East Pacific Rise at latitude 21°N: isotopic composition and origin of the hydrothermal sulphur     

Michel Arnold  Simon M.F. Sheppard 《Earth and Planetary Science Letters》1981

The sulphur isotope composition of 16 pyrite and chalcopyrite samples from recent sulphide deposits (“Cyana”—project RITA) and active sulphide mineralisation (“Alvin”—project RISE) associated with hydrothermal sources at 380±30°C on the East Pacific Rise at latitude 21°N have been measured. The³⁴S/³²S ratios are relatively uniform and essentially identical for both sites: δ³⁴S=+1.4to3.0%. (CDT), mean +2.1‰. The sulphides were analysed after the majority of the very numerous micro-inclusions of anhydrite had been removed.Two independent physico-chemical analyses of the data demonstrate that about 90% of the sulphur was leached from the basaltic host rocks by the circulating seawater-hydrothermal fluids.  相似文献   

Distribution coefficients of major and trace elements; fractional crystallization in the alkali basalt series of Chaîne des Puys (Massif Central,France)   总被引：1，自引：0，他引：1  

Benoît Villemant  Henri Jaffrezic  Jean-Louis Joron  Michel Treuil 《Geochimica et cosmochimica acta》1981,45(11):1997-2016

Major and seventeen trace element distribution coefficients between main phenocrysts (olivine, clinopyroxene, amphibole, mica, feldspars and Fe-Ti oxides) and groundmass have been measured in the alkali basalt suite of Chaîne des Puys (Massif Central, France). The suite appears to be a well behaved crystal fractionation series. We pinpoint key elements whose behavior is closely related to the appearance or disappearance of specific crystal phases in the fractionation process. Ta, for instance, clearly indicates the role of hydrous silicates (amphiboles and micas). Distribution coefficients are shown to vary systematically along the differentiation trend. Significantly the hygromagmaphile tendency (Treuilet al., 1979) of U, Th, Ta and La is variable along the series.The mass balance equations, where Dⁱ and D_jⁱ are the bulk and mineral/liquid distribution coefficients respectively, and x_j the weight fractions of the fractionating phases, are solved by least square resolution of the overdetermined system, taking into account the analytical errors on data. The solution applied to the Chaîne des Puys suite leads to a coherent and quantitative model of the fractional crystallization process. The suite has apparently evolved in three stages. Each stage is characterized by constant bulk distribution coefficients and a specific mineral assemblage. Amphibole fractionation plays an important role in the early stages. Some intensive parameters (T, ? ?_O2, P_H2O) as well as f (weight fraction of residual liquid) are also estimated.  相似文献   

International Comparison of Absolute Gravity Instruments and Workshop “Absolute Gravity Measurements”     

Michel Louis 《Journal of Geodesy》1984,58(1):V-V

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Late Hercynian remagnetization of Tournaisian series from the Laval syncline,Armorican Massif,France     

Jean-Bernard Edel  Michel Coulon 《Earth and Planetary Science Letters》1984,68(2):343-350

Paleomagnetic investigations have been conducted on Tournaisian volcanics and sediments from the Laval syncline, in order to evaluate the consequences of the Late Variscan tectonic and thermic phases. On the southern flank of the syncline, anisotropy measurements have yielded maximum susceptibility in the schistosity planes. Thermal demagnetization exhibits only remagnetizations, characterized by a large range of blocking temperatures (from 350° to 670°C). Two phases of remagnetization seem to follow each other. The first may have occurred during the Tournaisian major orogenic phase. The second has taken place during the latest Stephanian/earliest Permian, in relation with the latest Variscan thermal event. All results are in favour of a clockwise rotation by 15–40° of the Laval syncline after the latest overprints. According to results from other regions of Brittany, this clockwise rotation involved the whole Armorican Massif. This motion may be related to the latest compression phase which has tightened the Ibero-Armorican arc, well before the Permo-Triassic opening of the Bay of Biscay.  相似文献   

Fault patterns by space remote sensing and the rotation of western Oregon during Cenozoic times     

Michel Chaplet  Jean Chorowicz  Franois Roure 《Earth and Planetary Science Letters》1987,81(4)

We used MSS-Landsat images (bands 6 and 7) as well as previous studies to interpret fault patterns in western Oregon in terms of the rotations detected by paleomagnetism. These fault zones show a great concentration between the Cascade Range and the Idaho Batholite and have several distinct trends. The north-south striking structures are attributed to the Basin and Range province, while the large NW-SE right-lateral fault zones are interpreted as resulting from an extension between the Cascades Arc and the Olympic-Wallowa lineament. The latter was a paleoplate boundary during pre-Eocene times. This extension, beginning during Late Eocene/Oligocene times and continuing through Recent times, is accompanied by a migration of the rotation pole from southeast to northwest, and by a clockwise rotation of the Coast Range—Klamath Mountains—Cascade Range block, induced by the subduction of the Farallon plate.  相似文献   

