An interlaboratory comparison of piston-cylinder pressure calibration using the albite-breakdown reaction

The pressure of the reaction albite=jadeite and quartz was measured at 600° C by workers in six geophysical laboratories for the purpose of comparing pressure calibration procedures for the solid-pressure piston-cylinder apparatus. All groups used the same starting mix of crystalline reactant and products and all obtained hydrothermal reversals of the equilibrium. Solid pressure media used included talc, NaCl, boron nitride, pyrophyllite, pyrex glass and crushable ceramic. Various means of calibration were used, including internal standardization by transitions in indicator substances and the piston-in, piston-out bracketing method.There was agreement among all groups—the average preferred value of 16.3 kilobars at 600° C is enclosed by all of the error brackets assigned by the various investigators. This average preferred value is lower by nearly two kilobars than the often-quoted extrapolation of Birch and LeComte's data (1960). It will be important for both petrology and high-pressure technology to test this result in a very high gas pressure apparatus.     

Preliminary study of the redistribution and transformation of HgS from cinnabar mine tailings deposited in Honda Bay, Palawan, Philippines

Mining operations in Palawan, Philippines, resulted in cinnabar (HgS) mine tailings being used to build a 600 m long peninsula in Honda Bay. Samples collected from the peninsula as well as sediments from the surrounding waters had elevated mercury levels as high as 570 ppm. Natural processes are transporting mercury as much as 10 km from the peninsula, mainly in a coastwise direction, and preferentially associated with fine-grained, organic-rich sediments. Depth of penetration into sediments exceeds 10 cm near the source. As the HgS is transported away from the peninsula, it is rapidly altered to more bioavailable forms; 50% conversion occurs within a distance of only 10–40 m.     

Partitioning of rare earth elements between garnet and andesite melt: an autoradiographic study of P-T-X effects

High-pressure equilibrium studies were conducted in piston-cylinder apparatus to determine rare earth element (REE) partitioning between garnet and H₂O-vapor-saturated liquidus, from 20 kbar/980°C to 30 kbar/1060 °C. Ag capsules were employed to eliminate loss of Fe. Partition coefficients (K_D's) were determinined with autoradiographic techniques employing beta-active isotopes of Ce, Sm, and Tm. Major elements in garnet were determined by microprobe analysis. Synthesis and reversal runs of 24 hr or greater duration were used to bracket values of K_D's within analytical uncertainty.The K_D values for all three REE are constant over the radiogenic concentration range of 1 to 350 ppm, suggesting that the high abundance of natural REE in the starting materials may suppress possible deviations from Henry's Law behavior reported in similar autoradiographic studies of synthetic systems with no natural REE. Changes in K_D with increasing pressure and temperature at near-liquidus conditions suggest that the dominant control of K_D is the average size of cations occupying the 8-fold sites in garnet. Specifically, the substitution of 8-fold Ca for Mg and Fe causes an increase in K_D values greater than that attributable to the coincident effects of pressure and temperature. The inverse correlation of increasing K_D with REE ionic radius supports the interpretation that the average size of the 8-fold cation controls the relative variation of K_D among REE.These experimental K_D values produce less relative fractionation in melts between light REE and heavy REE than do previous K_D's derived from data on coexisting natural garnet phenocryst/rockmatrix pairs. Models for the derivation of orogenic andesites from partial melting of subducted basaltic eclogite are qualitatively improved by these new K_D's. Existing calculations of K_D values necessary for the viability of the eclogite fractionation are also in good agreement with these experimental K_D values.     

The effect of manganese on olivine-quartz-orthopyroxene stability

The effect of manganese on the stability of ferrosilite relative to fayalite + quartz has been experimentally determined to assess its importance to orthopyroxene barometry. Reaction reversals in a piston-cylinder apparatus were obtained to within 0.1-kbar intervals indicating instability of Fs₉₅Rh₅ below 10.3, 10.9, 11.4, 12.2, 12.9, 13.7 kbar and Fs₉₀Rh₁₀ below 9.8, 10.4, 10.9, 11.6, 12.4 and 13.2 kbar at 750, 800, 850, 900, 950 and 1000°C, respectively. Each mole % MnSiO₃ extends the pyroxene stability by approximately 0.12 kbar relative to FeSiO₃. Electron microprobe analyses of run products indicate a small preference of Mn for pyroxene over olivine withK_DMn-Fe^opx-oliv = 1.2?1.5, similar to values observed for natural pairs. Mössbauer spectra are consistent with a random distribution of Mn between the M1 and M2 sites in the orthopyroxene. These experimental data allow downward revision of pressure estimates based on the orthopyroxene barometer in areas where Mn is a significant component in orthopyroxene.     

