Semi-automatic determination of the carbon and oxygen stable isotope compositions of calcite and dolomite in natural mixtures

A semi-automatic, on-line method was developed to determine the δ¹³C and δ¹⁸O values of coexisting calcite and dolomite. An isotopic mass balance is used to calculate the compositions of dolomite after having measured that of calcite and of the “bulk” sample. The limit of validity of this method is established by performing isotopic measurements of artificial mixtures made of precisely weighted and isotopically-characterised dolomite and calcite. The accuracy and repeatability of the calculation of dolomite δ¹³C and δ¹⁸O are statistically determined with a Monte-Carlo procedure of error propagation. Stable isotope ratios are determined by using an automated MultiPrep™ system on-line with an isotope-ratio mass-spectrometer (IRMS). The reaction time and the temperature of reaction were optimised by comparing the results with the isotopic composition of known mixtures. The best results were obtained by phosphoric acid digestion after 20 min at 40 °C for calcite and 45 min at 90 °C for dolomite. This procedure allows an accurate determination of the isotopic ratios from small samples (300 μg). Application of this protocol to natural mixtures of calcite and dolomite requires the accurate determination of the relative abundance of calcite and dolomite by combining Mélières manocalcimetry (MMC) and X-ray diffractometry (XRD).     

Comparison of methods for quantifying active layer dynamics and bedload discharge in armoured gravel‐bed rivers

Several methods were employed in the Ardennian rivers (Belgium) to determine the depth of the active layer mobilized during floods and to evaluate the bedload discharge associated with these events. The use of scour chains has shown that the depth of the active layer is systematically less than the b‐axis of the average particle size (D₅₀) of the elements which compose the surface layer of the riffles. This indicates that only a partial transport exists during low magnitude floods. The bedload discharge has been evaluated by combining data obtained using the scour chains technique and the distance covered by tracers. Quantities of sediment transported during frequent floods are relatively low (0·02 t km^–2) due to the armour layer which protects the subsurface material. These low values are also related to the fact that the distance calculated for mobilized bedload only applies to tracers fitted with PIT (passive integrated transponder)‐tags (diameter > 20 mm), whereas part of the bedload discharge is composed of sand and fine gravel transported over greater distances than the pebbles. The break‐up of the armour layer was observed only once, for a decennial discharge. During this event, the bedload discharge increased considerably (2 t km^–2). The use of sediment traps, data from dredging and a Helley–Smith sampler confirm the low bedload transport in Ardennian rivers in comparison to the bedload transport in other geomorphological contexts. This difference is explained by the presence of an armoured layer but also by the imbricated structures of flat bed elements which increase the resistance to the flow. Finally, the use of the old iron industry wastes allowed to quantify the thickness of the bed reworked over the past centuries. In the Lembrée River, the river‐bed contains slag elements up to a depth of about 50 cm, indicating that exceptional floods may rework the bed to a considerable depth. Copyright © 2012 John Wiley & Sons, Ltd.     

含水大陆下地壳的部分熔融：大别山C型埃达克岩成因探讨

       根据大陆下地壳的成分、含水基性岩体系部分熔融的基本原理和实验岩石学资料,本文对大陆下地壳的熔融机制展 开了讨论,并在此基础上对比实验熔体与大别山C 型埃达克岩的成分,进而探讨约束源岩成分、熔融的温压条件和部分熔 融程度。研究结果表明,大陆下地壳总体上是中- 基性（SiO2　50%~60% ）和含少量水的,在缺乏流体相条件下伴随含水 矿物脱水的部分熔融是下地壳产生含水长英质熔体和无水残留体的主要机制。角闪岩在中等压力下（1.0~1.2 GPa,相当于 35~40 km）理论上能够产生石榴石含量超过~20% 的熔融残余,从而使得与之平衡的长英质熔体具有低Y,高Sr/Y 和La/Yb 比值等埃达克岩特征。基于水活度模型和变质基性岩p -t 相图的估算显示,含有40%~60% 角闪石的源岩（含水0.8%~1.2%） 在~950 ℃能够得到最大为15%~20% 的熔体,该熔体分数满足熔体分离的要求。大别山C型埃达克岩主要为高钾钙碱性系 列（K2O 3.5%~5%）,与实验熔体成分的对比可知,其无法由低钾源岩在合理的部分熔融程度形成。根据钾在角闪岩部分熔 融过程过表现为强不相容元素的原理,利用合理假设的残余体组合得到的分配系数,估算K2O 含量为~1% 的源岩在熔融程 度为15%~20% 的情况下能够得到类似大别山C 型埃达克岩成分的熔体。     

Effects of strong network modifiers on Fe<Superscript>3+</Superscript>/Fe<Superscript>2+</Superscript> in silicate melts: an experimental study

The effect of CaO, Na₂O, and K₂O on ferric/ferrous ratio in model multicomponent silicate melts was investigated in the temperature range 1450–1550?°C at 1-atm total pressure in air. It is demonstrated that the addition of these network modifier cations results in an increase of Fe³⁺/Fe²⁺ ratio. The influence of network modifier cations on the ferric/ferrous ratio increases in the order Ca?<?Na?<?K. Some old controversial conceptions concerning the effect of potassium on Fe³⁺/Fe²⁺ ratio in simple model liquids are critically evaluated. An empirical equation is proposed to predict the ferric/ferrous ratio in SiO₂–TiO₂–Al₂O₃–FeO–Fe₂O₃–MgO–CaO–Na₂O–K₂O–P₂O₅ melts at air conditions.     

