内蒙古鸡冠山斑岩钼矿床成矿时代和成矿流体研究

内蒙古鸡冠山钼矿床是西拉沐伦钼成矿带上的典型斑岩矿床。矿床产于火山侵入杂岩中,矿化类型以细脉浸染状矿化为主。对矿床5件辉钼矿样品进行了铼-锇同位素分析,获得了151.1±1.3Ma的等时线年龄,表明成矿作用发生在晚侏罗世。成矿作用可划分为三个阶段:早阶段为石英-黄铁矿阶段,发育乳白色石英和粗粒浸染状黄铁矿;中阶段包括早期石英-多金属硫化物亚阶段和晚期石英-萤石-金属硫化物亚阶段;晚阶段为石英-碳酸盐细脉,穿切早、中阶段脉体和矿物组合。鸡冠山钼矿床流体包裹体岩相学研究表明,与成矿有关的包裹体主要有六种类型:富液相、富气相、含子晶多相、含CO2三相、纯CO2及纯液相包裹体。其中,早阶段以富气和富CO2包裹体为主,中阶段多种包裹体共存,晚阶段则主要为富液包裹体。冷热台显微测温和激光拉曼显微探针(LRM)成分分析结果表明,早阶段石英中原生包裹体的均一温度480℃,盐度最高66.75%NaCleqv,包裹体气相成分富含水和CO2,液相成分则以水为主,子晶矿物有石盐、黄铜矿以及指示氧化条件的赤铁矿等,同时也说明成矿流体是富含成矿金属元素的。中阶段早期石英中的流体包裹体均一温度为320～480℃,晚期石英和萤石中的流体包裹体的均一温度为180～320℃。中阶段流体盐度介于4.65%～56.76%NaCleqv。中阶段包裹体含石盐、方解石、黄铜矿、赤铁矿等子矿物,富气相、富液相与含子晶多相包裹体共存,且具有相近的均一温度,而盐度相差悬殊,指示流体发生了沸腾。晚阶段流体的温度降低至100～180℃,盐度则低于10.86%NaCleqv,流体包裹体成分主要为水。鸡冠山钼矿成矿流体演化从早至晚为:从早阶段高温、高盐度、高氧逸度、富CO2、富成矿物质以岩浆热液为主成矿流体,演化至晚期低温、低盐度、无子晶、贫CO2、以大气降水为主的流体。沸腾作用是鸡冠山钼矿形成的重要机制。     

Experimentally validated numerical method for the hydrodynamic design of horizontal axis tidal turbines

Although a lot can be learnt from technology transfer from wind turbines and ship propellers, there have been a few experiments investigating marine current turbines. As a result, a study has been carried out on the power, thrust and cavitation characteristics of 1/20th scale model of a possible 16 m diameter horizontal axis tidal turbine. Cavitation tunnel experiments for different blade pitch settings have been compared with simulations based on a developed blade element-momentum theory. This theory has been shown to provide a satisfactory representation of the experimental turbine performance characteristics. As an example application, the developed theory has been used to design possible horizontal axis tidal turbines for the tidal flows around Portland Bill. The results show that there is a clear balance between design loads and optimisation of energy yields.     

Rotation of the solar core from BiSON and LOWL frequency observations

Determination of the rotation of the solar core requires very accurate data on splittings for the low-degree modes which penetrate to the core, as well as for modes of higher degree to suppress the contributions from the rest of the Sun to the splittings of the low-degree modes. Here we combine low-degree data based on 32 months of observations with the BiSON network and data from the LOWL instrument. The data are analysed with a technique that specifically aims at obtaining an inference of rotation that is localized to the core. Our analysis provides what we believe is the most stringent constraint to date on the rotation of the deep solar interior.     

