The effect of radiative feedback on Bondi–Hoyle flow around a massive star     

Richard Edgar  Cathie Clarke 《Monthly notices of the Royal Astronomical Society》2004,349(2):678-686

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LREE distribution in perovskite,apatite and titanite from South West Ugandan xenoliths and kamafugite lavas     

F. E. Lloyd  A. D. Edgar  K. V. Ragnarsdottir 《Mineralogy and Petrology》1996,57(3-4):205-228

Summary In-situ microprobe LREE analyses of perovskite and titanite (La, Ce, Nd), and apatite (La, Ce), from SW Ugandan clinopyroxenite xenoliths and kamafugite lavas indicate that LREE distribution in these minerals is determined by a number of factors related to their different parageneses: In particular LREE content is affected by whether the LREE-bearing minerals have crystallised from metasomatic carbonate or from silicate (i.e. metasomatic or magmatic) melts in the mantle. In this situation LREE partition favours carbonate over silicate melts. Distribution of LREE in perovskite and apatite crystallised from magmatic mantle melts or mantle-derived lavas is chiefly determined by preference of LREE for perovskite > apatite > titanite. LREE zoning in perovskite is influenced by changes in melt structure: increasing melt polymerisation enhancing mineral_LREE/melt_LREE partition into perovskite rims in magmatic xenoliths; decreasing melt polymerisation depleting LREE in lava perovskite rims. This zoning is reinforced by perovskite competition with apatite for LREE: perovskite (cores/rims) co-crystallising with apatite is reduced in LREE. There are 37 instances of perovskitewith Ce below detection while La and Nd levels are normal. These occur in both xenoliths and lavas; in grain zones or whole grains. Likewise Ce alone of the LREE is below detection in six out of ten titanite analyses. These observations are interpreted as evidence for increased f_{O 2}, Ce⁴ + being excluded from these mineral structures. Recognition of these various processes can elucidate the interpretation of bulk rock and bulk mineral LREE signatures in kamafugite volcanism.

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LREE Verteilung in Perovskit, Apatit und Titanit aus Xenolithen und kamafugitischen Laven Südwest-Ugandas

Zusammenfassung In-situ LREE Analysen von Perovskit und Titanit (La, Ce, Nd) und Apatit (La, Ce) aus Klinopyroxenit-Xenolithen und kamafugitischen Laven Südwest-Ugandas zeigen, daß die LREE Verteilung in diesen Mineralen durch eine Vielzahl von Faktoren, die mit Unterschieden in den Paragenesen zusammenhängen, bestimmt wird: Der LREE-Gehalt wird im besonderen davon bestimmt, ob die LREE-führenden Minerale aus metasomatischen Karbonat- oder aus (metasomatischen oder magmatischen) Silikatschmelzen im Mantel auskristallisierten. Dabei erfolgt die LREE Fraktionierung zu Gunsten der Karbonatschmelzen. Die LREE-Verteilung von Perovskit und Apatit, die aus magmatischen Mantelschmelzen oder -laven kristallisierten, wird vorrangig durch den bevorzugten Einbau der LREE in Perovskit > Apatit > Titanit kontrolliert. Der LREE Zonarbau von Perovskit wird durch die Änderungen der Schmelzstruktur beinflußt: Verstärkte Schmelzpolymerisation führt zu verstärkter Mineral_LFEE/Schmelze_LREE Fraktionierung in den Perovskiträndern magmatischer Xenolithe, eine Abnahme der Schmelzpolymerisation hingegen resultiert in einer Abreicherung der LREE in den Perovskiträndern. Diese Art der Zonierung wird durch den Wettbewerb von Perovskit mit Apatit um die LREE verstärkt. Perovskit (Kerne/Ränder), der mit Apatit gemeinsam auskristallisierte, ist ärmer an LREE. 37 Fälle, in denenCe nicht nachweisbar war, La und Nd aber in normaler Konzentration auftreten, wurden sowohl in den Xenolithen als auch in den Laven gefunden; und zwar entweder in Kornbereichen oder in ganzen Körnern. Vergleichsweise liegt Ce nur in sechs von zehn Titanitproben unterhalb der Nachweisgrenze. Diese Beobachtungen werden als Hinweise auf erhöhte SauerstoffFugazitäten, bei denen Ce^4– aus der Mineralstruktur ausgeschlossen wird, angesehen.Ein Verständnis dieser verschiedenen Prozesse kann zur besseren Interpretation von LREE Gesamtgesteins- und Gesamtmineral-Signaturen in Kamafugiten beitragen.

