Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling   总被引：32，自引：1，他引：31  

Yilin Xiao  Jochen Hoefs  Alfons M. van den Kerkhof  Jens Fiebig  Yongfei Zheng 《Contributions to Mineralogy and Petrology》2000,139(1):1-16

This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive H₂O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 ¹⁴C years Before Present (¹⁴C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H₂O contents of 3 to 6 wt% H₂O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding episodes of mafic magmatism (from 10,600 to ∼3000 ¹⁴C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H₂O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine Lake system have not always been low H₂O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence of H₂O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H₂O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to the liquidus. These combined effects generate SiO₂-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H₂O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H₂O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes. Received: 4 January 1999 / Accepted: 30 August 1999  相似文献   

Uniqueness conditions in a hyperbolic model for oil recovery by steamdrive     

J. Bruining  C.J. van Duijn 《Computational Geosciences》2000,4(1):65-98

In this paper we study a one-dimensional model for oil recovery by steamdrive. This model consists of two parts: a (global) interface model and a (local) steam condensation/capillary diffusion model. In the interface model a steam condensation front (SCF) is present as an internal boundary between the hot steam zone (containing water, oil and steam) and the cold liquid zone (containing only water and oil). Disregarding capillary pressure away from the SCF, a 2× 2 hyperbolic system arises for the water and steam saturation. This system cannot be solved uniquely without additional conditions at the SCF. To find such conditions we blow up the SCF and consider a parabolic transition model, including capillary diffusion. We study in detail the existence conditions for traveling wave solutions. These conditions provide the missing matching conditions at the SCF in the hyperbolic limit. We show that different transition models yield different matching conditions, and thus different solutions of the interface model. We also give a relatively straightforward approximation and investigate its validity for certain ranges of model parameters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Editors' note: Astron. Nachr. 8/2007     

E. Forgcs‐Dajka  I. Ballai  L. van Driel‐Gesztelyi 《Astronomische Nachrichten》2007,328(8):725-725

  相似文献   

Geochemical compositional changes at the Pliocene–Pleistocene transition in fluviodeltaic deposits in the Tegelen-Reuver area (southeastern Netherlands)     

D. J. Huisman  G. T. Klaver  A. Veldkamp  B. J. H. van Os 《International Journal of Earth Sciences》2000,89(1):154-169

2 O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. Increasing K₂O/Al₂O₃ can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay minerals during weathering in organic-rich layers. Local high TiO₂ anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of the fluvial system. Finally, (pyrite-) S contents drop (siderite-) Fe contents rise. Micromorphological observations indicate that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression at the Pliocene–Pleistocene transition. Received: 28 August 1999 / Accepted: 2 November 1999  相似文献   

A characteristics-based method for solving the transport equation and its application to the process of mantle differentiation and continental root growth     

Jeroen H. de Smet  Arie P. van den Berg  Nico J. Vlaar  & David A. Yuen 《Geophysical Journal International》2000,140(3):651-659

  相似文献   

Cool dust and gas in the Small Magellanic Cloud     

S. Stanimirovic  †  L. Staveley-Smith  J. M. van der Hulst  TJ. R. Bontekoe  D. J. M. Kester  P. A. Jones 《Monthly notices of the Royal Astronomical Society》2000,315(4):791-807

  相似文献   

Spectral evolution of the peculiar Ic Supernova 1998bw     

R. A. Stathakis  B. J. Boyle  D. H. Jones  M. S. Bessell  T. J. Galama  Lisa M. Germany  M. Hartley  D. M. James  C. Kouveliotou  I. J. Lewis  Q. A. Parker  K. S. Russell  E. M. Sadler  C. G. Tinney  J. van Paradijs  P. M. Vreeswijk 《Monthly notices of the Royal Astronomical Society》2000,314(4):807-814

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ -ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V -band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.  相似文献   

Radio galaxies with a 'double-double morphology'– I. Analysis of the radio properties and evidence for interrupted activity in active galactic nuclei     

Arno P. Schoenmakers  †  A. G. de Bruyn  H. J. A. Röttgering  H. van der Laan  C. R. Kaiser 《Monthly notices of the Royal Astronomical Society》2000,315(2):371-380

We present four Mpc-sized radio galaxies which consist of a pair of double-lobed radio sources, aligned along the same axis, and with a coinciding radio core. We call these peculiar radio sources 'double-double' radio galaxies (DDRGs) and propose a general definition of such sources: a 'double-double' radio galaxy consists of a pair of double radio sources with a common centre. Furthermore, the two lobes of the inner radio source must have a clearly extended, edge-brightened radio morphology. Adopting this definition, we find several other candidate DDRGs in the literature. We find that in all sources the smaller (inner) pair of radio lobes is less luminous than the larger (outer) pair, and that the ratio of 1.4-GHz flux density of these two pairs appears to be anticorrelated with the projected linear size of the inner source. Also, the outer radio structures are large, exceeding 700 kpc. We discuss possible formation scenarios of the DDRGs, and we conclude that an interruption of the jet-forming central activity is the most likely mechanism. For one of our sources (B 1834+620) we have been able observationally to constrain the length of time of the interruption to a few Myr. We discuss several scenarios for the cause of the interruption, and suggest multiple encounters between interacting galaxies as a possibility. Finally, we discuss whether such interruptions help the formation of extremely large radio sources.  相似文献   

Infrared emission from 6.7-GHz methanol maser sources     

S. Goedhart  †  D. J. van der Walt  A. J. Schutte ‡ 《Monthly notices of the Royal Astronomical Society》2000,315(2):316-324

Near-infrared photometry was performed on 56 southern 6.7-GHz methanol maser sources. A simple spherically symmetric model of the radiative transfer through a dust shell was developed and used to study the conditions in the dust cloud in which the masers are produced. The parameters investigated were the size of the cloud, the spectral type of the embedded star, the optical depth of the dust cloud and the dust density distribution. It was found that the infrared colours of the models have a complex dependence on the parameters and that no unique combination of parameter values explains the spectral energy distribution of any particular source. The model effectively reproduces the far-infrared ( IRAS ) colours but cannot simultaneously explain the near-infrared colours for any of the observed sources.  相似文献   

The harmonic and sideband structure of the kilohertz quasi-periodic oscillations in Sco X-1     

Mariano Méndez  Michiel van der Klis 《Monthly notices of the Royal Astronomical Society》2000,318(3):938-942

We use data from the Rossi X-ray Timing Explorer to search for harmonics and sidebands of the two simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) in Sco X-1. We do not detect any of these harmonics or sidebands, with 95 per cent confidence upper limits to their power between ∼1 and ∼10 per cent of the power of the upper kHz QPO. The oscillations produced at these frequencies may be attenuated in a scattering corona around the neutron star. We find that upper limits to the unattenuated power of some of the strongest theoretically predicted harmonics and sidebands are as low as ∼2 per cent of the unattenuated power of the high-frequency QPO in Sco X-1.  相似文献