Relationship between footwall composition,crustal contamination,and fluid–rock interaction in the Platreef,Bushveld Complex,South Africa

In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of 2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave. −7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef has generally higher plagioclase and pyroxene δ ¹⁸O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic evidence for sub-solidus interaction with fluids, and the Δ _{plagioclase–pyroxene} values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ _{plagioclase–pyroxene} in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO₂-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale. The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO₂ produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation.     

Integrating diverse methods to understand climate-land interactions in East Africa

The questions of how land use change affects climate, and how climate change affects land use, require examination of societal and environmental systems across space at multiple scales, from the global climate to regional vegetative dynamics to local decision making by farmers and herders. It also requires an analysis of causal linkages and feedback loops between systems. These questions and the conceptual approach of the research design of the Climate-Land Interaction Project (CLIP) are rooted in the classical human-environment research tradition in Geography.This paper discusses a methodological framework to quantify the two-way interactions between land use and regional climate systems, using ongoing work by a team of multi-disciplinary scientists examining climate-land dynamics at multiple scales in East Africa. East Africa is a region that is undergoing rapid land use change, where changes in climate would have serious consequences for people’s livelihoods, and requiring new coping and land use strategies. The research involves exploration of linkages between two important foci of global change research, namely, land use/land cover (LULC) and climate change. These linkages are examined through modeling agricultural systems, land use driving forces and patterns, the physical properties of land cover, and the regional climate. Both qualitative and quantitative methods are being used to illustrate a diverse pluralism in scientific discovery.     

Beyond the numbers: Understanding the value of vegetation to rural livelihoods in Africa

Different types of vegetation found in local environments are of value to rural livelihoods of many African households. However, the dominant way of expressing this value, which is mainly through economic valuation studies, is potentially limiting this knowledge’s usefulness in policy and research, due to the inability to present full picture. Using literature review and insights from field work, the paper argues that realized and notional values of vegetation to rural livelihoods are socially constructed and contested, and - in addition to understanding local livelihood context, which include social difference, and ecological dynamics - a focus on social institutions as terrains of negotiation is crucial. This means that resource value in rural livelihoods can be realized through contested and negotiated access arrangements that are mediated by complex institutions at local and external levels.     

Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America – Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil

Fossil charcoal, as direct evidence of palaeowildfires, has repeatedly been reported from several plant-bearing deposits from the Late Palaeozoic of the Northern Hemisphere. In contrast charcoal reports from the Late Palaeozoic deposits of the Southern Hemisphere are relatively rare in comparison to the Northern Hemisphere. Although the presence of pyrogenic coal macerals has repeatedly been reported from Late Palaeozoic coals from South America, no detailed anatomical investigations of such material have been published so far. Here is presented an anatomical analysis of charcoal originating from Early Permian sediments of the Quitéria Outcrop, Rio Bonito Formation, Paraná Basin, located in the central-eastern portion of Rio Grande do Sul, Brazil. This charcoal comes from two different coaly facies, and it was possible to scrutinize between three types, based on anatomical characters of the charcoal. Two of these charcoal types can be correlated to gymnosperm woods, and the other type corresponds to strongly permineralized bark with characteristic features of lycopsids. The presence of charcoal in different facies, ranging from parautochtonous to allochtonous origin, indicates that different vegetation types, i.e. plants which grew under wet conditions in the lowland as well as in the more dry hinterland, have experienced wildfires. Taking into account previous petrographic and lithological analyses from the facies in which the charcoal occurs and from the conditions of the wood and bark fragments, it was possible to speculate that the intensity of such wildfires most probably corresponds to forest-crown fires. Moreover, it is possible to state that wildfires have been a more or less common element in distinct Late Palaeozoic terrestrial ecosystems in the South American part of Gondwana. The data support previous assumptions on the occurrence of wildfires in the Early Permian of the Paraná Basin which were based solely on coal-petrographic data.     

南太平洋辐合带(SPCZ)的特征分析

根据热带西太平洋卫星云图资料及流场特征分析,讨论了南太平洋辐合带(SPCZ)的演变特征和形成机理。提出SPCZ是反映西太暖池同东太冷舌海气耦合系统以及暖池大气同相邻陆区大气间相互作用的重要特征。主要表现为在12～2月的热带西太平洋上的NW/SE辐合带,其形成原因主要应归因于西太暖池本身,以及暖池与东太赤道冷水舌强度与相对位置改变引发的Walker环流位置与走向的变动,另外,新几内亚岛及澳洲大陆也有重要影响。     

南海沉积岩芯的地球化学研究

本文对南海中部陆坡区和海盆区的5个岩芯中的 Si,Al,Fe,Mn,Ca,Mg 和 CaCO_3成分做了分析,并对其分布特征与有关影响因素进行了讨论。受沉积区环境差异的影响,元素的分布具有区域性特征;受海区特定地理位置的影响,元素的分布呈现出过渡性特征(浅海到大洋的过渡);受沉积过程中环境变化的影响,元素的分布展示了周期性变化或旋回性。根据岩芯中元素的分布特征,并参考有关古地磁,氧碳同位素和钙质超微化石的测试分析结果,将本区岩芯划分为14层地球化学层,并将本区划分为两个沉积地球化学区,揭示了早更新世以来本区沉积环境的变化和存在的两种沉积模式。     

南黄海灾害性地质研究

本文研完了南黄海10种灾害地质因素的性质、危害性及分布,对其进行了分类,在此基础上对本区之灾害地质进行了区划和评价。     

南黄海灾害地质因素及分区

尝试性地将南黄海灾害地质因素分为4大类。同时参考地貌沉积界线和其他因素将南黄海分成4个灾害地质区：即海岸带、苏北浅滩、海州湾和南黄海东部灾害地质区，并时各灾害地质区进行了定性评价，苏北浅滩灾害地质区是研究区内灾害地质环境最不稳定的区域。     

南沙西部海域伸缩型右旋走滑双重构造系统及其动力学过程

万纳断裂带为一典型的右旋走滑系统,由其南段前锋的拉奈—沙捞越走滑－收缩叠瓦扇、北段尾端的南海西南次海盆西南端走滑－伸展叠瓦扇和中段的万安盆地走滑－拉分双重构造所组成,其动力主要源自中生代末以来华南—印支陆缘岩石圈的拆沉作用和南海海底扩张,它的走滑拉分作用直接导致了万安盆地的产生,对该海域油气等资源的形成与聚集起了重要的控制作用。     

南海黄鲷性腺发育的初步研究

本文采用常规的生物学调查方法并取黄鲷性腺做石蜡切片，用显微镜观察黄鲷的性腺发育，进行组织学研究．其结果表明，南海黄鲷精巢可分成6期，精巢5期的成熟度指数为1．62％～2．71％，平均值为1．99％．雌性生殖细胞可见5个时相，卵巢发育也相应分成6期，卵巢5期时的成熟度指数为8．90％～13．90％，平均值为9．45％．南海黄鲷的繁殖期在11月至翌年的4月，繁殖高峰在12月至3月，黄鲷的产卵类型属于在同一繁殖季节中多次产卵类型．本文还对黄鲷的雌雄同体现象、繁殖力、繁殖时间进行了讨论．