藏南白垩系黑-红层沉积岩有机质组成分布特征   总被引：1，自引：0，他引：1  

傅培刚  宋之光  胡修棉  王成善 《地质学报》2008,82(1):85-91

对藏南江孜县床得剖面白垩系黑层和红层沉积岩进行的有机地球化学研究表明,黑层有机碳含量高于红层5～10倍,红层和黑层饱和烃主峰碳数分别为nC25和nC23;黑层和红层沉积有机质的母质来源都以水生植物和菌藻类等低等生物为主,陆源有机质的输入非常有限;但饱和烃的分布和主峰碳数的差异可能反映了有机母源物质在种群方面的差异,而这种差异可能主要是水体温度存在差异造成的,即红层发育时期水体温度可能高于黑层沉积时期.而在高温度条件下,水生生物和陆生植物的生长发育受到限制,造成原始有机质产率和有机质沉积保存量低可能是红层沉积岩形成的主要原因.  相似文献   

西藏东巧蛇绿岩中辉长岩锆石SHRIMP定年及其地质意义   总被引：9，自引：0，他引：9  

夏斌  徐力峰  韦振权  张玉泉  王冉  李建峰  王彦斌 《地质学报》2008,82(4):528-531

东巧蛇绿岩位于分割羌塘地块和拉萨地块的班公湖—怒江缝合带中段,是该带最著名的产铬铁矿床的蛇绿岩残片之一。该蛇绿岩遭受构造肢解,恢复后的蛇绿岩剖面各岩石单元齐全。本文应用SHRIMPⅡ锆石UPb法,对东巧蛇绿岩中堆晶辉长岩进行了测年,获得辉长岩年龄为187.8±3.7 Ma。该年龄代表了东巧洋盆的形成时代,为确定研究区特提斯洋盆的古构造格局及其发育演化过程等提供了重要的年代学制约。  相似文献   

Anoxic nitrification: Evidence from Humber Estuary sediments (UK)   总被引：3，自引：0，他引：3  

Rebecca Bartlett  Robert J.G. Mortimer  Katherine Morris 《Chemical Geology》2008,250(1-4):29-39

Conventional understanding of the nitrogen cycle in marine sediments has changed in recent years with the discovery of an alternative pathway for ammonia oxidation via the reduction of manganese oxides (during anoxic nitrification). In anoxic sediments, the potential for manganese oxides to serve as oxidant for nitrification may be considerable yet previous work on manganese-rich sediments has suggested anoxic nitrification may not be significant. In this study, the potential for anoxic nitrification in a range of sediment types was investigated. Laboratory incubation of sediment from three sites on the Humber Estuary, a microbially diverse environment, showed anoxic accumulation of nitrate, nitrite and dinitrogen gas, with and without the addition of synthetic manganese oxides. Incubation experiments confirmed anoxic nitrification as microbially mediated, with heat-killed controls yielding negative results. The anoxic nitrification reaction significantly depleted ammonia concentrations, and occurred simultaneously with manganese-, iron- and sulphate reduction, and methanogenesis. Taken in conjunction with other studies, results suggest anoxic nitrification may not only be dependent on total manganese concentrations but on manganese dynamics. Anoxic nitrification may be explained as a non-steady state reaction, dependent on the recent stability of a sediment system. Physical perturbation of sediments may cause the redistribution and/or introduction of manganese oxides and promote anoxic nitrification. The significance and persistence of anoxic nitrification is likely to depend on the frequency and magnitude of sediment perturbation, which explains why the reaction varies so widely across studied sites, and why it may not occur in some manganese-rich sediment.  相似文献   

A comparative study of four vulnerability mapping methods in a detritic aquifer under mediterranean climatic conditions     

M. Draoui  J. Vias  B. Andreo  K. Targuisti  J. Stitou El Messari 《Environmental Geology》2008,54(3):455-463

This paper presents the results of a comparative study relating to the application of four vulnerability mapping methods, GOD, AVI, DRASTIC and SINTACS, in a pilot detritic aquifer situated in NW Morocco, known as the Martil–Alila aquifer. The principal objective of this work is to determine the most suitable such methods for this aquifer type within a Mediterranean context, and to show the effect of the rainfall variations that are characteristic of the Mediterranean climate on the degree of vulnerability. The methods applied distinguish five classes of vulnerability, these being irregularly divided up in space, with the division varying according to the method in question. The vulnerability maps obtained by the different methods strongly suggest that the eastern half of the aquifer is more vulnerable to contamination than the western half, for all hydrological situations. The effect of climatic conditions on the degree of vulnerability is well represented by the DRASTIC, according to which the aquifer is moderately to strongly vulnerable during humid hydrological years and weakly to moderately vulnerable during dry ones. For the other methods, this climatic effect is limited to the area occupied by the two predominant classes (“High” and “Low” for GOD and “High” and “Moderate” for SINTACS) while it is null for AVI. In conclusion, DRASTIC appears the most suitable for mapping the vulnerability to contamination of Mediterranean coastal detritic aquifers such as the Martil–Alila aquifer.  相似文献   

Assessment of frozen-ground conditions for engineering geology along the Qinghai–Tibet highway and railway, China     

Huijun Jin  Zhi Wei  Shaoling Wang  Qihao Yu  Lanzhi Lü  Qingbai Wu  Yanjun Ji 《Engineering Geology》2008,101(3-4):96-109

The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions.  相似文献   

Triassic Nb-enriched basalts, magnesian andesites, and adakites of the Qiangtang terrane (Central Tibet): evidence for metasomatism by slab-derived melts in the mantle wedge   总被引：10，自引：0，他引：10  

