海南岛白垩纪古地磁结果及其构造地质意义

对海南岛地区白垩系鹿母湾组和报万组碎屑岩219个独立定向岩芯样品(29个采点)的岩石磁学和古地磁学研究表明,白垩纪的碎屑岩以赤铁矿为主要载磁矿物。逐步热退磁分析表明,绝大多数样品可分离出特征剩磁分量。综合前人的结果,获早白垩世特征剩磁方向D=6.5°,I=42.7°,κ=73.4,α95=8.2°;晚白垩世特征剩磁方向D=6.7°,I=44.7°,κ=125.5,α95=5.4°。其早白垩世古纬度24.8°(+6.2°/-5.8°),晚白垩世古纬度26.3°(+4.6°/-4.0°);均位于现在地理位置以北约5°～6°。与华南板块东南缘白垩纪的古地磁数据对比表明,晚白垩世海南地块仍是华南板块的一部分。海南岛白沙断裂东西两侧早白垩世古地磁数据的差异,表明存在一个北东向的构造走滑带,白沙断裂可能是华南沿海北东向构造带的南延部分。海南岛白垩纪古地磁结果也表明,相对印支地块,海南岛在早白垩世时发生了25°左右局部顺时针旋转。推测此局部旋转很可能与晚侏罗世—晚白垩世早期,印度洋开始第一次海底扩张,印度板块向北运动有关。     

Groundwater resources management under environmental constraints in Shiroishi of Saga plain, Japan

A sinking of the land surface due to the pumping of groundwater has long been recognized as an environmental issue in the Shiroishi plain of Saga, Japan. Land subsidence can have several negative economic and social implications such as changes in groundwater and surface water flow patterns, restrictions on pumping in land subsidence prone areas, localized flooding, failure of well casings as well as shearing of structures. To minimize such an environmental effect, groundwater management should be considered in this area. In this study, a new integrated numerical model that integrates a three-dimensional numerical groundwater flow model coupled with a one-dimensional soil consolidation model and a groundwater optimization model was developed to simulate groundwater movement, to predict ground settlement and to search for optimal safe yield of groundwater without violating physical, environmental and socio-economic constraints. It is found that groundwater levels in the aquifers greatly vary from season to season in response to the varying climatic and pumping conditions. Consequently, land subsidence has occurred rapidly throughout the area with the Shiroishi plain being the most prone. The predicted optimal safe yield of the pumping amount is about 5 million m³. The study also suggests that pumping with this optimal amount will minimize the rate of land subsidence over the entire area. An erratum to this article can be found at     

扬子地台西南缘高家村岩体成因：岩石学、地球化学和年代学证据

高家村岩体辉长岩-橄榄岩中矿物组合、矿物结晶顺序及岩浆成因角闪石的普遍出现,指示矿物结晶于富含水的岩浆体系.主量元素Al2O3、CaO与MgO呈明显的负相关关系,表明斜长石并非早期堆晶相.稀土元素含量为5.97×10-6～221.32×10-6,轻稀土元素相对富集,弱-中等程度轻重稀土元素分异,辉长岩-含辉石闪长岩无明显的Eu异常,而橄榄辉长岩-橄榄岩具有较明显的正Eu异常.微量元素中,辉长岩-含辉石闪长岩类具有明显的Nb、Ta、Zr、Hf和Ti负异常,Ba、Sr正异常,同时εNd(t)为0.59～1.86,低于同期的亏损地幔值,与岛弧基性岩浆特征类似.含辉石闪长岩SHRIMP锆石U-Pb年龄结果822±8Ma,为新元古代.综合分析认为,高家村岩体应形成于受俯冲带流体改造的亏损上地幔部分熔融.     

Simulation of groundwater flow and environmental effects resulting from pumping

In coastal lowland plains, increased water demand on a limited water resource has resulted in declining groundwater levels, land subsidence and saltwater encroachment. In southwestern Kyushu, Japan, a sinking of the land surface due to over pumping of groundwater has long been recognized as a problem in the Shiroishi lowland plain. In this paper, an integrated model was established for the Shiroishi site using the modular finite difference groundwater flow model, MODFLOW, by McDonald and Harbaugh (1988) and the modular three-dimensional finite difference groundwater solute transport model, MT3D, by Zheng (1990) to simulate groundwater flow hydraulics, land subsidence, and solute transport in the alluvial lowland plain. Firstly, problems associated with these groundwater resources were discussed and then the established model was applied. The simulated results show that subsidence rapidly occurs throughout the area with the central prone in the center part of the plain. Moreover, seawater intrusion would be expected along the coast if the current rates of groundwater exploitation continue. Sensitivity analysis indicates that certain hydrogeologic parameters such as an inelastic storage coefficient of soil layers significantly contribute effects to both the rate and magnitude of consolidation. Monitoring the present salinization process is useful in determining possible threats to fresh groundwater supplies in the near future. In addition, the integrated numerical model is capable of simulating the regional trend of potentiometric levels, land subsidence and salt concentration. The study also suggests that during years of reduced surface-water availability, reduction of demand, increase in irrigation efficiency and the utilization of water exported from nearby basins are thought to be necessary for future development of the region to alleviate the effects due to pumping.     

