Raman scattering and X-ray diffraction study of the thermal decomposition of an ettringite-group crystal

 A Raman scattering and X-ray diffraction study of the thermal decomposition of a naturally occurring, ettringite-group crystal is presented. Raman spectra, recorded with increasing temperature, indicate that the thermal decomposition begins at ≈55 °C, accompanied by dehydration of water molecules from the mineral. This is in contrast to previous studies that reported higher temperature breakdown of ettringite. The dehydration is completed by 175 °C and this results in total collapse of the crystalline structure and the material becomes amorphous. The Raman scattering results are supported by X-ray diffraction results obtained at increasing temperatures. Received: 9 July 2001 / Accepted: 14 August 2002     

Ultrasonic measurements of Vp and Qp: relaxation spectrum of complex modulus on basalt melts

Ultrasonic compressional wave velocity V_p and quality factor Q_p have been measured in alkali basalt, olivine basalt and basic andesite melts in the frequency range of 3.4–22 MHz and in the temperature range of 1100–1400°C. Velocity and attenuation of the melts depend on frequency and temperature, showing that there are relaxation mechanisms in the melts. Complex moduli are calculated from the ultrasonic data. The results fit well a complex modulus of Arrhenius temperature dependence with log-normal Gaussian distribution in relaxation times of attenuation. The analysis yields average relaxation time, its activation energy, relaxed modulus, unrelaxed modulus and width of Gaussian distribution in relaxation times. Relaxed modulus is smaller (17.5 GPa) for basic andesite melt of high silica and high alumina contents than for the other two basalt melts (18.1–18.4 GPa). The most probable relaxation times decrease from ～ 3 × 10^?10 s for basic andesite to ～ 10^?11 s for alkali basalt at 1400°C. Activation energies of attenuation, ranging from 270 to 340 kJ mol^?1 in the three melts, are highest in basic andesite. Longitudinal viscosity values and their temperature dependences are also calculated from V_p and Q_p data. The volume viscosity values are estimated from the data using the shear viscosity values. Longitudinal, volume and shear viscosities and their activation energies are highest in the basic andesite melt of the most polymerized structure.     

Temperature dependence of the compressional wave velocity in an anisotropic dunite: Measurements to 500°C at 10 kbar

Measurements of compressional wave velocity V_p were made in a gas apparatus to 500°C at 10 kbar in three cores of an anisotropic dunite specimen from Twin Sisters Mountain. The axial directions of the three chosen cores coincide with the preferred directions and concentration of olivine crystallographic axes (a [100], b [010], andc [001]).Measured (δV_p/δT)p values at 10 kbar in the three cores (−6.7, −5.4 and −6.2 · 10⁻⁴ km/sec · deg, respectively), and the mean value for the dunite (−6.1 · 10⁻⁴ km/sec · deg) are larger than the Voigt-Reuss-Hill values calculated from single-crystal data. This discrepancy is explained by the presence of internal thermal stresses, due to anisotropic expansion of olivine grains, causing grain boundary cracks to widen.It is concluded that high negative values of (δV_p/δT)p for rocks reported in the literature should be carefully evaluated in terms of the formation of new cracks or widening of cracks already present under high pressure-temperature environments.     

Estuarine and coastal connectivity of an estuarine-dependent fishery species,Pomadasys commersonnii (Haemulidae)

Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ～529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.     

Electrical conductivity of ultramafic rocks to 1820 kelvin

Electrical conductivity, σ, of six ultramafic rocks (garnet-bearing peridotites and an eclogite) has been investigated in the temperature range 670–1820 K under known environment. Between 670 and ～1320 K σ increases with 1/T monotonically, first slowly, by 1–1.5 orders of magnitude. Above 1320 K σ increases sharply; an increase of 3–4 orders of magnitude is observed between 1320 and 1670 K. In the same temperature range the σ values for all the six rocks fall within 1.5 orders of magnitude, the lowest conductivity being for a spinel lherzolite. The range of σ values is narrowed at higher temperatures. The differences in σ values above 1470 K may be explained on the basis of varying degrees of partial melting in the rocks. Over the entire range of temperature, the σ values for the ultramafic rocks are lower than those reported for basalts but higher (by 1–2 orders of magnitude) than those for single-crystal olivines.     

Crystal structure and compression of an iron-bearing Phase A to 33 GPa

Fe-bearing dense hydrous magnesium silicate Phase A, Mg_6.85Fe_0.14Si_2.00O₈(OH)₆ has been studied by single-crystal X-ray diffraction at ambient conditions and by high-pressure powder diffraction using synchrotron radiation to 33 GPa. Unit cell parameters at room temperature and pressure from single crystal diffraction are a=7.8678 (4) Å, c=9.5771 (5) Å, and V=513.43 (4) ų. Fitting of the P–V data to a third-order Birch-Murnaghan isothermal equation of state yields V ₀=512.3 (3) ų, K _T,0=102.9 (28) GPa and K′=6.4 (3). Compression is strongly anisotropic with the a-axes, which lie in the plane of the distorted close-packed layers, approximately 26% more compressible than the c-axis, which is normal to the plane. Structure refinement from single-crystal X-ray intensity data reveals expansion of the structure with Fe substitution, mainly by expansion of M-site octahedra. The short Si2–O6 distance becomes nearly 1% shorter with ~2% Fe substitution for Mg, possibly providing additional rigidity in the c-direction over the Mg end member. K _T obtained for the Fe-bearing sample is ~5.5% greater than reported previously for Fe-free Phase A, despite the larger unit cell volume. This study represents a direct comparison of structure and K _T–ρ relations between two compositions of a F-free dense hydrous magnesium silicate (DHMS) phase, and may help to characterize the effect of Fe substitution on the properties of other DHMS phases from studies of the Fe-free end-members.     

