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71.
The Lherz orogenic lherzolite massif (Eastern French Pyrenees) displays one of the best exposures of subcontinental lithospheric
mantle containing veins of amphibole pyroxenites and hornblendites. A reappraisal of the petrogenesis of these rocks has been
attempted from a comprehensive study of their mutual structural relationships, their petrography and their mineral compositions.
Amphibole pyroxenites comprise clinopyroxene, orthopyroxene and spinel as early cumulus phases, with garnet and late-magmatic
K2O-poor pargasite replacing clinopyroxene, and subsolidus exsolution products (olivine, spinel II, garnet II, plagioclase).
The original magmatic mineralogy and rock compositions were partly obscured by late-intrusive hornblendites and over a few
centimetres by vein–wallrock exchange reactions which continued down to subsolidus temperatures for Mg–Fe. Thermobarometric
data and liquidus parageneses indicate that amphibole pyroxenites started to crystallize at P ≥ 13 kbar and recrystallized at P < 12 kbar. The high AlVI/AlIV ratio (>1) of clinopyroxenes, the early precipitation of orthopyroxene and the late-magmatic amphibole are arguments for
parental melts richer in silica but poorer in water than alkali basalts. Their modelled major element compositions are similar
to transitional alkali basalt with about 1–3 wt% H2O. In contrast to amphibole pyroxenites, hornblendites only show kaersutite as liquidus phase, and phlogopite as intercumulus
phase. They are interpreted as crystalline segregates from primary basanitic magmas (mg=0.6; 4–6 wt% H2O). These latter cannot be related to the parental liquids of amphibole pyroxenites by a fractional crystallization process.
Rather, basanitic liquids mostly reused pre-existing pyroxenite vein conduits at a higher structural level (P ≤ 10 kbar). A continuous process of redox melting and/or alkali melt/peridotite interaction in a veined lithospheric mantle
is proposed to account for the origin of the Lherz hydrous veins. The transitional basalt composition is interpreted in terms
of extensive dissolution of olivine and orthopyroxene from wallrock peridotite by alkaline melts produced at the mechanical
boundary layer/thermal boundary layer transition (about 45–50 km deep). Continuous fluid ingress allowed remelting of the
deeper veined mantle to produce the basanitic, strongly volatiles enriched, melts that precipitated hornblendites. A similar
model could be valid for the few orthopyroxene-rich hydrous pyroxenites described in basalt-hosted mantle xenoliths.
Received: 15 September 1999 / Accepted: 31 January 2000 相似文献
72.
L. Eymard S. Planton P. Durand C. Le Visage P. Y. Le Traon L. Prieur A. Weill D. Hauser J. Rolland J. Pelon F. Baudin B. Bénech J. L. Brenguier G. Caniaux P. De Mey E. Dombrowski A. Druilhet H. Dupuis B. Ferret C. Flamant P. Flamant F. Hernandez D. Jourdan K. Katsaros D. Lambert J. M. Lefèvre P. Le Borgne B. Le Squere A. Marsoin H. Roquet J. Tournadre V. Trouillet A. Tychensky B. Zakardjian 《Annales Geophysicae》1996,14(9):986-1015
The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale) experiment has been conducted from June to November 1993 in the Northeast Atlantic between the Azores and Madeira. It was centered on the study of the mesoscale ocean circulation and air-sea interactions. The experimental investigation was achieved at the mesoscale using moorings, floats, and ship hydrological survey, and at a smaller scale by one dedicated ship, two instrumented aircraft, and surface drifting buoys, for one and a half month in October-November (IOP: intense observing period). Observations from meteorological operational satellites as well as spaceborne microwave sensors were used in complement. The main studies undertaken concern the mesoscale ocean, the upper ocean, the atmospheric boundary layer, and the sea surface, and first results are presented for the various topics. From data analysis and model simulations, the main characteristics of the ocean circulation were deduced, showing the close relationship between the Azores front meander and the occurrence of Mediterranean water lenses (meddies), and the shift between the Azores current frontal signature at the surface and within the thermocline. Using drifting buoys and ship data in the upper ocean, the gap between the scales of the atmospheric forcing and the oceanic variability was made evident. A 2 °C decrease and a 40-m deepening of the mixed layer were measured within the IOP, associated with a heating loss of about 100 W m−2. This evolution was shown to be strongly connected to the occurrence of storms at the beginning and the end of October. Above the surface, turbulent measurements from ship and aircraft were analyzed across the surface thermal front, showing a 30% difference in heat fluxes between both sides during a 4-day period, and the respective contributions of the wind and the surface temperature were evaluated. The classical momentum flux bulk parameterization was found to fail in low wind and unstable conditions. Finally, the sea surface was investigated using airborne and satellite radars and wave buoys. A wave model, operationally used, was found to get better results compared with radar and wave-buoy measurements, when initialized using an improved wind field, obtained by assimilating satellite and buoy wind data in a meteorological model. A detailed analysis of a 2-day period showed that the swell component, propagating from a far source area, is underestimated in the wave model. A data base has been created, containing all experimental measurements. It will allow us to pursue the interpretation of observations and to test model simulations in the ocean, at the surface and in the atmospheric boundary layer, and to investigate the ocean-atmosphere coupling at the local and mesoscales. 相似文献
73.
