Thermochronology of the PoSen complex,northern Vietnam: Implications for tectonic evolution in SE Asia

The PoSen complex, located closely adjacent to the southwestern margin of the Red River shear zone represents the uplifted basement of north Vietnam and may record the motion of the shear zone. However, its thermochronological history has not been fully examined yet. Here we applied U–Pb and ⁴⁰Ar/³⁹Ar dating methods to reveal its thermochronological history. U–Pb analysis of composite zircon grains by TIMS yielded an average age of 760 ± 25 Ma, clustering on the concordia line. Twelve SHRIMP U–Pb analyses also yielded a consistent result of 751 ± 7 Ma. Along with the geochemical features, the U–Pb dating results suggest the PoSen complex was a late Proterozoic magmatic complex, which could correspond to the Chengjiang orogeny, a widespread thermal event in southwest China. Results of ⁴⁰Ar/³⁹Ar dating of micas and K-feldspars were in the range of 36–30 Ma, revealing a rapid cooling and exhumation history of the PoSen complex during the late Paleogene. The time span of cooling and exhumation of the PoSen complex is slightly older than the main cooling phases of the Ailao Shan–Red River (ASRR) metamorphic massifs (28–17 Ma), but is synchronous with the early igneous activity stage in the eastern Indo-Asian collision zone of southeast China and north Vietnam. Owing to the ongoing debate about the initiation and offset of the ASRR shear zone, the tectonic force for the late Paleogene cooling of the PoSen complex is still inconclusive. The rapid exhumation of the PoSen complex could be in response to either the detachment of the Neo-Tethyan slab or a transpressional phase of continental subduction along the ASRR shear system in the eastern Indo-Asian collision zone.     

Numerical investigation on the performance of Wells turbine with non-uniform tip clearance for wave energy conversion

The performance of a Wells turbine with various non-uniform tip clearances was investigated using computational fluid dynamics (CFD). The investigation was performed on numerical models of a NACA0020 blade profile under steady flow conditions. The performance of turbines with uniform and non-uniform tip clearances was compared. The results were also compared with experimental results in literature. It was shown that the performance of turbine with non-uniform tip clearance is similar with that of turbine with uniform one in terms of torque coefficient, input power coefficient, and efficiency. However, the turbine with non-uniform tip clearance seems to have a preferable overall performance. An investigation on the flow-field around the turbine blade was performed in order to explain the phenomena.     

The UNEP/GEF South China Sea Project: Lessons learnt in regional cooperation

The UNEP/GEF project entitled “Reversing environmental degradation trends in the South China Sea and Gulf of Thailand” implemented by United Nations Environment Programme (UNEP) in partnership with seven riparian states bordering the South China Sea was initiated in 2002 and completed in 2008. The project was complex since it addressed three priority areas of concern identified in the Transboundary Diagnostic Analysis namely the loss and degradation of coastal habitats, over-exploitation of fisheries, and land-based pollution. The fourth component of the project was concerned with regional co-ordination including facilitation of national level execution and securing inter-country agreement on project related matters. A number of lessons learnt from implementing the project include, inter alia: the need for a well designed management framework to ensure smooth co-ordination and information exchanges among and within participating countries; the importance of individuals in terms of the success or failure of Inter-Ministry Committees at the national level; separation of scientific and technical issues from political decision-making; the importance of the demonstration site network in encouraging cooperation at the local level; ownership of the project by participating countries; strong involvement of regional and national experts in implementing project tasks; linkages between habitat and fisheries management for developing a regional fisheries refugia network; sharing data through the development of regional databases; productive services of the project coordinating unit; and development of a framework for long-term cooperation in environment management.     

Valuing direct use values of wetlands: A case study of Tam Giang–Cau Hai lagoon wetland in Vietnam

Tam Giang–Cau Hai lagoon wetland directly or indirectly provides the likelihoods for about 300,000 persons living around as well as on the lagoon. Due to expansion of aquacultures, intensive fishing, and lack of an appropriate management scheme, the biological resources in the lagoon are degraded. This study provides information on the direct use values of the lagoon wetland, using market price approach. This information on economic values can be used for designing new policies and making trade-offs among alternative management options for the lagoon wetland.     

