The Temperature and Pressure Dependence of Nickel Partitioning between Olivine and Silicate Melt

We measured Ni partitioning between olivine and melt, D^(ol/liq)_(Ni), in experiments on mid-ocean ridge basalt (MORB) encapsulated in olivine at pressures from 1 atm to 3·0 GPa and temperatures from 1400 to 1550°C. We present a series of experiments where the temperature (T) at each pressure (P) was selected so that the liquid composition remained approximately constant over the entire P–T range. This approach allowed us to investigate the effects of T and P on D^(ol/liq)_(Ni), independent of substantial changes in liquid composition. Our experiments show that for a liquid with ∼18 wt% MgO, D^(ol/liq)_(Ni) decreases from 5·0 to 3·8 as the temperature increases from 1400 to 1550°C. Fitting our experimental results and literature data to thermodynamic expressions for D^(ol/liq)_(Ni) as a function of both temperature and liquid composition shows that the small variations in liquid composition in our experiments account for little of the observed variation of D^(ol/liq)_(Ni). Because the changes in volume and heat capacity of the exchange reaction MgSi_(0-5)O^(ol)_2 + D^(ol/liq)_(Ni) ↔ NiSi_(0-5)O^(ol)_2 + MgO^(liq) are small, D^(molar)_(Ni), the Ni partition coefficient on a molar basis, is well described by In(D^(molar)_(Ni))=-^(Δ_rHo_(T_(ref)),P_(ref)/_(RT) + ^Δ_rSo_(T_(ref),P_(ref))/_R - In (X^(liq)_(MgO)/X^(ol)_(MgSi)_(0-5)O_2) with Δ_rH^o_T_(ref),_P_(ref)/_R = 4375 K and Δ_rSo_T_(ref),_P_(ref)/_R = –2·023 for our data (Δ_rH^o_T_(ref),_P_(ref)/_R = 4338 K and Δ_rSo_T_(ref),_P_(ref)/_R = –1·956 for our experiments combined with a compilation of literature data). This expression is easy to use and applicable to a wide range of pressures, temperatures, and phase compositions. Based on our results and data from the literature, the temperature dependence of D^(ol/liq)_(Ni) leads to the prediction that when a deep partial melt from a peridotitic mantle source is brought to low pressure and cooled, the first Mg-rich olivines to crystallize can have significantly higher NiO contents than those in the residual source from which the melt was extracted. This enrichment in Ni is driven by the difference between the temperature of low-pressure crystallization and the temperature of melt extraction from the residue. The average observed enrichment of Ni in forsteritic olivine phenocrysts from Hawaii—relative to the typical olivines from mantle peridotites—is consistent with a simple scenario of high-temperature partial melting of an olivine-bearing source at the base of the lithosphere followed by low-temperature crystallization of olivine. The most extreme enrichments of Ni in Hawaiian olivine phenocrysts and the lower Ni contents of some olivines can also be explained by the known variability of Ni contents of olivines from mantle peridotites via the same simple scenario. Although we cannot rule out alternative hypotheses for producing the high-Ni olivines observed in Hawaii and elsewhere, these processes or materials are unnecessary to account for NiO enrichments in olivine. The absolute temperature, in addition to the difference between the temperature of melt segregation from the residue and the temperature of low-pressure crystallization, is a significant factor in determining the degree of Ni enrichment in olivine phenocrysts relative to the olivines in the mantle source. The moderate Ni enrichment observed in most komatiitic olivines compared with those of Hawaii may result from the higher absolute temperatures required to generate MgO-rich komatiitic melts. Observed NiO enrichments in early crystallizing komatiitic olivine are consistent with their high temperatures of crystallization and with a deep origin for the komatiite parental melts

Fe-Mg Partitioning between Olivine and High-magnesian Melts and the Nature of Hawaiian Parental Liquids

