Carboniferous and Triassic eclogites in the western Dabie Mountains,east‐central China: evidence for protracted convergence of the North and South China Blocks     

Weidong Sun  I. S. Williams  Shuguang Li 《Journal of Metamorphic Geology》2002,20(9):873-886

SHRIMP U–Pb dating and laser ablation ICP‐MS trace element analyses of zircon from four eclogite samples from the north‐western Dabie Mountains, central China, provide evidence for two eclogite facies metamorphic events. Three samples from the Huwan shear zone yield indistinguishable late Carboniferous metamorphic ages of 312 ± 5, 307 ± 4 and 311 ± 17 Ma, with a mean age of 309 ± 3 Ma. One sample from the Hong'an Group, 1 km south of the shear zone yields a late Triassic age of 232 ± 10 Ma, similar to the age of ultra‐high pressure (UHP) metamorphism in the east Qinling–Dabie orogenic belt. REE and other trace element compositions of the zircon from two of the Huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase, namely in the eclogite facies, an interpretation supported by the presence of garnet, omphacite and phengite inclusions. Zircon also grew during later retrogression. Zircon cores from the Huwan shear zone have Ordovician to Devonian (440–350 Ma) ages, flat to steep heavy‐REE patterns, negative Eu anomalies, and in some cases plagioclase inclusions, indicative of derivation from North China Block igneous and low pressure metamorphic source rocks. Cores from Hong'an Group zircon are Neoproterozoic (780–610 Ma), consistent with derivation from the South China Block. In the western Dabie Mountains, the first stage of the collision between the North and South China Blocks took place in the Carboniferous along a suture north of the Huwan shear zone. The major Triassic continent–continent collision occurred along a suture at the southern boundary of the shear zone. The first collision produced local eclogite facies metamorphism in the Huwan shear zone. The second produced widespread eclogite facies metamorphism throughout the Dabie Mountains–Sulu terrane and a lower grade overprint in the shear zone.  相似文献   

On the ejection velocity of meteoroids from comets   总被引：1，自引：0，他引：1  

Yuehua Ma  I. P. Williams  Wenping Chen 《Monthly notices of the Royal Astronomical Society》2002,337(3):1081-1086

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Space shuttle observations of terrestrial impact structures using SIR‐C and X‐SAR radars     

John F. Mchone  Ronald Greeley  Kevin K. Williams  Dan G. Blumberg  Ruslan O. Kuzmin 《Meteoritics & planetary science》2002,37(3):407-420

Abstract— Ten terrestrial impact structures were imaged during two flights of the 1994 space radar laboratory (SRL) experiment. These craters include Wolf Creek, Australia; Roter Kamm, Namibia; Zhamanshin, Kazakhstan; BP and Oasis, Libya; Aorounga, Chad; Amguid, Algeria; and Spider, Connolly Basin and Henbury, Australia. SRL contained two co‐registered instruments; the United States shuttle imaging radar‐C (SIR‐C) polarimetric radar system operating in L‐band (λ = 24 cm) and C‐band (λ = 5.6 cm), and the joint German/Italian synthetic aperture radar (X‐SAR) operating in vertically‐polarized X‐band (λ = 3 cm). Comparisons show SRL images to be complementary to, or in some cases superior to, corresponding optical images for evaluating size, location, and relative age of impact features. Regardless of wavelength or polarization, craters with significant relief appear prominently on radar as a result of slope and roughness effects. In desert regions, longer wavelengths penetrate dry sand mantles to reveal hidden crater dimensions or associated buried landforms. Radar polarities and wavelengths are particularly sensitive to vegetation, surface roughness, and soil moisture or electrical properties. In the more temperate environments of Kazakhstan and Australia, SRL images show detailed stream patterns that reveal the location and structure of otherwise obscured impact features.  相似文献   

On the origin of diffuse clouds     

Richard J. Price  Serena Viti  David A. Williams 《Monthly notices of the Royal Astronomical Society》2003,343(4):1257-1262

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An observational study of a magneto-acoustic wave in the solar corona     

D. R. Williams  M. Mathioudakis  P. T. Gallagher  K. J. H. Phillips  R. T. J. MAteer  F. P. Keenan  P. Rudawy  A. C. Katsiyannis 《Monthly notices of the Royal Astronomical Society》2002,336(3):747-752

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Enhanced molecular abundances in low-mass star-forming cores     

Serena Viti  Sukina Natarajan  David A. Williams 《Monthly notices of the Royal Astronomical Society》2002,336(3):797-802

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Ocean acoustic sensor installation at the South Florida OceanMeasurement Center     

Nguyen  H.B. DeFerrari  H.A. Williams  N.J. Venezia  W.A. 《Oceanic Engineering, IEEE Journal of》2002,27(2):235-244

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Observational Indicators of Formation Excitation of H2     

S. Tiné  D.A. Williams  D.C. Clary  A.J. Farebrother  A.J. Fisher  A.J.H.M. Meijer  J.M.C. Rawlings  C.J. Davis 《Astrophysics and Space Science》2003,288(3):377-389

Theoretical predictions by Farebrother et al. and Meijer et al. of rovibrational excitation probabilities in H₂ arising from formation by Eley-Rideal processes on a graphite surface are incorporated into a model of the chemistry and excitation of interstellar H₂. The model includes the usual radiative and collisional pumping of H₂ rotational and vibrational states, in addition to the formation processes. Predictions are made for HH₂ rovibrational emission line intensities for representative points in diffuse and in dark interstellar clouds. We find that – if all the interstellar HH₂ is formed by this Eley-Rideal process – then the consequences of formation pumping, as distinct from collisional and radiative pumping, should be clearly evident in both cases. In particular, we predict a clear spectral signature of this direct HH₂ formation process on graphite, distinct from radiative and collisional pumping; this signature should be evident in both diffuse and dark clouds; but the emissivity for dark clouds is predicted to be some 500 times greater than that in diffuse clouds in which the dense material may be embedded. An observational search for this signature in two dark cloud sources was made, but a preliminary analysis of the data did not yield a detection. The implications of and possible reasons for this preliminary conclusion are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Chemistry and clumpiness in planetary nebulae     

M. P. Redman  S. Viti  P. Cau  D. A. Williams 《Monthly notices of the Royal Astronomical Society》2003,345(4):1291-1296

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An electronic version of the second volume of the General Catalogue of Variable Stars with improved coordinates     

N. N. Samus’  V. P. Goranskii  O. V. Durlevich  A. V. Zharova  E. V. Kazarovets  N. N. Kireeva  E. N. Pastukhova  D. B. Williams  M. L. Hazen 《Astronomy Letters》2003,29(7):468-479

We present a new electronic version of the second volume of the fourth edition of the General Catalogue of Variable Stars (GCVS), which contains data on 13480 variable stars in the constellations Cygnus-Orion (the order of constellations in the Catalogue follows the Latin alphabet). The new version takes into account the Name Lists of Variable Stars from no. 67 to 76 for the same constellations. The main distinctive feature of the new version is that it contains improved equatorial J2000.0 coordinates for 13446 stars (including those for 5052 stars with an allowance made for proper motions), based on the identifications with positional catalogs using finding charts, as well as on our new measurements. We searched for a number of stars on original plates from the collections of several observatories and using digital sky survey images. The new version also includes a file of remarks to the second and third GCVS volumes. Apart from a complete update of the positional information, we took into account several corrections that were found to be necessary after the publication of the second GCVS volume (1985). We present a list of references to new Internet resources.  相似文献