西藏当雄地区拉屋矿床二长花岗岩地球化学特征及构造背景

西藏拉屋矿床位于冈底斯铜铅锌多金属成矿带东段。通过对拉屋矿区出露的二长花岗岩地球化学研究表明,岩石中SiO_2、Al_2O_3和CaO等的含量均高、贫Fe和低Na_2O;w(SiO_2)含量为65.40%~74.43%,A/CNK值在1.41~2.20之间,为强过铝质花岗岩。岩石稀土总量ΣREE(不含Y)较低,为(5.08~80.38)×10~(-6),LaN/YbN值为2.43~5.65,ΣLREE/ΣHREE为1.63~3.64,稀土元素配分型式为右倾型,具负铕异常。Nb、Ti、Zr、Ce等高场强元素和Ba明显的亏损,K、Rb、Sr等大离子亲石元素明显的富集。综合研究认为,本区花岗岩的物质来源于上部陆壳,岩浆源区岩石成分为泥质岩;该岩体为形成于同碰撞构造环境、地壳加厚阶段的过铝质花岗岩。     

Rainfall over Oman and its teleconnection with El Niño Southern Oscillation

The Sultanate of Oman is located in the south-eastern part of the Arabian Peninsula and covers the larger part of the southern coasts of the Arabian Peninsula in both arid and semi-arid environments except for the southern part which is swept by the monsoon affecting the Arabian Sea during the period from June to September. The summer rainfall over Oman shows year-to-year variability, and this is caused by oceanic and atmospheric influences. In the present study, we tried to explore the influence of El Niño on the rainfall over Oman using different data sets. The empirical orthogonal function (EOF) technique employed to the zonal wind at 850 hPa for the 30-year period shows that the second and third modes of EOF are showing high variability over the Oman regions. The corresponding PCs were subjected to FFT analysis, and it showed a peak about 5–6 years. In addition to this, the zonal wind over the Oman regions is correlated with the global zonal wind and found a significant correlation (1 % significant level). It has already been proved that the wind and rainfall during summer monsoon is in phase. Moreover, the spectral analysis of rainfall at Masirah station and the Niño3.4 index show the similar mode of variability indicating a direct relationship. The correlation between rainfall and the Niño3.4 index is also showing a positive significant value, and therefore, it can be concluded that the El Niño in the Pacific favours rainfall over the Oman region.     

Multichannel analysis of surface waves (MASW) for seismic site characterization using 2D genetic algorithm at Bahrah area,Wadi Fatima,Saudi Arabia

The present study deals with the seismic site classification of Bahrah area, Wadi Fatima, to characterize the local site conditions. The dynamic behavior of sediments was studied by the application of surface wave inversion. The multichannel analysis of surface waves (MASW) shallow geophysical technique was utilized for site classification. MASW survey was carried out at 66 sites along with 13 seismic refraction profiles at suitable localities. MASW and seismic refraction profiles were processed and compared with the available borehole data. The integration of MASW techniques with seismic refraction and borehole data progressively enhanced the subsurface visualization and reliability of the shear wave velocity estimation in the subsurface in the study area. The subsurface shear-wave velocity model was achieved by the solution of an inverse problem-based dispersion of surface waves and propagation in a vertically heterogeneous medium. The 2D genetic algorithm was employed for the inversion of dispersion curves to obtain velocity and thickness of subsurface layers. The depth to engineering bedrock and velocity of shear waves in the first 30 m was deciphered and mapped. The depth of bedrock in study area varies from 4 to 30 m, and V _{S 30} ranges from 320 to 800 m/s. The most of study area falls in B and C class categories in addition to few sites of D class according to the NEHRP guidelines.     

