华北克拉通南缘早白垩世天目山A型花岗岩的锆石稀土元素和岩石地球化学特征

天目山正长花岗岩位于华北克拉通南缘、北秦岭构造带及桐柏—大别造山带构造拼合地区,其岩石成因模型可为秦岭—大别造山带燕山期深部构造演化提供新的限定。它的n(206Pb)/n(238U)加权平均年龄为129. 2±1. 7 Ma,形成于早白垩世。天目山花岗岩锆石稀土元素具有轻稀土亏损、重稀土富集、Ce和Sm正异常及明显Pr、Nd和Eu负异常（δEu值介于0. 01 ~ 0. 19）,锆石的形成温度介于603 ~ 788 ℃之间,天目山锆石/熔体体系中稀土元素分配系数波动特征表明其形成中存在深部岩浆/流体混合作用。天目山花岗岩样品具有富硅、碱和贫钙、镁的特征,在SiO2 —K2O图解中落入高钾钙碱性系列。在微量元素蛛网图中,它们显示了明显的Rb、Th及Zr、Hf的异常峰和Sr、P、Ti的异常谷。它们的稀土总量介于106??10-6~ 139??10-6之间,(La/Yb)N值范围是5. 94 ~ 9. 22,其稀土配分模式具轻稀土富集、中稀土亏损和重稀土略微富集的“V”型（海鸥型）特征,Eu负异常明显（δEu值介于0. 06 ~ 0. 16）。它们的10000Ga/Al值介于3. 38 ~ 4. 15,Nb和Ta的含量分别为63. 5??10-6~ 131??10-6和3. 20??10-6~ 7. 55??10-6（Nb/Ta值介于17. 3 ~ 22. 9）,天目山花岗岩属于A型花岗岩中富Nb的A1亚类。天目山花岗岩部分熔融源区位于角闪岩相,源区残余相主要为角闪石和斜长石且无石榴子石残余。天目山花岗岩形成于板内构造环境,它是早白垩世~130 Ma桐柏山三合店—鸡公山区域岩石圈拆沉作用的岩浆响应,幔源富Nb岩浆/流体因此得以快速释放,上侵途中混合活化壳源岩浆/流体库之后就位固结成岩。     

赤峰南部金地球化学块体评价

以“地球化学块体”理论为基础,以赤峰南部的区域地质为背景,利用1/20万化探扫面所提供的地化信息,对该区域的金矿资源特征进行了系统研究。圈出地球化学块体1个,区域地球化学异常体8个;并提出：北东向断裂与东西向断裂交汇部位、太古界矿源层及其附近及燕山早期中酸性侵入岩体及其附近为地球化学块体含矿的主要标志。     

Structure and deformation around the Gyirong basin,north Himalaya,and onset of the south Tibetan detachment system

Gyirong basin and its adjacent area are located at a special position in the Himalayan orogen, where the south Tibetan detachment system (STDS) and N-S trending rift converged. The north Himalayan orogen here can be divided into five petrologic-tectonic units successively from south to north: 1) the Greater Himalayan crystalline complex (GHC); 2) the STDS shear zone; 3) the Tethyan Himalayan sedimentary sequence (THS); 4) the late Cenozoic sedimentary basins, such as Gyirong and Oma basins; and 5) the Malashan gneiss dome. Structural studies show that this area experienced four stages of deformation: 1) the earlier south-directed thrusting, preserved both in the GHC and THS; 2) top-down-to-north slip along the STDS, normal faults related to this slip formed the early controlling structures of the Cenozoic basins, and the tilted pattern of the blocks between the basins indicated a north-directed slip; 3) east-west extension, the resultant N-S trending normal fault formed the eastern boundary of the basins; and 4) late gravitational collapse. Zircon SHRIMP U-Pb dating on the syn-deformational (leuco-) granite along the STDS indicates that the major activity of the STDS occurred at ca. 26 Ma, but its onset may have begun as early as ca. 36 Ma. Supported by National Natural Science Foundation of China (Grant Nos. 40821002, 40572115)     