Experimental investigation and application of garnet granulite equilibria

Two mineralogic geobarometers based on the assemblages olivine-plagioclase-garnet and orthopyroxeneplagioclase-garnet-quartz have been calibrated from the reaction (1) fayalite+anorthite?garnet (Gr₁Alm₂). The reaction boundary has been determined to within 0.2 kbar using piston-cylinder apparatus. It is located at 4.7, 5.1, 5.5, 5.8, 6.2, 6.6, and 7.0 kbar at 750, 800, 850, 900, 950, 1,000, and 1,050° C, respectively. Summation of ΔG for reaction (1) and fayalite +quartz?ferrosilite locates to within 0.3 kbar the following model garnet-forming reaction for quartz-saturated granulites: (2) ferrosilite+ anorthite?garnet(Gr₁ Alm₂) + quartz. Geobarometers based on (1) and (2) are widely applicable in granulite terranes and yield precise pressures that are in agreement with other well-calibrated barometers. Pressures of 7–10 kbar are inferred for many granulite terranes requiring the widespread development of 60–70 km thick continental crust by mid-Proterozoic.     

Genetic variation among age-classes of the mangrove Avicennia marina in clean and contaminated sediments

An examination was made of the genetic variation with age in mangrove populations in two estuaries in south-east Australia, one contaminated, the other uncontaminated. Sediment nutrient and metal levels, and isozyme/allozyme complements were measured in three age-classes in four stands in each estuary, to identify site and intergenerational genetic composition, and influences of sediment contamination. Within each river, there were greater genetic distances among the age-classes than among sampling sites. A downstream gradient of genetic distance was found in the uncontaminated river, but not the contaminated one, where genetic distances seemed to reflect site-specific factors, though apparently not the present sediment metal or nutrient levels. It appears that genetic distances in the polluted river may reflect past fluctuations in pollution pressures. In both rivers, genetic distances indicate that the mangroves within one estuary form one population, with 'neighbourhood' differentiation.     

Whole-bird models for the magnetic cleansing of oiled feathers

Iron powder, a promising dry-cleansing agent for oiled feathers where both the contaminant and the cleansing agent may be harvested magnetically, has been tested on the plumage of whole-bird models. The breast and back plumage of Mallard Duck (Anas platyrhynchos) and Little Penguin (Eudyptula minor) carcasses were patch-contaminated with commercial-grade engine oil, three different crude oils, and an oil/seawater emulsion. The plumage was then subjected to a magnetic cleansing protocol. The contaminant removal was assessed gravimetrically and was found to reflect the outcomes for a previously reported in vitro study using feather clusters. Between 92-98% of the contaminants, and effectively all of the cleansing agent, were removed from the feathers.     

Methodological challenges posed in studying an elite in the field

This paper engages with recent debates in geography and associated disciplines that are concerned with the wider analytic issues to be confronted in researching an elite. Drawing on a case study of the construction of a policy position on GMOs and the Environment in Ireland, the methodological challenges encountered researching up the hybrid elite central to this development are interrogated. In particular, emphasis is placed on the politics of time, which becomes central when a new sector is emerging, and meanings and definitions are being constructed.     

Evidence of Strain Partitioning Between the Sierra Madre Fault and the Los Angeles Basin, Southern California from Numerical Models

— Geodetic data indicate that the northern Metropolitan Los Angeles region is shortening at a rate of 4.5–6.0 mm/yr between downtown Los Angeles and the San Gabriel Mountains. If we assume that all of the uplift of the San Gabriel Mountains is due to the major frontal fault system (the Sierra Madre fault) and use reported values for bedrock uplift, slip per event and recurrence intervals to determine the slip rate on the Sierra Madre fault, we obtain slip rates between 0.6–1.27 mm/yr. Using these slip rates, the horizontal shortening attributable to the Sierra Madre fault accounts for only ~33% of the observed shortening across the basin, leaving ~67% of the shortening to be accounted for elsewhere. Herein we present a suite of models that test possible shortening mechanisms to account for this strain deficit. The models incorporate a range of fault geometries and have a layered structure with variable vertical and horizontal rheologies. The models demonstrate how lower-crust rheology and the presence of a low rigidity, anelastically deforming sedimentary basin affects the dissipation of stress imposed on the viscous layers by elastic failure of the faults. We found that viscoelastic models with a single fault, vertically strong crust and a compliant sedimentary basin yield a horizontal velocity profile that best matches the geodetically observed velocity profile across the Los Angeles Basin. Our models also indicate that we are still not accounting for all of the observed deformation. Therefore, more complex models that include both laterally varying rheologies and frictional properties on faults must be considered.