972 resultados para margin
Resumo:
The platinum-group elements (PGE), including Os, Ir, Ru, Rh, Pt and Pd, axe strongly siderophile and chalcophile. On the basis of melting temperature, the PGE may be divided into two groups: the Ir group (IPGE, >2000°C) consisting of Os, Ir and Ru, and the Pd group (PPGE, <20GO°C) consisting of Rh, Pt and Pd. Because of their unique geochemical properties, PGE provide critical information on global-scale differentiation processes, such as core-mantle segregation, late accretionary history, and core-mantle exchange. In addition, they may be used to identify magma source regions and unravel complex petrogenetic processes including partial melting, melt percolation and metasomatism in the mantle, magma mixing and crustal contamination in magma chambers and melt crystallization.Compared with other rocks, (ultra)mafic rocks have lower REE content but higher PGE content, so PGE have advantages in studying the petrogeneses and evolution of them. In this study, we selected (ultra)mafic rocks collected in Dabie Orogen and volcanic rocks from Fuxin Region. Based on the distribution and behaviour of platinum-group elements, combined with other elements, we speculate the magma evolution and source mantle of these (ultra)mafic rocks and volcanic rocks.Many (ultra)mafic rocks are widely distributed in Dabie Region. According to their deformation and metamorphism, we classed them into three types. One is intrusive (ultra)mafic rocks, which are generally undeformed and show no or little sign of metamorphism, such as (ultra)mafic intrusions in Shacun, zhujiapu, Banzhufan, qingshan, Xiaohekou, Jiaoziyan, Renjiawan and Daoshichong. The other one is ultrahigh pressure metamorphic (ultra)mafic rocks, some of them appeared as eelogites, such as complex in Bixiling and adjacent Maowu. Another one is intense deformed and metamorphic, termed as tectonic slice, alpine-type (ultra)mafic rocks. The most representative is Raobazhai and Dahuapin. However, there are many controversies about the formation of those (ultra)mafic rocks. Here, we select typical rocks of the three types. The PGE were determined by inductively coupled plasma mass spectrometry (ICP-MS) ater NiS fire-assay and tellurium co-precipitation.The PGE tracing shows that three components are needed in the source of the cretaceous (uitra)mafic intrusions. They could be old enriched sub-continental lithospheric mantle, lower crust and depleted asthenospheric mantle. The pattern of PGE also shows the primitive magma of these intrusions underwent S saturation. According to palladium, we can conclude that the mantle enrich in PGE. Distribution of PGE in Bixiiing and Maowu (ultra)mafic rocks display they are products of magmas fractional crystallization. The (ultra)mafic rocks in Bixiiing and Maowu are controlled by various magmatic processes and the source mantle is depleted in PGE. Of interest is that the mantle produced UHP (ultra)mafic rocks are PGE-depleted, whereas the mantle of cretaceous (ultra)mafic intrusions are enrich in PGE. This couldindicate that the mantle change from PGE-enriched to PGE-depleted during120-OOMa, which in accord with the time of tectonic system change in the East China. At the same time, (ultra)mafic intrusions in cretaceous took information of deep mantle, which means the processes in deep mantle arose structural movement in the crust The character of PGE in alpine-type (ultra)mafic rocks declared that the rocks had experienced two types of metasomatic processes - hydrous melt derived from slab and silicate melt. In addition, we analyze the platinum-group elements in volcanic rocks on the northern margin of the North China Craton, Fuxin. The volcanic rocks characterized by negative anomalies of platinum. This indicates that platinum alloys, which may host some Pt resided in the mantle. The PGE patterns also show that Jianguo alkali basalts derived from asthenospheric mantle source, but wulahada high-Mg andesites derived from lithospheric mantle.
