Petrology and geochemistry of the Juzzak Sill,western Chagai arc (Pakistan): implications for petrogenesis and emplacement

The Juzzak Sill occurs in the western part of the east-west trending, subduction-related magmatic belt known as the Chagai arc. The sill is concordantly emplaced in the Paleocene Juzzak Formation and locally cross-cuts the Early to Middle Eocene Robat Limestone and Eocene Saindak Formation. The sill is a porphyritic pyroxene diorite that grades into a porphyritic andesite (60.12–61.57 wt% SiO₂) along the chilled margins. It comprises phenocrysts of hypersthene and plagioclase (An_32–45) in a medium- to fine-grained groundmass of these minerals, opaque oxide, and apatite. The rocks are high-K (2.37–2.86 wt% K₂O) calc-alkaline with low Mg# (42–55), Cr (51–80 ppm), and Ni (22–30 ppm) contents. Mantle-normalized trace element patterns, exhibited by marked negative Nb anomalies and positive spikes for Sr, Rb, and Zr and are akin to island arc signatures. The relatively higher ratios of Zr/Y (3.57–6.58), Ti/V (46.05–54.36), Ta/Yb (0.14–0.15), and Th/Yb (2.56–2.65) and high ⁸⁷Sr/⁸⁶Sr ratio (0.70524) suggest the role of continental crust materials, thus implying continental margin-type arc affinity. The source diagnostic ratios including K/Ba, P/Zr, and La/Ce of Juzzak Sill andesite and Eocene andesite from the Chagai arc are more or less similar, but the former has a much higher K/Y and Ba/Y ratios, which suggests assimilations of the host sediments during intrusion.     

Integration between morphometric parameters,hydrologic model,and geo-informatics techniques for estimating WADI runoff (case study WADI HALYAH—Saudi Arabia)

In arid and semiarid areas, the only surface and groundwater recharge source is the runoff generated through flash floods. Lack of hydrological data in such areas makes runoff estimation extremely complicated. Flash floods are considered catastrophic phenomena posing a major hazardous threat to cities, villages, and their infrastructures. The objective of this study is to assess the flash flood hazard and runoff in Wadi Halyah and its sub-basins. Integration of morphometric parameters, geo-informatics, and hydrological models has been done to overcome the challenge of scarcity of data.Advanced Spaceborne Thermal Emission and Reflection (ASTER) data was used to prepare a digital elevation model (DEM) with 30-m resolution, and geographical information system (GIS) was used in the evaluation of network, geometry, texture, and relief features of the morphometric parameters. Thirty-eight morphometric parameters were estimated and have been linked together for producing nine effective parameters for evaluation of the flash flood hazard in the study basin.Flash flood hazard in Wadi Halyah and its sub-basins was identified and grouped into three classes depending on nine effective parameters directly influencing the flood prone areas. Calculated runoff volume of Wadi Halyah ranges from 26.7 × 10⁶ to 111.4 × 10⁶ m³ with an inundation area of 15 and 27 km² at return periods of 5 and 100 years, respectively. Mathematical relationships among rainfall depth, runoff volume, infiltration losses, and rainfall excess demonstrate a strong directly proportional relationships with correlation coefficient of about 0.99.     

Geochemical assessment of groundwater contamination with special emphasizes on fluoride,a case study from Midyan Basin,northwestern Saudi Arabia

Water samples for chemical analyses were collected in January 2012. A total of 72 samples of groundwater were collected from 72 boreholes in the Midyan Basin, northwestern Saudi Arabia. Samples were collected in polyethylene bottles and preserved and the used analytical techniques were in accordance with the standard methods from American public health association. Geochemical analyses of the groundwater samples from Midyan Basin reveal the concentration of fluoride (F) between 0.98 and 2.1 mg/l. Other parameters, e.g, pH, EC, TDS, HCO₃, SO₄, NO₃, Cl, K, Na, Mg, and Ca have been found in a variable proportion. Among them, the concentration of EC, HCO₃, K, Na and Mg is higher than the permissible limits. According to thermodynamical considerations, most of the analysed samples are graded under-saturated with respect to calcite and fluoride, while saturation has been observed in some samples. The under-saturation could probably be attributed to low concentration of calcite and fluoride in the studied wells. Fluoride concentration shows weak positive correlation with EC, TDS, Na, Cl, and SO₄. Factors controlling the concentration of fluoride (F) in the studied samples are the area climate, water chemistry and the presence of accessory minerals in the rocks through which groundwater is circulating, besides the anthropogenic activities in the area.     

