Petrological imaging of an active pluton beneath Cerro Uturuncu,Bolivia     

Duncan D. Muir  Jon D. Blundy  Michael C. Hutchinson  Alison C. Rust 《Contributions to Mineralogy and Petrology》2014,167(3):1-25

Uturuncu is a dormant volcano in the Altiplano of SW Bolivia. A present day ~70 km diameter interferometric synthetic aperture radar (InSAR) anomaly roughly centred on Uturuncu’s edifice is believed to be a result of magma intrusion into an active crustal pluton. Past activity at the volcano, spanning 0.89 to 0.27 Ma, is exclusively effusive and almost all lavas and domes are dacitic with phenocrysts of plagioclase, orthopyroxene, biotite, ilmenite and Ti-magnetite plus or minus quartz, and microlites of plagioclase and orthopyroxene set in rhyolitic groundmass glass. Plagioclase-hosted melt inclusions (MI) are rhyolitic with major element compositions that are similar to groundmass glasses. H₂O concentrations plotted versus incompatible elements for individual samples describe a trend typical of near-isobaric, volatile-saturated crystallisation. At 870 °C, the average magma temperature calculated from Fe–Ti oxides, the average H₂O of 3.2 ± 0.7 wt% and CO₂ typically <160 ppm equate to MI trapping pressures of 50–120 MPa, approximately 2–4.5 km below surface. Such shallow storage precludes the role of dacite magma emplacement into pre-eruptive storage regions as being the cause of the observed InSAR anomaly. Storage pressures, whole-rock (WR) chemistry and phase assemblage are remarkably consistent across the eruptive history of the volcano, although magmatic temperatures calculated from Fe–Ti oxide geothermometry, zircon saturation thermometry using MI and orthopyroxene-melt thermometry range from 760 to 925 °C at NNO ± 1 log. This large temperature range is similar to that of saturation temperatures of observed phases in experimental data on Uturuncu dacites. The variation in calculated temperatures is attributed to piecemeal construction of the active pluton by successive inputs of new magma into a growing volume of plutonic mush. Fluctuating temperatures within the mush can account for sieve-textured cores and complex zoning in plagioclase phenocrysts, resorption of quartz and biotite phenocrysts and apatite microlites. That Fe–Ti oxide temperatures vary by ~50–100 °C in a single thin section indicates that magmas were not homogenised effectively prior to eruption. Phenocryst contents do not correlate with calculated magmatic temperatures, consistent with crystal entrainment from the mush during magma ascent and eruption. Microlites grew during ascent from the magma storage region. Variability in the proportion of microlites is attributed to differing ascent and effusion rates with faster rates in general for lavas >0.5 Ma compared to those <0.5 Ma. High microlite contents of domes indicate that effusion rates were probably slowest in dome-forming eruptions. Linear trends in WR major and trace element chemistries, highly variable, bimodal mineral compositions, and the presence of mafic enclaves in lavas demonstrate that intrusion of more mafic magmas into the evolving, shallow plutonic mush also occurred further amplifying local temperature fluctuations. Crystallisation and resorption of accessory phases, particularly ilmenite and apatite, can be detected in MI and groundmass glass trace element covariation trends, which are oblique to WRs. Marked variability of Ba, Sr and La in MI can be attributed to temperature-controlled, localised crystallisation of plagioclase, orthopyroxene and biotite within the evolving mush.  相似文献   

Compositional variation in pillow lavas from the Mid-Atlantic Ridge     

Fumiko Shido  Akiho Miyashiro  Maurice Ewing 《Marine Geology》1974,16(4):177-190

Five fresh, two weathered, and two metamorphosed basalt pillows with a presently or originally glassy outermost layer, together with a weathered and a metamorphosed basalt fragment without an originally glassy layer, all from the Mid-Atlantic Ridge, were investigated in detail. Fresh pillows usually show only very slight compositional heterogeneity, except for the glassy outermost layer where the total iron and MgO contents are higher and the K₂O content and the $\text{Fe}{}_2\text{O}{}_3\text{FeO}$ ratio are lower than the interior. In particular, the K₂O content of the glassy outermost layer is only about a half of that of the core in some pillows. In weathered pillows the surface layer shows higher total iron, TiO₂, P₂O₅ and H₂O contents and a higher $\text{Fe}{}_2\text{O}{}_3\text{FeO}$ ratio and a much lower CaO content than the interior. Most of the compositional heterogeneity observed in metamorphosed pillows may be ascribed to chemical migration during weathering, though metamorphism also may cause considerable heterogeneity.  相似文献   

Prediction of depth‐integrated fluxes of suspended sediment in the Amazon River: particle aggregation as a complicating factor     