Resumo:
The foreland basin on the northern margin of the lower reach of the Yangtze river (the lower Yangtze foreland basin) is tectonically situated in the basin-mountain transitional area along the southeastern flank of the Dabie mountains. The early formation and development of the basin is closely related to the open-up of the Mian-Lue paleo-oceanic basin on the southern margin of the Central Orogenic System represented by Qinling-Dabei orogenic belt, while the tectonic evolution of the middle-late stage of the basin is mainly related to development of the Mian-Lue tectonic zone that occurred on the basis of the previous Mian-Lue paleo-suture. The foreland basin of the northern rim of the lower reach of the Yangtze river was formed during the middle-Triassic collision between the Yangtze and North China plates and experienced an evolution of occuirence-development-extinction characterized by marine facies to continental facies and continental margin to intracontinent in terms of tectonic setting.The foreland basin (T2-J2) was developed on the basis of the passive continental marginal basin on the south side of the Mian-Lue paleo-ocean and superimposed by late Jurassic-Tertiary fault basin. The tectonic setting underwent a multiple transformation of rifting-collisional clososing-tensional faulting and depression, which resulted in changes of the property for the basin and the final formation of the superposed compose basin in a fashion of 3-story-building. According to the tectonic position and evolution stages of plate collision happening on the southeastern margin of the Dabie mountains, and tectono-tratigraphic features shown by the foreland basin in its main formational period, the evolution of the foreland basin can be divided into four stages: 1) pre-orogenic passive margin (P2-Ti). As the Mian-Lue ocean commenced subduction in the late-Permian, the approaching of the Yangtze and North China plates to each other led to long-periodical and large-scale marine regression in early Triassic which was 22 Ma earlier than the global one and generated I-type mixed strata of the clastic rocks and carbonate, and I-type carbonate platform. These represent the passive stratigraphy formed before formation of the foreland basin. 2) Foreland basin on continental margin during main orogenic episode (T2.3). The stage includes the sub-stage of marine foreland basin (T2X remain basin), which formed I-type stratigrphy of carbonate tidal flat-lagoon, the sub-stage of marine-continental transition-molasse showing II-type stratigraphy of marine-continental facies lake - continental facies lake. 3) Intracontinental foreland basin during intracontinental orogeny (Ji-2)- It is characterized by continental facies coal-bearing molasses. 4) Tensional fault and depression during post-orogeny (J3-E). It formed tectono-stratigraphy post formation of the foreland basin, marking the end of the foreland evolution. Fold-thrust deformation of the lower Yangtze foreland basin mainly happened in late middle-Jurassic, forming ramp structures along the Yangtze river that display thrusting, with deformation strength weakening toward the river from both the Dabie mountains and the Jiangnan rise. This exhibits as three zones in a pattern of thick-skinned structure involved the basement of the orogenic belt to decollement thin-skinned structure of fold-thrust from north to south: thrust zone of foreland basin on northern rim of the lower reach of the Yangtze river, foreland basin zone and Jiannan compose uplift zone. Due to the superposed tensional deformation on the earlier compressional deformation, the structural geometric stratification has occurred vertically: the upper part exhibits late tensional deformation, the middle portion is characterized by ramp fault -fold deformation on the base of the Silurian decollement and weak deformation in the lower portion consisting of Silurian and Neo-Proterozoic separated by the two decollements. These portions constitutes a three-layered structural assemblage in a 3-D geometric model.From the succession of the lower reach of the Yangtze river and combined with characteristics of hydrocarbon-bearing rocks and oil-gas system, it can be seen that the succession of the continental facies foreland basin overlies the marine facies stratigraphy on the passive continental margin, which formed upper continental facies and lower marine facies hydrocarbon-bearing rock system and oil-gas forming system possessing the basic conditions for oil-gas occurrence. Among the conditions, the key for oil-gas accumulation is development and preservation of the marine hydrocarbon-bearing rocks underlying the foreland basin. The synthetic study that in the lower Yangtze foreland basin (including the Wangjiang-Qianshan basin), the generation-reservoir-cover association with the Permian marine facies hydrocarbon-bearing rocks as the critical portion can be a prospective oil-gas accumulation.Therefore, it should aim at the upper Paleozoic marine hydrocarbon-bearing rock system and oil-gas forming system in oil-gas evaluation and exploration. Also, fining excellent reservoir phase and well-preserved oil-gas accumulation units is extremely important for a breakthrough in oil-gas exploration.
