The urban land debate in the global South: New avenues for research     

《Geoforum》2017

The global ‘land grab’ debate is going urban and needs a specific conceptual framework to analyze the diverse modalities through which land commodification and speculation are transforming cities across the globe. This article identifies new avenues for research on urban land issues by drawing on an extensive body of academic literature and concrete cases of urban land transformations in Asia, Latin America and Africa. These transformations are analyzed by focusing on three types of urban investments – investments in property, investments in public space and public services, and investments in speculation, image building and ‘worlding’ – and the way these investments are intermingled with and enhanced by processes of gentrification and speculative urbanism. Addressing real estate and infrastructure investments, speculation and gentrification through a land-based lens allows us to deepen the discussion on urban land governance in the global South. We argue that urban land acquisition cannot be thoroughly understood in isolation from the workings of urban real estate markets, public policies, and displacement processes. The urban land grab debate needs to consider the dialectic interplay between land use change and general socio-spatial transformations both in central – or recentralized – and peripheral areas. This is why we plea for a kaleidoscopic perspective on urban land governance by uncovering the complex patchwork of urban land acquisitions and their diverse temporalities and spatialities, their hybrid character in terms of actors involved, and the multiple and often unpredicted ways in which urban dwellers try to gain control over and access to urban land.  相似文献   

Structural styles and depositional architecture in the Triassic of the Ninian and Alwyn North fields: Implications for basin development and prospectivity in the Northern North Sea     

Mark Tomasso  John R. Underhill  Richard A. Hodgkinson  Mike J. Young   《Marine and Petroleum Geology》2008,25(7):588-605

Interpretation of well-calibrated three-dimensional seismic volumes, sedimentological analysis and electrical well-log correlations from the Ninian and Alwyn North fields challenge the long-held view that Mid-Late Jurassic extensional faults in the East Shetland Basin represent a simple reactivation of older (Triassic) fault systems. Restoration for the effects of the younger, predominantly eastward-dipping, Mid-Late Jurassic structures clearly demonstrates that Triassic precursors had a steep, westerly dip. In contrast to the eastern flank of the Viking Graben (e.g. Troll and Oseberg areas), where the west-dipping Triassic structures are reutilised in the Mid-Late Jurassic, those of the East Shetland Basin have largely been dissected and rotated during the later event. Those west-dipping faults that did see later movement appear to have simply acted as minor antithetic structures to the throughgoing east-dipping ones.The Triassic normal fault patterns actively controlled sediment thicknesses and facies distribution within the Lunde and Teist Formations in the basin. Use of seismic stratigraphic surfaces, calibrated by biostratigraphy and chemostratigraphic markers, provides strong evidence that the Triassic depocentres are spatially offset from their Mid-Late Jurassic counterparts. The combination of structural, stratigraphic and sedimentary effects reveal the existence of an emergent deeper Triassic play opportunity in footwall locations to the Mid-Late Jurassic normal faults, which has the potential to extend the life of what is otherwise mature acreage.  相似文献   

中国北方特强沙尘暴的天气系统分型研究   总被引：32，自引：10，他引：22  

刘景涛  钱正安  姜学恭  郑明倩 《高原气象》2004,23(4):540-547

使用中国中央气象台出版的历史天气图资料,对1957—1996年和2001—2002年间发生在我国北方的33次特强沙尘暴过程的天气系统进行了分析研究,重点归纳了形成各次沙尘暴过程的天气系统的热力和动力结构、活动特征及高低层系统的相互配置。在此基础上,以触发沙尘暴强风的主要地面天气系统为主要依据,将形成我国北方特强沙尘暴的天气系统,划分成纯冷锋型、蒙古气旋与冷锋混合型、蒙古冷高压型和干飑线与冷锋混合型4种类型。研究了各类型天气系统在沙尘暴强风形成中的作用、各类型强风的特点及沙尘暴天气的时空分布特征,给出了各类型特强沙尘暴的天气学概念模型。  相似文献   

CCM3模式中LSM积雪方案的改进研究(Ⅰ):修改方案介绍及其单点试验   总被引：4，自引：3，他引：1  

吴统文  钱正安  宋敏红 《高原气象》2004,23(4):444-452

为了改进美国NCARCCM3全球模式中LSM陆面模型中的积雪方案的模拟效果,在Sun等[1]SAST积雪模型的基础上,作了部分修改后,加进CCM3模式LSM模型中.该方案根据格点区域平均积雪深度的不同,把地面雪盖划分为1到3层不等,能在积雪表层和中间层更好地描述温度的日变化和季节变化;较详细地考虑了雪的热传导、太阳辐射的穿透吸收、雪的融化、液态水的储存、渗透和再冻结等积雪内部的主要物理过程;根据Nimbus-7卫星实测雪深资料修改了积雪覆盖度和雪面反照率的计算方案.利用前苏联6个台站1978-1983年的实测积雪资料和大气强迫数据,进行了单点模拟试验,结果表明,新的积雪参数化方案能够较好地再现积雪深度和雪水当量的逐日和季节变化特征,部分提高了积雪参数化方案对积雪的模拟能力.  相似文献   