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With 3 Figures  相似文献   

Topography as a major factor in the development of arcuate thrust belts: insights from sandbox experiments   总被引：2，自引：0，他引：2  

F. O. Marques  P. R. Cobbold 《Tectonophysics》2002,348(4)

We have used sandbox experiments to investigate and to illustrate the effects of topography upon the development of arcuate thrust belts. In experiments where a sand pack shortened and thickened in front of an advancing rectilinear piston, the geometry of the developing thrust wedge was highly sensitive to variations in surface topography. In the absence of erosion and sedimentation, the surface slope tended to become uniform, as predicted by the theory of critical taper. Under these conditions, the wedge propagated by sequential accretion of new thrust slices. In contrast, where erosion or sedimentation caused the topographic profile to become irregular, thrusts developed out of sequence. For example, erosion throughout a hinterland caused underlying thrusts to remain active and inhibited the development of new thrusts in the foreland. Where initial topography was irregular in plan view, accreting thrusts tended to be arcuate. They were convex towards the foreland, around an initially high area; concave towards the foreland, around an initially low area. Initial plateaux tended to behave rigidly, while arcuate thrust slices accreted to them. Thrust motions were radial with respect to each plateau. Within transfer zones to each side, fault blocks rotated about vertical axes and thrust motions were oblique-slip. At late stages of deformation, the surface slope of the thrust wedge tended towards a uniform value. Initial mountains of conical shape (representing volcanoes) also escaped deformation, except at depth, where they detached. Arcuate thrust slices accreted to front and back. Where a developing thrust wedge was subject to local incision, accreting thrust slices dipped towards surrounding areas of high topography, forming Vs across valleys.Arcuate structural patterns are to be found around the three highest plateaux on Earth (Tibet, Pamirs and Altiplano) and around the Tromen volcanic ridge in the Neuquén Basin of northern Patagonia. We infer that these areas behaved in quasi-rigid fashion, protected as they were by their high topography.  相似文献   

Origin of spongy textures in clinopyroxene and spinel from mantle xenoliths, Hessian Depression, Germany   总被引：1，自引：0，他引：1  

R. L. Carpenter  A. D. Edgar  Y. Thibault 《Mineralogy and Petrology》2002,74(2-4):149-162

Summary Spongy textures are observed in anhydrous Group 1 mantle xenoliths (harzburgite, lherzolite and wehrlite) hosted in Tertiary alkali basaltic lavas from the Hessian Depression, Germany. These textures are developed only on clinopyroxene and spinel, and occur as rims or cross-cutting veinlets and patches showing optical continuity with the host grain. They are often associated with pools of amorphous glassy material. There is no preferential development of spongy domains against the xenolith-lava contact suggesting that the host magma did not play any significant role in their formation. Spongy clinopyroxene and spinel occur in all rock types, but, are more pervasive in wehrlite. Chemically, spongy domains of clinopyroxene and spinel are more refractory than unaffected areas, which is consistent with their formation through a partial melting event. The associated glassy material shows chemical characteristics which suggest that the melt pools are genetically related to the development of the spongy textures. The partial melting event was probably triggered by the infiltration of a low-density fluid. The fluid may have evolved from a silicate melt responsible for the metasomatic Fe-enrichment recorded in wehrlite. In this context, the more pervasive development of spongy clinopyroxene in wehrlite may be explained by a higher concentration of the evolved fluid phase at proximity to its silicate melt source. Received March 15, 2000; revised version accepted September 6, 2001  相似文献   

Lower crustal melting and the role of open-system processes in the genesis of syn-orogenic quartz diorite–granite–leucogranite associations: constraints from Sr–Nd–O isotopes from the Bandombaai Complex, Namibia     

Tina van de Flierdt  Stephan Hoernes  Stefan Jung  Peter Masberg  Edgar Hoffer  Urs Schaltegger  Hans Friedrichsen 《Lithos》2003,67(3-4):205-226

The Bandombaai Complex (southern Kaoko Belt, Namibia) consists of three main intrusive rock types including metaluminous hornblende- and sphene-bearing quartz diorites, allanite-bearing granodiorites and granites, and peraluminous garnet- and muscovite-bearing leucogranites. Intrusion of the quartz diorites is constrained by a U–Pb zircon age of 540±3 Ma.

