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691.
平果县2008年11月致洪暴雨天气成因分析 总被引:3,自引:2,他引:1
利用常规气象资料、自动站资料和广西百色SB雷达资料等,分析了2008年10月28日~11月3日的高空环流形势、地面气压场,物理量场、单站降雨量随时间的演变、组合反射率与基本速度图等.结果表明:(1)大范围短时暴雨和大暴雨是导致平果县境内山洪暴发成灾的主要原因;(2)暴雨雨带通常位于500hPa副高588线外侧的100~200Km范围内.稳定的副高有利于对流性降水发生"列车效应";(3)热带气旋和副高南沿之间的低空东南急流为暴雨区输送大量的水汽,并提供主要的对流触发条件;(4)边界层冷空气的入侵对静止锋前暖区对流具有明显的增强作用. 相似文献
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694.
为更好地利用FY-3A气象卫星上中分辨率光谱成像仪(MERSI)资料高空间分辨率及多光谱的优势,细致分析云系在宏、微观方面的多重特征,首先利用平面平行辐射传输模式(SBDART)证明了MERSI的0.65,1.6 μm和11.25 μm通道能够分别反映云光学厚度、云粒子大小、云顶高度的信息,然后采用三通道合成彩色图像的方法,对FY-3A气象卫星云图进行云的分类解释判读.该技术可直观区分有云区、无云区,显示海陆分界,并且使不同云类在云图上体现为不同颜色.同时,FY-3A气象卫星高达1000 m甚至250m的空间分辨率也使云的细致结构更为清晰,两项优势的叠加,大大提升了云的分类解释判读的准确程度和精细化水平.文中还尝试寻找典型云系的三通道特征值,以期为模糊C均值聚类(FCM)方法中聚类中心的选定提供经验值参考. 相似文献
695.
Yan-Jie Tang Hong-Fu Zhang Eizo Nakamura Ji-Feng Ying 《Contributions to Mineralogy and Petrology》2011,161(6):845-861
Elemental and Li–Sr–Nd isotopic data of minerals in spinel peridotites hosted by Cenozoic basalts allow us to refine the existing
models for Li isotopic fractionation in mantle peridotites and constrain the melt/fluid-peridotite interaction in the lithospheric
mantle beneath the North China Craton. Highly elevated Li concentrations in cpx (up to 24 ppm) relative to coexisting opx
and olivine (<4 ppm) indicate that the peridotites experienced metasomatism by mafic silicate melts and/or fluids. The mineral
δ7Li vary greatly, with olivine (+0.7 to +5.4‰) being isotopically heavier than coexisting opx (−4.4 to −25.9‰) and cpx (−3.3
to −21.4‰) in most samples. The δ7Li in pyroxenes are considerably lower than the normal mantle values and show negative correlation with their Li abundances,
likely due to recent Li ingress attended by diffusive fractionation of Li isotopes. Two exceptional samples have olivine δ7Li of −3.0 and −7.9‰, indicating the existence of low δ7Li domains in the mantle, which could be transient and generated by meter-scale diffusion of Li during melt/fluid-peridotite
interaction. The 143Nd/144Nd (0.5123–0.5139) and 87Sr/86Sr (0.7018–0.7062) in the pyroxenes also show a large variation, in which the cpx are apparently lower in 87Sr/86Sr and slightly higher in 143Nd/144Nd than coexisting opx, implying an intermineral Sr–Nd isotopic disequilibrium. This is observed more apparently in peridotites
having low 87Sr/86Sr and high 143Nd/144Nd ratios than in those with high 87Sr/86Sr and low 143Nd/144Nd, suggesting that a relatively recent interaction existed between an ancient metasomatized lithospheric mantle and asthenospheric
melt, which transformed the refractory peridotites with highly radiogenic Sr and unradiogenic Nd isotopic compositions to
the fertile lherzolites with unradiogenic Sr and radiogenic Nd isotopic compositions. Therefore, we argue that the lithospheric
mantle represented by the peridotites has been heterogeneously refertilized by multistage melt/fluid-peridotite interactions. 相似文献
696.
