Quantifying the P–T–t conditions of north–south Lhasa terrane accretion: new insight into the pre‐Himalayan architecture of the Tibetan plateau          下载免费PDF全文

O. M. Weller  M. R. St‐Onge  M. P. Searle  D. J. Waters  N. Rayner  S. Chen  S.‐L. Chung  R. M. Palin 《Journal of Metamorphic Geology》2015,33(1):91-113

An integrated field, petrological and geochronological study of the Basong Tso region of south‐eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high‐grade metamorphic belts are recognized in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25 °C at c. 204–201 Ma, whereas the Zhala complex experienced peak metamorphic conditions of 5.0 ± 1.0 kbar and 740 ± 40 °C at c. 198–192 Ma. Microstructural analysis suggests that the two belts share a common early prograde history, after which the Basong Tso complex attained peak conditions following rapid burial, and the Zhala complex approached peak conditions along an isobaric path. Overall it is inferred that the Basong Tso and Zhala complexes represent the lower and upper structural levels of an evolving orogen that underwent Barrovian‐type metamorphism following collision (M1), followed by Buchan‐style overprinting at higher structural levels due to heat advection by syn‐tectonic granites (M2). Mylonitization (sensu lato) of the Basong Tso complex and juxtaposition of the two units occurred after attainment of peak conditions. The dominance of Mesozoic regional metamorphism across most of the Tibetan plateau indicates that Cenozoic crustal thickening processes, where present, are only manifested at depth.  相似文献   

Strengthening regional governance to protect the marine environment in Northeast Asia: From a fragmented to an integrated approach     

Suh-Yong Chung 《Marine Policy》2010

Northeast Asia is failing in its attempts to protect its regional seas from irreversible ecological damage and contamination. At the policy level, the regional architecture for marine protection has several glaring structural problems that need to be identified and resolved in an expeditious and politically sensitive manner. Although the UNDP/GEF Yellow Sea Large Marine Ecosystem Project (YS LME) and the Northwest Pacific Action Plan (NOWPAP) are the two most likely institutions from which to build the next phase of regional marine cooperation, synergies between the two institutions remain limited. Both institutions are endowed with unique opportunities, challenges and limitations that must be taken into full consideration when planning the next step of coordinated action for regional marine protection. For the purpose of developing a more effective phase of marine cooperation in Northeast Asia, this paper advocates the formation of a Marine Environmental Community based on an integrated approach towards Northeast Asia's regional marine programs. This will facilitate improvements in funding, policy coordination through high level policy dialogue, transparency and efficiency of information sharing systems and full participation of all the coastal states in the region.  相似文献   

Hydrological effects of climate change,groundwater withdrawal,and land use in a small Korean watershed     

Kil Seong Lee  Eun‐Sung Chung 《水文研究》2007,21(22):3046-3056

The effects of variability in climate and watershed (groundwater withdrawal and land use) on dry‐weather streamflows were investigated using SWAT (Soil and Water Assessment Tool). The equation to predict the total runoff (TR) using climate data was derived from simulation results for 30 years by multiple regression analysis. These may be used to estimate effects of various climate variations (precipitation during the dry period, precipitation during the previous wet period, solar radiation, and maximum temperature). For example, if daily average maximum temperature increases by 3 °C, TR during the dry period will decrease by 27·9%. Similarly, groundwater withdrawals strongly affect streamflow during the dry period. However, land use changes (increasing urbanization) within the forested watershed do not appear to significantly affect TR during the dry period. Finally, a combined equation was derived that describes the relationships between the TR during the dry period and the climate, groundwater withdrawal and urban area proportion in a small monsoon watershed. This equation will be effective to predict the water availability during the dry periods in the future since it is closely related to changes of temperature, precipitation, solar radiation, urban area ratio, and groundwater withdrawal quantity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Spatial variation of abundant picoeukaryotes in the subtropical Kuroshio Current in winter     

Ya-Fan Chan  Chih-Ching Chung  Gwo-Ching Gong  Ching-Wei Hsu 《Marine Ecology》2020,41(1):e12579

To understand the importance of picoeukaryotes in the biogeochemical cycle in the subtropical Kuroshio Current, a year-round survey of the hydrography and the distribution of picoeukaryotes were conducted in four oceanographic cruises from October 2012 to July 2013. In comparison with other seasons, the highest abundancy of photosynthetic picoeukaryotes, with concentrations >10⁴ cells/ml, was observed around the eastern boundary of the Kuroshio in the winter. Accordingly, the composition of picoeukaryotes in this cold season was further studied by a metabarcoding analysis of the 18S rRNA gene. The majority of picoeukaryotes comprised Alveolata, followed by Haptophyta and Stramenopiles. Their composition was diverse in the waters affected by the Kuroshio and in the offshore province. For Haptophyta, in contrast to clade A prevailing in the Kuroshio waters, clade B1, which was considered the host of uncultivated diazotrophic cyanobacterium group A (UCYN-A), appeared only in the offshore area. Similarly, in Stramenopiles, Pseudo-nitzschia spp. and MAST-1D, respectively, dominated in the Kuroshio-influenced and offshore areas. While Alveolata was the most abundant group, the distributions of all lineages were similar. The association between picoeukaryote succession and hydrographic change is yet to be fully understood. Our results will assist future studies on the community composition of picoplankton and their relationship with marine ecology in the region.  相似文献   

