 120 Sites 总被引：12，自引：11，他引：12
FREY FREDERICK A.; WEIS DOMINIQUE; BORISOVA ANASTASSIA YU.; XU G. 《Journal of Petrology》2002,43(7):1207-1239
The basaltic basement of the large igneous province formed bythe Kerguelen Plateau and Broken Ridge in the southeastern IndianOcean has been sampled by three Ocean Drilling Program cruises(Legs 119, 120 and 183). Although the Cretaceous parts of thisplateau formed in the embryonic Indian Ocean basin, presumablyby melting associated with the Kerguelen plume, trace elementabundances and isotopic ratios of Sr, Nd and Pb of Cretaceousbasalt from several drill sites indicate that continental lithospherewas involved in their petrogenesis. On the basis of relativedepletions in Nb, Ta and Th, and isotopic characteristics similarto those of EMI ocean island basalt, lavas from Leg 120 Site747 in the Central Kerguelen Plateau contain a component derivedfrom lower continental crust. On the basis of relative abundancesof Sr and Eu and EMI-like Pb isotopic ratios, the source ofbasalt from Leg 120 Site 750 in the northeastern part of theSouthern Kerguelen Plateau also contained a component derivedfrom lower continental crust; in this case, the crustal componentformed as a plagioclase-rich, clinopyroxene-bearing cumulate.Basalts from Leg 120 Site 749 define two distinct isotopic (Sr,Nd and Pb) groups which differ from the isotopic fields forSite 747 and 750 basalts. Among Site 749 lavas, there is subtleevidence for a continental component, broadly similar (i.e.moderate 206Pb/204Pb 相似文献
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A Bimodal Alkalic Shield Volcano on Skiff Bank: its Place in the Evolution of the Kerguelen Plateau 总被引：3，自引：4，他引：3
A bimodal volcanic sequence of 230 m thickness on Skiff Bank,a western salient of the northern Kerguelen Plateau, was drilledduring ODP Leg 183. The sequence comprises three main units:a mafic unit of trachybasalt flows sandwiched between two unitsof trachytic or rhyolitic flows and volcaniclastic rocks. Althoughinterpretation is complicated by moderate to strong alterationof the rocks, their original chemical character can be establishedusing the least mobile major and trace elements (Al, Th, highfield strength elements and rare earth elements). High concentrationsof alkalis and incompatible trace elements indicate that bothmafic and felsic rocks are alkalic. The felsic rocks may havebeen derived by partial melting of mafic rocks, followed byfractionation of feldspar, clinopyroxene, Fe–Ti oxidesand apatite. The mafic and felsic rocks have similar Nd andPb isotopic compositions; 206Pb/204Pb ratios are low (17·5–18·0)but, like the 143Nd/144Nd ratios (0·5125–0·5126),they are comparable with those of basalts from the central andsouthern Kerguelen Plateau (e.g. Sites 747, 749, 750). The Srisotopic system is perturbed by later alteration. There is nochemical or isotopic evidence for a continental crustal component.The bimodal alkalic character and the presence of quartz-phyricrhyolites is interpreted to indicate that the sequence formspart of a shield volcano built upon the volcanic plateau. Theage of 68 Ma, obtained on Site 1139 rocks by Duncan (A timeframe for construction of the Kerguelen Plateau and Broken Ridge,Journal of Petrology 43, 1109–1119, 2002), provides onlya minimum age for the underlying flood volcanic rocks. The highage indicates none the less that Skiff Bank is not the presentlocation of the Kerguelen plume. KEY WORDS: Ocean Drilling Program; Kerguelen Plateau; Skiff Bank 相似文献
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PETER NIELSEN PHILIPPE MUCHEZ WOUTER HEIJLEN A. E. TONY FALLICK† EDDY KEPPENS‡ DOMINIQUE WEIS§ RUDY SWENNEN 《Sedimentology》2005,52(5):945-967
In topographic flat areas, sedimentary settings may vary from one outcrop to another. In these settings, calcite precipitates may yield macroscopically similar columnar features, although they are products of different sedimentary or diagenetic processes. Three columnar calcite crystal fabrics, i.e. rosettes, palisade crusts and macro-columnar crystal fans, have been differentiated near and at the contact between Upper Tournaisian dolomites and limestones along the southern margin of the Brabant-Wales Palaeohigh. Their petrographic characteristics, and geochemical and fluid inclusion data provide information on the (dia)genetic processes involved. Rosettes composed of non-luminescent columnar calcite crystal fans (1–5 cm in diameter) developed on top of one another, forming discrete horizons in repetitive sedimentary cycles. The cycles consist of three horizons: (I) a basal horizon with fragments from the underlying horizon, (II) a micrite/microspar horizon with incipient glaebules, (III) an upper horizon consisting of calcite rosettes, with desiccation features. The petrographical features and δ18O signatures of −10·0 to −5·5‰ and δ13C values of −5·5 to −3·2‰ support either evaporative growth, an evaporative pedogenic origin, or overprinting of marine precipitates. Palisade crusts, composed of a few to 10 mm long non-luminescent calcite crystals, coat palaeokarst cavities. Successive palisade growth-stages occur which are separated by thin laminae of micrite or detrital quartz, displaying a geopetal arrangement. Palisade crusts are interpreted as intra-Mississippian speleothems. This interpretation is supported by their petrographic characteristics and isotopic signature (δ18O = −8·7 to −6·5‰ and δ13C = −4·8 to −2·5‰). Macro-columnar crystals, 1–50 cm long, developed mainly perpendicular to cavity walls and dolomite clasts. Crystal growth stages in the macro-columnar crystals are missing. δ18O values vary between −16·4 and −6·8‰ and δ13C values between −5·2 and −0·9‰. These features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification. 相似文献
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Tidal deposits dating from the penultimate interglacial (Oxygen Isotope Stage 7) are preserved on a bank of the River Seine at Tancarville. The foraminiferal assemblages indicate a gradual cooling towards Arctic conditions, which corresponds to the onset of the penultimate cold period. This cooling started before or during the drop in sea level in Europe, in contrast to the situation at the end of the last interglacial (Eemian) when Europe remained warm even during the period of falling sea level. 相似文献