We conducted 1 atm experiments on a synthetic Hawaiian picrite at fO_2 values ranging from the quartz–fayalite–magnetite (QFM) buffer to air and temperatures ranging from 1302 to 1600°C. Along the QFM buffer, olivine is the liquidus phase at ~1540°C and small amounts of spinel (< 0·2 wt %) are present in experiments conducted at and below 1350°C. The olivine becomes progressively more ferrous with decreasing temperature [Fo_(92·3) to Fo_(87·3), where Fo = 100 × Mg/(Mg + Fe), atomic]; compositions of coexisting liquids reflect the mode and composition of the olivine with concentrations of SiO_2, TiO_2, Al_(2)O_3, and CaO increasing monotonically with decreasing temperature, those of NiO and MgO decreasing, and FeO^* (all Fe as FeO) remaining roughly constant. An empirical relationship based on our data, T(°C) = 19·2 × (MgO in liquid, wt %) + 1048, provides a semi-quantitative geothermometer applicable to a range of Hawaiian magma compositions. The olivine–liquid exchange coefficient, K_(D,Fe^(2+)-Mg) = (FeO/MgO)^(ol)/(FeO/MgO)^(liq), is 0·345 ± 0·009 (1σ ) for our 11 experiments. A literature database of 446 1 atm experiments conducted within 0·25 log units of the QFM buffer (QFM ± 0·25) yields a median K_(D,Fe^(2+)-Mg) of 0·34; K_(D,Fe^(2+)-Mg) values from single experiments range from 0·41 to 0·13 and are correlated with SiO_2 and alkalis in the liquid, as well as the forsterite (Fo) content of the olivine. For 78 experiments with broadly tholeiitic liquid compositions (46–52 wt % SiO_2 and ≤ 3 wt % Na_(2)O + K_(2)O) coexisting with Fo_(92–80) olivines, and run near QFM (QFM ± 0·25), K_(D,Fe^(2+)-Mg) is approximately independent of composition with a median value of 0·340 ± 0·012 (error is the mean absolute deviation of the 78 olivine–glass pairs from the database that meet these compositional criteria), a value close to the mean value of 0·343 ± 0·008 from our QFM experiments. Thus, over the composition range encompassed by Hawaiian tholeiitic lavas and their parental melts, K_(D,Fe^(2+)-Mg) ~ 0·34 and, given the redox conditions and a Fo content for the most magnesian olivine phenocrysts, a parental melt composition can be reconstructed. The calculated compositions of the parental melts are sensitive to the input parameters, decreasing by ~1 wt % MgO for every log unit increase in the selected fO_2, every 0·5 decrease in the Fo-number of the target olivine, and every 0·015 decrease in K_(D,Fe^(2+)-Mg). For plausible ranges in redox conditions and Fo-number of the most MgO-rich olivine phenocrysts, the parental liquids for Hawaiian tholeiites are highly magnesian, in the range of 19–21 wt % MgO for Kilauea, Mauna Loa and Mauna Kea

Confidentiality and public protection: ethical dilemmas in qualitative research with adult male sex offenders

This paper considers the ethical tensions present when engaging in in-depth interviews with convicted sex offenders. Many of the issues described below are similar to those found in other sensitive areas of research. However, confidentiality and public protection are matters that require detailed consideration when the desire to know more about men who have committed serious and harmful offences is set against the possibility of a researcher not disclosing previously unknown sensitive information that relates to the risk of someone being harmed.</p

Are codes of ethics promoting religious literacy for social work practice?

As codes of ethics play at least a symbolic, if not educational, role in highlighting and informing professional priorities, 16 codes of ethics for social work practice were examined for references to religion and belief and analysed against the four domains of Dinham’s religious literacy framework. Although religion and belief are mentioned in all but two of the documents, approximately half the surveyed codes only mention religion and belief in respect of either knowledge or skills. Some recognise the need for social workers to be aware of their own biases, but very few recognise the need to explain what is meant by religion and belief, despite these terms being in flux. While codes of ethics can contribute to the development of religious literacy among social workers, this requires social workers who already have some religious literacy to actively participate when codes of ethics are being revised

Effects of pH_2O, pH_2 and fO_2 on the diffusion of h-bearing species in lunar basaltic liquid and an iron-free basaltic analog at 1 atm

We have experimentally determined the diffusivity of water in a representative lunar basaltic liquid composition (LG) and in an iron-free analog of a basaltic liquid (AD) at the low water concentrations and low oxygen fugacities (fO_2) relevant to the eruption of lunar basalts. Experiments were conducted at 1 atm and 1350 °C over a range of pH_2/pH_2O from near zero to ∼10 and a range in fO_2 spanning ∼9 orders of magnitude (from 2.2 log units below the iron-wüstite buffer, IW–2.2, to IW+6.7). The water concentrations measured in our quenched experimental glasses by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) vary from a few ppm to ∼430 ppm. Water concentration gradients in the majority of our AD experiments are well described by models in which the diffusivity of water (D*_(water)) has a constant value of ∼2×10^(–10) m^2/s, while our LG results indicate that D*_(water) in LG melt has a constant value of ∼6×10^(–10) m^2/s under the conditions of our experiments. Water concentration gradients in hydration and dehydration experiments that were run simultaneously in H_2/CO_2 gas mixtures are well described by the same D*_(water), and water concentrations measured near the melt-vapor interfaces of these experiment pairs are approximately the same. These observations strongly support an equilibrium boundary condition for our experiments containing >70 ppm H_2O. However, dehydration experiments into nominally anhydrous CO_2, N_2, and CO/CO_2 gas mixtures leave some scope for the importance of kinetics during dehydration of melts containing less than a few 10’s of ppm H_2O. Comparison of our results with the modified speciation model (Ni et al., 2013) in which both molecular water and hydroxyl are allowed to diffuse suggests that we have resolved the diffusivity of hydroxyl (D_(OH)) in AD and LG melts. Our results support a positive correlation between D_(OH) and melt depolymerization. Best-fit values of D*_(water) for our LG experiments vary within a factor of ∼2 over a range of pH_2/pH_2O from 0.007 to 9.7 and a range of logf O_2 from IW–2.2 to IW+4.9. The relative insensitivity of our best-fit values of D*_(water) to variations in pH_2 suggests that H_2 diffusion did not control the rate of degassing of H-bearing species from the lunar glasses of Saal et al. (2008); however, we cannot rule out a role for molecular H2 diffusion under lower-temperature and/or higher-pressure conditions than explored in our experiments. The value of D*_(water) chosen by Saal et al. (2008) for modeling the diffusive degassing of the lunar volcanic glasses is within a factor of ∼2 of our measured value in LG melt at 1350 °C. By coupling our LG results at 1350 °C with an activation energy of 220 kJ/mol (Zhang et al. 2017), we obtain the following Arrhenius relationship, which can be used to model syneruptive diffusive water loss from lunar melt beads: D*_(water)(m^2/s) = 7.2×10^(-3)exp(-2.6×10^4/T(K))

