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361.
Diego Bernini Michael Wiedenbeck David Dolejš Hans Keppler 《Contributions to Mineralogy and Petrology》2013,165(1):117-128
We have performed phase equilibrium experiments in the system forsterite–enstatite–pyrope-H2O with MgCl2 or MgF2 at 1,100 °C and 2.6 GPa to constrain the solubility of halogens in the peridotite mineral assemblage and the fluid–mineral partition coefficients. The chlorine solubility in forsterite, enstatite and in pyrope is very low, 2.1–3.9 and 4.0–11.4 ppm, respectively, and it is independent of the fluid salinity (0.3–30 wt% Cl), suggesting that some intrinsic saturation limit in the crystal is reached already at very low chlorine concentrations. Chlorine is therefore exceedingly incompatible in upper-mantle minerals. The fluorine solubility is 170–336 ppm in enstatite and 510–1,110 ppm in pyrope, again independent of fluid salinity. Forsterite dissolves 1,750–1,900 ppm up to a fluid salinity of 1.6 wt% F. At higher fluorine contents in the system, forsterite is replaced by the minerals of the humite group. The lower solubility of chlorine by three orders of magnitude when compared to fluorine is consistent with increasing lattice strain. Fluid–mineral partition coefficients are 100–102 for fluorine and 103–105 for chlorine. Since the latter values are orders of magnitude higher than those for hydroxyl partitioning, fluid flow from the subducting slab through the mantle wedge will lead to an efficient sequestration of H2O into the nominally anhydrous minerals in the wedge, whereas chlorine becomes enriched in the residual fluid. Simple mass balance calculations reveal that rock–fluid ratios of up to >3,000 are required to produce the elevated Cl/H2O ratios observed in some primitive arc magmas. Accordingly, fluid flow from the subducted slab into the zone of melting in the mantle wedge does not only occur rapidly in narrow channels, but at least in some subduction zones, fluid pervasively infiltrates the mantle peridotite and interacts with a large volume of the mantle wedge. Together with the Cl/H2O ratios of primitive arc magmas, our data therefore constrain the fluid flow regime below volcanic arcs. 相似文献
362.
Daniele Morgavi Diego Perugini Cristina P. De Campos Werner Ertel-Ingrisch Donald B. Dingwell 《Contributions to Mineralogy and Petrology》2013,166(2):615-638
We present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts. The mixing process is triggered by a recently developed apparatus that generates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The study of the interplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing experiments under controlled chaotic dynamic conditions. The variation of major and trace elements is studied in detail by electron microprobe and Laser Ablation ICP-MS. The mobility of each element during mixing is estimated by calculating the decrease in the concentration variance in time. Both major and trace element variances decay exponentially, with the value of exponent of the exponential function quantifying the element mobility. Our results confirm and quantify how different chemical elements homogenize in the melt at differing rates. The differential mobility of elements in the mixing system is considered to be responsible for the highly variable degree of correlation (linear, nonlinear, or scattered) of chemical elements in many published inter-elemental plots. Elements with similar mobility tend to be linearly correlated, whereas, as the difference in mobility increases, the plots become progressively more nonlinear and/or scattered. The results from this study indicate that the decay of concentration variance is in fact a robust tool for obtaining new insights into chemical exchanges during mixing of silicate melts. Concentration variance is (in a single measure) an expression of the influence of all possible factors (e.g., viscosity, composition, and fluid dynamic regime) controlling the mobility of chemical elements and thus can be an additional petrologic tool to address the great complexity characterizing magma mixing processes. 相似文献
363.
G. Diego Gatta Ilaria Adamo Martin Meven Erica Lambruschi 《Physics and Chemistry of Minerals》2012,39(10):829-840
The chemical composition and the crystal structure of pezzottaite [ideal composition Cs(Be2Li)Al2Si6O18; space group: ${\it{R}} \overline{\text{3}} $ c, a?=?15.9615(6) ?, c?=?27.8568(9) ?] from the type locality in Ambatovita (central Madagascar) were investigated by electron microprobe analysis in wavelength dispersive mode, thermo-gravimetric analysis, Fourier-transform infrared spectroscopy, single-crystal X-ray (at 298?K) and neutron (at 2.3?K) diffraction. The average chemical formula of the sample of pezzottaite resulted Cs1,Cs2(Cs0.565Rb0.027K0.017)Σ0.600 Na1,Na2(Na0.101Ca0.024)Σ0.125Be2.078Li0.922 Al1,Al2(Mg0.002Mn0.002Fe0.003Al1.978)Σ1.985 Si1,Si2,Si3(Al0.056Si5.944)Σ6O18·0.27H2O. The (unpolarized) IR spectrum over the region 3,800–600?cm?1 was collected and a comparison with the absorption bands found in beryl carried out. In particular, two-weak absorption bands ascribable to the fundamental H2O stretching vibrations (i.e. 3,591 and 3,545?cm?1) were observed, despite the mineral being nominally anhydrous. The X-ray and neutron structure refinements showed: (a) a non-significant presence of aluminium, beryllium or lithium at the Si1, Si2 and Si3 sites, (b) the absence (at a significant level) of lithium at the octahedral Al1, Al2 and Al3 sites and (c) a partial lithium/beryllium disordering between tetrahedral Be and Li sites. 相似文献
364.
365.
Andrea Tiengo Paolo Esposito Sandro Mereghetti Lara Sidoli Diego Götz Marco Feroci Roberto Turolla Silvia Zane Gian Luca Israel Luigi Stella Peter Woods 《Astrophysics and Space Science》2007,308(1-4):33-37
We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 105?s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period. 相似文献
366.
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368.
Ariel G. Sánchez Nelson D. Padilla Diego G. Lambas † 《Monthly notices of the Royal Astronomical Society》2002,337(1):161-171
We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation σ( M ) using the expression for the mass function in the Press & Schechter, Sheth, Mo & Tormen and Jenkins et al. formalisms. We apply different techniques to recover the adimensional power spectrum Δ2 ( k ) from σ( M ) namely the k eff approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the τCDM and ΛCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (FKP) method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k . This estimate is comparable to, or even better behaved than, the FKP solution.
The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution. 相似文献
The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution. 相似文献
369.
370.