The intermediate lavas (andesites, trachyandesites, doreites, sancyites) of the Cenozoïc volcanic districts of the Massif Central (France) are compared with lavas of the alkaline and calc-alkaline suites. On ground of mineralogical and chemical data, two groups may be recognized. The rocks of the first group bear a close resemblance with the intermediate rocks that result of the differentiation of an alkaline basaltic magma. The rocks of the second group, less numerous, possess one or several characters identical to those of calc-alkaline andesites.The contamination suffered by some lavas of both groups has not been sufficient to blot out their comagmatic characteristics. 相似文献
74.
Résumé Dans le Haut-Atlas marocain, entre l'oued Sous au Sud, Asif AÏt Moussa à l'Ouest, le bled Seksaoua au Nord et Tizi n'Test à l'Est, plus exactement dans la partie sud-ouest du Massif du Tichka et au Nord-Ouest de ce massif affleurent en de nombreux endroits des roches charbonneuses: grès, arkoses, pélites, schistes, cipolins et coméennes dont la principale est la tisrouimite (7). Cette dernière s'est déposée un peu avant les calcaires àArchaeocyatha du Cambrien inférieur, puis en mÊme temps que leurs couches de base. Les autres roches charbonneuses sont sensiblement contemporaines de la tisrouimite. On peut en conclure qu'il a existé un bassin sédimentaire riche en matière organique à une époque correspondant, en première approximation, a l'Assadasien.
The area of study in the moroccan High-Atlas area is included between wady Sous to the South, Asif AÏt Moussa to the West, bled Seksaoua to the North and Tizi n'Test to the East; more exactly it is located in the south-western and nordwestern Tichka. In this area we have noticed numerous outcrops of carbonaceous rocks, such as sandstones, arkoses, mudstones, shales, cipolins and hornfels, the principal variety of which is tisrouimite (7). Tisroumite first was deposited shortly before the Lower Cambrian Archaeocyathid limestones, and again later contemporaneously with the basal layers of these limestones. The other carbonaceous rocks are more or less contemporaneous with the tisrouimite. Therefore we conclude approximately at the time of the Assedasian (early Cambrian II) a sedimentary basin existed the sediments of which were rich in organic matter
Zusammenfassung Im marokkanischen Hoch-Atlas, zwischen Wadi Sous im Süden, Asif AÏt Moussa im Westen, der Gegend um Seksoua im Norden und Tizi n'Test im Osten, sind im SW-Teil und NE-Teil des Tichka-Gebirgsstockes dunkle, kohlenstoffreiche Gesteine aufgeschlossen: Sandstein, Arkose, Pelit, Schiefer, grüner Marmor und Homfels, dessen Hauptvariante tisrouimite genannt wird. Die Hornfelse sind etwas älter als die Archaeocyathiden-Kalke des Unterkambriums und bilden ihre Basis Die übrigen Gesteine sind etwa gleich alt wie die Hornfelse. Wir schließen daraus, daß hier zur Zeit des Assadassien (tieferes Kambrium II) ein Sedimentationsbecken lag, dessen Sedimente reich an organischen Substanzen waren.
Bushveld Rooiberg , - , : ) - , ; ) , ; ) , . — , . — , ghoststratigraphy , . — . — , , , Rooiberg, , .相似文献
75.