Assessing groundwater storage changes in the Nubian aquifer using GRACE data

Gravity Recovery and Climate Experiment (GRACE) level two (L2) data is used in estimating the groundwater storage changes (GWSC) in the Nubian Sandstone Aquifer System (NSAS). This set of data consists of spherical harmonics coefficients with specific degree and order. The GRACE data is de-correlated using a sixth degree polynomial in order to reduce the effect of the noise error resulting from the correlation between the spherical harmonics coefficients with the same degree parity. The GRACE estimates of GWSC are smoothed using Gaussian filter with half width of 1000 km. This half width is chosen in order to maximize the correlation between the GRACE estimates of GWSC and previous modeling results of the NSAS. The loss in groundwater storage occurring in each of the four countries sharing the NSAS is calculated to assess the sustainability of using the NSAS as a water resource in each country. The overarching finding in this study is that NSAS is losing its groundwater storage at a very high rate. Also, it is found that Egypt is the fastest in losing its groundwater storage from the NSAS. This loss of groundwater storage in Egypt may not necessarily be resulting from in-country extractions because of the trans-boundary nature of this aquifer. The GRACE-based estimates are found to be close to available data and previous modeling results of the NSAS.     

Detachment folding in a Lower Cambrian–Upper Permian karst reservoir: 3D model of the Yubei 3D area (eastern Markit Slope,Tarim Basin,Northwest China)

A three-dimensional (3D) structural modeling of the Lower Cambrian–Upper Permian Yubei 3D area was performed to understand its structural evolution. This model reproduces the present-day structure of the basin and comprises 11 horizons within Lower Cambrian to Upper Permian rocks. The analysis is based on 3D depth views and faults. The results image salt movements due to tectonics and/or burial. From these observations, this paper deduces that salt structures are correlated to the main faults and tectonic events. From the model analysis, we interpret the timing and geometry of Tarim Basin tectonics. The fault geometry can be resolved based on the strike of the fault, the morphology of hanging wall strata, and the stratigraphic distribution. Emphasis is placed on gypsum rock detachment, considering its movements during the Middle Caledonian event and decoupling effects during tectonic evolution. Moreover, we point to the structural control of the Paleozoic basement and the crustal architecture (Yubei 3D Zone) on the geometry of the Tarim Basin.     

A GIS-index integration approach to groundwater suitability zoning for irrigation purposes

In recent decades, the high population growth has increased the demand for agricultural lands and products. Groundwater offers reliability and flexibility in access to water for irrigation purposes, especially in arid and semi-arid areas, such as Amol-Babol Plain, Iran. However, the quality and quantity of groundwater may not be suitable for irrigation purposes in all areas due to urbanizations, and intensive agricultural and industrial activities. Groundwater suitability zoning for irrigation purposes could be useful to improve water resources and land use planning, mostly in areas with water scarcity. Therefore, a GIS-based indices method is proposed to assess suitable zones for agricultural activities, integrating the irrigation water quality (IWQ) index and hydrogeological factors. IWQ index was utilized to assess groundwater quality based on salinity hazard, infiltration hazard, specific ions, and trace elements hazards, and miscellaneous effects such as pH, bicarbonate, and nitrate. The potential of the aquifer for irrigation water abstraction was investigated using hydrogeological surveys such as slope angle of the plain, hydraulic conductivity, and aquifer thickness. The groundwater suitability index classified most of the study area (more than 90 %) as “excellent” or “good” suitability zones for irrigation purposes. A limited area of around 5.6 % of the total area has moderate suitability for irrigation purposes due to the Caspian Seawater intrusion and the presence of fossil saline water. The proposed methodology provides useful information in order to allow irrigation management to prevent water and soil deterioration.     

Groundwater potential assessment in a sedimentary terrain,southwestern Nigeria

Geoelectrical resistivity techniques are increasingly being applied in addressing a wide range of hydrological, environmental, and geotechnical problems. This is due to their effectiveness in near-surface characterization. In the present study, a suite of vertical electrical soundings (VESs) was integrated with 2D geoelectrical resistivity and time-domain induced polarization (IP) imaging to characterize the near-surface and delineate the underlying aquifer in a sedimentary terrain. The geophysical survey was conducted as part of preliminary studies to evaluate the potential of groundwater resource in Iyana-Iyesi and Canaan Land area of Ota, southwestern Nigeria. A high-yield confined sandy aquifer overlain by a low-yield aquitard was delineated; overlying the aquitard is a very resistive and thick layer that is predominantly composed of kaolinitic swelling clay intercalated with phosphate mineral.     

