三塘湖盆地航磁异常特征及油气远景预测

三塘湖盆地是我国西部典型的火山岩油气盆地。本文基于1：5万高精度航磁资料,结合区域地质、区域重力、地面踏勘和物性资料,对三塘湖盆地进行了航磁综合解释;详细分析了磁场和重力场特征及其与区域构造的对应关系,圈定了盆地火山岩分布范围,采用欧拉反褶积方法计算了磁性体埋深,初步揭示了盆地磁性基底起伏情况;结合盆地火山岩油气成藏模式,开展了航磁油气远景预测。结果表明,三塘湖盆地中央坳陷内有隐伏火山岩存在的次级凹陷中心具有寻找火山岩油藏的良好前景：汉水泉凹陷区中的2个次级凹陷中心、条湖凹陷区北段次级凹陷中心应作为油气勘探重点区域;石头梅凸起和岔哈泉凸起区可作为重要油气勘探方向;方方梁凸起及其以南区域可作为下一步油气勘探工作的预研区。研究结果可为盆地油气资源后续勘探开发提供指导。     

Chromium spinels in North Chinese kimberlites,Huabei platform

Samples from diamondiferous pipes in the Mengyin and Fuxian regions were investigated. The chemical compositions of Cr spinels in kimberlites of China were found to be similar to those in kimberlites of the Arkhangelsk province in Russia. A long and complex evolution that was individual for each pipe was demonstrated. The kimberlites of the Shandong Province proved to be rich in high-Cr chromites. This means that the kimberlites formed at large depths in the field of diamond thermodynamic stability. Variations in the redox conditions were noted. They manifested themselves as a wide range of fluctuations of the chemical composition of microcrystalline spinels, up to formation to Ti-magnetite and magnetite.     

Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.     

Effect of voluntary cooperativisation on livelihood capital of smallholder dairy farmers in the southwest of Bangladesh

GeoJournal - This study investigated the effects of voluntary cooperativisationas conducted by the Community-Based Dairy Veterinary Foundation (CDVF) on the livelihood capital of smallholder dairy...     

A STUDY ON THE VARIATIONS OF CIRCULATION PATTERN IN THE NORTHERN HEMISPHERE AND CLIMATE CHANGE IN CHINA FOR THE RECENT 100 YEARS

The time series of annual frequency of the circulation patterns W,C,E in the Northern Hemisphere and annual mean temperature of Beijing (T_B),Shanghai (T_S) and the whole country (T_C) in the period 1891-1990 are expanded as a long-term tendency,a periodic function and a random function.The coherence between circulation and temperature is calculated and analyzed.The abrupt change of circulation and temperature in the last 100 years is revealed with the methods of the accumulated anomalous curves,the signal/noise ratio as well as the Mann-Kendall test.The correlations between anomalous circulation and climate are discussed with some explanations.     

Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation?

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.     

Fluoride and arsenic hydrogeochemistry of groundwater at Yuncheng basin,Northern China

High fluoride and arsenic concentrations in groundwater have led to serious health problems to local inhabitants at Yuncheng basin, Northern China. In this study, groundwater with high fluoride and arsenic concentration at Yuncheng basin was investigated. A majority of the samples (over 60%) belong to HCO₃ type water. The predominant water type for the shallow groundwater collected from southern and eastern mountain areas was Ca/Mg-Ca-HCO₃ types. For the shallow groundwater from flow through and discharge area it is Na-HCO₃/SO₄-Cl/SO₄/Cl type. The predominant water type for the intermediate and deep groundwater is of Na/Ca/Mg-Ca-HCO₃ type. According to our field investigation, fluoride concentration in groundwater ranges between 0.31 and 14.2 mg/L, and arsenic concentration ranges between 0.243 and 153.7 μg/L. Out of seventy collected groundwater samples, there are 31 samples that exceed the World Health Organization (WHO) standard of 1.5 mg/L for fluoride, and 15 samples exceeds the WHO standard of 10 μg/L for arsenic. Over 40% of high fluoride and arsenic groundwater are related to the Na-HCO₃ type water, and the other fifty percent associated with Na-SO₄-Cl/HCO₃-SO₄-Cl type water; little relation was found in calcium bicarbonate type water. A moderate positive correlation between fluoride and arsenic with pH were found in this study. It is due to the pH-dependent adsorption characteristics of F and As onto the oxide surfaces in the sediments. The observed negative correlation between fluoride and calcium could stem from the dissolution equilibrium of fluorite. The high concentration of bicarbonate in groundwater can serve as a powerful competitor and lead to the enrichment of fluoride and arsenic in groundwater. Most of the groundwater with high fluoride or arsenic content has nitrate content about or over 10 mg/L which, together with the observed positive correlations between nitrate and fluoride/arsenic, are indicative of common source of manmade pollution and of prevailing condition of leaching in the study area.     

