Improved salt imaging in a basin context by high resolution potential field data: Nordkapp Basin,Barents Sea     

Christopher Stadtler  Christine Fichler  Ketil Hokstad  Eva Andrea Myrlund  Susann Wienecke  Bente Fotland 《Geophysical Prospecting》2014,62(3):615-630

The seismic imaging of salt diapirs in the Nordkapp Basin gave rise to considerable problems in defining their shape and volume. Independent information was added by integrating the interpretation with high resolution gravity and magnetic data. We developed a novel, iterative workflow, separated into sub‐categories: sediments, salt structures, basement and Moho. Distinctions between the sources of the anomalies from different depths was achieved by utilizing the different decay characteristics of gravity, gravity gradiometry and high resolution magnetic anomalies. The workflow was applied to the southern part of the Nordkapp Basin. It started with the sedimentary model derived from seismics, populated with measured densities and magnetic susceptibilities and a starting model for the base salt. The residual after the removal of this model was interpreted in terms of a crustal model, including flexural isostatic calculations for the Moho with the sedimentary load. The residual after the removal of crustal and early sedimentary model was used to tune the salt model. As these major and minor modelling steps depend on each other, an iterative process was applied to stepwise improve the density and magnetic susceptibility model. The first vertical gradient of gravity and the magnetic field were found to give most information about the cap rock of the diapirs. The improvement in salt imaging, integrated with results from controlled‐source electromagnetic and magneto‐telluric modelling is shown for the salt diapir Uranus, where a well, terminated in the salt, constrains the minimum of the depth to base salt.  相似文献   

The two polymorphs of TlPbSbS3 and the structural relations of phases in the system TlSbS2-PbS     

Dr. T. Balić Zunić  Prof Dr. K. Bente 《Mineralogy and Petrology》1995,53(4):265-276

Summary The synthetic TlPbSbS₃ represents a rare example of a sulphosalt with statistical distribution of Tl, Pb and Sb in the structure. Within the TlSbS₂-PbS system, TlPbSbS₃ is the end member of the solid solution series with TlSbS₂, but no solubility with PbS is detected. The high temperature-TlPbSbS₃ is orthorhombic and inverts at about 620 K to the low-temperature phase. The low-temperature modification of TlPbSbS₃ was structurally investigated by X-ray powder diffraction and by the Rietveld analysis of the data. The structure is monoclinic, with a = 4.1707(4) Å, b = 4.2856(4) Å, c = 12.157(1) Å, = 105.49(1)°, space group P2₁/c. Like in the high-temperature form, there is a cation disorder over the equivalent positions in the structure. The interatomic distances of (Tl, Ph, Sb) to S are 2.71, 2.72, 2.88, 3.15, 3.29, 3.51 (Å). There is a close similarity between the TlPbSbS₃ polymorphs and the and forms of SnS, as regards the atomic coordinations and the general structure types and the same type of phase transformation is supposed for both cases. The small differences in the structure type and symmetry, between the low temperature forms of SnS and TlPbSbS₃, result probably from stronger metal-metal interactions in the latter. A substitution-derivative relation to SnS type is established owing to the strong structural effect of the lone electron pairs of Tl and Sb. The substitution of Ag for Tl and Bi for Sb in ABCS₃ type compounds diminishes this effect and PbS type structures are produced.

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Die zwei Polymorphen von TlPbSbS₃ und die Strukturellen Beziehungen von Phasen in System TlSbS₂-PbS

Zusammenfassung Die synthetische Phase TlPbSbS₃ ist ein seltenes Beispiel von einem Sulfosalz mit der statistischen Verteilung von TI, Pb und Sb in der Struktur. In der TlSbS2-PbS Phasensystem, ist TlPbSbS₃ das Endmitglied der Mischkristallreihe, die sich im Richtung TlSbS₂ ausstreckt. Weitere Ausdehnung der Mischkristallreihe in der Richtung SbS konnte nicht bewiesen werden. Die Hochtemperatur-TlPbSbS₃ ist rhombisch und wird beim 620 K in die Tieftemperatur Modifikation umgewandelt. Die Tieftemperaturphase ist mit der Röntgenpulverdiffraktion und Rietveld Methode strukturell untersucht worden. Die ist monoklin, mit den Gitterkonstanten: a = 4.1707(4) Å, b = 4.2856(4) Å, c = 12.157(1) Å, = 105.49(1)°, Raumgruppe P2₁/c. Die statistische Verteilung von Kationen ist auch hier vorhanden. Die zwischenatomare Abstande (Tl, Pb, Sb)-S sind: 2.71, 2.72, 2.88, 3.14, 3.28, 3.51 (Å). Es besteht eine enge Verwandschaft zwischen den polymorphen Modifikationen von TlPbSbS₃ und den und Polymorphen von SnS, was die atomare Koordinationen und den generellen Strukturtypus betrifft, wobei ein ähnlicher Mechanismus der Phasenumwandlung für die beiden Fälle vermutet werden könnte. Die Differenzen in der Struktur und Symmetrie zwischen der Tieftemperaturmodifikationen von SnS und TlPbSbS₃ sind wahrscheinlich durch die bedeutende Metall-Metall Wirkungen in der zweiten verursacht. Die Phase TlPbSbS₃ ist ein substitution-derivative von der SnS Struktur, was durch die starke lone-electron-pair Aktivität von Kationen zu erklären ist. Die Ersetzung von Tl durch Ag und Sb durch Bi vermindert diese Aktivität und die entstandenen Strukturen sind in dem Fall dem PbS-Typus verwandt.

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With 3 Figures  相似文献   

Crystal chemistry of Fe-containing sphalerites   总被引：2，自引：0，他引：2  

P. Lepetit  K. Bente  T. Doering  S. Luckhaus 《Physics and Chemistry of Minerals》2003,30(4):185-191

 Cell dimensions and solvus properties of Fe-containing sphalerites, depending on temperature and sulfur fugacity, were investigated using equilibrated powdered materials synthesized from elements and binary sulfides under vacuum. The Fe solvus in sphalerite, determined by optical microscopy and microprobe analysis, are directly correlated with increasing temperature and decreasing sulfur fugacity controlled by solid-state buffers. The increase of lattice parameters with Fe correlates with an increase of FeS independent of sulfur fugacity up to 10 mol% FeS within ZnS. Above about 10 mol% the lattice parameters are strongly depending on the sulfur fugacity controlled Fe³⁺/Fe²⁺ ratios. The Fe³⁺/Fe²⁺ ratios determined by Moessbauer spectroscopy and involving metal vacancies depend on the sulfur fugacity. The critical Fe²⁺ content determined by experimental simulations as well as the minimal Fe³⁺/ Fe²⁺ ratios agree with the required minimal Fe content for CuFeS₂-DIS in sphalerite. The critical Fe²⁺ content also agrees with the change of Moessbauer signal from a singlet to a doublet for Fe²⁺ containing sphalerite. Pyrrhotite exsolutions in sphalerite caused by higher sulfur fugacity show orientationally intergrown with the sphalerite matrix. Density data calculated from lattice parameters and composition are compared with experimental density measurements. Received: 25 April 2001 / Accepted: 14 February 2003  相似文献