地下水溶质运移三维有限元模拟软件的设计与应用

介绍了含水层系统地了下水溶质运移三维有限元要模拟软件（ＧＴＳ３ｄ）的设计思路，该软件充分考虑到从模型的建立，数据与参数的输入，模拟计算到计算结果可视化与表达的整个过程，通过键盘或鼠标控制下拉式菜单结构而有机地组织在一起，实现了数据输入，计算结果输出的全部图形功能，该软件成功地用于广西北海市涠洲岛含有水层系统的海水入侵模拟研究     

Groundwater in a coral island

 Freshwater aquifers in small coral islands usually occur as thin lenses which are significantly influenced by stresses such as groundwater pumping, sea tides, etc. Kavaratti, a coral island, is one of the 36 such islands in the Arabian Sea off the western coast of India. Detailed hydrogeological investigations were carried out to determine the quantity of freshwater that could be pumped in addition to the present usage. Salinity of groundwater must remain within permissible limits and a 2-D solute mass transport model with a vertical section of the island was constructed by the computer code SUTRA. The model was calibrated by obtaining a match of computed and observed values of the water table, tidal efficiency, and salinity of groundwater at the water table. The model analysis showed that the salinity of groundwater continues to increase unless groundwater pumping is kept below a certain rate. Groundwater potential can be augmented by reducing the subsurface outflow to the sea and by raising the water table by a subsurface dam. Received: 8 September 1997 · Accepted: 27 April 1998     

西藏冈底斯带洛巴堆组火山岩地球化学及构造意义

冈底斯带中-新生代火山岩的成因和地质演化是青藏高原地质研究的热点领域,但是对晚古生代火山岩的性质及其形成的构造背景仍缺乏研究.冈底斯带二叠系显示缓慢的海退过程,并伴随基性和中酸性两期火山活动,具有活动大陆边缘特征.笔者对墨竹工卡县唐家乡和林周县勒青拉地区二叠纪洛巴堆组火山岩进行了常量、微量元素和St、Nd、Pb同位素地球化学测试.研究认为二叠纪是冈底斯岛弧的形成和演化时期.洛巴堆组玄武岩从下部(可能为早二叠世)到上部(中二叠世),MgO含量从7.43%降到3.99%,Al2O3含量从15.54%上升到17.57%,后者类似于岛弧高铝玄武岩;稀土总量∑REE从54.12(10-6)上升到108.82(10-6),LREE/HREE比值从3.00上升到5.40.洛巴堆组玄武岩均具有明显的Nb、Ta负异常,但中二叠世更显著.岩石地球化学示踪表明,冈底斯洛巴堆组玄武岩代表二叠纪初始岛弧环境.早期玄武岩形成于略亏损地幔和下地壳成分的混合源区,地壳相对较薄,源区或岩浆的壳源成分比例较低.到中二叠世地壳逐渐加厚.壳源成分在源区或岩浆中所占比例增大,代表向陆缘弧的演化过程.冈底斯带二叠纪岛弧是古特提斯洋向南的俯冲、消减的产物.     

Heavy Metal Distributions and Source Tracing in the Lacustrine Sediments of Dongdao Island, South China Sea

The levels and depth distributions of As,Cd,Cu,Zn,Pb,Hg,Fe and Mn in two sediment cores DY2 and DY4 collected from the"Cattle Pond"of Dongdao Island,South China Sea,were determined and analyzed with the main objective to identify the sources of these elements and evaluate the corresponding sedimentological and geochemical processes.Lithological characters and sedimentary parameters such as LOI_(950℃),CaO,LOI_(550℃) and TOC indicate that the depth of 96 cm and 87 cm are the critical points for DY2 and DY4 cores,respectively.As,Cd,Cu,Zn,Hg and P are remarkably enriched in the ornithogenic sediments above the critical depth points;their concentration-versus-depth profiles are similar to those of TOC and LOIssooc;the ratios of As,Cd,Cu, Zn,Hg over Ca are significantly correlated with P/Ca.Statistical and comparative analyses of these elements' levels in the ornithogenic sediments of DY2 and DY4 strongly suggest that seabird droppings are the main source of these elements.Additionally,for the upper sediment layers of DY2 and DY4 cores,Fe oxide sorption mechanism,like organic matter,may also play an important role in the abundances of heavy metals.Heavy metal Pb has geochemical characteristics distinctly different from those of As,Cd,Cu,Zn,Hg and P,and its isotope composition indicates an origin of anthropogenic emissions from the surrounding countries.These geochemical characteristics in the orinithogenic sediments of Xisha Islands are compared with the studies in the remote Antarctic and Arctic regions.     

Lateral textural grading in overwash sediments

Overwash deposits are characterized by horizontally layered laminations. Vertical sequences could be interpreted in terms of individual storm deposits by recognizing time breaks or discontinuities in the stratigraphic section. Results from comparison of channel deposit data for textural grading across the washover fan were inconclusive. Samples taken from individual laminations revealed the true textural grading when traced along a 61 m trench and sampled at designated localities. The overwash deposit was found to become finer in grain size from the apex to the margins of sedimentation in the direction of transport.     

海南抱板金矿田流体包裹体地球化学研究

对海南抱板金矿田的外山，抱板和二甲等三个金矿进行的液体包裹体研究表明成矿流体为低盐度（０．１－６ｗｔ％ＮａＣｌ），中低温（２００－２４０℃）热液，处于中低压力（６０－１６０ＭＰａ）下，其ＣＯ２含量较低，探针质谱分析表明流体包裹体中存在Ｈ２Ｓ，结合ＳＯ＾２－４的存在，金在热液中可能是以硫氢络合物的形式迁移的。