²¹⁰Po, an atmospheric tracer of long-range transport of volcanic plumes     

EUN-YUN NHO  MARIE-FRANÇOISE LE CLOAREC  BÉNÉDICTE ARDOUIN  MICHEL RAMONET 《Tellus. Series B, Chemical and physical meteorology》1997,49(4):429-438

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Modelled and observed sea surface fCO2 in the southern ocean: a comparative study     

FERIAL LOUANCHI  MARIO HOPPEMA  DOROTHÉE C. E. BAKKER  ALAIN POISSON  MICHEL H. C. STOLL  HEIN J. W. DE BAAR  BERNARD SCHAUER  DIANA P. RUIZ-PINO  DIETER WOLF-GLADROW 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):541-559

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Extensive carbonate algal bioherms in upper Pleistocene saline lakes of the central Altiplano of Bolivia   总被引：1，自引：0，他引：1  

JEAN MARIE ROUCHY  MICHEL SERVANT†  MARC FOURNIER†  CHRISTIANE CAUSSE 《Sedimentology》1996,43(6):973-993

During the upper Pleistocene the Central Altiplano of Bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations. Development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands, discontinuously covering the 300-km-long and 100-km-wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of Uyuni. Distribution, size and shape of the bioherms are diverse due to various factors, e.g. the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth. On larger palaeoterraces, the build-ups coalesced to form platform-like carbonate accumulations. Although the morphologies closely resemble those induced by cyanobacteria, they were predominantly constructed by other plant communities, probably dominated by filamentous green algae. Cyanobacterial communities flourished in association with these plants, but they did not contribute significantly to the architecture of the bioherms; they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build-ups. A prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects. The build-ups located between 3660 and 3680 m elevation display up to three major parts: (1) a massive inner core formed during an early Minchin highstand, before 40 ka; (2) a large peripheral envelope deposited at about 40 ka (late Minchin) and (3) a thinner outermost crust formed during a late glacial event. Lake level dropped during interlacustrine stages, sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system, i.e. the present-day salar of Uyuni.  相似文献   

Glacial dispersal of boulders in the James Bay Lowlands of Quebéc, Canada     

MICHEL A. BOUCHARD  VELI-PEKKA SALONEN 《Boreas: An International Journal of Quaternary Research》1989,18(3):189-199

Paleozoic fossiliferous limestones from the Hudson Bay area were dispersed southeastward a total distance of 110 km in the Québec part of theJames Bay Lowlands during the surging Cochrane flow event of the Laurentide Ice Sheet. The dispersal by the surging ice appears comparable to non-surging ice dispersal events elsewhere in terms of the dispersal index and the half distance of transportation; however, the total distance of transportation of the limestone clasts and their relatively high abundance far away from their source suggest that part of the transport of the debris during the surge was englacial, with the load later deposited as a surface mantle, or that the flow of the surging ice was limited to rapid basal sliding, with little or no internal shear within the ice mass. The glacial transport characteristics of earlier non-surging flow events in the same area were determined using the Total Transport Distance (TTD) method of measurements. Based on an indirect measurement of the half distance of transportation, the Selbaie till is characterized by longer transport distance than the Matheson till, and the Nouveau-Québec till has the shortest transport distance of all the tills of the area.  相似文献   

Palaeo-ice streams and the subglacial landscape mosaic of the North American mid-continental prairies     

MARTIN ROSS  JANET E. CAMPBELL  MICHEL PARENT  ROBERTA S. ADAMS 《Boreas: An International Journal of Quaternary Research》2009,38(3):421-439

The analysis of the glacial landscape of southern Saskatchewan (Canada) through multiple data sets (e.g. digital elevation model, till compositional data) has revealed previously unrecognized subglacial sediment–landform assemblages. A southwest-trending corridor of mega-scale till lineations (Maskwa corridor) bounded on each side by hummocky terrain extends from the Canadian Shield to southwestern Saskatchewan. This landform assemblage is clearly cross-cut by a broad south to southeast trending corridor (Buffalo corridor) consisting of subparallel curvilinear till ridges. The carbonate content of the surface till is spatially consistent within these assemblages, suggesting a strong sediment–landform relationship. The two corridors are interpreted as the product of palaeo-ice streams. The Maskwa palaeo-ice stream flowed up the regional slope and across preglacial valleys, indicating it was thick and stable. Narrow dispersal trains extending across as well as down-glacier from the Athabasca Basin suggest that the Maskwa palaeo-ice stream extended far into the ice sheet across contrasting shield and platform terrains. In comparison, the Buffalo palaeo-ice stream was thinner and largely controlled by subglacial geology and topography. Its catchments were located at the Canadian Shield boundary and the system was oriented along-slope. It experienced lateral shifts and it was fed by a network of tributaries. The glacial dynamics shift from the Maskwa to the Buffalo system occurred at about 13.5 ¹⁴C kyr BP. The Buffalo system later evolved into thin outlet lobes until final deglaciation of the area. The proposed model has implications for ice-sheet reconstruction and the assessment of till properties in the prairies and in similar terrains.  相似文献   

