东秦岭火山岩的地球化学特征和成因模式

熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。     

论秦岭造山带的成矿作用

对秦岭造山带区域成矿背景、矿床的时空分布、典型矿床矿田赋存部位、区域成矿元素地球化学背景、多重岩片控矿理论,构造成矿体系、成矿物质来源、矿床成因类型、矿床区域成矿模式进行了讨论,在对大量资料研究的基础上提出了新认识。最后指出秦巴地区进一步寻找大型矿床的地区。     

六盘山植物区系基本特征的初步分析

六盘山位于陕甘宁交接地区,属于半湿润气候向半干旱气候的过渡带,是黄土高原生物多样性最丰富的地区之一,有维管植物836种,隶属于93科,359属。本区属于泛北极植物区、中国-日本森林植物亚区、华北植物地区的黄土高原亚地区。全部种子植物可分为13个分布区类型和12个变型,以北温带分布类型为主,与其他植物区系联系广泛,但特有属较贫乏。六盘山与小陇山、太白山和中条山的属相似性系数较高,均达60%以上,表明几座山体处于相似的生物气候背景之下,地理隔离性不明显。与贺兰山的属相似性系数低于60%,因为贺兰山位于干旱的荒漠与半荒漠区,可能有地理隔离作用。     

基于Hkr值的北天山冰川侵蚀空间分布特征及其主控因素研究

确定冰川侵蚀的主控因素及其与各影响因素间的相互作用方式,不仅对深入认识冰川侵蚀的物理机制和理解冰川作用区地貌演化具有重要的意义,也是探讨构造、气候、地形间相互关系的根本。然而,以往的学者仅在构造活动略单一的区域研究冰川侵蚀的主控因素,致使对构造的影响认识不足,那么,构造是否是冰川侵蚀的主控因素呢？又是如何作用于冰川侵蚀？北天山第四纪冰川作用规模巨大,留下了丰富的冰川遗迹,其气候与构造条件也多样,因而成为探讨上述问题的理想区域。本文在北天山北坡自西向东选取了7个冰川流域,基于每个流域的Hkr值和冰川侵蚀影响因子的定性定量数据,分析了该区域冰川侵蚀的分布规律及其影响因素。结果表明,北天山各流域冰川侵蚀自西向东有减小趋势,该变化趋势是构造、气候、地形共同作用所致。其中,山顶高度和降水对冰川侵蚀的影响最显著,两者均通过对冰川规模施加作用来控制冰川侵蚀,而构造也可能通过影响顶点高程、积累区面积、冰川规模,进而作用于冰川侵蚀,但是其是否发挥主要作用有待进一步认识。因此,冰川规模可能才是导致北天山各冰川流域侵蚀差异的根本原因。     

南岭山地湖泊多环芳烃的大气沉降历史记录

高大山脉对大气环流具有阻挡或屏障作用.通过分析测定南岭山地湖泊沉积物中多环芳烃(PAHs)的垂直分布,结合210Pb定年,探讨了大气PAHs污染在南岭山地的沉积历史.结果显示,沉积物中的PAHs主要以低环数化合物为主,其中尤以菲的含量为最高.在剖面深度0～28 cm范围内,总多环芳烃的含量范围为86～778 ng/g.自1970年开始,PAHs含量持续增加,其中20世纪80、90年代中后期PAHs含量略有降低;在2000年后,沉积柱中的PAHs含量呈急剧增加之势态.多环芳烃在大气迁移过程中发生了组成分异,沉积物中相对富集轻组分(低环数)PAHs,与颗粒物结合的大气干湿沉降是PAHs向偏远山地积的主要途径.     

西南天山中—新生界层控砂砾岩型铜铅锌矿成矿规律

西南天山是新疆中—新生界层控砂砾岩型铜铅锌矿的重要产出地区,以萨热克铜矿、乌拉根铅锌矿、花园铜矿、伽师铜矿为代表,均产于隆起剥蚀区边缘的红层盆地中并严格受层位控制,赋矿盆地的下部为煤系生烃岩,中部为渗透性良好的砂砾岩铜铅锌矿储集层,上覆膏岩及泥岩等密闭盖层,具有铜铅锌-铀-煤-天然气同盆共存富集的成矿特征。文章总结了西南天山赋矿盆地沉积-构造演化及赋矿层位特征,研究了铜铅锌典型矿床的控矿条件和成矿作用特征。通过对比分析,总结了中—新生界砂砾岩型铜铅锌矿的区域成矿规律,认为有机质与铜铅锌成矿关系密切,推测在原始矿源层的基础上,在隆起部位经油田卤水叠加形成铜铅锌贫矿体,喜马拉雅期断裂构造沟通深源成矿流体再次叠加形成铜铅锌富矿体。总结构建了西南天山中—新生界层控砂砾岩型铜铅锌矿的成矿模式,以期为已知矿山深边部勘查及区域找矿工作部署提供依据。     