Resumo:
This paper is concerned of the I0Be and 26A1 exposure ages of bedrocks in the Grove Mountains (GMs), inland of East Antarctica, and in the Larsemann Hills, peripheral alongshore of East Antarctica, respectively. The results of our study indicate that the higher bedrock samples in two profiles in the GMs have minimum exposure ages of-2 Ma, and their 26Al/10Be can be projected into the erosion island, which means they only have simple exposure history. The actual exposure ages may be mid-late Pliocene because the bedrocks should have erosion. The relationship between the altitudes and cosmogenic nuclide concentrations of those higher samples suggests that they have not reached secular equilibrium, means that a higher than -2300m East Antarctic Ice Sheet (EAIS) existed in the GMs before mid-Pliocene, and decreased monotonously for a period since mid-Pliocene. Lower samples of the two profiles have much younger exposure ages, and had been covered at least once obviously implicated by that their 26Al/10Be are projected down to the erosion island. Using a 10Be-26Al project figure to determine the history of the GMs samples shows that the lower samples have minimum total initial exposure and cover time of 1.7-2.8Ma, suggesting that those samples were exposed initially since about late Pliocene too, and the interior EAIS fluctuated after late Plicoene obviously. The altitudes and exposure ages of all the GMs samples indicate that the ice surface level of the interior EAIS in the GMs was >2300m during or before mid Pliocene (more than 200m higher than present ice surface level), and only rose to -2200m during the fluctuation occurred after late Pliocene, thus the elevation of the interior EAIS in the GMs after mid-Pliocene was never higher than during or before mid Pliocene even during the Quaternary Glacial Maximum. According to data from the GMs and other parts of East Antarctica, a larger East Antarctic Ice Sheet existed before mid-Pliocene, thus the elevation decrease of interior EAIS in the GMs after mid Pliocene may be a director of volume decrease of the EAIS. Since the Antarctic climate has a cooling trend since ~3Ma, similar to the global climate change, the volume decrease of the EAIS since mid-Pliocene may beause of moisture supply decrease directly rather than atmosphere temperature change. As for the Larsemann Hills, samples farther to the glacier have exposure age of 40~50ka, means they exposed in the early time of Last Glacier Cycle, obviously earlier than the Last Glacial Maximum (LGM). Samples nearer to the glacier have exposure ages younger than LGM. Thus, different to the GMs, exposure ages of the Larsemann Hills samples have more obvious relationship to their distance from the glacier margin rather than to the altitudes of the samples.
Resumo:
作为铅锌金属的主要来源,赋存于沉积岩中的铅锌矿床吸引了全球范围的地质学家和矿床学家。在过去的50年内塔里木西南缘陆续发现了一批赋存于沉积岩中的铅锌矿,并开展相应的研究。但还是存在一些关键问题值得探讨,例如成矿时代、金属及硫的来源,以及成矿机制。 塔木铅锌矿床是塔里木西南缘最为重要的赋存于沉积岩中的铅锌矿床之一,其位于西昆仑和塔里木地块接触带北侧塔里木边缘,区域地层均变形或被错断。矿床赋存于下石炭统碳酸盐岩角砾岩带中,具有经济价值的矿体五个,铅锌资源量约0.2Mt。 自20世纪40年代塔木铅锌矿被发现以来,已陆续开展的研究工作有流体包裹体、铅同位素、硫同位素、碳同位素、氧同位素以及稀土元素等,但矿床成因依然困惑着众多的矿床学家。其中一部分认为矿床属密西西比河谷型,另一部分则认为应属沉积喷流型。但从前人发表的文献看,矿石结构构造、角砾和填隙物等基础研究被普遍忽视了。 在中国科学院知识创新项目(KZCX2-YW-107-6)和科技部国家科技支撑计划(2006BAB07B04-04)的资助下,本次研究以塔木铅锌矿为突破口,运用矿物学、岩石学、矿床学、地球化学方法和手段对其加以研究,以揭示成矿机制及矿床成因。以下就获得的一些新的数据、调查结论、观点作一概述: (1). 