Amateur decision-making in avalanche terrain with and without a decision aid: a stated choice survey

Avalanches pose a serious threat to recreational backcountry travelers in mountainous terrain. This study explores how the three main amateur user groups of avalanche terrain in western Canada (backcountry skiers, out-of-bound skiers, and snowmobile riders) balance recreational goals with safety concerns when choosing backcountry destinations under varying avalanche conditions. Using a discrete choice experiment (DCE), a stated preference technique, the study first examines the strengths and weaknesses in the decision process of the three amateur groups by comparing their responses with the choice patterns of professional mountain guides. The results show that the decision-making strategies employed by the respective amateur groups vary considerably in their level of complexity and the degree to which avalanche safety considerations are incorporated. Second, we examine the effects of a decision aid that preprocesses the most crucial pieces of avalanche hazard information on the decision preferences of the amateur groups in the DCE. The results show that a relatively simple decision aid can influence the decision-making process considerably and steer users towards more avalanche hazard sensitive behaviour.     

Method Development and Optimisation of Sodium Peroxide Sintering for Geological Samples

This work provides a measurement procedure for the complete digestion of rock samples containing refractory minerals such as zircon and chromite. Their dissolution by wet acid digestion is often incomplete but, although providing complete digestions, alkali fusion techniques can result in solutions with a high blank and total dissolved solid content. It was established by the systematic study with reference material trachyandesite MTA‐1 that a 1:6 sample to sodium peroxide (Na₂O₂) ratio is conservative for the complete digestion and recovery of all the analytes especially those contained in zircon. The sample decomposition time was 120 min for the zircon‐bearing rhyolite reference material MRH‐1. Complete digestion of chromite was obtained in the harzburgite RM MUH‐1. The sample solutions were stable for at least 1 year. Accurate measurements of SiO₂, Al₂O₃, TiO₂, P₂O₅ and K₂O could be made with ICP‐MS by not discarding the supernatant of the sinter solution and by using geological reference materials for external calibration. HF digestions are slow, not universal, and may form new mineral/phases that are insoluble under high temperature conditions. The validated sample decomposition procedure combined with ICP‐MS presents an alternative to the use of HF in routine analysis of difficult to digest geological materials.     

Using multivariate statistical analyses to evaluate groundwater contamination in the northwestern part of Saudi Arabia

Chemical characteristics of groundwater in the Midyan Basin (northwestern Saudi Arabia) were investigated and evaluated. A total of 72 water samples were collected from existing shallow wells and analyzed for different elements. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the data set in terms of their usefulness for groundwater classification, and to identify the processes controlling groundwater geochemistry. The subgroup consisted of 46 water samples out of 72 samples and 24 variables included major elements (Ca²⁺, Na⁺, Mg²⁺, K⁺, Cl^?, HCO₃ ^?, NO₃ ^?, SO₄ ^2?), minor and trace element (SiO₂, Al, As, B, Ba, Cd, Cr, F, Fe, Mo, P, Pb, Sb, Sn, Ti, and V). For water samples, four geochemically distinct clusters (i.e., C1, C2, C3 and C4) have been observed by hierarchical cluster analysis. Cr, F and Pb are the dominant ions in cluster C2. Al, As, Cd, Mo, Sb and Ti are the dominant ions in cluster C3, while B, Ca, Cl, HCO₃, K, Mg, Na, SO₄ and V are identified as dominant ions in the cluster C4. In the PCA, a total of five components are extracted form the data set, which explained 73.37 % of the total data variability. Among them the first component reveals strong associations between As, B, Cd, Cr, F, Mo, Pb, Sb and Ti. The second component reveals the associations between Ca, Cl, HCO₃, Mg, Na, SO₄ and V.     

Urban Surface Modification as a Potential Ozone Air-quality Improvement Strategy in California: A Mesoscale Modelling Study

Two of several surface modification (heat-island reduction) strategies, increased surface albedo and urban reforestation, are evaluated via mesoscale meteorological and photochemical modelling of regulatory episodes in central and southern California. The simulations suggest that these strategies can have beneficial impacts on air quality, with increased albedo being relatively more effective than urban reforestation. The simulations also show that air quality indices, such as regional 1-h peaks, area peaks, 8-h relative reduction factors, 24-h averages, etc., improve for both central and southern California and that for the range of strategies evaluated here, the improvements in air quality can be significant. The simulations of southern California suggest that there may be a threshold beyond which further surface modifications tend to produce smaller net improvements in ozone air quality.     