Experimental Crystallization of a High-K Arc Basalt: the Golden Pumice, Stromboli Volcano (Italy)   总被引：6，自引：0，他引：6  

DI CARLO  IDA; PICHAVANT  MICHEL; ROTOLO  SILVIO G.; SCAILLET  BRUNO 《Journal of Petrology》2006,47(7):1317-1343

The near-liquidus crystallization of a high-K basalt (PST-9golden pumice, 49·4 wt % SiO₂, 1·85 wt % K₂O,7·96 wt % MgO) from the present-day activity of Stromboli(Aeolian Islands, Italy) has been experimentally investigatedbetween 1050 and 1175°C, at pressures from 50 to 400 MPa,for melt H₂O concentrations between 1·2 and 5·5wt % and NNO ranging from –0·07 to +2·32.A drop-quench device was systematically used. AuPd alloys wereused as containers in most cases, resulting in an average Feloss of 13% for the 34 charges studied. Major crystallizingphases include clinopyroxene, olivine and plagioclase. Fe–Tioxide was encountered in a few charges. Clinopyroxene is theliquidus phase at 400 MPa down to at least 200 MPa, followedby olivine and plagioclase. The compositions of all major phasesand glass vary systematically with the proportion of crystals.Ca in clinopyroxene sensitively depends on the H₂O concentrationof the coexisting melt, and clinopyroxene Mg-number shows aweak negative correlation with NNO. The experimental data allowthe liquidus surface of PST-9 to be defined. When used in combinationwith melt inclusion data, a consistent set of pre-eruptive pressures(100–270 MPa), temperatures (1140–1160°C) andmelt H₂O concentrations is obtained. Near-liquidus phase equilibriaand clinopyroxene Ca contents require melt H₂O concentrations<2·7–3·6 and 3 ± 1 wt %, respectively,overlapping with the maximum frequency of glass inclusion data(2·5–2·7 wt % H₂O). For olivine to crystallizeclose to the liquidus, pressures close to 200 MPa are needed.Redox conditions around NNO = +0·5 are inferred fromclinopyroxene compositions. The determined pre-eruptive parametersrefer to the storage region of golden pumice melts, which islocated at a depth of around 7·5 km, within the metamorphicarc crust. Golden pumice melts ascending from their storagezone along an adiabat will not experience crystallization ontheir way to the surface. KEY WORDS: basalt; pumice; experiment; phase equilibria; Stromboli  相似文献   

Rapid Change of Lava Composition from 1998 to 2002 at Piton de la Fournaise (Reunion) Inferred from Pb Isotopes and Trace Elements: Evidence for Variable Crustal Contamination     

VLASTELIC  IVAN; STAUDACHER  THOMAS; SEMET  MICHEL 《Journal of Petrology》2005,46(1):79-107

After an unusually long quiet period of nearly 6 years, in 1998the Piton de la Fournaise volcano started a new cycle of intensevolcanic activity. We report geochemical data on the first nineevents (53 samples), from the long-lived initial eruption (sixand a half months) of 1998 to the high-flux picritic eruptionof January 2002. Pb isotopes and trace elements display systematic,coupled variations, which are mostly confined to the beginningand the end of the period. Two well-defined binary mixing trendsare shown by Pb–Pb and Pb–trace element relationships.These trends indicate a change of end-member components betweenMarch and June 2001 that coincides with the transition fromsteady-state basalts to picrites. A three-component mixing modelinvolving a homogeneous plume and two contaminants successfullyexplains the data. The Pb–Pb relationship requires thattwo mixing processes occur successively: plume-derived magmainteracts first with altered oceanic crust, and the resultinghybrid product then interacts at shallower level with the oldlavas constituting the base of the volcanic edifice. Assimilationof edifice material decreased continuously from 1998 to 2002,whereas assimilation of oceanic crust drastically increasedduring the late-stage picritic eruption. These results suggestthat picrites may have resided for an unusually long time atan oceanic crustal level before ascending rapidly through thevolcanic edifice with little interaction with channel walls. KEY WORDS: assimilation; lead isotopes; picrites; Piton de la Fournaise; trace elements  相似文献   

