MODELING OF THE DIVERSION CHANNEL CLOSURE FOR THE THIRD STAGE OF THE THREE GORGES PROJECT

The closure of third stage diversion channel for the Three Gorges Dam is characterized by large closure discharge, large drop in water surface, and high gap velocity. 1D and 2D flow mathematical models were used in this paper to simulate the hydraulic conditions during the closure. The variation of discharge in the diversion channel and the drops in water surface shared by the upstream and downstream cofferdams were computed using the ID model, and the detailed hydraulic patterns in the diversion channel were simulated using the 2D model. The computed results indicate that the designed closure scheme for discharge of 9,010 m^3/s was feasible for construction, while the designed closure scheme for discharge of 12,200 m^3/s was inapplicable.     

Denitrification in Qi'ao Island coastal zone, the Zhujiang Estuary in China

Samples of sediments and the overlying water were collected in the Qi'ao Island coastal zone, the Zhujiang (Pearl River) Estuary (ZE). Denitrification rates, sediment oxygen demand (SOD) , and fluxes of inorganic nitrogen compounds were investigated with N2 flux method, using a self-designed continuous flow through and auto-sampling system. The results indicate that the denitrification rates varied between 222 and 908 μmol/(m2·h) with an average of 499 μmol/(m2·h). During incubation, the sediments absorbed dissolved oxygen in the overlying water with SOD ranging from 300 to 2 363 μmol/(m2·h). The denitrification rates were highly correlated with the SOD (r2 =0.77) regardless of the NO3- + NO2- concentrations in the overlying water, organ- ic carbon contents in sediments and water temperature, suggesting that the SOD was probably the main environ-mental factor controlling the denitrification in the Qi'ao Island coastal zone. There was a net flux of NO3- + NO2-into the sediments from the overlying water. The NH4+ flux from sediments into water as the result of mineraliza-tion was between 12. 3 and 210. 3 μmol/(m2·h) ,which seems limited by both organic carbon content in sedi-ment and dissolved oxygen concentration in the overlying water.     

环流分解及其在沉积地层旋回分析中的应用

本文应用马尔柯夫链进行地层序列分析。当一个地层序列形成一个具有马尔柯夫性质和极限概率分布的马尔柯夫链时,它的转移概率矩阵可分解为细致平衡部分和环流部分。根据环流矩阵可确定该序列中的主要沉积旋回趋势,为地层序列分析提供重要依据。本文给出了两个研究实例。     

EUTROPHICATION AND RED TIDES AS CONSEQUENCES OF ECONOMIC DEVELOPMENT

1 mTRoorcnoxThe EnvirDment AgenCy of UK (l997) defins eUtIDPhication as "the enrichInnt of waters byinorgedc plant nUtrientS that result in the simulation of an mp Of syInPtOInati changes. These includethe inCrased PrOduCtiOn Of aigae or othe aquatic PlantS, affeChng the quallty of the water and distUIbingthe balance Of orpedsms Present within it. Such changes Inay be undesirable and intetw with wateuses." Sndth et al. (l999) indicated tha eopation of waters is mainly caused by h…     

Sea-level changes and hydrothermal sedimentary mineralization of large-superlarge ore deposits among Sinian to Triassic in South China

Among the Sinian to Triassic strata in South China, the stratiform, quasi-stratiform and lenticular metallic deposits in association with hydrothermal sedimentation mainly occur in the four periods: (1) the Sinian Datangpo interglacial period, (2) the early period of Early Cambrian, (3) the late period of Middle Devonian to early period of Late Devonian, and (4) the late period of Early Permian. The four mineralization periods all happened around the maximum flooding period in the third-order seal-level cycle during the ascending stage in the first-order sea-level cycle. The deep seawater layer, starved and non-compensatory basin, low sedimentary rate, and low energy and anoxic environment during the maximum flooding period are very suitable for the formation and preservation of large to superlarge hydrothermal sedimentary deposits. The maximum flooding period also coincided with the intensified regional tectonism, extensive deep magmatism and hydrothermal sedimentation, which provide, for the formation of large to superlarge hydrothermal sedimentary deposits through the rapid accumulation of hydrothermal sediments, the needed dynamics, ore-forming materials and favorable passway for hydrothermal fluids to enter the basin.     

