Early Palaeozoic sub-arc chromitite-bearing peridotite in the Kudi ophiolite on the westernmost Tibetan Plateau

ABSTRACT

A chromite deposit was discovered in the Kudi ophiolite in the Palaeozoic western Kunlun orogenic belt. Chromite forms elongated (<2 m in width) and banded chromitite bodies (<0.1 m in width for each band) in dunite and podiform chromitite bodies (<1.5 m in width) in harzburgite. Dunite is classified into two types. Type I dunite hosting massive and banded chromitites shows low Fo in olivine (88.1–90.9), moderate Cr^# [=Cr/(Cr + Al), 0.47–0.56] in chromite, and a positively sloped primitive mantle-normalized platinum group elements (PGE) pattern, suggesting that it is a cumulate of a mafic melt. Harzburgite and type II dunite show olivine with high Fo (>91.1) and chromite with moderate to high Cr^# (0.44–0.61), and flat to negatively sloped primitive mantle-normalized PGE patterns, indicating that they are residual mantle peridotite after partial melting. Chromite in all three types of chromitites has relatively uniform moderate values Cr^# ranging from 0.43 to 0.56. Massive chromitite contains euhedral chromite with high TiO₂ (0.40–0.43 wt.%) and has a positively sloped primitive mantle-normalized PGE pattern, suggesting that it represents a cumulate of a melt. Rocks containing disseminated and banded chromite show overall low total PGE, < 117 ppb, and a negatively sloped primitive mantle-normalized PGE pattern. Chromite grains in these two types of occurrences are irregular in shape and enclose olivine grains, suggesting that chromite formed later than olivine. We suggest that chromite-oversaturated melt penetrated into the pre-existing dunite and crystallized chromite. The oxygen fugacity (fO₂ values of chromitites and peridotites are high, ranging from FMQ+0.8 (0.8 logarithmic unit above the fayalite-magnetite-quartz buffer) to FMQ+2.3 for chromitites and from FMQ+0.9 to FMQ+2.8 for peridotites (dunite and harzburgite). The mineral compositions and high fO₂ values as well as estimated parental magma compositions of the chromitites suggest that the Kudi ophiolite formed in a sub-arc setting.     

钦杭成矿带西段古龙花岗岩株群岩石学、地球化学及年代学

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宁夏王洼煤矿补充勘探区8号煤组特征及对比研究

宁夏王洼煤矿补充勘探区延安组第二含煤段中8号煤组厚度大、结构复杂,在详细叙述8煤组各分煤层特征基础上．根据标志层特征、层间距特征及地球物理特征对各分煤层进行了对比,对比结果显示,8煤层为煤组主体煤层,厚度变化小,属稳定煤层;8—2煤层为局部可采不稳定煤层;8—3煤层为有可采见煤点但不连成片的不可采煤层;勘探区西部边界外由于地处鄂尔盆地盆地边缘存在无煤区。     

Dragon Tails: Convergent Caudal Morphology in Winged Archosaurs

In the tails of dromaeosaurid dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally. The fully articulated and three-dimensionally preserved caudal series of some dromaeosaurid specimens show that individually these caudal rods were flexible, not rigid as previously thought. However, examination of the arrangement of the caudal rods in cross-section indicates that the combined effect of multiple caudal rods did provide substantial rigidity in the dorsoventral, but not in the lateral, plane. The results of digital muscle reconstructions confirm that dromaeosaurids and rhamphorhynchids also shared greatly reduced caudofemoral muscles in the anterior tail region. The striking similarities between the tails of dromaeosaurids and rhamphorhynchids suggest that both evolved under similar behavioral and biomechanical pressures. Combined with recent discoveries of primitive deinonychosaurs that phylogenetically bracket the evolution of dromaeosaurid caudal rods between two arboreal gliding/flying forms, these results are evidence that the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.     

宁强县小燕子沟金矿地质特征及成矿条件浅析

勉略宁三角区分布大量的韧性剪切带型金矿。小燕子沟金矿按矿化类型可分为石英脉型、构造蚀变岩型、磁铁石英岩型等,主要控矿因素为碧口群地层及韧性剪切带,其中韧性剪切变形对矿体的形成起了主导控制作用。     

陕北延河流域水土资源承载力评价研究

基于陕北延河流域2000-2009年的水土资源相关数据,依据《国家人口发展功能区工作技术导则》中对水土地资源承载力的测评模型,计算流域水土资源承载力和承载指数,并对比评价了流域各区县的水土资源承载现状。结果表明:①延河流域各区县的水资源承载状况均为超载,其中延长县和志丹县为过载,宝塔区和安塞县为严重超载。②延河流域各区县的土地资源承载状况存在一定的地域差异性,其中宝塔区和延长县的为严重超载,安塞县和志丹县的为平衡有余。研究可为水土资源在县域之间、省际之间等不同级别行政区域中的合理均衡和分配提供科学依据。     