Thermal expansion of single-crystal forsterite to 1023 K by Fizeau interferometry

Using a Fizeau interferometry technique, we have measured the coefficients of linear thermal expansion of single-crystal forsterite (Mg₂SiO₄) along three axial directions to 1023 K during heating and cooling cycles. Overall, the present data are consistent in magnitude (within 1 to 2%) with those previously reported but have less scatter. We used the Grüneisen statistical mechanical approach in analzying the data. The least-squares method was applied to evaluate thermal parameters (?, Q ₀, k and a) in two cases. The expansion coefficients in wider temperature ranges were extrapolated by using the parameters of solution 2 (i.e., solution by fixing ? and k). In contrast to earlier findings, our results show that for forsterite the Grüneisen parameter decreases with temperature, implying that it does not behave too differently from fayalite (Fe₂SiO₄) and periclase (MgO).     

Marine Boundary-Layer Variability Over The Indian Ocean During Indoex (1998)

The variability in boundary-layerstructure over the Indian Ocean during a north-eastmonsoon and the factors influencing it areinvestigated. This study was made possible as acomponent of the Indian Ocean Experiment (INDOEX),conducted from February 19 to March 30, 1998. The dataused are, surface-layer mean and turbulencemeasurements of temperature, humidity and wind, andvertical soundings of temperature and humidity.Significant spatio-temporal variability was observedin the boundary-layer structure throughout the cruise.The ITCZ was characterized as the region withstrongest winds and maximum surface turbulent fluxesof momentum and heat. One of the important findingsfrom this study was a strong influence of continentalair masses on the boundary-layer structure in theNorthern Hemisphere, even at a distance of 600 km offthe Indian coast. This was generally evident in theform of an elevated plume of dry continental airbetween altitudes of 1500 m and 2700 m. Advection ofcontinental aerosols in this layer presents potentialfor significant entrainment into shallow clouds inthis region, which eventually feed deeper clouds atthe ITCZ. This finding provides an explanation foranomalous higher aerosol concentrations found duringprevious studies. The structure of the marineboundary layer was influenced by various factors suchas proximity to land, an anomalous warm pool in theocean and the ITCZ. In the southern hemisphere, theboundary-layer height was primarily governed bysurface-layer sensible heat flux and was found to behighest in the vicinity of the ITCZ. North of theequator it was strongly influenced by land-air-seainteractions. In addition to this synoptic modulation,there was also a significant diurnal variability inthe boundary-layer height.     

豫西沙沟脉状Ag-Pb-Zn矿床地质特征和成矿流体研究

豫西沙沟薄脉状Ag-Pb-Zn硫化物矿床位于华北陆块南缘熊耳山地区,主要由多金属硫化物-石英-碳酸盐脉型和石英-碳酸盐-绢云母-多金属硫化物蚀变岩型两种矿化类型组成。主要矿脉的矿物共生序列可以分为成矿前的石英-黄铁矿阶段(Ⅰ)、闪锌矿-石英-方铅矿-少量银矿物阶段(Ⅱ1)、方铅矿-石英-闪锌矿-含铁白云石-银矿物阶段(Ⅱ2)和成矿后的方解石-(石英)阶段(Ⅲ)。对不同阶段的成矿流体研究表明,石英-黄铁矿阶段(Ⅰ)中的含氯化钠子晶三相(LVH)包裹体(Ⅰ1)可能是直接从饱和水的结晶岩浆熔体中出溶形成或是由岩浆流体的减压沸腾形成,显示该区很可能存在岩浆流体端元。多金属硫化物阶段(Ⅱ1Ⅱ2)捕获富液相包裹体(LV型)和个别CO2包裹体(C型),这两个阶段流体包裹体反映了主成矿阶段流体的基本特征,结合包裹体气相和液相成分色谱分析以及包裹体初融温度,认为成矿流体应该为中-低温低盐度含CO2的H2O-NaCl体系。其中,阶段(Ⅱ2)的均一温度(145～288℃,平均为194℃)比阶段(Ⅱ1)的均一温度(185～357℃,平均240℃)低46℃;同时,阶段(Ⅱ2)的盐度(1.91%～10.86%,平均6.38%)较阶段(Ⅱ1)盐度(4.65%～10.11%,平均7.77%)略低。对这一温度和盐度的总体下降趋势的合理解释是大气水的逐渐混入。多金属硫化物阶段(Ⅱ1Ⅱ2)之后的方解石-(石英)阶段普遍为富液相包裹体(LV型),该阶段显著降低的温度(129～208℃,平均165℃)和盐度(1.40%～4.03%,平均2.50%),进一步佐证大气水的不断混入。而且,流体混合可能在引起矿石矿物从热液中沉淀方面起到重要作用。