Résumé L'existence de relations entre les teneurs en carbonates et en sulfures dans les eaux des bassins réducteurs, ainsi que l'irreversibilité de la réaction sulfate-sulfure, conduisent à proposer le remplacement des diagrammes Eh. pH, par les diagrammes log S, pH (S désignant la concentration totale de S (-II)). Nous donnons ici le principe de construction, des exemples de diagrammes et quelques applications.
The existence of relations between the amounts of carbonates and the sulfides in the water of anoxic basins and the irreversibility of the reaction sulphate-sulfide lead us to propose the substitution of diagrams Eh, pH by diagrams log S, pH (S being the total concentration of S (-II)). The principle of how diagrams should be drawn is outlined and some examples and applications are given.相似文献
76.
C. Lefèvre 《Contributions to Mineralogy and Petrology》1973,41(3):259-272
Chemical data on late cenozoic lavas (83 new analyses) from southern of Peru indicate a zonal arrangement of lavas types according to their distance from the trench. The nearest belong to a calc-alkaline suite and the farthest are shoshonites rocks. The calc-alkaline rocks show progressive increase in K2O content and in K2O/Na2O ratio in northeastern direction. The shoshonitic rocks are more potassic and titaniferous, and the K2O/Na2O ratio is approximatively constant. The potash content of the two series correlate with the depth of the inclined seismic zone beneath the volcanoes, but this correlation is less well established than in island arcs. 相似文献
77.
生物质燃烧颗粒物有机示踪化合物的测定和应用 总被引:2,自引:0,他引:2
使用气相色谱-质谱法对2002年7月-2003年7月的北京市大气粗、细颗粒物样品中的左旋葡聚糖等糖类化合物进行了测定。结果表明,左旋葡聚糖主要存在于细颗粒中,可以作为示踪化合物来研究生物质燃烧现象。生物质燃烧对北京市大气颗粒物有较重要的贡献。对应于12%-40%的PM2.5有机碳和10%-33%的PM10有机碳。北京市在2002年10月和11月受到明显的生物质燃烧的影响,可能由于农田秸杆焚烧和秋季落叶焚烧。2003年5月7日颗粒物样品受到直线距离约为1000km以外的内蒙古自治区呼伦贝尔市大兴安岭林区森林大火烟雾的影响。生物质燃烧事件具有突发性,可以长距离传输;生物质作为农村生物燃料的使用其燃烧排放具有经常性和持久性的特征。 相似文献
78.
Adam Carter Benjamin van Wyk de Vries Karim Kelfoun Patrick Bachèlery Pierre Briole 《Bulletin of Volcanology》2007,69(7):741-756
A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor
activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island,
Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping
eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large
collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures
are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal
fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related
fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°,
normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof
to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to
act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that
define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern
reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump
head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m.
Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important
on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled
by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system
may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently
increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally
control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve
monitoring. 相似文献
79.
Yves Grosdidier Anthony F.J. Moffat Agnès Acker 《Astrophysics and Space Science》1998,260(1-2):181-184
We present HST-WFPC2/Hα deep images of the ejected nebula M1-67. Our data suggest that M1-67 is the imprint of a previous,
slow LBV wind ejected from the central star WR124, now a WN8 star. We find evidence that the LBV wind is highly variableand anisotropic. Some dense, persisting clumps have possibly been ejected directly from the stellar surface.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
80.
Jacques Fabriès 《Contributions to Mineralogy and Petrology》1979,69(4):329-336
An empirical calibration of the spinel-olivine geothermometer (Evans and Frost, 1975) is attempted and applied to parageneses of lherzolitic rocks. In ultramafic complexes, most of the derived temperature estimates range between 700 ° and 850 °C, and appear generally lower than those given by other geothermometers, based upon Ca or Al contents of coexisting pyroxenes. A comparison of the different thermometric data in two well studied occurrences, the Ronda ultramafic complex and the San Carlos xenolith field, suggests that differential rates of diffusion and recrystalization may account for the large range of temperatures (between 700 ° and 1200 °C) determined by various mineral geothermometers in peridotites. The equilibrium exchange of Mg and Fe between spinel and olivine would be the fastest one and would continue effectively during the cooling down to relatively low temperatures, while other exchange reactions used as geothermometers in peridotites, like partitioning of Ca and Al in coexisting pyroxenes, are blocked at higher temperatures. 相似文献