利用卫星影像获得汶川地震之同震地表变形来探讨其断层几何模型(英文)

On 12th May 2008, a MW7.9 earthquake occurred on the Longmenshan fault in the mountains to the west of Sichuan Province, which shook many Asian cities and killed at least 69 000 people.     

Observations of atmospheric water vapor above the Tharsis volcanoes on Mars with the OMEGA/MEx imaging spectrometer

The OMEGA imaging spectrometer onboard the Mars Express spacecraft is particularly well suited to study in detail specific regions of Mars, thanks to its high spatial resolution and its high signal-to-noise ratio. We investigate the behavior of atmospheric water vapor over the four big volcanoes located on the Tharsis plateau (Olympus, Ascraeus, Pavonis and Arsia Mons) using the 2.6 μm band, which is the strongest and most sensitive H₂O band in the OMEGA spectral range. Our data sample covers the end of MY26 and the whole MY27, with gaps only in the late northern spring and in northern autumn. The most striking result of our retrievals is the increase of water vapor mixing ratio from the valley to the summit of volcanoes. Corresponding column density is often almost constant, despite a factor of ∼5 decrease in air mass from the bottom to the top. This peculiar water enrichment on the volcanoes is present in 75% of the orbits in our sample. The seasonal distribution of such enrichment hints at a seasonal dependence, with a minimum during the northern summer and a maximum around the northern spring equinox. The enrichment possibly also has a diurnal trend, being the orbits with a high degree of enrichment concentrated in the early morning. However, the season and the solar time of the observations, due to the motion of the spacecraft, are correlated, then the two dependences cannot be clearly disentangled. Several orbits exhibit also spatially localized enrichment structures, usually ring- or crescent-shaped. We retrieve also the height of the saturation level over the volcanoes. The results show a strong minimum around the aphelion season, due to the low temperatures, while it raises quickly before and after this period. The enrichment is possibly generated by the local circulation characteristic of the volcano region, which can transport upslope significant quantities of water vapor. The low altitude of the saturation level during the early summer can then hinder the transport of water during this season. The influence of the coupling between atmosphere and surface, due mainly to the action of the regoliths, can also contribute partially to the observed phenomenon.     

On the detection of the Yarkovsky effect on near-Earth asteroids by means of Gaia

The Yarkovsky effect, which causes a slow drifting of the orbital elements (mainly the semimajor axis) of km-sized asteroids and meteors, is the weak non-gravitational force experienced by these bodies due to the emission of thermal photons. This effect is believed to play a role in the delivery of near-Earth asteroids (NEAs) from the main belt, in the spreading of the orbital elements of asteroid families, and in the orbital evolution of potentially hazardous asteroids.Here we present preliminary results of simulationing indicating that the perturbations induced by the Yarkovsky effect on the positions of some tens of NEAs can be observed by means of the high-precision astrometric observations that will be provided by the ESA mission Gaia.     

煤矸石堆周围土壤重金属污染特征分析--以焦作市中马村矿为例

利用扇形布点法采集了焦作市中马村矿矸石堆周围土壤，对其中的Cr、Pb、Cu、Mn4种重金属含量进行了研究。结果表明：煤矸石的堆放对周围土壤造成不同程度的污染，重金属的含量随离矸石堆距离增大呈减小的趋势，主要受到风向的影响。     

Ecotoxicological effects of a semi-submerged municipal dump (Castle harbour, Bermuda) on the Calico scallop Argopecten gibbus

A biomarker study was undertaken using the Calico scallop Argopecten gibbus to assess the ecotoxicological effects of a semi-submerged municipal dump on the adjacent patch reef lagoon ecosystem (Castle harbour, Bermuda). Caged scallops were deployed in situ for 2 months at various distances from the dump (50 m, 900 m and 2.7 km) and at a reference site (14 km). A suite of biomarkers comprising metallothionein (MT), lipid peroxidation (LPO), vitellin-like proteins (Vn), glutathione S-transferase (GST), DNA strand breaks and condition factor (CF) were investigated in various tissues of the scallop (gill, digestive gland and gonad). Levels of heavy metals were also measured in the whole scallop soft tissue. While there was some variation in response between tissues, in general the results indicated that the dump was negatively impacting scallops deployed in the adjacent marine environment: elevated levels of MT, DNA strand breaks, Vn and GST and reduced condition factor were found for scallops deployed nearest to the dump and at the site 1.5 km from this point source of contamination (Tuckers town) in Castle harbour, with respect to the reference site, North Rock (although this exhibited some degree of metal contamination). The gills from scallops deployed at the dump site were the most responsive tissue, with the highest expression of MT, LPO and DNA damage. This study indicates the potential of the Calico scallop as a convenient bioindicator species in the marine tropical benthos.