辽宁瓦房店金伯利岩中尖晶石族矿物种类划分及指示意义

晶体矿物学理论认为不同成岩环境金伯利岩中尖晶石族矿物由于形成物理化学条件不同,其晶体结构和化学成分会发生明显的变化,通过对无矿、贫矿、富矿金伯利岩岩管中的尖晶石族矿物晶胞参数和化学成分的测定,研究尖晶石族矿物化学成分和晶胞参数变化与无矿、贫矿、富矿金伯利岩的内在关系,可以提高金伯利岩型金刚石矿床找矿效率。为了确定辽宁瓦房店金伯利岩中的尖晶石族矿物种属,探讨辽宁瓦房店金伯利岩中尖晶石族矿物化学成分和晶胞参数与金伯利岩含矿性关系,本文运用电子探针波谱仪对50件尖晶石族矿物中的MgO、FeO、TiO2、Al2O3、MnO及Cr2O3进行微区化学成分分析,运用单晶X射线衍射仪对136个尖晶石族矿物晶胞参数进行测定。数据统计显示:瓦房店金伯利岩中尖晶石族矿物为铬铁矿和镁铬铁矿,以化学分子式中A、B组主要阳离子占位特征为基础,可把矿区的尖晶石族矿物划分为10个亚种;如果用尖晶石族矿物化学成分中Cr2O3与(Cr2O3+Al2O3)含量的比值Cr'来表示尖晶石族矿物与金伯利岩含矿性的关系,金伯利岩岩体含矿性由富矿→中等含矿→贫矿,相应岩体中尖晶石族矿物Cr'值分别为89.5%、83.4%~87.1%和70.2%,逐渐变低;从无矿金伯利岩岩体→贫矿和中等含矿金伯利岩岩体→富矿金伯利岩岩体,金伯利岩体中第一世代尖晶石族矿物晶胞参数分别为0.831~0.832 nm、0.834~0.836 nm、0.837 nm,有逐渐变大的趋势。本文认为,辽宁瓦房店金伯利岩中第一世代尖晶石族矿物晶胞参数大小和Cr'参数可以作为判断辽宁瓦房店金伯利岩含矿性的指示标型。     

干酪根分子结构在低熟阶段的演化特征：基于红外光谱分析

为研究低熟气形成过程中大分子结构的变化情况,对吐哈盆地侏罗系八道湾组的煤与碳质泥岩干酪根在不同升温速率下进行了热解实验,借助于红外光谱分析,研究了不同热模拟温度下干酪根结构的特征与变化。结果表明,随热演化的进行,煤与碳质泥岩干酪根的芳香结构不断缩合,含氧官能团不断脱落,碳质泥岩干酪根中的脂肪族类有所降低。吐哈盆地低熟气主要来源于煤与碳质泥岩干酪根中的含氧官能团--羧基与甲氧基,以及碳质泥岩干酪根上的脂肪族。从干酪根结构上揭示了低熟气主要来源于Ⅲ型有机质的原因。     

相山火山盆地西部铀矿床分布特征

相山铀矿田目前已发现的矿床主要分布于火山盆地西部和北部。笔者通过对盆地西部铀矿床分布特征、断裂构造及火山岩组间界面控矿特点的研究,认为铀矿区域上受断裂构造控制;火山岩组间界面为铀矿富集空间,西部铀矿床主要富集于火山岩组间界面附近。     

基于动态空间面板模型的中国港口竞争与合作关系研究

港口之间的竞争与合作关系是港口资源整合所要理顺和优化的关键问题,关系着港口体系的健康可持续发展。本文采用动态空间面板模型,研究了2000年以来中国港口整体及沿海和内河各区域港口群的竞争与合作关系,并探讨其影响因素。研究表明：中国港口货物吞吐量和集装箱吞吐量存在空间正相关性,且呈现逐渐增强的趋势;从货物吞吐量看,全国范围内的港口和内河港口之间不存在显著的竞争效应,沿海港口之间竞争态势显著,而三者在集装箱运输方面均为竞争关系;五大沿海港口群在货物吞吐量方面的竞争激烈程度排序为环渤海港口群>珠江三角洲港口群>长江三角洲港口群>西南沿海港口群>东南沿海港口群,内河港口群中,仅珠江水系港口群呈竞争态势;珠江三角洲港口群、东南沿海港口群、长江三角洲港口群、长江水系和珠江水系港口在集装箱运输中竞争激烈;港口供求关系、港口规模结构、港口职能结构、港口规划与管理等是影响竞争与合作关系及竞争激烈程度的重要因素。本研究有助于丰富港口地理学的理论研究,并为港口资源整合提供思路和方向。