Quartz diorites, granodiorites and granites display heterogeneous initial Nd- and O isotope compositions (_{Nd (540 Ma)}=−6.3 to −19.8; δ¹⁸O=9.0–11.6‰) but rather low and uniform initial Sr isotope compositions (⁸⁷Sr/⁸⁶Sr_initial=0.70794–0.70982). Two leucogranites and one aplite have higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.70828–0.71559), but similar initial _Nd (−11.9 to −15.8) and oxygen isotope values (10.5–12.9‰). The geochemical and isotopic characteristics of the Bandombaai Complex are distinct from other granitoids of the Kaoko Belt and the Central Zone of the Damara orogen. Our study suggests that the quartz diorites of the Bandombaai Complex are generated by melting of heterogeneous mafic lower crust. Based on a comparison with results from amphibolite-dehydration melting experiments, a lower crustal garnet- and amphibole-bearing metabasalt, probably enriched in K₂O, is a likely source rock for the quartz diorites. The granodiorites/granites show low Rb/Sr (<0.6) ratios and are probably generated by partial melting of meta-igneous (intermediate) lower crustal sources by amphibole-dehydration melting. Most of the leucogranites display higher Rb/Sr ratios (>1) and are most likely generated by biotite-dehydration melting of heterogeneous felsic lower crust. All segments of the lower crust underwent partial melting during the Pan-African orogeny at a time (540 Ma) when the middle crust of the central Damara orogen also underwent high T, medium P regional metamorphism and melting. Geochemical and isotope data from the Bandombaai Complex suggest that the Pan-African orogeny in this part of the orogen was not a major crust-forming episode. Instead, even the most primitive rock types of the region, the quartz diorites, represent recycled lower crustal material.  相似文献   

9: Processes of tectonism, magmatism and mineralization: Lessons from Europe     

Derek Blundell  Nicholas Arndt  Peter R. Cobbold  Christoph Heinrich 《Ore Geology Reviews》2005,27(1-4):333

Metallogenic provinces in Europe range in age from the Archaean to the Neogene. Deposit types include porphyry copper and epithermal Cu–Au, volcanic-hosted massive sulphide (VMS), orogenic gold, Fe-oxide–Cu–Au, anorthosite Fe–Ti-oxide and sediment-hosted base-metal deposits. Most of them formed during short-lived magmatic events in a wide range of tectonic settings; many can be related to specific tectonic processes such as subduction, hinge retreat, accretion of island arcs, continental collision, lithosphere delamination or slab tear. In contrast, most sediment-hosted deposits in Europe evolved in extensional, continental settings over significant periods of time. In Europe, as elsewhere, ore formation is an integral part of the geodynamic evolution of the Earth's crust and mantle. Many tectonic settings create conditions conducive to the generation of water-rich magma, but the generation of ore deposits appears to be restricted to locations and short periods of change in temperature and stress, imposed by transitory plate motions. Crustal influence is evident in the strong structural controls on the location and morphology of many ore deposits in Europe. Crustal-scale fault–fracture systems, many involving strike-slip elements, have provided the fabric for major plumbing systems. Rapid uplift, as in metamorphic core complexes, and hydraulic fracturing can generate or focus magmatic–hydrothermal fluid flow that may be active for time spans significantly less than a million years. Once a hydrologically stable flow is established, ore formation is strongly dependent on the steep temperature and pressure gradients experienced by the fluid, particularly within the upper crust. In Europe, significant fracture porosity deep in the crystalline basement (1%) is not only important for magmatic–hydrothermal systems, but allows brines to circulate down through sedimentary basins and then episodically upward, expelled seismically to produce sediment-hosted base-metal deposits and Kupferschiefer copper deposits. Emerging research, stimulated by GEODE, can improve the predicting power of numerical simulations of ore-forming processes and help discover the presence of orebodies beneath barren overburden.  相似文献   

Identification of Uranyl Minerals Using Oxygen K‐Edge X‐Ray Absorption Spectroscopy          下载免费PDF全文

Jesse D. Ward  Mark Bowden  C. Tom Resch  Steven Smith  Bruce K. McNamara  Edgar C. Buck  Gregory C. Eiden  Andrew M. Duffin 《Geostandards and Geoanalytical Research》2016,40(1):135-148