Groundwater status and associated issues in the Mekong-Lancang River Basin: International collaborations to achieve sustainable groundwater resources

Groundwater is an important and readily available source of fresh water in the Mekong-Lancang River Basin. With a rapid population growth and increasing human activities, an increasing number of countries in the Mekong-Lancang River Basin are experiencing depleted and degraded groundwater supplies. In transboundary river basins, such as the Mekong-Lancang River, prioritizing the use of the shared aquifer by one riparian government may affect the opportunities of other riparian governments and lead to potential water conflicts between neighboring countries. To promote the sharing of strategies and information for the sustainable and equitable use of water resources of the shared basin, international collaborative workshops on groundwater resources have been organized for all Mekong-Lancang River countries. These workshops provide an opportunity to communicate and discuss nationally sensitive issues on groundwater by the associated countries, with topics covering multiple aspects of groundwater, such as the groundwater status in the basin, quality issues, water use conflicts, hydrological information gaps, management policies and capacity building for successful water resource management. Consensus has been reached by all countries on the importance of catchment-based groundwater management and the need for close communication among the countries. Strategies for managing transboundary aquifer issues must foster international collaboration based on the regional network, influence national networks and enhance the capacity to building maps and monitoring systems based on associated databases. The sustainability of water resources cannot be achieved without the integrated involvement and contributions by multiple countries and various stakeholders. Therefore, collaborative workshops provide a great opportunity to further our understanding of the hydrologic processes of the Mekong River Basin, share the benefits of the aquifer and provide a strategy and vision for sustainable water resource management in the Mekong-Lancang River countries.     

High Temperature Strain Structures and Quartz C-Axis Fabrics from Mylonitic Rocks in the Ailaoshan-Red River Shear Zone, Yunnan, and Their Tectonic Implication

<正>The Ailaoshan-Red River(ASRR) shear zone is one of the major Southeast Asian tectonic discontinuities that have figured the present tectonic framework of the eastern Tibet.Several metamorphic massifs are distributed linearly along the shear zone,e.g.Xuelongshan,Diancangshan, Ailaoshan and Day Nui Con Voi from north to south.They bear a lot of lines of evidence for the tectonic evolution of the eastern Tibetan at different crustal levels in different tectonic stages.Controversy still exists on the deformation structures,microstructures and their relationship with metamorphisms along the ASRR.In this paper detailed microstructural and EBSD(Electron Backscattered Diffraction) fabric analysis of some highly sheared granitic rocks from different massifs along the ASRR are conducted.High temperature structures and microstructures are preserved in unsheared gneisses,in weakly sheared xenoliths or in some parts of the highly sheared rocks(mylonites).Several types of high temperature quartz c-axis fabrics show symmetrical patterns or transitions from symmetrical to asymmetrical patterns.The former are attributed to coaxial deformation during regional shortening in an early stage of the Indian-Eurasian tectonic interaction and the latter are related to the transitions from coaxial compression to noncoaxial shearing during the post-collisional ASRR left lateral shearing.     

小麦冠层理化参量的高光谱遥感反演试验研究

以国产成像光谱仪所获高光谱遥感数据为基础，根据田间同步采样数据建立的基于反射光谱特征的小麦冠层生物物理和生物化学估计模型，实现了用航空高光谱遥感数据对田间小麦冠层理化参量的整体反演。结果表明：用高光谱遥感方法估计小麦冠层理化参量是可行的；以理化参数为“波段”的数字图像及其处理，为农学家以理化参量的空间分布及其差异解释作物产量空间分布差异和研究作物生态生理机理提供了新的手段。     

Hydrogeological investigation in the Mekong Delta around Ho-Chi-Minh City (South Vietnam) by electric tomographyInvestigation hydrogéologique dans le delta du Mékong,autour de la ville de Ho-Chi-Minh (Sud-Vietnam), par tomographie électrique

In the Mekong Delta (South Vietnam), the agglomeration of Ho-Chi-Minh (HCM) City, with more than 5 million inhabitants, is confronted with a dramatic shortage of fresh water supply because of the pollution of several aquifers at different depths. The electric tomography, obtained by concurrent inversion of two complementary geoelectrical methods, the Vertical Electrical Sounding (VES) and the Magneto-Telluric Sounding (MTS), turned out to be very efficient to provide a complete electrical image of the underground from the surface until about 800 m depth. This methodology constitutes a very cheap guide for the evaluation of the quality of the groundwater resources in the vast alluvial plain of the Mekong Delta. To cite this article: V.N. Pham et al., C. R. Geoscience 334 (2002) 733–740.     

Streamflow generation regarding storage components and runs' characteristics

An attempt is made in this study to search for a model which is capable of reproducing the reservoir storage components and runs' characteristics along with the mean, standard deviation, skewness and correlation coefficients of historical monthly streamflows. The model based upon the method of fragments and a scheme devised for annual values is found to yield satisfactory results and is, therefore, recommended for use.