Titanium in phengite: a geobarometer for high temperature eclogites   总被引：1，自引：1，他引：0  

Estelle Auzanneau  M. W. Schmidt  D. Vielzeuf  J. A. D Connolly 《Contributions to Mineralogy and Petrology》2010,159(1):1-24

Phengite chemistry has been investigated in experiments on a natural SiO₂–TiO₂-saturated greywacke and a natural SiO₂–TiO₂–Al₂SiO₅-saturated pelite, at 1.5–8.0 GPa and 800–1,050°C. High Ti-contents (0.3–3.7 wt %), Ti-enrichment with temperature, and a strong inverse correlation of Ti-content with pressure are the important features of both experimental series. The changes in composition with pressure result from the Tschermak substitution (Si + R²⁺ = Al^IV + Al^VI) coupled with the substitution: Al^VI + Si = Ti + Al^IV. The latter exchange is best described using the end-member Ti-phengite (KMgTi[Si₃Al]O₁₀(OH)₂, TiP). In the rutile-quartz/coesite saturated experiments, the aluminoceladonite component increases with pressure while the muscovite, paragonite and Ti-phengite components decrease. A thermodynamic model combining data obtained in this and previous experimental studies are derived to use the equilibrium MgCel + Rt = TiP + Cs/Qz as a thermobarometer in felsic and basic rocks. Phengite, rutile and quartz/coesite are common phases in HT-(U)HP metamorphic rocks, and are often preserved from regression by entrapment in zircon or garnet, thus providing an opportunity to determine the T–P conditions of crystallization of these rocks. Two applications on natural examples (Sulu belt and Kokchetav massif) are presented and discussed. This study demonstrates that Ti is a significant constituent of phengites that could have significant effects on phase relationships and melting rates with decreasing P or increasing T in the continental crust.  相似文献   

Bioturbation, short-lived radioisotopes, and the tracer-dependence of biodiffusion coefficients     

Pascal Lecroart  Olivier Maire  Sabine Schmidt  Pierre Anschutz 《Geochimica et cosmochimica acta》2010,74(21):6049-6063

Bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity. It is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes. In models, bioturbation is usually treated as a diffusive process where the biodiffusion coefficient (D_b) characterizes the biological mixing intensity. Biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle-bound radioisotopes. One peculiar observation is tracer-dependence: D_b values from short-lived tracers tend to be larger than those obtained from long-lived tracers from the same site. Recent theoretical work, based on random walk theory and Lattice Automaton Bioturbation Simulations (LABS), has suggested that this tracer-dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short-lived radioisotopes. Here we have compiled a global dataset of D_b values obtained from different radiotracers to assess tracer-dependence from a data perspective. Tracer-dependence is significant in low-mixing environments like slope and deep-sea sediments, but is not present in intensely mixed coastal areas. Tracer-dependence is absent when the number of mixing events is larger than 20, or the potential length scale is greater than 0.5 cm. Roughly this comes down to tracer-derived D_b values greater than 2 cm² yr⁻¹. This condition is met for 68%, 50%, and 8% of published D_b values obtained from coastal, continental slope, and abyssal environments, respectively. These results show that short-lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation.  相似文献   

Influence of water flux and redox conditions on chlorobenzene concentrations in a contaminated streambed     