Although most of the world's uranium exists as pitchblende or uraninite, this mineral can be weathered to a great variety of secondary uranium minerals, most containing the uranyl cation. Anthropogenic uranium compounds can also react in the environment, leading to spatial–chemical alterations that could be useful for nuclear forensics analyses. Soft X‐ray absorption spectroscopy (XAS) has the advantages of being non‐destructive, element‐specific and sensitive to electronic and physical structure. The soft X‐ray probe can also be focused to a spot size on the order of tens of nanometres, providing chemical information with high spatial resolution. However, before XAS can be applied at high spatial resolution, it is necessary to find spectroscopic signatures for a variety of uranium compounds in the soft X‐ray spectral region. To that end, we collected the near edge X‐ray absorption fine structure (NEXAFS) spectra of a variety of common uranyl‐bearing minerals, including uranyl carbonates, oxyhydroxides, phosphates and silicates. We find that uranyl compounds can be distinguished by class (carbonate, oxyhydroxide, phosphate or silicate) based on their oxygen K‐edge absorption spectra. This work establishes a database of reference spectra for future spatially resolved analyses. We proceed to show scanning X‐ray transmission microscopy (STXM) data from a schoepite particle in the presence of an unknown contaminant.  相似文献   

Occurrence and distribution of selected potentially toxic elements in soils of playing sites: a case study from Bratislava,the capital of Slovakia     

Edgar Hiller  Lucia Lachká  Ľubomír Jurkovič  Ondrej Ďurža  Katarína Fajčíková  Jaroslav Vozár 《Environmental Earth Sciences》2016,75(20):1390

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The accuracy of standard enthalpies and entropies for phases of petrological interest derived from density-functional calculations     

Artur?BenisekEmail authorView author&#;s OrcID profile  Edgar?Dachs 《Contributions to Mineralogy and Petrology》2018,173(11):90

The internal energies and entropies of 21 well-known minerals were calculated using the density functional theory (DFT), viz. kyanite, sillimanite, andalusite, albite, microcline, forsterite, fayalite, diopside, jadeite, hedenbergite, pyrope, grossular, talc, pyrophyllite, phlogopite, annite, muscovite, brucite, portlandite, tremolite, and CaTiO₃–perovskite. These thermodynamic quantities were then transformed into standard enthalpies of formation from the elements and standard entropies enabling a direct comparison with tabulated values. The deviations from reference enthalpy and entropy values are in the order of several kJ/mol and several J/mol/K, respectively, from which the former is more relevant. In the case of phase transitions, the DFT-computed thermodynamic data of involved phases turned out to be accurate and using them in phase diagram calculations yields reasonable results. This is shown for the Al₂SiO₅ polymorphs. The DFT-based phase boundaries are comparable to those derived from internally consistent thermodynamic data sets. They even suggest an improvement, because they agree with petrological observations concerning the coexistence of kyanite?+?quartz?+?corundum in high-grade metamorphic rocks, which are not reproduced correctly using internally consistent data sets. The DFT-derived thermodynamic data are also accurate enough for computing the P–T positions of reactions that are characterized by relatively large reaction enthalpies (>?100 kJ/mol), i.e., dehydration reactions. For reactions with small reaction enthalpies (a few kJ/mol), the DFT errors are too large. They, however, are still far better than enthalpy and entropy values obtained from estimation methods.  相似文献   

Book review of ENCYCLOPEDIA OF NONLINEAR SCIENCE,edited by Alwyn Scott,Routledge, Taylor and Francis Group, 2005, VII +1053 pp., 135, $225 hardback (ISBN 1-57958-385-7).     

Edgar Knobloch 《地球物理与天体物理流体动力学》2013,107(6):535-536

We present three-dimensional (3D) solutions of the magnetohydrostatic equations in the co-rotating frame of reference outside a magnetized rigidly rotating cylinder. We make no symmetry assumption for the magnetic field, but to be able to make analytical progress we neglect outflows and specify a particular form for the current density. The magnetohydrostatic equations can then be reduced to a single linear partial differential equation for a pseudo-potential U, from which the magnetic field can be calculated by differentiation. The equation for U can be solved by standard methods. The solutions can also be used to determine the plasma pressure, density and temperature as functions of all three spatial coordinates. Despite the obvious limitations of this approach, it can, for example, be used as a simple tool to create 3D models for the closed field line regions of rotating magnetospheres without rotational symmetry.  相似文献