Magma and hydrothermally driven sector collapses: The 3100 and 11,500 y. B.P. eruptions of la Grande Decouverte (la Soufrière) volcano, Guadeloupe, French West Indies     

Georges Boudon  Michel P. Semet  Pierre M. Vincent   《Journal of Volcanology and Geothermal Research》1987,33(4)

We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits.  相似文献   

Late Permian/early Triassic orogeny in Japan: piling up of nappes, transverse lineation and continental subduction of the Honshu block   总被引：1，自引：0，他引：1  

Michel Faure  Jacques Charvet 《Earth and Planetary Science Letters》1987,84(2-3)

Field surveys in the Oga-Atetsu and Yamaguchi areas of Southwest Japan have been conducted in order to precise the structure of the Permian orogen. A stack of nappes is recognized comprising from top to bottom: (1) the Oga nappe which is considered to be a seamount complex, (2) HP Sangun metamorphics, (3) the Permian Yakuno ophiolite, and (4) the Permian detrital Maizuru group which is interpreted as the sedimentary cover of a continental block, called here the Honshu block, outcropping as the Older Granite. This stack of nappes is overthrust by the Paleozoic Hida basement consisting of HT gneisses, granites and late Carboniferous shallow-water sediments. Microtectonic analysis of the Sangun schists shows that the subhorizontal schistosity bearing a submeridian lineation was formed during the synmetamorphic phase. Asymmetric pressure shadows, shear bands and sigmoidal minerals show that the synmetamorphic deformation corresponds to a ductile shear from north to south. The Permian/early Triassic orogeny is interpreted as the result of a collision between the Hida gneiss (or South China block) and the Honshu block, the intervening oceanic area gave rise to southward directed nappes. The Permian orogenic belt extends at least from Taiwan to central Japan.  相似文献   

Past Antarctic Peninsula climate (1850–1980) deduced from an ice core isotope record     

Alberto J. Aristarain  Jean Jouzel  Michel Pourchet 《Climatic change》1986,8(1):69-89

A detailed climatic study of the Antarctic Peninsula from 1850 to 1980 has been carried out through the analysis of deuterium content in the snow layers of Dalinger Dome (James Ross Island, Antarctic Peninsula). It is based on the high correlation found between mean deuterium contents at this site and temperature data from stations within this region going back as far as April 1903 for the Argentine Orcadas station.The strong correlation between isotopes and temperatures first reveals a 1956 isotope reference for the region considered. Secondly, the isotope-temperature gradient is estimated at 4.5%. °C^–1 for deuterium.After checking that the major temperature anomalies on the Antarctic Peninsula recorded since 1904 (according to available data) correspond to annual mean stable isotope peaks at Dalinger Dome, the amplitude of four prior anomalies are estimated in °C. Finally, a cooling of about 2 °C since 1850 is suggested for the region.  相似文献   

Book reviews     

Bert Bolin  G. Shaw  Michel M. Verstraete  M. J. Salinger 《Climatic change》1986,9(3):363-366

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A chlorite solid solution geothermometer the Los Azufres (Mexico) geothermal system   总被引：24，自引：1，他引：24  

Michel Cathelineau  David Nieva 《Contributions to Mineralogy and Petrology》1985,91(3):235-244

Chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites, in the active geothermal system of Los Azufres (Mexico). Electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition. Correlation coefficients among chemical constituents were calculated. It is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content, and there is almost no correlation with the octahedral aluminium and magnesium content. A procedure is proposed to select end-members and substitution vectors, and to give a general formula for these chlorites.Their formation temperatures are estimated with great accuracy, combining results of microthermometric data on fluid inclusions from gangue minerals of chlorites (quartz, calcite), direct measurements in wells (Kuster equipment), and chemical geothermometers. Correlations between chlorite compositions, range and nature of site occupancy, and temperature are good. Formation temperatures of chlorites range from 130° C to 300° C. As no other thermodynamic parameter varies significantly in the studied field (composition of the host rocks, nature of the geothermal fluids, pressure, ...), these variations of site occupancy (mainly Al(IV) and the octahedral occupancy (6-Al(VI)-(Mg+Fe(2+)) = VAC) are considered mainly as temperature dependent.Molar fractions of each end-member show very different variations with increasing temperature: X-kaolinite decreases, and X-chamosite increases, while X-talc-3 brucite does not show significant change. From these data, activity coefficients and standard state chemical potential of major components, and molar free energy formation of chlorite have been calculated for each temperature of crystallisation.  相似文献