在分析矿体形态和与围岩接触关系基础上,提出塔木铅锌矿床为同生断层控制,角砾岩带为断层的组成部分;通过细致的镜下观察,深入探讨了角砾、填隙物及其结构构造,提出填隙物中沥青在成矿中的具有重要作用,并首次发现赋存于填隙物中的钡-钾长石。角砾可根据几何形态特征和角砾间接触关系分为五类:内碎屑角砾(IB)、成岩期角砾(DB)、后生角砾(EB)、崩塌角砾(FB)、断层角砾(DB),其中断层角砾可以分为矿化断层角砾(MFB)和无矿化断层角砾(WFB)。填隙物可以根据结构划分为三种类型:同沉积-成岩作用填隙物(纹层构造),溶蚀-交代填隙物(细粒,颗粒边缘具有溶蚀港湾结构),以及空洞充填填隙物(粗晶结构)。塔木铅锌矿演化具有三个清晰的期次:沉积期、成岩期和后生期。矿化是成岩期和后生期的产物,主要为后生期。矿化可分为两个主要阶段:溶蚀-交代阶段和空洞充填阶段,其中溶蚀-交代阶段是矿化的主要阶段。管/脉状构造是溶蚀-交代阶段最重要的特征,其多见于后生角砾的填隙物中。 (2). 在对角砾(白云石)和填隙物(白云石)的微量元素、稀土元素、C、O同位素以及填隙物白云石流体包裹体研究基础上提出水/岩作用和TSR过程控制着流体的演化。充填阶段流体为低温(119~191°C),盐度介于10.9~11.4wt% NaCl eq.,压强介于2~39MPa,含有少量H2S,缺乏SO42-的流体。Ca2+和HCO3-为流体主要的阳离子和阴离子。填隙物与角砾具有相似的稀土元素配分模式—海相碳酸盐岩。如果填隙物中混入钡-钾长石,其稀土元素配分模式则发生显著改变。氧同位素和碳同位素显示填隙物较角砾富集轻同位素。由于闪锌矿流体包裹体氧同位素值显著低于角砾,暗示存在大气降水的参与。根据氧同位素质量平衡方程可估计水/岩比值,封闭体系水/岩比值在0.16~0.67(119°C)或0.12~0.43(191°C),开放体系水/岩比值在0.13~0.37(119°C)或0.10~0.28(191°C)。热化学硫酸盐还原过程(TSR)可能对沥青和H2S的形成起了重要的作用,并影响碳同位素值变化。 (3). 塔木铅锌矿硫可能来自海水或蒸发盐,存在有机物硫的加入,并受TSR过程和硫储库效应的控制,铅可能为来自淋滤结晶基底的产物。 (4). 讨论了闪锌矿流体包裹体Rb-Sr法的理论基础和应用前提,指出对定年闪锌矿必须开展细致的矿物学研究,并进行了该矿床的定年尝试。 (5). 最终得出塔木铅锌矿为赋存于碳酸盐岩受同生断层和热化学硫酸盐还原过程控制的后生铅锌矿床。
Resumo:
The work comprises a new theoretical development applied to aid decision making in an increasingly important commercial sector. Agile supply, where small volumes of high margin, short life cycle innovative products are offered, is increasingly carried out through a complex global supply chain network. We outline an equilibrium solution in such a supply chain network, which works through limited cooperation and coordination along edges (links) in the network. The links constitute the stochastic modelling entities rather than the nodes of the network. We utilise newly developed phase plane analysis to identify, model and predict characteristic behaviour in supply chain networks. The phase plane charts profile the flow of inventory and identify out of control conditions. They maintain quality within the network, as well as intelligently track the way the network evolves in conditions of changing variability. The methodology is essentially distribution free, relying as it does on the study of forecasting errors, and can be used to examine contractual details as well as strategic and game theoretical concepts between decision-making components (agents) of a network. We illustrate with typical data drawn from supply chain agile fashion products.
Resumo:
This paper focuses on the analysis of the relationship between maritime trade and transport cost in Latin America. The analysis is based on disaggregated (SITC 5 digit level) trade data for intra Latin maritime trade routes over the period 1999-2004. The research contributes to the literature by disentangling the effects of transport costs on the range of traded goods (extensive margin) and the traded volumes of goods (intensive margin) of international trade in order to test some of the predictions of the trade theories that introduce firm heterogeneity in productivity, as well as fixed costs of exporting. Recent investigations show that spatial frictions (distance) reduce trade mainly by trimming the number of shipments and that most firms ship only to geographically proximate customers, instead of shipping to many destinations in quantities that decrease in distance. Our analyses confirm these findings and show that the opposite pattern is observed for ad-valorem freight rates that reduce aggregate trade values mainly by reducing the volume of imported goods (intensive margin).