LOCAL SCOUR ESTIMATION AT CHECK DAMS IN TORRENTIAL STREAMS IN SOUTH EAST SPAIN

For several decades, the check dam building has been one of the most commonly used structural measures in the Forestry Hydrological Restoration Programs and Plans in the torrential basins of south east Spain. Two examples are the catchments studied here, drained by the Cárcavo and Torrecilla torrential streams belonging to the Segura Basin. Obtaining a more stable bed and a less powerful flow requires transitory hydro-morphological stages such as check dam filling upstream or local erosion downstream. The main aims of this paper are to estimate local scouring induced by check dams downstream, and to find evolution stages of scouring depth, the response time of the local erosion point and the local maximum depth to reach a stable bed situation. To do this, the results obtained by different methods were compared with measured scour depths for various hydraulic radii. From this comparison, performed in non-uniform sediment size beds and in clear-water conditions, the Fahlbusch's formula gives a better fit, while the Jaeger's and Bormann and Julien's methods tend to underestimate the results. These may be used to calculate local instantaneous scouring in flows less than bankfull, but give a worse estimate for maximum equilibrium scouring. Under active bed conditions, the temporal response of the cross-sections experiencing local scour processes below these structures reflects the variations in hydraulic regime during flooding. In general, a rapid evolution phase is followed by a slow stage, which in the most torrential sectors has still not reached the equilibrium threshold.     

冲绳海槽南部基底构造特征

利用最新的重磁数据对冲绳海槽南部的基底构造进行了推断解释,研究表明,在冲绳海槽南部,莫霍面构造为一南北两端高,中间低的鞍状构造,地壳厚度在15.5~21 km之间变化.基底深度一般在4~6 km之间变化,表现为南段深度大,北段深度小,在北西向断裂系的作用下,基底局部构造大都成北西向展布,说明冲绳海槽早期的北东向带状构造受到了后期的北西向构造活动的强烈改造作用.在冲绳海槽南部发育有两条沿北北东向展布的火成岩带,一条分布在冲绳海槽扩张轴以东及琉球岛弧西侧下坡;另一条分布在冲绳海槽与琉球岛弧隆褶带的结合部位,火成岩主要是由北东向构造活动产生的,而与北西向断裂关系不密切.     

藏南拉轨岗日变质核杂岩带三层结构的影像证据及意义

拉轨岗日变质核杂岩带是喜马拉雅造山带的组成部分,从几何学角度查明其结构是该变质核杂岩带研究的一个重要内容。利用遥感技术来宏观地研究该变质核杂岩带的空间结构及物质组成,是对野外调研成果的有效验证和有益补充。从遥感图像信息提取的结果可以看出,变质核、过渡带及盖层在色调(色彩)、空间形态、水系类型与分布状况、影纹图案等各个方面均存在不同程度的差异。这些光谱及空间特征的综合使得变质核杂岩的三层结构被清晰地显现出来,尤其是过渡带的弱信息也在有TM6加入的K-L变换等图像处理手段中被有效地提取出来,从而更确切地证明该变质核杂岩带具有三层结构。同时,结合已有资料从遥感信息机理方面探讨三层结构各自的物质组成及其演变,为西部地区深入分析区域地质构造提供了一种有效的方法。     

Characterization of seasonal local recharge using electrical resistivity tomography and magnetic resonance sounding

A groundwater recharge process of heterogeneous hard rock aquifer in the Moole Hole experimental watershed, south India, is being studied to understand the groundwater flow behaviour. Significant seasonal variations in groundwater level are observed in boreholes located at the outlet area indicating that the recharge process is probably taking place below intermittent streams. In order to localize groundwater recharge zones and to optimize implementation of boreholes, a geophysical survey was carried out during and after the 2004 monsoon across the outlet zone. Magnetic resonance soundings (MRS) have been performed to characterize the aquifer and measure groundwater level depletion. The results of MRS are consistent with the observation in boreholes, but it suffers from degraded lateral resolution. A better resolution of the regolith/bedrock interface is achieved using electrical resistivity tomography (ERT). ERT results are confirmed by resistivity logging in the boreholes. ERT surveys have been carried out twice—before and during the monsoon—across the stream area. The major feature of recharge is revealed below the stream with a decrease by 80% of the calculated resistivity. The time‐lapse ERT also shows unexpected variations at a depth of 20 m below the slopes that could have been interpreted as a consequence of a deep seasonal water flow. However, in this area time‐lapse ERT does not match with borehole data. Numerical modelling shows that in the presence of a shallow water infiltration, an inversion artefact may take place thus limiting the reliability of time‐lapse ERT. A combination of ERT with MRS provides valuable information on structure and aquifer properties respectively, giving a clue for a conceptual model of the recharge process: infiltration takes place in the conductive fractured‐fissured part of the bedrock underlying the stream and clayey material present on both sides slows down its lateral dissipation. Copyright © 2007 John Wiley & Sons, Ltd.     