Zero-valent iron/persulfate(Fe0/PS) oxidation acetaminophen in water

Zero-valent iron (Fe⁰), as an alternative iron source, was evaluated to activate persulfate (PS) to degrade acetaminophen (APAP), a representative pharmaceutically active compound in water. Effects of key factors in the so-called Fe⁰/PS process, including Fe⁰ dosage, initial pH, temperatures and chelating agents, were studied. Under all the conditions tested, the APAP degradation followed a pseudo-first-order kinetics pattern. The degradation efficiency of APAP was highest when the Fe⁰ to PS molar ratio increased to 1:1, and the degradation rate constant and removal were 23.19 × 10^?3 min^?1 and 93.19 %, respectively. Comparing with Fe²⁺, Fe⁰ served as an alternative iron source that can gradually release Fe²⁺ into water, thereby consistently activating PS to produce sulfate radicals. The Fe⁰/PS system was effective in a broader pH range from 3 to 8.5. Heat could facilitate production of sulfate radicals and enhance the APAP degradation in the Fe⁰/PS system. High reaction temperature also improved the Fe²⁺/PS oxidation of APAP. Finally, sodium citrate (a chelating agent) at an appropriate concentration could improve the APAP degradation rate in the Fe²⁺/PS and Fe⁰/PS system. The optimal molar ratio of Fe⁰ to citrate depended on solution pH. Our results demonstrated that Fe⁰ was an alternative iron source to activate PS to degrade APAP in water.     

Speciation and behavior of arsenic in evaporation basins,California, USA

Disposal of saline subsurface drainage waters from croplands into evaporation basins (or ponds) in the San Joaquin Valley of California causes excessive accumulation of salts and elevated concentrations of arsenic (As), a potentially high risk element with little information about its fate, in the agricultural evaporation ponds. We examined dissolved As concentration, speciation, and distribution in waters as well as As fractionation in sediments in the 10-cell South Evaporation Basin for better understanding of processes and conditions affecting As transformations and fate in a specific drainage disposal facility. The increase of total dissolved As concentrations were observed with higher Cl⁻ and electric conductivity along flow path indicating that evaporation was an important factor regulating total dissolved As concentration. The increases of reduced As species such as arsenite [As(III)] and organic As (monomethylarsonic acid and dimethylarsinic acid) were found towards the terminal flow pathway. However, arsenate [As(V)], the oxidized species remained greater than 67% of total dissolved As in all cell waters. Sequential extractions of sediments indicated that reducing conditions may influence As behavior in sediments to be more soluble and exchangeable. Arsenic association with oxides was appreciable only under oxidizing condition. Carbonate minerals played an important role in immobilizing As into the sediments under alkaline condition and a broad range of redox conditions. However, these sink mechanisms did not significantly reduce As concentrations in the cell waters. The reducing condition facilitated by high concentration of organic matter might be a major factor for the increase in As mobility.     

Local responses in 2D assemblies of elliptical rods when subjected to biaxial shearing

Acta Geotechnica - This study explored the characteristics of local responses in 2D assemblies of elliptical particles when subjected to shearing. A biaxial shearing system was designed for this...