Qiang Wang  Derek A. Wyman  Jifeng Xu  Yusheng Wan  Chaofeng Li  Feng Zi  Ziqi Jiang  Huaning Qiu  Zhuyin Chu  Zhenhua Zhao  Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490

New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized by high Sr/Y (25–45), La/Yb (14–42) and Na₂O/K₂O (12–49) ratios, high Al₂O₃ (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and ε_ND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive ε_ND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids. A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite. The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series” recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane.  相似文献   

Urban consolidation and house prices: a case study of Melbourne 1990–2004     

Sun Sheng Han  Kevin O’Connor 《GeoJournal》2008,73(4):285-295

This paper explores the links between a strategic policy, urban consolidation, and house prices by examining the changes in the mix of housing and in house price for the period 1991–2004. We contend that urban consolidation could be seen as a source of additional supply, (which might be expected to be felt in lower prices and so contribute to a local policy objective) but also as a stimulus to demand (by developers who could bid up the price of lots where it was understood more housing could be built). Analyses were carried out at the metropolitan and sub-regional scales using correlation tests. The research finds very weak statistical connections, and concludes that this policy has not been associated with price changes.  相似文献   

西藏马攸木金矿床金银互化物的赋存状态   总被引：3，自引：0，他引：3  

孙燕  温春齐  多吉  霍艳 《地质与勘探》2008,44(5):42-46

马攸木金矿床是西藏近年发现的首例规模较大、矿石品位富、金成色高的岩金矿床.作者通过对马攸木金矿床矿石组构、矿石共生组合及矿物特征研究发现,金银互化物主要有自然金、含银自然金、银金矿、自然银.载金矿物为黝铜矿、针铁矿、脆硫锑铅矿及石英;金银互化物的赋存形式主要为包裹体金、裂隙金及粒间金.金银互化物的形成、富集与热液成矿作用及表生风化作用关系密切.  相似文献   

青藏高原东南木里地区二叠纪苦橄岩的Os-Sr-Nd同位素地球化学研究   总被引：3，自引：2，他引：1  

李杰  许继峰  何斌  徐义刚  董彦辉 《岩石学报》2008,24(2)

本文报道了在青藏高原东南木里地区发现的二叠纪苦橄岩和与其共生玄武岩的主微量元素地球化学特征以及Os-Sr-Nd同位素组成。苦橄岩和与其共生玄武岩受地壳混染作用影响较小。根据苦橄岩的Ti/Y比值和初始的Os同位素组成,将木里苦橄岩分为两类:高Ti/Y型苦橄岩和低Ti/Y型苦橄岩,其中高Ti/Y型苦橄岩具有高的γ_(Os)= 5.3～ 10.7和ε_(Nd)= 5.9～ 6.4,与全球典型洋岛玄武岩的Os和Nd同位素组成接近,代表了地幔柱源区的同位素特征;而低Ti/Y型苦橄岩具有低的γ_(Os)=-4.1～ 1.2和ε_(Nd)= 3.2～ 5.0,可能表明受到了SCLM(大陆岩石圈地幔)源区物质的混染。与其共生的玄武岩具有低的γ_(Os)=-3.5～-1.6和ε_(Nd)=-0.6～ 0.7,表明其来自于不同于低Ti/Y型苦橄岩也有异于高Ti/Y型苦橄岩的地幔源区,但是也可能受到了SCLM物质的混染。基于Nd-Os同位素的地幔柱与SCLM的二端元混合模型显示:低Ti/Y型苦橄岩可能是SCLM物质组分与地幔柱起源的苦橄质原始岩浆混合形成的;与苦橄岩共生的玄武岩可能是由地幔柱来源的玄武质岩浆与SCLM小比例熔融的熔体混合形成的。  相似文献   

西藏冈底斯带措勤地区则弄群火山岩锆石U-Pb年代学格架及构造意义   总被引：29，自引：12，他引：17  

朱弟成  周肃  莫宣学  赵志丹  许继峰  周长勇  孙晨光  王立全  陈海红  董国臣 《岩石学报》2008,24(3)

大规模的则弄群火山岩呈带状近东西向展布于西藏冈底斯带中北部地区.对出露状况较好的措勤地区则弄群火山岩进行了锆石U-Pb定年,以建立其年代学格架便于区域对比.措勤地区则弄群火山岩多数锆石具有生长振荡环带,部分锆石显示核边结构.在措勤达雄北西部上覆于中二叠统下拉组灰岩的1件则弄群英安岩样品的LA-ICP-MS锆石U-Ph年龄为130±1Ma,1件则弄群流纹岩样品的SHRIMP锆石U-Pb年龄为129±3Ma;在措勤达雄北东部与下白垩统多尼组碎屑岩呈断层接触的1件则弄群英安岩样品中的锆石具有两组LA-ICP-MS锆石U-Pb年龄,最年轻的一组(包括增生边)为121±1Ma,较老的一组(包括核部)为131±1Ma;在措勤南西部1件则异群流纹岩样品的LA-ICP-MS锆石U-Pb年龄为111±1Ma,与措勤地区花岗岩类的侵位时代相当.这些高质量的锆石U-Pb年代学数据表明,措勤地区的则弄群火山作用很可能开始于约130Ma,停息于约110Ma,持续时间约20Ma.区域对比表明,东西延伸约1000km的则弄群火山作用同时发生在约130Ma.区域上目前的年代学数据结合同时代岩浆作用的分布特征表明,冈底斯带中北部地区早白垩世岩浆作用不太可能由新特提斯洋壳向北的低角度或平板俯冲产生.  相似文献