西藏冈底斯北带首例主碰撞造山期铜矿——林周县程巴矽卡岩型铜矿床地质特征、辉钼矿Re- Os同位素年龄及成矿意义   总被引：2，自引：0，他引：2  

郑文宝  丁帅  李盛俊  冷秋锋  李超  王豪  李茂田  戴成龙 《地质学报》2019,93(2):459-469

通过近十年的地质勘查,在冈底斯北带多座具有经济价值的矿床得到开发利用,该带已经成为西藏地区矿床勘查与研究的又一热点地区。程巴铜矿是冈底斯北带近年来新发现的唯一一例中-大型规模的富铜矿床。矿床为典型的富含石榴子石的矽卡岩型矿床,铜矿体主要呈似层状、脉状产于林布宗组角岩和多底沟组大理岩的层间构造带内,矿石中富铜,伴生钼、锌、金、银、铋。本文在矿床成矿地质背景和矿床地质特征研究的基础上,用Re-Os同位素方法测试辉钼矿,获得等时线年龄为58.49±0.43 Ma(MSWD=0.61),模式年龄加权平均为58.49±0.33Ma(MSWD=0.25),确定程巴铜矿是主碰撞期成矿作用的产物,程巴铜矿的发现证明在冈底斯成矿带主碰撞造山过程能够形成铜矿床。因此,主碰撞成矿阶段由深变浅的矿床组合模型应在前人研究的基础上修改为矽卡岩型Cu(Mo)矿+矽卡岩型Fe-Pb-Zn-Mo(Cu)矿+斑岩型Mo(W)矿。此外,辉钼矿中Re含量介于84.6×10~(-6)～461.3×10~(-6)之间,平均值为252×10~(-6),暗示程巴矿区物源具有壳幔混合的特征。  相似文献   

华北克拉通北缘与陆缘弧相关的早二叠世流纹岩 ——锆石U-Pb定年及地球化学证据     

崔玉良  渠洪杰  陈英富  王森 《地质论评》2019,65(6):1299-1314

华北克拉通北缘内蒙古赤峰北部朝阳沟村地区的原认为是志留纪的八当山流纹岩,现测得其中的锆石SHRIMP U-Pb年龄为277.3±3.3 Ma,应当属于早二叠世。岩石化学分析表明,流纹岩SiO_2含量为75.24%～76.07%,K_2O和Na_2O含量分别为3.40%～5.31%和3.66%～4.88%,属于高钾钙碱性火山岩。岩石具高Al_2O_3(12.92%～13.28%)、低CaO(0.13%～0.47%),铝饱和指数(A/CNK)为0.99～1.06,显示准铝质到弱过铝质特征。Hf同位素分析结果表明,锆石ε_(Hf)(t)均为负值,为-10.7～-16.1,两阶段模式年龄(T_(DM2))为1736～2016 Ma,表明该火山岩起源于华北克拉通古老地壳物质的部分熔融。结合区域地质资料分析,朝阳沟村地区八当山火山岩主体岩性为中酸性火山岩,其形成于早二叠世古亚洲洋向南俯冲于华北克拉通北缘(包含华北克拉通北部和白乃庙岛弧带)之下的安第斯型活动大陆边缘构造环境。  相似文献   

Proterozoic VanDieland in Central Victoria: ages,compositions and source depths for late devonian silicic magmas     

J. D. Clemens  I. S. Buick 《Australian Journal of Earth Sciences》2019,66(4):519-530

The Proterozoic to Cambrian VanDieland microcontinent was accreted to mainland Australia at ca 400?Ma, and its northern tip, the Selwyn Block, forms the basement in central Victoria. Here, mainly Late Devonian, silicic magmas were derived from the Selwyn Block and intruded into the shallow crust. We use the phase petrology of Late Devonian, S-type rhyolitic ignimbrites and a xenolith of pelitic migmatite, together with Nd-model ages for the silicic magmatic rocks to constrain the lithological characteristics of the metasedimentary component of the Selwyn Block, to infer minimum depths and temperature conditions here in the Late Devonian, and the likely ages of the source rocks for the S-type magmas. The most abundant source rocks are inferred to be volcaniclastic metagreywackes, with minor metadacites, meta-andesites and metapelites. The metapelitic xenolith cannot have been the source for any of the silicic magmas but constrains the upper amphibolite-facies part of the Selwyn Block to depths around 17?km, where temperatures reached ～775?°C. The older ignimbrite magma was formed by partial melting at perhaps 770?°C and a depth of at least 33?km, while the younger ignimbrite magma formed at ～23?km and 900?°C. These depths suggest source rocks in the Paleoproterozoic to Mesoproterozoic lower parts of the Selwyn Block. Nd-model ages of the silicic magmatic rocks confirm a dominance of Mesoproterozoic to Paleoproterozoic sources. If the inferred rock types in the Mesoproterozoic formations were as current correlations suggest, the sources for the Late Devonian silicic magmas would have to lie in the undocumented Paleoproterozoic basement of the Selwyn Block. Rock types here must include andesitic to dacitic volcanic components as well as volcaniclastic greywackes and minor pelites, which suggests a continental arc setting. The Late Devonian magmatism in the region may record the progression from amphibolite- to granulite-facies conditions during post-orogenic extension, with heat advected to the crust by mantle-derived mafic magmas. These processes would have resulted in mafitisation of the deep Selwyn Block.  相似文献   

