6,539 research outputs found
Palladium, platinum, and gold distribution in serpentinite seamounts in the Mariana and Izu-Bonin forearcs: evidence from Leg 125 fluids and serpentinites
Palladium, platinum, and gold were analyzed for 20 interstitial water samples from Leg 125. No Pd or Pt was detected in fluids from serpentinite muds from Conical Seamount in the Mariana forearc, indicating that low-temperature seawater-peridotite interaction does not mobilize these elements into the serpentinizing fluids to levels above 0.10 parts per billion (ppb) in solution. However, Au may be mobilized in high pH solutions. In contrast, fluids from vitric-rich clays on the flanks of the Torishima Seamount in the Izu-Bonin forearc have Pd values of between 4.0 and 11.8 nmol/L, Pt values between 2.3 and 5.0 nmol/L and Au values between 126.9 and 1116.9 pmol/L. The precious metals are mobilized, and possibly adsorbed onto clay mineral surfaces, during diagenesis and burial of the volcanic-rich clays. Desorption during squeezing of the sediments may produce the enhanced precious metal concentrations in the analyzed fluids. The metals are mobilized in the fluids probably as neutral hydroxide, bisulfide, and ammonia complexes. Pt/Pd ratios are between 0.42 and 2.33, which is much lower than many of the potential sources for Pt and Pd but is consistent with the greater solubility of Pd compared with Pt in most natural low-temperature fluids
Palladium, platinum, and gold distribution in serpentinite seamounts in the Mariana and Izu-Bonin forearcs: evidence from Leg 125 fluids and serpentinites
Palladium, platinum, and gold were analyzed for 20 interstitial water samples from Leg 125. No Pd or Pt was detected in fluids from serpentinite muds from Conical Seamount in the Mariana forearc, indicating that low-temperature seawater-peridotite interaction does not mobilize these elements into the serpentinizing fluids to levels above 0.10 parts per billion (ppb) in solution. However, Au may be mobilized in high pH solutions. In contrast, fluids from vitric-rich clays on the flanks of the Torishima Seamount in the Izu-Bonin forearc have Pd values of between 4.0 and 11.8 nmol/L, Pt values between 2.3 and 5.0 nmol/L and Au values between 126.9 and 1116.9 pmol/L. The precious metals are mobilized, and possibly adsorbed onto clay mineral surfaces, during diagenesis and burial of the volcanic-rich clays. Desorption during squeezing of the sediments may produce the enhanced precious metal concentrations in the analyzed fluids. The metals are mobilized in the fluids probably as neutral hydroxide, bisulfide, and ammonia complexes. Pt/Pd ratios are between 0.42 and 2.33, which is much lower than many of the potential sources for Pt and Pd but is consistent with the greater solubility of Pd compared with Pt in most natural low-temperature fluids
Trace element geochemistry of peridotites from the Izu-Bonin-Mariana Forearc, Leg 125
Trace element analyses (first-series transition elements, Ti, Rb, Sr, Zr, Y, Nb, and REE) were carried out on whole rocks and minerals from 10 peridotite samples from both Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc using a combination of XRF, ID-MS, ICP-MS, and ion microprobe. The concentrations of incompatible trace elements are generally low, reflecting the highly residual nature of the peridotites and their low clinopyroxene content (n ratios in the range of 0.05-0.25; several samples show possible small positive Eu anomalies. LREE enrichment is common to both seamounts, although the peridotites from Conical Seamount have higher (La/Ce)n ratios on extended chondrite-normalized plots, in which both REEs and other trace elements are organized according to their incompatibility with respect to a harzburgitic mantle. Comparison with abyssal peridotite patterns suggests that the LREEs, Rb, Nb, Sr, Sm, and Eu are all enriched in the Leg 125 peridotites, but Ti and the HREEs exhibit no obvious enrichment. The peridotites also give positive anomalies for Zr and Sr relative to their neighboring REEs. Covariation diagrams based on clinopyroxene data show that Ti and the HREEs plot on an extension of an abyssal peridotite trend to more residual compositions. However, the LREEs, Rb, Sr, Sm, and Eu are displaced off this trend toward higher values, suggesting that these elements were introduced during an enrichment event. The axis of dispersion on these plots further suggests that enrichment took place during or after melting and thus was not a characteristic of the lithosphere before subduction.
