Thermodynamic properties and equation of state of fcc aluminum and bcc iron, derived from a lattice vibrational method

We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure–temperature space. This semi-empirical technique is based on either the Mie–Grüneisen–Debye (MGD) approach or an extension of Kieffer’s model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane’s equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet’s universal and the Birch–Murnaghan equation of state. It appears that the MGD and Mie–Grüneisen–Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between –1 and 0 K/GPa.     

Symplectite formation during decompression induced garnet breakdown in lower crustal mafic granulite xenoliths: mechanisms and rates

The complex microstructure of kelyphitic rims around garnet in lower crustal garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field, Central Pannonian Basin has been studied in order to identify controls on garnet breakdown. Symplectites comprised of a vermicular intergrowth of submicron sized anorthite, orthopyroxene and spinel replace garnet at a sharp reaction front. Based on element distribution maps the transformation of garnet to symplectite is isochemical. Phase diagram calculations indicate that this reaction was induced by a pressure decrease and/or a temperature increase. In site-specific TEM foils prepared by focused ion beam technique and oriented parallel and perpendicular to the reaction front 200 nm wide rods of anorthite and 20 nm wide rods of spinel are identified. The rods are oriented approximately perpendicular to the replacement front and are embedded in an orthopyroxene matrix. The regular spacing of the symplectite phases along the reaction front suggests that their growth is controlled by diffusion. The kinetics of symplectite formation has been modelled based on irreversible thermodynamics. During interaction of the xenolith with the host basalt the microstructure and chemistry of the An–Opx–Spl symplectite was significantly modified and it was partially replaced by an olivine bearing symplectite. In contrast to primary symplectite formation, these processes were metasomatic in nature including addition of sodium, titanium and some trace elements from the basaltic melt and can clearly be discerned from the garnet breakdown. Based on these observations it is inferred that symplectite formation took place within the deep crust during the extension of the Pannonian Basin between 15 and 30 km depth at high temperature (850–1,050°C) prior to the volcanic transport to the surface.     

Iodine Chemistry and its Role in Halogen Activation and Ozone Loss in the Marine Boundary Layer: A Model Study

A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O 2OH, HO2 + O3 OH + 2O2, and OH + O3 HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.     

石英ESR测年信号衰退特征研究进展

电子自旋共振(ESR)测年法是第四纪地质年代学的重要测试方法之一,其测年范围广,特别是对于20万年至百万年尺度的第四纪样品有着重要意义.准确测量古剂量是影响ESR测年法精度和可信度的重要因素之一,而掌握ESR信号衰退特征及机制是获得准确、可信古剂量的重要前提.ESR测年法适用的地质样品种类较多,如热液石英脉、地质断层泥、水系沉积物等,不同样品的ESR信号衰退特征和机制有较大差异.近年来,国内外学者针对不同地质样品中石英ESR信号的衰退特征和机制深入开展了一系列的实验室模拟和野外观测研究,取得了诸多新认识.回顾了近年来在石英ESR信号衰退特征领域取得的进展,特别是水系沉积物石英ESR信号的衰退特征,并展望了这一领域的未来工作重点.     

Determination of bioavailable Fe(III) content in column experiments with the reactive tracer phosphate

Different methods were compared to evaluate the oxidation capacity of ferric iron in column studies. The specific adsorption of the reactive tracer phosphate on the Fe(III) oxide surface was used as an alternative approach to determine the oxidation capacity utilizing the linear correlation between the long-term extent of Fe(III) reduction and the specific surface area of the oxide. Although a low crystalline form of ferric iron (two-line ferrihydrite) was used as electron acceptor and toluene as a carbon source, only 31 and 24% respectively of the total iron was reduced by Geobacter metallireducens in parallel experiments. The results of the phosphate tracer tests were in good agreement with the Fe(III) that was actually reduced and the microbially oxidized toluene. The oxidation capacity of ferric iron is therefore overestimated by the chemical extraction methods, which completely dissolve the ferrihydrite and neglect surface-dependent limitations.     

Detrital,metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ ¹¹B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ ¹¹B ≈ +0.9‰). The varying δ ¹¹B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ ¹¹B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ ¹¹B values (up to +7.7‰) towards the margins of the grains. The δ ¹¹B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.