Normal fault linkage and reactivation,Dampier Sub-basin,Western Australia     

S. McHarg  C. Elders  J. Cunneen 《Australian Journal of Earth Sciences》2019,66(2):209-225

The Northern Carnarvon Basin of Western Australia has experienced a polyphase deformation history during the breakup of Gondwana. Extension during the Carboniferous–Permian and a subsequent Early Jurassic rift event imposed two distinct fault systems, separated by a several kilometre-thick Triassic sedimentary sequence. Inboard areas, where Triassic sequences are thinner, Jurassic faults both detach above and also penetrate into Permian sequences. Other large-scale faults demonstrate a vertical hard/soft linkage between the two fault systems. In outboard areas where the Triassic is thicker, the relationship is less clear owing to the lower resolution of Permian sequences in seismic data. Here we undertake fault displacement analysis on three faults on the southern margin of the Exmouth Plateau to investigate the growth mechanism of Jurassic-aged faults and possible structural influence of deeper Permian faults. We find evidence of low-throw faults restricted to Mesozoic strata as more complex-segmented faults that have nucleated at a depth below that resolvable on seismic data. When considered in a regional context, the nature of faults in this study suggest oblique reactivation of the NE-trending Permian fabric, under east–west-oriented extension.  相似文献   

粤北仁化棉花坑铀矿床成矿热液演化及其对成矿过程的约束   总被引：4，自引：1，他引：3  

祁家明  朱捌  吴建勇  曹豪杰  刘文泉  徐争启 《岩石学报》2019,35(9):2711-2726

本文以棉花坑(302)铀矿床成矿期紫黑色萤石、浅粉红色方解石及赤红色微晶石英等含铀脉石矿物及与之共生的黄铁矿为研究对象,采用流体包裹体热力学、群体成分分析及黄铁矿微量元素分析等方法,对成矿流体演化特性及对成矿过程的指示与约束开展了研究。研究表明,成矿期的萤石、方解石、微晶石英中流体包裹体类型以富液相两相Na Cl-H_2O型为主,平均均一温度分别为185. 8℃、177. 0℃、140. 4℃,平均盐度分别为2. 24%Na Cleqv、1. 36%Na Cleqv、1. 75%Na Cleqv,矿床流体具有中低温低盐度特征;计算出平均成矿压力分别为39. 5MPa、38. 0MPa、30. 1MPa,平均成矿深度分别为1. 5km、1. 3km、1. 1km。流体包裹体群体成分显示成矿流体中富含K~+、Na~+、Ca~(2+)等阳离子和HCO_-~3、F~-、SO_4~(2-)等阴离子及CO_2、H_2O等气相成分。这些脉石矿物为成矿期不同阶段沉淀的产物,随着成矿流体温度、压力逐渐降低,流体存在演化分异和不混溶现象,流体内的∑M+/∑M-逐渐升高,矿物沉淀按先析出萤石、其次方解石、最后微晶石英的顺序进行。成矿期黄铁矿Y/Ho平均比值变化显示,矿物沉淀过程逐渐改变了成矿流体性质,使得Zr/Hf、Nb/La、Co/Ni等稀土、高场强元素平均比值逐渐变小,还原性的成矿环境也会发生轻微波动;铀元素在流体演化的最晚阶段才大量与微晶石英一同沉淀,沉淀出的黄铁矿U/Th平均比值逐渐升高。  相似文献   

Using MaxEnt Model to Predict Suitable Habitat Changes for Key Protected Species in Koshi Basin,Central Himalayas     

LIU Linshan  ZHAO Zhilong  ZHANG Yili  WU Xue 《资源与生态学报(英文版)》2017,8(1):77-87

Because of its landscape heterogeneity, Koshi Basin (KB) is home to one of the world’s most abundant, diverse group of species. Habitat change evaluations for key protected species are very important for biodiversity protection in this region. Based on current and future world climate and land cover data, MaxEnt model was used to simulate potential habitat changes for key protected species. The results shows that the overall accuracy of the model is high (AUC > 0.9), suggesting that the MaxEnt-derived distributions are a close approximation of real-world distribution probabilities. The valley around Chentang Town and Dram Town in China, and Lamabagar and the northern part of Landtang National Park in Nepal are the most important regions for the protection of the habitat in KB. The habitat area of Grus nigricollis, Panax pseudoginseng, and Presbytis entellus is expected to decrease in future climate and land cover scenarios. More focus should be placed on protecting forests and wetlands since these are the main habitats for these species.  相似文献