Resumo:
Hunt, C. Elrishi, H. Gilbertson, D. Grattan, J. McLaren, S. Pyatt, B. Rushworth, G. Barker, G. Early-Holocene environments in the Wadi Faynan, Jordan. The Holocene. 2004. 14,6 pp 921-930
Resumo:
Enot, D. P., Beckmann, M., Overy, D., Draper, J. (2006). Predicting interpretability of metabolome models based on behavior, putative identity, and biological relevance of explanatory signals. Proceedings of the National Academy of Sciences of the USA, 103(40), 14865-14870. Sponsorship: BBSRC RAE2008
Resumo:
James Macduff, Neil Raistrick and Mervyn Humphreys (2002). Differences in growth and nitrogen productivity between a stay-green genotype and a wild-type of Lolium perenne under limiting relative addition rates of nitrate supply. Physiologia Plantarum, 116 (1), 52-61. Sponsorship: BBSRC RAE2008
Resumo:
Estetyka w archeologii. Antropomorfizacje w pradziejach i starożytności, eds. E. Bugaj, A. P. Kowalski, Poznań: Wydawnictwo Poznańskie.
Resumo:
This schematic geological cross-section of Angola offshore is representative of the majority of the Atlantic-type divergent margins. It illustrates the main geological features allowing to understand the different petroleum systems occurring, particularly, in South Atlantic divergent margins : (i) Pre-Pangea rocks (Precambrian granite-gneiss basement, volcanic rocks an/ or Paleozoic sediments, more or less, metamorphosed), which lie underneath the pre-rifting unconformity (PRU), in blue in the cross-section ; (ii) The rift-type basins developed during the lengthening of the Pangea supercontinent ; (iii) The breakup unconformity (BUU), which highlight the upper limit of the rift-type basins, in which organic rich lacustrine shales with a parallel internal configuration are potential source-rocks (organic matter type I) ; (iv) The SDRs (seaward dipping reflectors), which, generally, do not have any generating hydrocarbon potential (just 5 m of lacustrine shales are known in Austral basin) ; (v) The BUU is fossilized by SDRs (subaerial volcanism) or by margin infra-salt sediments (forming the mistakenly called by some American geoscientists "sag basin") ; (vi) The Loeme salt basin, which is a twin of the Brazilian salt basin, that is to say, that both basins have always been individualized ; (vii) The transgressive (backstepping) and regressive (forestepping) phases of the post-Pangea continental encroachment cycle ; (v) The interface between these sedimentary phases, correspond to the emplacement of potential marine source-rocks (organic matter type-II) ; (vi) Potential dispersive source rocks (organic matter type III) are possible in the regressive sedimentary interval.
Resumo:
Sound propagation in shallow water is characterized by interaction with the oceans surface, volume, and bottom. In many coastal margin regions, including the Eastern U.S. continental shelf and the coastal seas of China, the bottom is composed of a depositional sandy-silty top layer. Previous measurements of narrow and broadband sound transmission at frequencies from 100 Hz to 1 kHz in these regions are consistent with waveguide calculations based on depth and frequency dependent sound speed, attenuation and density profiles. Theoretical predictions for the frequency dependence of attenuation vary from quadratic for the porous media model of M.A. Biot to linear for various competing models. Results from experiments performed under known conditions with sandy bottoms, however, have agreed with attenuation proportional to f1.84, which is slightly less than the theoretical value of f2 [Zhou and Zhang, J. Acoust. Soc. Am. 117, 2494]. This dissertation presents a reexamination of the fundamental considerations in the Biot derivation and leads to a simplification of the theory that can be coupled with site-specific, depth dependent attenuation and sound speed profiles to explain the observed frequency dependence. Long-range sound transmission measurements in a known waveguide can be used to estimate the site-specific sediment attenuation properties, but the costs and time associated with such at-sea experiments using traditional measurement techniques can be prohibitive. Here a new measurement tool consisting of an autonomous underwater vehicle and a small, low noise, towed hydrophone array was developed and used to obtain accurate long-range sound transmission measurements efficiently and cost effectively. To demonstrate this capability and to determine the modal and intrinsic attenuation characteristics, experiments were conducted in a carefully surveyed area in Nantucket Sound. A best-fit comparison between measured results and calculated results, while varying attenuation parameters, revealed the estimated power law exponent to be 1.87 between 220.5 and 1228 Hz. These results demonstrate the utility of this new cost effective and accurate measurement system. The sound transmission results, when compared with calculations based on the modified Biot theory, are shown to explain the observed frequency dependence.