Petrogenetic Model of A-Type Granitoids of the Kullampatti Area, Salem District, Tamil Nadu, India

The late Proterozoic granitoids at Kullampatti are of A-type and comprise three phases: (1) barren phase I (granite-adamellite), (2) fertile phase II (trondjhemite) and (3) rarely-mineralized phase III (pegmatitic granite). They were emplaced within the Archean cratonic granulite terrane of southern India, close to the Moyar-Bhavani-Attur shear zone, and form a consanguinous association with the Suriyamalai or Sankari granite-adamellite batholithic dome. On the basis of their field, tectonic, petromineragraphic and geochemical aspects, a petrogenetic model involving a two-stage melting of an undepleted middle to lower crustal granulitic protolith is envisaged. In this, the first-stage melting led to the formation of an LCT-rich hydrous melt that was removed from the site of its generation, followed by second-stage partial melting of the depleted granulite during post-orogenic or anorogenic environment, resulting in the HCD- and HFS-rich, NYF- and A-type melt that on fractional crystallization, together with hydrothermal activity, led to the formation of these granitoids.     

Use of remote sensing,GIS and C++ for soil erosion assessment in the Shakkar River basin,India

Soil is an essential resource for human livelihoods. Soil erosion is now a global environmental crisis that threatens the natural environment and agriculture. This study aimed to assess the annual rate of soil erosion using distributed information for topography, land use and soil, with a remote sensing (RS) and geographical information system (GIS) approach and comparison of simulated with observed sediment loss. The Shakkar River basin, situated in the Narsinghpur and Chhindwara districts of Madhya Pradesh, India, was selected for this study. The universal soil loss equation (USLE) with RS and GIS was used to predict the spatial distribution of soil erosion occurring in the study area on a grid-cell basis. Thematic maps of rainfall erosivity factor (R), soil erodibility factor (K), topographic factor (LS), crop/cover management factor (C), and conservation/support practice factor (P) were prepared using annual rainfall data, soil map, digital elevation model (DEM) and an executable C++ program, and a satellite image of the study area in the GIS environment. The annual rate of soil erosion was estimated for a 15-year period (1992–2006) and was found to vary between 6.45 and 13.74 t ha^?1 year^?1, with an average annual rate of 9.84 t ha^?1 year^?1. The percentage deviation between simulated and observed values varies between 2.68% and 18.73%, with a coefficient of determination (R²) of 0.874.     

Assessment and evaluation of potential climate change impact on monsoon flows using machine learning technique over Wainganga River basin,India

In this study, classification- and regression-based statistical downscaling is used to project the monthly monsoon streamflow over the Wainganga basin, India, using 40 global climate model (GCM) outputs and four representative concentration pathways (RCP) scenarios. Support vector machine (SVM) and relevance vector machine (RVM) are considered to perform downscaling. The RVM outperforms SVM and is used to simulate future projections of monsoon flows for different periods. In addition, variability in water availability with uncertainty and change point (CP) detection are accomplished by flow–duration curve and Bayesian analysis, respectively. It is observed from the results that the upper extremes of monsoon flows are highly sensitive to increases in temperature and show a continuous decreasing trend. Medium and low flows are increasing in future projections for all the scenarios, and high uncertainty is noticed in the case of low flows. An early CP is detected in the case of high emissions scenarios.