Assessment and treatment of distorted schemas in sexual offenders

The aim of this review is to examine the literature related to the assessment and treatment of sex offenders’ distorted schemas. Where appropriate, the review draws upon current insights from the field of social cognition to aid in the critical evaluation of the findings. First, the review considers the various different methodologies for assessing distorted schemas, discussing their strengths and limitations. Second, the review examines the work related to the treatment of sex offenders’ schemas. Suggestions for future research, and the implications for clinical practice, are highlighted in the article

The Las Campanas Infrared Survey. III. The H-band Imaging Survey and the Near-Infrared and Optical Photometric Catalogs

(Abridged) The Las Campanas Infrared Survey, based on broad-band optical and near-infrared photometry, is designed to robustly identify a statistically significant and representative sample of evolved galaxies at redshifts z>1. We have completed an H-band imaging survey over 1.1 square degrees of sky in six separate fields. The average 5 sigma detection limit in a four arcsecond diameter aperture is H ~ 20. Here we describe the design of the survey, the observation strategies, data reduction techniques, and object identification procedures. We present sample near-infrared and optical photometric catalogs for objects identified in two survey fields. We perform object detection in all bandpasses and identify ~ 54,000 galaxies over 1,408 square arcminutes of sky in the two fields. Of these galaxies, ~ 14,000 are detected in the H-band and ~ 2,000 have the colors of evolved galaxies, I - H >3, at z > 1. We find that (1) the differential number counts N(m) for the H-band detected objects has a slope of 0.44 at H 19. In addition, we find that (2) the differential number counts for the H detected red objects has a slope of 0.85 at H 20, with a mean surface density ~ 3,000 degree^{-2} mag^{-1} at H=20. Finally, we find that (3) galaxies with red optical to near-IR colors (I-H > 3) constitute ~ 20% of the H detected galaxies at H ~ 21, but only 2% at H = 19. We show that red galaxies are strongly clustered, which results in a strong field to field variation in their surface density. Comparisons of observations and predictions based on various formation scenarios indicate that these red galaxies are consistent with mildly evolving early-type galaxies at z ~ 1, although with a significant amount of on-going star formation as indicated by the large scatter in their V-I colors.Comment: 48 pages, 13 figures, accepted for publication in the Astrophysical Journa

XANES and Mg isotopic analyses of spinels in Ca-Al-rich inclusions: Evidence for formation under oxidizing conditions

Ti valence measurements in MgAl_2O_4 spinel from calcium-aluminum-rich inclusions (CAIs) by X-ray absorption near-edge structure (XANES) spectroscopy show that many spinels have predominantly tetravalent Ti, regardless of host phases. The average spinel in Allende type B1 inclusion TS34 has 87% Ti^(+4). Most spinels in fluffy type A (FTA) inclusions also have high Ti valence. In contrast, the rims of some spinels in TS34 and spinel grain cores in two Vigarano type B inclusions have larger amounts of trivalent titanium. Spinels from TS34 have approximately equal amounts of divalent and trivalent vanadium. Based on experiments conducted on CAI-like compositions over a range of redox conditions, both clinopyroxene and spinel should be Ti^(+3)-rich if they equilibrated with CAI liquids under near-solar oxygen fugacities. In igneous inclusions, the seeming paradox of high-valence spinels coexisting with low-valence clinopyroxene can be explained either by transient oxidizing conditions accompanying low-pressure evaporation or by equilibration of spinel with relict Ti^(+4)-rich phases (e.g., perovskite) prior to or during melting. Ion probe analyses of large spinel grains in TS34 show that they are enriched in heavy Mg, with an average Δ^(25)Mg of 4.25 ± 0.028‰, consistent with formation of the spinel from an evaporating liquid. Δ^(25)Mg shows small, but significant, variation, both within individual spinels and between spinel and adjacent melilite hosts. The Δ^(25)Mg data are most simply explained by the low-pressure evaporation model, but this model has difficulty explaining the high Ti^(+4) concentrations in spinel