深圳地区中生代火山地层分布区是我国东南沿海浙闽粤港火山活动带的一个重要组成部分,是我国沿海地区侏罗纪—白垩纪火山地层较有代表性地段,也是研究我国东南沿海侏罗纪—白垩纪火山活动的天然博物馆。近期通过野外观察,测制火山地层剖面,进行锆石同位素激光定年测试,对大鹏半岛国家地质公园中生代火山地层的时代提出新的认识,将原划分为上侏罗统高基坪群划分为早—中侏罗世塘厦组(181.8 Ma?)、中侏罗世吉岭湾组(165.8 Ma)、晚侏罗世梧桐山组(156.9~145.6 Ma)、晚侏罗世—早白垩世七娘山组(146.3~131.0 Ma)、早白垩世官草湖群等。 相似文献
697.
Li Lianchong Yang Tianhong Liang Zhengzhao Zhu Wancheng Tang Chunan 《International Journal of Coal Geology》2011,85(3-4):276-288
Permeable geologic faults in the coal seam can cause intermittent production problems or unexpected amounts of groundwater outburst from the underlying aquifers. With the acknowledgment of the basic mechanism for groundwater outbursts, the groundwater outburst along the fault zones in coal mines are numerically investigated using RFPA, a numerical code based on FEM. The fracture initiation, propagation, and coalescence in the stressed strata and the seepage field evolution in the stress field are represented visually during the whole process of groundwater outburst. The numerically obtained damage evolution shows that the floor strata could be classified as three zones, i.e. mining induced fracture zone, intact zone and fault reactivation zone, in which the intact zone is the key part for resisting groundwater outburst and directly determines the effective thickness of water-resisting rock layer. With understanding of the evolution of stress field and seepage flow in floor strata, the groundwater outburst pathway is calibrated and the transformation of floor rock mass from water-resisting strata to outburst pathway is clearly illuminated. Moreover, it is shown that geometrical configuration, including inclination angle of faults and seam drop along faults, have an important influence on groundwater outburst. Finally, based on geological, hydrogeology survey and numerical results, the mechanism analysis of groundwater outburst in an engineering case is studied, which can provide significantly meaningful guides for the investigation on mechanism and prevention of groundwater outburst induced by faults in practice. 相似文献
698.
Yuanzhi Tang 《Geochimica et cosmochimica acta》2011,75(17):4951-4962
Siderite (FeCO3) is an important reduced phase iron mineral and end product of bacteria anaerobic respiration. This study addresses its dissolution behavior in the presence of the oxidant chromate, which is a common environmental contaminant. Macroscopic dissolution experiments combined with microscopic observations by atomic force microscopy show that at pH < 4.5 the dissolution rate with chromate is slower than that in control solution without chromate. Isolated deep dissolution pits and clustered shallow pits occur simultaneously with surface precipitation. The implication is that the surface precipitate inhibits further dissolution. For 5 < pH < 9.5, the slowest dissolution and the fastest precipitation rates are observed, both at edge steps and on terraces. For pH > 10, the dissolution rate in the presence of chromate exceeds that of the control, plausibly due to electron transfer facilitated by [Fe3+(OH)4]-. Dissolution and re-precipitation of round hillocks are observed. X-ray photoelectron spectroscopy indicates the presence of Cr(III) as well as reaction products in a hydroxide form. Based on the redox reaction mechanism, macroscopic dissolution behavior, and previous studies on the reaction products of Fe(II) with Cr(VI), we propose the formation of a low solubility nano-sized Cr(III)-Fe(III)-hydroxide as the surface precipitate. Results from this study provide a basis for understanding and quantifying the interactions between reduced-iron minerals and aqueous-phase oxidants. 相似文献
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700.
塔里木盆地库车坳陷东部阳霞煤矿一带出露绿泥绢云母石英片岩,原被划分为古元古界地层,该片岩中的碎屑锆石呈自形形态,锆石的环带丰富,具有典型的岩浆锆石特点。对锆石进行的ICP MS U Pb同位素地质年代学研究表明,锆石的年龄介于1179~794 Ma之间,峰期年龄集中于810~794 Ma,说明该片岩之原岩的沉积上限年龄不早于794 Ma。结合区域资料分析认为,该基底地层应该属于新元古界,形成时代相对较新,因此导致库车坳陷具有较高的地温梯度和较强的构造活动性。此外,在810~794 Ma时塔里木地块东北部发生过岩浆事件,该事件应该与塔里木地块的裂解有关。 相似文献