Soil wedge polygons in northern Québec: description and paleoclimatic significance     

ELIZABETH JETCHICK  MICHEL ALLARD 《Boreas: An International Journal of Quaternary Research》1990,19(4):353-365

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Adakite-like Lavas from Antisana Volcano (Ecuador): Evidence for Slab Melt Metasomatism Beneath Andean Northern Volcanic Zone   总被引：6，自引：1，他引：6  

BOURDON  ERWAN; EISSEN  JEAN-PHILIPPE; MONZIER  MICHEL; ROBIN  CLAUDE; MARTIN  HERVE; COTTEN  JOSEPH; HALL  MINARD L. 《Journal of Petrology》2002,43(2):199-217

Extensive sampling of the Antisana volcano in Ecuador (NorthernVolcanic Zone of the Andes) has revealed the presence of adakite-likerocks throughout the edifice, i.e. rocks with geochemical characteristicsclose, but not identical, to those of slab melts. Two main volcanicgroups have been distinguished, characterized by two distinctevolutionary trends. The AND group, mostly composed of andesites,shows the clearest adakitic characteristics such as high La/Yband Sr/Y ratios and low heavy rare earth element (HREE) contents.The CAK group, composed of high-K andesites and dacites, displaysless pronounced adakitic-like characteristics. Although themore basic rocks of each group are difficult to distinguishon many geochemical diagrams, a geochemical study shows thatthe evolution of the AND and CAK groups is dominated by differentpetrogenetic processes. The isotopic characteristics of theCAK rocks suggest that evolution of this group is dominatedby a limited assimilation–fractional crystallization processwithin the granitic continental basement of the cordillera.In the AND group, the abundances of incompatible elements, suchas Nb or HREE, suggest that the series was produced by a partialmelting process in a mantle rich in garnet, amphibole and/orclinopyroxene. Such a mantle source has been demonstrated (experimentallyand by exhumed mantle xenoliths) to be produced in subductionzones where slab melts react with and metasomatize the mantlewedge. In Ecuador, magmas erupted in the Western Cordillera(trenchward relative to Antisana volcano) are true adakites,suggesting that slab melts can be responsible for the metasomatismof the mantle wedge beneath the NVZ in Ecuador. If mantle convectioncan drag down this modified mantle beneath Antisana volcano,destabilization of metasomatic amphibole at appropriate pressuresin this modified garnetiferous mantle can adequately explainthe formation and the geochemical features of Antisana lavas. KEY WORDS: subduction; adakite; metasomatism; Ecuador; AFC; Sr and Nd isotopes  相似文献   

Geochemical and Isotopic Evidence for Crustal Assimilation Beneath Krafla, Iceland   总被引：7，自引：3，他引：7  

NICHOLSON  HUGH; CONDOMINES  MICHEL; FITTON  J. GODFREY; FALLICK  ANTHONY E.; GR?NVOLD  KARL; ROGERS  GRAEME 《Journal of Petrology》1991,32(5):1005-1020

The Krafla volcanic system consists of a central volcano andassociated fissure swarm in the NE axial rift zone of Iceland.Lavas spanning the whole of Krafla's exposed volcanic history(estimated to be 0-> 300 ka) have been analysed and rangein composition from olivine tholeiite to rhyolite. Major-elementcompositions suggest that fractional crystallization exertsthe main control over the differentiation process. However,K₂O and the very incompatible trace elements, Rb, Th, and U,are all enriched beyond the extent expected by closed-systemfractional crystallization. Fractionation coupled with periodicreplenishment and tapping of the reservoir is unlikely to beresponsible for this enrichment, despite the geophysical evidencesuggesting a large number of inflations and deflations of ashallow magma reservoir (Tryggvason, 1986). Th- and O-isotope results confirm the work of previous authorsthat crustal assimilation is operating on a local scale beneathKrafla. A model is suggested, fitting both the Th- and O-isotopicdata, which involves the partial melting and incorporation ofa hydrothermally altered wall-rock contaminant during fractionalcrystallization (i. e., AFC processes). This process of partialmelting is likely to enhance the most highly incompatible elementconcentrations (e. g., increasing Rb/Zr) more than expectedby closed-system fractional crystallization.  相似文献