Influence from Hydrological Modification on Energy and Nutrient Transference in a Deltaic Food Web

Alterations of hydrology are known to trigger changes in coastal ecosystems, such as the composition and abundances of local flora and fauna. It is less well known how these alterations lead to changes in nutrient and energy transfers in these systems. We used comparisons of stable isotope signatures (δ ¹³C, δ ¹⁵N, and δ ³⁴S) in the tissues of conspecific plants and animals collected on each side of the Mobile Bay Causeway to determine the extent to which the causeway may have altered energy and nutrient exchange between the Mobile–Tensaw Delta and upper Mobile Bay. While the δ ¹³C signatures of most plants and animals varied irrespective of their location relative with causeway location, their δ ¹⁵N and δ ³⁴S signatures were almost always more enriched south of the causeway, indicating significant alterations of trophic linkages within this estuarine food web. Dual isotope plots and mixing model analyses indicated that while terrestrial and floating plants were trophically important to consumers north of the causeway, submerged aquatic vegetation was more important to consumers south of the causeway. Although limited in spatial and temporal scale, our results preliminarily show that there are noteworthy differences in stable isotope signatures most likely due to the Mobile Bay Causeway altering energy and nutrient transference.     

Anomalous variations in low-degree helioseismic mode frequencies

We compare changes in the frequencies of solar acoustic modes with degree between 0 and 2, as derived from Global Oscillation Network Group (GONG), Birmingham Solar Oscillations Network (BiSON) and Michelson Doppler Imager (MDI) spectra obtained between 1995 and 2003. We find that, after the solar-activity dependence has been removed from the frequencies, there remain variations that appear to be significant, and are often well correlated between the different data sets. We consider possible explanations for these fluctuations, and conclude that they are likely to be related to the stochastic excitation of the modes. The existence of such fluctuations has possible relevance to the analysis of other low-degree acoustic mode spectra such as those from solar-type stars.     

Extended search for correlation between solar mean magnetic field Bison data and coronal mass ejections

The Birmingham Solar-Oscillations Network (BiSON) has acquired high-precision solar mean magnetic field (SMMF) data on a 40-s cadence for a decade. We present attempts to compare such data from recent years with the occurrence of coronal mass ejections (CMEs) as recorded by LASCO, using correlation techniques applied to measurements from different BiSON instruments to maximise the sensitivity to CME-related SMMF responses. SMMF measurements were recorded at the time of occurrence of several hundred CMEs. No CME event shows a convincing response in our SMMF data at short periods setting a threshold amplitude of 12 mG. By averaging data sets we are able to set lower thresholds, which depend somewhat on the distribution of response strengths. A brief summary of the very first results of this study is also given in Chaplin et al.     

On the measurement precision of solar p-mode eigenfrequencies

We make use of 3456 d of observations of the low-ℓ p-mode oscillations of the Sun in order to study the evolution over time of the measurement precision of the radial eigenfrequencies. These data were collected by the ground-based Birmingham Solar-Oscillations Network (BiSON) between 1991 January and 2000 June. When the power spectrum of the complete time series is fitted, the analysis yields frequency uncertainties that are close to those expected from the returned coherence times of the modes. The slightly elevated levels compared with the prediction appear to be consistent with a degradation of the signal-to-noise ratio in the spectrum that is the result of the influence of the window function of the observations (duty cycle 71 per cent). The fractional frequency precision reaches levels of a several parts in 10⁶ for many of the modes. The corresponding errors reported from observations made by the GOLF instrument on board the ESA/NASA SOHO satellite, when extrapolated to the length of the BiSON data set, are shown to be (on average) about ∼25 per cent smaller than their BiSON counterparts owing to the uninterrupted nature of the data from which they were derived.
An analysis of the BiSON data in contiguous segments of different lengths, T , demonstrates that the frequency uncertainties scale as T ^−1/2. This is to be expected in the regime where the coherence (life) times of the modes, τ _{n ℓ}, are smaller than the observing time T (the 'oversampled' regime). We show that mode detections are only now beginning to encroach on the 'undersampled' regime (where   T < τ _{n ℓ})  .