Morphometric analysis of a subtropical Andean basin (Tucumán, Argentina)

A morphometric analysis was done to determine the drainage characteristics of Lules River basin using land-sat imageries and topographical maps. This catchment was divided into seven sub-basins for the analysis: Liquimayo, Hoyada, Ciénaga, De Las Tablas, Siambón, Potrerillo and San Javier. Yungas ecoregion covers almost all the watershed. The drainage patterns of the sub-basins are dendritic and parallel. The basin includes seventh order stream and lower streams order mostly dominate the basin. The development of stream segments is affected by slope and local relief. The mean bifurcation ratio indicates that the drainage pattern is not much influenced by geological structures. The shape parameters also reveal the elongation of the basin and sub-basins.     

Mesoproterozoic diamondiferous ultramafic pipes at Majhgawan and Hinota, Panna area, central India: Key to the nature of sub-continental lithospheric mantle beneath the Vindhyan basin

Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites, dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’ mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (∼ 1100 Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics, such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar occurrences elsewhere.     

中国中新生代咸化湖盆烃源岩沉积的问题及相关进展

我国东部断陷湖盆和西部坳陷湖盆第三系均有蒸发岩与烃源岩共生现象。前者水体深、咸化范围小，在氯化盐和碳酸盐沉积环境中形成了优质烃源岩，后者水体浅、咸化范围大，在氯化盐和硫酸盐沉积环境中发育了优质烃源岩，作者认为两种湖盆出现的水体分层是有机质堆积和保存的重要条件。济阳坳陷和柴达木盆地为两类咸化湖盆的典型代表，对它们的研究可以深化蒸发岩-烃源岩共生区油气地质的认识、促进勘探发展。     

鄂尔多斯盆地北部底河道砂岩型铀矿地质特征

鄂尔多斯盆地北部直罗组中的铀矿,是典型的产于河道中的砂岩铀矿,该矿床发育较好的卷状矿体。通过对该铀矿地质特征的研究,认识到发育卷状矿体的底河道砂岩型铀矿必须具备两大条件:其一是成矿砂体条件,即砂体要有较好的成层性、连通性和渗透性;其二是地层结构条件,即砂体必须存在较好的上、下隔水岩层。就砂体而言,河流相辫状沉积砂体是形成卷状矿体的主要砂体,并且以具有从辫状河向曲流河完整演化的辫状沉积砂体较好。砂体的上、下隔水岩层则有多种表现形式:下隔水层可由不透水的基岩或湖相沉积泥岩等构成;上隔水层由不透水的湖相泥岩、曲流沉积地层或岩浆岩等构成。在层间氧化作用过程上,存在纵横两个方向的氧化,即存在与河道方向一致的纵向氧化和与河道垂直的横向氧化,两种氧化作用成矿常叠加形成复杂的矿体类型;在矿化赋存的部位上,铀砂体通常发育在基底之上或不同建造之间;在古气候演变上,成矿作用发生在干旱气候条件下,或由潮湿向干旱的气候转变阶段。     

深部找铀及湘南-桂北地区深部找铀潜景分析

概述了国内外深部找矿的研究成果,指出深部找矿是当今发展的趋势。国内外重大矿产的成功发掘,其深度均在千米以上,铀矿化垂向分布深度可达4 km以上。综合介绍了国内外勘查深大矿床的特点和条件,认为岩石-构造条件是深部矿化定位的重要因素,复式岩体、成矿系统的垂向变化、构造地球物理-地球化学异常模型是深部找矿的关键依据。综述了中国南方湘南—桂北地区深部找铀的有利地质构造条件和潜力,成矿流体是该区铀矿化的根源,白垩—第三纪重大地质事件是该区深部铀成矿的重要前提,重大地质事件引发的NE-NNE,NW向深大断裂及断陷盆地是铀矿化赋存的重要场所和勘查靶区。在已知铀矿田、成矿带勘查范围基础上,在该区进行深部探索将会获得重大突破。探讨了湘南—桂北地区深部找铀的勘查思路和方法。     

吉尔嘎朗图凹陷宝饶洼槽下白垩统层序地层与沉积体系

运用高分辨率层序地层学原理和方法,通过对钻井和地震资料的综合分析,在二连盆地吉尔嘎朗图凹陷下白垩统中识别出1个超长期基准面旋回(二级层序)SSC1和5个长期基准面旋回(三级层序):LSC1,LSC2,LSC3,LSC4,LSC5,分析了各旋回的发育特征。识别出五种类型的沉积体系:滨浅湖近岸水下扇、较深水湖浊积扇、滨浅湖扇三角洲、滨浅湖辫状河三角洲和河流沉积体系,并在等时地层格架内分析了各基准面旋回的沉积体系构成和储层砂体的发育情况。综合分析生、诸、盖条件后认为,在垂向上,LSC3旋回为本区最有利的储集层段,在平面上,本区的油气勘探应主要寻找宝饶构造带辫状河三角洲前缘砂体,主要储层砂体类型为前缘分流水道砂和前缘席状砂。     

参数在线自调整模糊控制算法研究

针对间歇式热处理炉温度控制对象的特性要求,提出了参数在线自调整模糊控制与智能积分相结合的一种新型模糊控制方法。该方法的基本思想是在系统误差较大时,用参数在线自调整模糊控制算法以提高系统的响应;在系统误差较小时,加入智能积分作用以消除静态误差,智能积分作用是有选择的施加积分作用,克服了一般连续积分控制的缺点。论述了带智能积分参数在线自调整模糊控制器的设计及软件实现。并且通过在MATLAB软件上的仿真分析表明该方法的合理性及可行性。     

致密砂岩孔隙度计算方法

鄂尔多斯盆地北部下二叠系下石盒子组为纵横向变化大,岩性、孔隙结构等复杂的河流相地层,很难用统一的计算公式来完成对孔隙度的计算。采用多元统计分析、散点图和孔隙度对比图来确定其孔隙度。运用上述方法,比较精确地确定鄂尔多斯盆地北部下二叠系下石盒子组的孔隙度,对鄂尔多斯盆地油气储量的估计,提供一个很好的基础资料。     

A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

1IntroductionThe northern segment of the South LancangjiangBelt refers to the terrain about200km east of theYunxian-Lingcang granite in the South LancangjiangBelt(Fig.1).During the seventh Five-Year Plan peri-od,Mo Xuanxue et al.(1993)undertook the resear…     

Vertical variation of phosphorus forms in surface sediments from Wuli Bay, Taihu Lake, China

1IntroductionPhosphorus,an essential nutrient for the primaryproductivity in freshwater systems,is an important fac-tor controlling lacustrine eutrophication.Although ex-ternal input of phosphorus has been assumed as the vi-tal responsibility for the eutrophication of lakes(ZhuJun et al.,2005),the remobilization of phosphorus insediments has a distinct influence on it as well(Bostr m et al.,1982).The concentrations of totalphosphorus(Ptotal)in the sediments are often related tothe trophic st…