Christian Schmidt  Marion Martienssen  Edda Kalbus 《水文研究》2011,25(2):234-245

Significant natural attenuation may occur on the passage of groundwater plumes through streambed sediments because of the transition from anaerobic to aerobic conditions and an increased microbial activity. Varying directions and magnitudes of water flow in the streambed may enhance or inhibit the supply of oxygen to the streambed and thus influence the redox zoning. In a field study at a small stream in the industrial area of Bitterfeld‐Wolfen, we observed the variability of hydraulic gradients, streambed temperatures, redox conditions and monochlorobenzene (MCB) concentrations in the streambed over the course of 5 months. During the observation period, the hydrologic conditions changed from losing to gaining. Accordingly, the temperature‐derived water fluxes changed from recharge to discharge. Redox conditions were highly variable between ? 170 and 368 mV in the shallow streambed at a depth of 0·1 m below the streambed surface. Deeper in the streambed, at depths of 0·3 m and 0·5 m, the redox conditions were more stable between ? 198 and ? 81 mV and comparable to those typically found in the aquifer. MCB concentrations in the streambed at 0·3 and 0·5 m depth increased with increasing upward water flux. The MCB concentrations in the shallow streambed at 0·1 m depth appeared to be independent of the hydrologic conditions suggesting that degradation of MCB may have occured. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Pressure,temperature and fluid composition variation of the mineralising system at the Kanmantoo Cu-Au deposit: Combining fluid inclusion analysis with Ti in quartz thermometry     

D. Focke  A. Schmidt Mumm  A. Tedesco  T. Seifert  R. Bradey 《Journal of Geochemical Exploration》2009

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Reply to discussion of “Is there a close spatial relationship between faults and plutons?”     

S. R. Paterson  K. L. Schmidt 《Journal of Structural Geology》2001,23(12)

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International Association of Geomorphologists Newsletter No. 18 (3/2001)     

Paul Williams  Selma Simes De Castro  Janet Hooke  Wang Ying  Vít Vilímek  Karl‐Heinz Schmidt  Anto Raukas  Tsuguo Sunamura  Algimantas Cesnulevicios  Irasema Alcntara‐Ayala  James P. Terry  Milos Stankoviansky  Carol P. Harden 《地球表面变化过程与地形》2001,26(12):1353-1360

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Spatial transport and spectral transfer of solar wind turbulence composed of Alfvén waves and convective structures II: numerical results     

J. M. Schmidt 《Annales Geophysicae》1995,13(5):475-493

This work follows the paper titled “Spatial transport and spectral transfer of solar wind turbulence composed of Alfvén waves and convective structures I: The theoretical model”, and deals with the detailed physics and numerical solution of a two-component solar wind model, consisting of small-scale Alfvén waves and convected structures. In particular, we present numerical results which qualitatively reflect many of the observed features of the radial and spectral evolution of the turbulent energies, the residual energy, the cross-helicity and Alfvén-ratio in high-speed solar wind streams. These features are the following: the formation of a characteristic “inclined eye”, which evolves between the energy spectra displayed over the frequency axis and tends to close in the radial development of the spectra, a steepening of all spectra towards Kolmogorov-like f^-5/3 spectra, the development of the normalized cross-helicity towards a constant not much less than one and the formation of a “trough” form of the Alfvén ratio with a z-shaped left boundary, By weighting special terms in the equations differently, we can also cast light on the physical role of parametric conversion model terms, wave-structure scattering model terms, nonlinear terms, spherical expansion terms and their effects on the radial evolution of turbulent energies in high-speed solar wind streams.  相似文献   

The distribution of acetaldehyde in the lower troposphere during TROPOZ II     

D. W. Arlander  D. Brüning  U. Schmidt  D. H. Ehhalt 《Journal of Atmospheric Chemistry》1995,22(3):243-249

A series of 72 measurements of the acetaldehyde (CH₃CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurements are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH₃CHO mixing ratio with increasing altitude and indicate higher CH₃CHO concentrations in the Northern Hemisphere — in general agreement with a model-derived average CH₃CHO distribution. Deviations of the observed CH₃CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios.  相似文献   

Über die Ursache von Rissen in der Eiskappe des nördlichen Polarmeeres     

Prof. Dr.-Ing. Ernst Schmidt 《Meteorology and Atmospheric Physics》1969,18(3-4):391-394

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Heavy metal distribution in different compartments of the northern North Sea and adjacent areas     

Dr. Michael Haarich  Wolfgang Kienz  Dr. Michael Krause  Dr. Gerd-Peter Zauke  Diether Schmidt 《Ocean Dynamics》1993,45(5):313-336

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