Can 234U–230Th dating be used to date large semi‐arid tufas? Challenges from a study in the Naukluft Mountains,Namibia

The large, extensive tufa deposits of the semi‐arid Naukluft Mountains, Namibia are potentially important palaeoenvironmental indicators in an area with few proxy records. Tufas are reliable indicators of increased moisture availability, and have been shown to be amenable to ²³⁴U–²³⁰Th dating, although two challenges are detrital contamination and open‐system behaviour. Densely cemented tufa facies are good candidates for dating, minimising these problems. We report attempts to date five densely‐cemented units, which are only found rarely within the Naukluft deposits. We applied a detailed methodology using multiple subsample analysis, measurement of insoluble residues, application of ‘isochron’ mixing lines, and attempted open‐systems modelling, alongside observations of micromorphology and cathodoluminescence in order to assess the validity of any obtained dates. Surprisingly, densely cemented tufas were found not always to be suitable for dating. Two units contained detrital contamination, which could not be corrected for using a single leachate correction or ‘isochron’ methods. Two units contained ‘excess ²³⁰Th’. This could result under a closed‐system if initial (²³⁴U/²³⁸U) was sufficiently high. Alternatively this may be the result of open‐system behaviour, and loss of uranium, or incorporation of initial unsupported ²³⁰Th, which render samples unsuitable for ²³⁴U–²³⁰Th dating. Micromorphological appearance and cathodoluminescence behaviour are used to explore these possibilities. This study exemplifies the need for careful sample selection, and highlights the importance of analysing multiple subsamples from any tufa sample. The detailed methodology applied proves to be a powerful tool for identifying the range of problems that can be encountered when selecting suitable candidate samples for successful dating. It also shows that semi‐arid tufa sequences may contain very little material suitable for dating. A reliable age of c 80 ka was obtained for a banded unit within a large fluvial barrage, with less reliable dates suggesting tufa deposition during times since >350 ka through to the late Holocene. Copyright © 2010 John Wiley & Sons, Ltd.     

北祁连山中段早中奥陶世蛇绿岩中席状岩墙杂岩的发现及其地质意义

作为蛇绿岩套重要组成部分之一的席状岩墙杂岩(Sheeted dyke complex)近来在北祁连山中段肃南县大岔大坂北坡的早中奥陶世蛇绿岩中被发现。这一发现对于祁连山早古生代蛇绿岩来说尚属首次,而且对于研究蛇绿岩的发展演化及探讨奥陶纪时洋底扩张都有重要意义。席状岩墙杂岩由一系列具单向冷凝边的辉绿岩墙组成,以一墙挨一墙的形式产出,岩墙间无任何填充物。席状岩墙杂岩在矿物组合上,常量元素、稀土元素及痕量元素地球化学特征和配分模式,甚至金属硫化物矿化作用方面都有类似之处。这些证据表明席状岩墙杂岩是连通其下岩浆房与其上枕状熔岩的通道。席状岩墙的单向冷凝边为岩浆上升方式和扩张洋脊的存在提供了令人信服的证据。根据Zr/Y—Zr关系图式,得出该区洋脊的扩张速率大约为2cm/a。     

大别山前寒武纪变质地体基本组成

本文以新城－圻春断裂为界将大别山前寒武纪变质地体划分为华北陆块南缘和场子陆块北缘两个次级变质地体，两个次级地体不仅在地球物理，构造变形方面明显不同，而且在物质成分上有显著差异，它们有各自独立的变质地层系统，遭受了不同类型的变质作用，有完全不同的岩浆活动图象，上述差异均可指示华北，扬子两古陆碰掸对接时扬子陆块北缘向北俯冲至华北陆块南缘之下，这可能包括两次合作用，从元古代开始至中生代最终结束的长期复杂     

Tectonic evolution of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts from central China

Abstract In the Triassic suture between the Sino-Korean and Yangtze cratons, the Dabie metamorphic Complex in central China includes three tectonic units: the northern Dabie migmatitic terrane, the central ultrahigh-P coesite- and diamond-bearing eclogite belt, and the southern high-P blueschist-eclogite belt. This complex is bounded to the north by a north-dipping normal fault with a Paleozoic accretionary complex and to the south by a north-dipping reverse fault with Yangtze basement plus its foreland fold-and-thrust sequence. Great differences in metamorphic pressure suggests that these units reached different depths during metamorphism and their juxtaposition occurred by wedge extrusion of subducted old continental fragments. These units were subsequently subjected to (i) Barrovian type regional metamorphism and deformation at shallow depths; (ii) intrusion of Cretaceous granitic plutons; and (iii) doming and segmentation into several blocks by normal and strike-slip faults. A new speculative model of tectonic exhumation of UHP rocks is proposed.