Effect of remote forcings on the winter precipitation of central southwest Asia part 1: observations

Summary We investigate the effects of the North Atlantic Oscillation (NAO) and the El Nino Southern Oscillation (ENSO) on winter precipitation in Central Southwest Asia (CSWA) using an analysis of available observed climate data. The analysis is based on correlations, composites and Singular Value Decomposition (SVD) performed using the gridded dataset of the Climatic Research Unit (CRU) and station data for the region. We find that both the NAO and ENSO affect climate over the region. In particular a positive precipitation anomaly is typically found in correspondence of the positive NAO phase and warm ENSO phase over a sub-region encompassing northern Pakistan, Afghanistan, Tajikistan and southern Uzbekistan. This conclusion is supported by a consistency across the different analysis methods and observation datasets employed in our study. A physical mechanism for such effect is proposed, by which western disturbances are intensified over the region as they encounter a low pressure trough, which is a dominant feature during positive NAO and warm ENSO conditions. Our results give encouraging indications towards the development of statistically-based prediction tools for winter precipitation over the CSWA region.     

Uncertainties in the regional climate models simulations of South-Asian summer monsoon and climate change

The uncertainties in the regional climate models (RCMs) are evaluated by analyzing the driving global data of ERA40 reanalysis and ECHAM5 general circulation models, and the downscaled data of two RCMs (RegCM4 and PRECIS) over South-Asia for the present day simulation (1971–2000) of South-Asian summer monsoon. The differences between the observational datasets over South-Asia are also analyzed. The spatial and the quantitative analysis over the selected climatic regions of South-Asia for the mean climate and the inter-annual variability of temperature, precipitation and circulation show that the RCMs have systematic biases which are independent from different driving datasets and seems to come from the physics parameterization of the RCMs. The spatial gradients and topographically-induced structure of climate are generally captured and simulated values are within a few degrees of the observed values. The biases in the RCMs are not consistent with the biases in the driving fields and the models show similar spatial patterns after downscaling different global datasets. The annual cycle of temperature and rainfall is well simulated by the RCMs, however the RCMs are not able to capture the inter-annual variability. ECHAM5 is also downscaled for the future (2071–2100) climate under A1B emission scenario. The climate change signal is consistent between ECHAM5 and RCMs. There is warming over all the regions of South-Asia associated with increasing greenhouse gas concentrations and the increase in summer mean surface air temperature by the end of the century ranges from 2.5 to 5 °C, with maximum warming over north western parts of the domain and 30 % increase in rainfall over north eastern India, Bangladesh and Myanmar.     

洋中脊扩张速率对洋壳速度结构的约束

洋中脊速度结构是揭示大洋岩石圈演化过程的重要约束.为探讨不同扩张速率下洋中脊的洋壳速度结构特征,挑选了全球152处快速（全扩张速率> 90 mm·a^-1）、慢速（全扩张速率20~50 mm·a^-1）和超慢速（全扩张速率 < 20 mm·a^-1）扩张洋中脊和非洋中脊的洋壳1-D地震波速度结构剖面,通过筛选统计、求取平均值等方法对分类的洋壳1-D速度结构进行对比研究,获得了不同扩张速率下洋中脊洋壳速度结构差异以及洋中脊与非洋中脊洋壳速度结构差异的新认识：（1）快速、慢速和超慢速扩张洋中脊的平均正常洋壳厚度分别为6.4 km、7.2 km和5.3 km,其中洋壳层2的厚度基本相似,洋壳厚度差异主要源自洋壳层3;其洋壳厚度变化范围分别为4.9~8.1 km、4.6~8.7 km和4.2~10.2 km,随着洋中脊扩张速率减小,洋壳厚度的变化范围逐渐增大;（2）快速扩张洋中脊的洋壳速度大于慢速和超慢速,可能与快速扩张脊洋壳生成过程中深部高密度岩浆上涌比较充足有关;（3）非洋中脊（>10 Ma）的洋壳比洋中脊（< 10 Ma）的洋壳厚~0.3 km,表明洋壳厚度与洋壳年龄有一定的正相关性.