Coal-measure source rock characteristics and burial evolution history in the Shisanjianfang Area,Tuha Basin

Shisanjianfang Area in the eastern margin of Taibei Sag, Tuha Basin, is an important region for oil and gas exploration. In this study, a large number of source rock geochemical data were used to analyze the geochemical characteristics of coal-measure source rocks in the Shisanjianfang Area, Tuha Basin, from three aspects, i.e., organic matter abundance, organic matter type, and organic maturity. The results show that the Jurassic Xishanyao Formation (J₂x) in the study area has great thickness, continuous distribution, and high source rock maturity, and is the major source rock horizon in the study area. The seismic data are used in combination with 1D and 2D basin simulation technology to study the distribution characteristics of the source rocks in Shisanjianfang Area. The results of the simulation research on the source rock maturity history in the study area indicate the following: (1) The source rocks in the Xishanyao Formation (J₂x) have a hydrocarbon generation threshold depth of 1800 m, threshold temperature of 95 °C, and hydrocarbon generation threshold time of about 162 Ma. (2) The Xishanyao Formation (J₂x) has a current formation temperature of 50~110 °C and Ro of 0.6~1.1 % in the peak oil generation stage. (3) The source rock maturity in the study area is shown as being higher in the west while lower in the east, and higher in the north while lower in the south, and the favorable exploration area mainly lies in the northwest of the study area. The results of this study could have important implications for the oil and gas exploration in the margins of Xiaocaohu Sag, Tuha Basin.     

Sensitivity analysis of runoff hydrographs due to temporal rainfall patterns in Makkah Al-Mukkramah region,Saudi Arabia

Runoff peak and volume in flood studies are estimated relying on temporal rainfall distribution from various storm patterns. Usually, SCS distributions types (I, II, III, IA) are commonly used. Using these distributions in runoff calculations assume that the in situ temporal rainfall pattern typically behaves as the one described by the SCS-type distribution, which is due to cyclonic frontal storms and actually developed in temperate environment. To what extent such assumption is valid in the arid environment? How much the impacts of rainfall temporal patterns are reflected in runoff volumes and peaks? The aim objectives of the current study are to answer the above two questions and clarify the validity of aforementioned assumption and exemplify such effect. Real rainfall data collected from rain gauges of Makkah Al-Mukkramah region over a period of more than 20 years are utilized. Temporal rainfall patterns and their parameters are deduced. Many hydrological simulations are performed and comparisons, in terms of runoff volume and peak flows, are made to show the effects of the common rainfall storm patterns and the developed rainfall storm patterns in the region based on the current study. Results indicate that major bursts of the design rainfall storm pattern are located in the first time of the storm period in the two quartiles which is mainly due to convective rainfall type in thunderstorms unlike the commonly used by SCS types relying on frontal cyclonic storms. Makkah Al-Mukkramah temporal rainfall pattern does not behave as the “typical pattern” assumed by SCS distributions that are deduced from different environments. The impacts of the temporal pattern reflected as an overestimate in the runoff peak reached to 68 %. The developed hyetographs and tables presented in the current study are recommended to enhance economical and rational design practice in watersheds of Makkah Al-Mukkramah region.     

The geochemistry of uranium occurrences and speciation in groundwater of Chinnar sub basin,South India

An attempt has been made in Chinnar sub basin of Dharmapuri district, South India to isolate the geochemistry of uranium occurrences in groundwater. The geology of the area is mainly of charnockite and granite gneiss. Groundwater samples were collected for two different seasons post and pre monsoon in two different litho units (granite gneiss and charnockite) and analysed for major, minor and uranium concentrations. Higher uranium (18.45 μg L^?1) has been recorded during pre monsoon season in granite gneiss with increasing pH. The saturation index calculation for the groundwater isolated minerals like uaraninite, coffinite, haiweeite and soddyite to be precipitating and uranium oxides like UO_2.25, UO_2.25beta, UO_2.33beta as oversaturated. The Eh-pH diagram attempted represents solubility of uraninite within the pH range of 6.0 to 8.0. The study isolate uranium in groundwater of the study area is controlled by the presence of (U₄O₉) uranium oxide.