华南震旦纪基性火山岩的地球化学及构造环境

华南地区产于震旦纪地层中的火山岩主要见于震旦纪裂谷盆地两侧的边缘,湖南新化和广东高思火山岩为其中的二个发育地区,镜下鉴定为玄武岩系。在ＳｉＯ２－Ｋ２Ｏ＋Ｎａ２Ｏ的分类图中主要为玄武岩类,有一样品为碧玄岩类,含有较多石英杏仁体玻璃质火山岩角砾的样品为玄武质安山岩类。在ＦｅＯ＊－Ｎａ２Ｏ＋Ｋ２Ｏ－ＭｇＯ三角图中所有样品均为拉斑质岩系。样品的重元素丰度模式具大陆－初始裂谷－Ｅ－ＭＯＲＢ拉斑玄武岩的过渡特征,在Ｎｂ、Ｚｒ、Ｙ、Ｔｉ图上属板内环境。在ＴｉＯ２－Ｋ２Ｏ－Ｐ２Ｏ５三角图上显示以大洋环境为主、大陆环境为次。湖南新化拉斑玄武岩的Ｓｍ、Ｎｄ同位素特征反映岩浆来源于亏损的地幔,并受到了老基底的污染。     

华南晚古生代礁硅岩套的组成和分类及地质涵义

礁硅岩套是一种重要的含矿岩石组合,它是由生物礁相碳酸盐岩、热水沉积岩（矿）、细碎屑岩和泥灰岩、同怪位或相邻地区地层中的火山质岩或潜火山岩,以较为固定的时空有序的状态组合而成。根据生物礁的形成环境和热水沉积作用的产出方式,礁硅岩套可分为盆地型、台地型和过渡型三类。它是在特征地质背景下,在盆地演化的一定阶段内,由盆地正常沉积作物、盆地中的生物作用、盆下源的热水沉积作用和岩石圈深部岩浆作用综合形成的产物     

浙江景宁鹤溪群斜长角闪岩变质新生锆石特征、离子探针(SHRIMP)U-Pb年龄及地质意义

景宁鹤溪群斜长角闪岩变质新生锆石特征是粒度均匀（约70μm）,晶体结晶和透明度极好,色调一致的淡粉红色,呈金刚光泽．未见裂隙、表面熔蚀、环带和核心构造。离子探针质谱GHRIMPⅡ）的206Pb／238U、207Pb／235U两组年龄在误差范围内基本谐和,206Pb／238U年龄的加权平均值（252±5Ma）为变质新生铁石的结晶年龄。锆石的精确定年（252±5Ma）为丽水—余姚断裂以东地区呈“天窗式”零星出露于中生代火山岩系中的鹤溪群提供了一个变质作用的确切年龄,也为印支运动在丽水—余姚断裂以东地区的存在提供了重要的年代学佐证。     

Temporal and spatial variations of potential evaporation and the driving mechanism over Tibet during 1961–2001

Potential evaporation (PE) is the basic component of the global hydrological cycle and energy balance. This study detected the temporal and spatial variations of PE and related driving factors in Tibet, China, for the period 1961–2001, based on observed data recorded at 22 meteorological stations. The results showed that (1) Tibet experienced a statistically significant decrease of PE between 1961 and 2001, which started mainly in the 1980s, along with accelerated warming; (2) the mean annual PE in Tibet showed an east–west increasing trend, and the annual PE at most stations presented decreasing trends; (3) an inverse correlation of mean annual PE with elevation was detected (low–high decreasing trend), and the statistical equations to estimate PE were established based on longitude, latitude and elevation; and (4) PE in Tibet can be well expressed by related meteorological variables, with vapour pressure deficit the dominant factor in determining PE.

EDITOR Z. W. Kundzewicz ASSOCIATE EDITOR not assigned     

沉降监测网络的数据处理方法

传统意义上的沉降监测网的数据处理大多采用自由网平差的方法,需进行大量的矩阵计算,内业工程浩繁。本文以杭州市沉降监测网为例,充分利用了其监测网络的结构特点,提出了采用间接平差法,即按路线测站数定权对结点网先行平差,减少了计算强度,便于实现程序模块化处理;最后对今后的研究方向提出了建议。