Sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions

The effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite, ±anhydrite, melt and fluid have been determined at 200 MPa and 800–1,100 °C via apatite crystallization and dissolution experiments. The presence of a small amount of sulfur in the system (0.5 wt.% S) under oxidizing conditions increases the solubility of phosphorus in the melt, probably due to changing calcium activity in the melt as a result of the formation of Ca-S complexing cations. Apatite solubility geothermometers tend to overestimate temperature in Ca-poor, S-bearing system at oxidizing conditions. In crystallization experiments, the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt. The sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature (Kd_S^apatite/melt=4.5–14.2 at T=1,100–900 °C) under sulfur-undersaturated conditions (no anhydrite). The sulfur partition coefficient is lower in anhydrite-saturated melt (~8 at 800 °C) than in anhydrite-undersaturated melt, suggesting that Kd_S^apatite/melt depends not only on the temperature but also on the sulfur content of the melt. These first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions.Editorial responsibility: J. Hoefs     

Deep sea diapirs and bottom simulating reflector in Fairway Basin (SW Pacific)

A recent swath-bathymetry and geophysical survey of the R/V L'Atalante in the Fairway Basin between Australia and New Caledonia allowed to confirm the Cretaceous age of the creation of the basin by continental stretching. This first stage of opening of the Fairway Basin is associated with the deposition of a continuous salt/mud layer feeding today numerous diapirs, some of them piercing the 3 to 4 km thick sedimentary cover and reaching the seafloor. In close link with this salt/mud layer a Bottom Simulating Reflector indicator of gas hydrates level occupies a 70000 km² surface at about 500 to 600 m-depth beneath the sea floor. The coexistence of both BSR and diapirs suggests a thermogenic better than biogenic origin for the gas hydrates horizon.     

Hydrological Evaluation of the Canadian Meteorological Ensemble Reforecast Product

This paper evaluates the quality of the ensemble hydrological reforecasts obtained using the 18-year ensemble meteorological reforecast dataset available from the Canadian Centre for Meteorological and Environmental Prediction (CCMEP). This study focuses on four large watersheds in the province of Quebec. A distribution-based scaling (DBS) post-processing method is used to correct the 18-year ensemble precipitation reforecasts. An Ensemble Kalman Filter (EnKF) assimilation technique is also assessed to improve the initial conditions of the hydrologic model. There is a slight improvement in performance and reliability after applying the DBS approach to precipitation reforecasts, but this technique induces a reduction in the spread. The impact of the integration of the post-processed precipitation into the hydrologic model is also quite marginal. However, the addition of an EnKF provides better ensemble hydrological reforecasts with high performance, reliability, and skill, especially in the first reforecast horizons. The best results are, however, generally obtained when using DBS and an EnKF together. Combining DBS and an EnKF, hydrological forecasts for the next two weeks are obtained using the CCMEP reforecast and also the second generation Global Ensemble Forecast System (GEFS v2) reforecast, which is considered a reference. Forecasts of comparable skill and spread are obtained, with CCMEP-based forecasts showing better spread during the first week, and GEFS v2–based reforecasts showing better skill and spread during the second week. Finally, it is shown that the two meteorological reforecast products assessed in this study have similar economic value for hydrological forecasting applications based on the cost–loss model.     

Separable and partially separable systems in the light of the inverse problem of dynamics

Using a generalization of Joukovsky's formula, we determine three-dimensional families of curves that are orbits only in separable potentials and we note the importance of iso-energetic families of orbits. We also obtain more general families that are orbits of partially separable systems and we examine from this point of view the classical curvilinear coordinate systems.     

Foreland and Hinterland basins: what controls their evolution?

Compressional systems are usually characterized by a positive topography above the sea level, which is continuously modified by the conjugate effects of tectonic contraction or post-orogenic collapse, thermo-mechanical processes in the deep lithosphere and asthenosphere, but also by climate and other surface processes influencing erosion rates.Different types of sedimentary basins can develop in close association with orogens, either in the foreland or in the hinterland. Being progressively filled by erosional products of adjacent uplifted domains, these basins provide a continuous sedimentary record of surficial, crustal and lithospheric deformation at and near plate boundaries.Selected integrated basin-scale studies in the Circum-Mediterranean thrust belts and basins, in Pakistan and the Americas, are used here to document the effects of structures inherited from former orogens, rifts and passive margins, active tectonics and mantle dynamics on the development and long term evolution of synorogenic basins.     

Lithostratigraphy and U-Pb zircon dating in the overturned limb of the Siviez-Mischabel nappe: a new key for Middle Penninic nappe geometry.

Detailed field work and zircon analysis have improved the knowledge of the lithostratigraphy at the base of the Siviez-Mischabel nappe in the Mattertal (St-Niklaus-Törbel area). They confirm the existence of an overturned limb and clarify the structure of the St-Niklaus syncline. The following formations can be observed:

• Polymetamorphic gneisses; composed of paragneisses, amphibolites and micaschists (Bielen Unit, pre-Ordovician).
• Fine-grained, greyish quartzite and graywacke with kerogen-rich horizons (Törbel Formation, presumed Carboniferous).
• Green or white micaschists characterized by brown carbonate spots associated with white conglomeratic quartzites (Moosalp Formation, Early Permian).
• Massive, green or white, fine grained, microconglomeratic or conglomeratic quartzites with characteristic pink quartz pebbles (Bruneggjoch Formation, Late Permian-Early Triassic).

This coherent overturned sequence can be observed from the St-Niklaus area to the Moosalp pass to the north. Detailed mapping revealed that the St-Niklaus syncline is symmetrical and connects the overturned limb of the Siviez-Mischabel nappe to the normal series of the Upper Stalden zone. U-Pb zircon geochronology on magmatic and detrital zircons allowed constraining ages of these formations. Detrital zircons display ages ranging from 2900 ± 50 to 520 ± 4 Ma in the Törbel Formation, and from 514 ± 6 to 292 ± 9 Ma in the Moosalp Formation. In addition, the Permian Randa orthogneiss is intrusive into the polymetamorphic gneisses and into the Permo-Carboniferous metasediments of the overturned limb of the Siviez-Mischabel nappe. This revision clarified also the lithostratigraphy of the nearby and subjacent Lower Stalden zone composed of an overturned limb with Permo-Carboniferous formations. This has critical implications for the tectonic setting of the nappes in the region, speaking for few recumbent folds with well preserved normal and overturned limbs instead of a succession of imbricate thrust sheets in a normal stratigraphic position.