Copper‐gold mineralisation in New Guinea: Tectonics,lineaments, thermochronology and structure

In New Guinea, the upper crust is rich in Late Miocene and Pliocene copper‐gold deposits, yet the host intrusives are mainly in the New Guinea Fold Belt and are of mantle origin and not directly subduction‐related. Structural, thermochronological and geodynamic analyses of the Grasberg, Porgera, Ok Tedi and Frieda River deposits show that the richest deposits occur along the eastern edge of the intersections between long‐lived crustal transfers perpendicular to strike and strike‐parallel crustal extensional faults that were strongly inverted during Late Miocene ‐ Pliocene orogenesis. The deposits are all associated with north‐northeast‐trending transfers, parallel to the aeromagnetic grain in basement, across which the continent‐ocean suture shows >50 km horizontal separation, as identified by the southern limit of the central New Guinea ophiolites. In the fold belt, the transfers coincide with the termination of regional anticlines or uplifts that are 150–200 km long and 30–60 km wide. Balanced sections reveal that the southern limit of these regional anticlines is commonly fault‐bound and coincides with major facies and thickness changes, indicating long‐lived, crustal extensional faults that were inverted. Fission track and ⁴⁰Ar/³⁹Ar cooling ages show that mineralisation occurred during inversion of these faults and, hence, correlates with propagation of orogenesis from northeast to southwest. It is proposed that the pre‐compression New Guinea margin comprised step‐like promontories and embayments delineated by long‐lived crustal fracture zones, as on Australia's North West Shelf. During Late Miocene ‐ Pliocene compression the crust was thickened, accompanying melting of the underlying mantle, and the crustal fracture zones were reactivated as transfers. Where the transfers intersected crustal extensional faults that were being inverted, local zones of dilation occurred, allowing emplacement of mantle magmas and associated mineralisation. When the deformation propagated southwards, so did the crustal thickening and the reactivation of major faults, allowing emplacement of younger magmas and mineralisation.     

Fertilization Effects on Elevation Change and Belowground Carbon Balance in a Long Island Sound Tidal Marsh

We report the results of a 5-year fertilization experiment in a central Long Island Sound salt marsh, aimed at understanding the impacts of high nutrient loads on marsh elevational processes. Fertilization with nitrogen led to some significant changes in marsh processes, specifically increases in aboveground primary production and in CO₂ fluxes from the soil. However, neither nitrogen nor phosphorus fertilization led to elevation loss (relative to controls), reduced soil carbon, or a decrease in belowground primary production, all of which have been proposed as links between elevated nutrient loads and marsh drowning. Our data suggest that high nutrient levels increase gross carbon loss from the sediment, but that this is compensated for by other processes, leading to no net deleterious effect of nutrient loading on carbon storage or on marsh stability with respect to sea level rise.     

Extremely metal‐poor stars in SDSS fields

Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal‐poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metallicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X‐shooter has the unique capability of performing the necessary follow‐up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our Franco‐Italian X‐shooter GTO. The two stars were targeted to be of metallicity around –3.0, the analysis of the X‐shooter spectra showed them to be of metallicity around –2.0, but with a low α to iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X‐shooter allows an in situ study of the outer halo, for the two stars studied here we estimate distances of 3.9 and 9.1 kpc, these are likely the most distant dwarf stars studied in detail to date (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elemental abundance analyses with DAO spectrograms: XXXII. HR 6455 (A3 III), δ Aqr (A3 V), η Lep (F2 V), and 1 Boo (A1 V)

We examine the sharp‐lined stars HR 6455 (A3 III, v sin i = 8.7 km s^–1) and η Lep (F2 V, v sin i = 13.5 km s^–1) as well as δ Aqr (A3 V, v sin i = 81 km s^–1) and 1 Boo (A1 V, v sin i = 59 km s^–1) to increase the number consistently analyzed A and F stars using high dispersion and high S/N (≥200) spectrograms obtained with CCD detectors at the long Coudé camera of the 1.22‐m telescope of the Dominion Astrophysical Observatory. Such studies contribute to understanding systematic abundance differences between normal and non‐magnetic main‐sequence band chemically peculiar A and early F stars. LTE fine analyses of HR 6455, δ Aqr, and 1 Boo using Kurucz's ATLAS suite programs show the same general elemental abundance trends with differences in the metal richness. Light and iron‐peak element abundances are generally solar or overabundant while heavy element and rare earth element abundances are overabundant. HR 6455 is an evolved Am star while δ Aqr and 1 Boo show the phenomenon to different extents. Most derived abundances of η Lep are solar (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Imaging X-ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20?C50 keV energy range during an M- or X-class flare, and will provide imaging information at the ??10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions.     

Comparison of local grid refinement methods for MODFLOW

Many ground water modeling efforts use a finite-difference method to solve the ground water flow equation, and many of these models require a relatively fine-grid discretization to accurately represent the selected process in limited areas of interest. Use of a fine grid over the entire domain can be computationally prohibitive; using a variably spaced grid can lead to cells with a large aspect ratio and refinement in areas where detail is not needed. One solution is to use local-grid refinement (LGR) whereby the grid is only refined in the area of interest. This work reviews some LGR methods and identifies advantages and drawbacks in test cases using MODFLOW-2000. The first test case is two dimensional and heterogeneous; the second is three dimensional and includes interaction with a meandering river. Results include simulations using a uniform fine grid, a variably spaced grid, a traditional method of LGR without feedback, and a new shared node method with feedback. Discrepancies from the solution obtained with the uniform fine grid are investigated. For the models tested, the traditional one-way coupled approaches produced discrepancies in head up to 6.8% and discrepancies in cell-to-cell fluxes up to 7.1%, while the new method has head and cell-to-cell flux discrepancies of 0.089% and 0.14%, respectively. Additional results highlight the accuracy, flexibility, and CPU time trade-off of these methods and demonstrate how the new method can be successfully implemented to model surface water-ground water interactions.