Compared with boninites sampled from the Izu-Bonin-Mariana forearc, the peridotites are significantly more enriched in LREEs. Modeling of the melting process indicates that if they represent the most depleted residues of the melting events that generated forearc boninites they must have experienced subsolidus enrichment in these elements, as well as in Rb, Sr, Zr, Nb, Sm, and Eu. The lack of any correlation with the degree of serpentinization suggests that low-temperature fluids were not the prime cause of enrichment. The enrichment in the high-field-strength elements also suggests that at least some of this enrichment may have involved melts rather than aqueous fluids. Moreover, the presence of the hydrous minerals magnesio-hornblende and tremolite and the common resorption of orthopyroxene indicate that this high-temperature peridotite-fluid interaction may have taken place in a water-rich environment in the forearc following the melting event that produced the boninites. The peridotites from Leg 125 may therefore contain a record of an important flux of elements into the mantle wedge during the initial formation of forearc lithosphere. Ophiolitic peridotites with these characteristics have not yet been reported, perhaps because the precise equivalents to the serpentinite seamounts have not been analyzed
X-ray pulsations from the radio-quiet gamma-ray pulsar in CTA 1
Prompted by the Fermi LAT discovery of a radio-quiet gamma-ray pulsar inside
the CTA 1 supernova remnant, we obtained a 130 ks XMM-Newton observation to
assess the timing behavior of this pulsar. Exploiting both the unprecedented
photon harvest and the contemporary Fermi LAT timing measurements, a 4.7 sigma
single peak pulsation is detected, making PSR J0007+7303 the second example,
after Geminga, of a radio-quiet gamma-ray pulsar also seen to pulsate in
X-rays. Phase-resolved spectroscopy shows that the off-pulse portion of the
light curve is dominated by a power-law, non-thermal spectrum, while the X-ray
peak emission appears to be mainly of thermal origin, probably from a polar cap
heated by magnetospheric return currents, pointing to a hot spot varying
throughout the pulsar rotation.Comment: 19 pages, 4 figures. Accepted for publication in ApJ Letter
Understanding small music venues: a report by the Music Venue Trust
This report presents the findings of a research project undertaken by the Institute of Contemporary Music Performance (hereafter The Institute) investigating the experiences of small music venues in the UK. The project was commissioned by the Music Venue Trust (MVT) and funded by Arts Council England (ACE) via an allocation of a grant awarded to MVT (Grant for the Arts ref. 27555752) and by The Institute
Excitation of the auroral green line by dissociative recombination of O plus over 2 - Analysis of two rocket experiments
Excitation of auroral green line by dissociative recombination of oxygen ion
Absorption line series and autoionization resonance structure analysis in the ultraviolet spectrum of Sr I
Photoelectric spectrometer to measure absorption line series and autoionization resonance in ultraviolet spectrum of strontium vapo
Bayesian analysis of Friedmannless cosmologies
Assuming only a homogeneous and isotropic universe and using both the 'Gold'
Supernova Type Ia sample of Riess et al. and the results from the Supernova
Legacy Survey, we calculate the Bayesian evidence of a range of different
parameterizations of the deceleration parameter. We consider both spatially
flat and curved models. Our results show that although there is strong evidence
in the data for an accelerating universe, there is little evidence that the
deceleration parameter varies with redshift.Comment: 7 pages, 3 figure
Probable absence of a quadrupolar spin-nematic phase in the bilinear-biquadratic spin-1 chain
We study numerically the ground-state phase diagram of the
bilinear-biquadratic spin-1 chain near the ferromagnetic instability point,
where the existence of a gapped or gapless nondimerized quantum nematic phase
has been suggested. Our results, obtained by a highly accurate density-matrix
renormalization-group (DMRG) calculation are consistent with the view that the
order parameter characterizing the dimer phase vanishes only at the point where
the system becomes ferromagnetic, although the existence of a gapped or gapless
nondimerized phase in a very narrow parameter range between the ferromagnetic
and the dimerized regimes cannot be ruled out.Comment: 6 pages, 6 figure
Application of Bayesian model averaging to measurements of the primordial power spectrum
Cosmological parameter uncertainties are often stated assuming a particular
model, neglecting the model uncertainty, even when Bayesian model selection is
unable to identify a conclusive best model. Bayesian model averaging is a
method for assessing parameter uncertainties in situations where there is also
uncertainty in the underlying model. We apply model averaging to the estimation
of the parameters associated with the primordial power spectra of curvature and
tensor perturbations. We use CosmoNest and MultiNest to compute the model
Evidences and posteriors, using cosmic microwave data from WMAP, ACBAR,
BOOMERanG and CBI, plus large-scale structure data from the SDSS DR7. We find
that the model-averaged 95% credible interval for the spectral index using all
of the data is 0.940 < n_s < 1.000, where n_s is specified at a pivot scale
0.015 Mpc^{-1}. For the tensors model averaging can tighten the credible upper
limit, depending on prior assumptions.Comment: 7 pages with 7 figures include
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