J. Bouchez  F. Métivier  M. Lupker  L. Maurice  M. Perez  J. Gaillardet  C. France‐Lanord 《水文研究》2011,25(5):778-794

Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Gemini/GMOS spectra of globular clusters in the Leo group elliptical NGC 3379     

Michael Pierce  Michael A. Beasley  Duncan A. Forbes  Terry Bridges  Karl Gebhardt  Favio Raul Faifer  Juan Carlos Forte  Stephen E. Zepf  Ray Sharples  David A. Hanes  Robert Proctor 《Monthly notices of the Royal Astronomical Society》2006,366(4):1253-1264

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A 20cm 2 CCD mosaic camera for a dark matter search part II : Electronics,data acquisition and performance     

Arnaud  M.  Aubourg  E.  Bareyre  P.  Br';ehin  S.  Caridroit  R.  de Kat  J.  Dispau  G.  Djidi  K.  Gros  M.  Lachièze-Rey  M.  Laigneau  Y.  Laurent  B.  Lesquoy  E.  Lavocat  Ph.  Magneville  C.  Mazeau  B.  Milsztajn  A.  Moscoso  L.  Pasquaud  J.  Paul  B.  Perrin  P.  Petibon  J.  Piret  Y.  Queinnec  F.  Rich  J.  Spiro  M.  de Trogoff  J.  Vigroux  L.  Zylberajch  S.  Ansari  R.  Cavalier  F.  Moniez  M.  Beaulieu  J. P.  Ferlet  R.  Grison  Ph.  Vidal-Madjar  A.  Adrianzyk  G.  Berger  J. P.  Burnage  R.  Delclite  J. C.  Kohler  D.  Magnan  R.  Richaud  A.  Guibert  J.  Moreau  O.  Tajahmady  F.  Baranne  A.  Maurice  E.  Prévôt  L.  Gry  C. 《Experimental Astronomy》1994,4(3-4):279-296

Conclusion To summarize, the readout and the control system of the CCD mosaic camera are running since December 1991 at the La Silla Observatory (ESO). The overall performance of the camera has been good. About 12000 pictures (data and flat-fields) have been successfully registered up to now. We will report in the near future preliminary scientific results of the EROS experiment.  相似文献   

Electric charge and magnetic flux on rotating black holes in a force-free magnetosphere     

Hyun KyuLee  Chul H.Lee  Maurice H. P. M.van Putten 《Monthly notices of the Royal Astronomical Society》2001,324(3):781-784

The electric charge on rotating black holes is calculated to be ∼ BJ in the force-free configuration of Ghosh, with a horizon flux of ∼ BM ². This charge is gravitationally weak for B ∼10¹⁵ G , so that the Kerr metric applies. Being similar to the electric charge of a magnetar, both electric charge and magnetic flux should be, in sign and order of magnitude, continuous during stellar collapse into a black hole. Extraction of the rotational energy from newly formed black holes may proceed by interaction with the magnetic field.  相似文献   

Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy     

Søren S. Larsen  Duncan A. Forbes  Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,327(4):1116-1126

We explore the rich globular cluster (GC) system of the nearby Sa galaxy M104, the 'Sombrero' (NGC 4594), using archive Wide Field Planetary Camera 2 data. The GC colour distribution is found to be bimodal at the >99 per cent confidence level, with peaks at     and     . The inferred metallicities are very similar to those of GCs in our Galaxy and M31. However, the Sombrero reveals a much enhanced number of red (metal-rich) GCs compared to other well-studied spirals. Because the Sombrero is dominated by a huge bulge and only has a modest disc, we associate the two subpopulations with the halo and bulge components, respectively. Thus our analysis supports the view that the metal-rich GCs in spirals are associated with the bulge rather than with the disc. The Sombrero GCs have typical effective (half-light) radii of ∼2 pc with the red ones being ∼30 per cent smaller than the blue ones. We identify many similarities between the GC system of the Sombrero and those of both late-type spirals and early-type galaxies. Thus both the GC system and the Hubble type of the Sombrero galaxy appear to be intermediate in their nature.  相似文献   

The photometric properties of isolated early-type galaxies     

Fatma M. Reda  Duncan A. Forbes  Michael A. Beasley  Ewan J. O'Sullivan  Paul Goudfrooij 《Monthly notices of the Royal Astronomical Society》2004,354(3):851-869

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Radio observations of super star clusters in dwarf starburst galaxies     

Ian R. Stevens  Duncan A. Forbes  Ray P. Norris 《Monthly notices of the Royal Astronomical Society》2002,335(4):1079-1084

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A stochastic model for the synthesis and degradation of natural organic matter. Part III: Modeling Cu(II) complexation     

Stephen E. Cabaniss  Patricia A. Maurice  Greg Madey 《Applied Geochemistry》2007

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