Use of stable water isotopes to assess sources and influences of slope groundwater on slope failure     

Tsung‐Ren Peng  Chung‐Ho Wang  Shih‐Meng Hsu  Nai‐Chin Chen  Tai‐Wei Su  Jiin‐Fa Lee 《水文研究》2012,26(3):345-355

This study employs stable oxygen and hydrogen isotopes as natural tracers to assess the headwater of a landslide next to a drainage divide and the importance of the slope's headwater in the study area. The study is undertaken near Wu‐She Township in the mountains of central Taiwan. Because a reservoir is located on the other side of the divide, this study evaluates the relationship between the reservoir water and headwater of the landslide as well. Over a 1‐year period, water samples from September 2008 to September 2009, including local precipitation (LP), Wu‐She Reservoir's water (WSRW), slope groundwater (SGW), upper‐reach stream water (USTW), and down‐reach stream water (DSTW), were analysed for deuterium (δD) and oxygen (δ¹⁸O) stable isotopes. Results indicate that WSRW is the predominant component in SGW: approximately 70% of SGW originates from WSRW and 30% from LP based on a two end‐member mass‐balance mixing model for δ¹⁸O. The similar two end‐member mixing model is also employed to assess the contributions of USTW and SGW to DSTW. Model results indicate that SGW is the major source of DSTW with a contribution of about 67%. Accordingly, about 47% of DSTW sources from the WSRW. In short, owing to reservoir leakage, WSRW contributes the greater part of both SGW and DSTW. Plentiful WSRW in SGW threatens the stability of the slope in the divide area. To avoid subsequent continuous slope failure, necessary mitigation steps are required. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Diurnal variation of outgoing longwave radiation associated with high cloud and UTH changes from Meteosat-5 measurements     

Eui-Seok Chung  Byung-Ju Sohn  Johannes Schmetz 《Meteorology and Atmospheric Physics》2009,105(3-4):109-119

Diurnal variations of outgoing longwave radiation (OLR) are examined in conjunction with diurnal variations of high cloud and upper tropospheric humidity (UTH) over the Indian Ocean and surrounding land areas using Meteosat-5 measurements. Most land areas exhibit a significant diurnal variation of OLR with the largest amplitude over the Arabian Peninsula, whereas the diurnal variation of OLR is much weaker over the Indian Ocean. While diurnal maxima of OLR are found in the early afternoon over many regions of the analysis domain following the diurnal cycle of solar heating, convectively active regions of both land and ocean where high cloud and UTH exhibit distinct diurnal variations show OLR maxima before local noon. These results indicate that high cloud development in the afternoon induces a shift in local time of OLR maxima over convective regions. In agreement with earlier studies it is shown that UTH diurnal variations are less important in regard to their impact on the OLR variations.  相似文献   

二次离子质谱第四纪锆石年代学:台湾金瓜石英安岩定年   总被引：2，自引：0，他引：2       下载免费PDF全文

高钰涯  李献华  李秋立  锺孙霖 《地学前缘》2010,17(2):146

高精度第四纪年代学是第四纪研究的基础,对了解地球演化和发展非常关键。大型二次离子质谱(SIMS)锆石U-Th-Pb定年方法,集高空间分辨率、高精度、高效率和近无损分析等优势于一体,可以提取矿物微区中记录的丰富地质信息,在第四纪年代学研究中具有很大的应用潜力。文中对SIMS第四纪锆石原位微区年龄测定的基本原理、分析校正方法进行介绍,并报道我们测定台湾第四纪金瓜石英安岩锆石U-Pb年龄的结果((1.166±0.020)Ma)。  相似文献   

Microphytobenthic biomass and species composition in intertidal flats of the Nakdong River estuary, Korea   总被引：1，自引：0，他引：1  

GuoYing Du  Moonho Son  Misun Yun  Soonmo An  Ik Kyo Chung   《Estuarine, Coastal and Shelf Science》2009,82(4):663-672

Intertidal microphytobenthos (MPB) were investigated monthly from August 2006 to March 2008 at four different sites in the sand flats of Nakdong River estuary, Korea. Samples of surface sediment (ca. 1 cm) were collected, and chlorophyll a was extracted as biomass estimation. Species identification and enumeration were carried out by light microscopy, assisted where necessary by scanning electronic microscopy. Biomass varied between 0.47 and 16.58 μg cm⁻³, abundance changed from 5.25 to 414.75 × 10³ cells cm⁻³, while the Shannon diversity indexes ranged between 0.69 and 2.35 H′. Thirty-nine MPB taxa were identified, primarily composed of epipelic diatoms, among which Amphora and Navicula were the most abundant genera. Based on the biomass, abundance, species composition and their dynamics, MPB assemblages of sampling sites were grouped into three distinct communities corresponding to their sediment composition characteristics. Multivariate correlation analysis revealed that biomass was positively related to mud and very fine sand, negatively related to fine and medium sand, but not significantly related to environmental factors such as pore water nutrients, light intensity and salinity, which fluctuated rapidly during emersion period. Cluster analysis corroborated the division of MPB communities according to site types on seasonal scales, and also showed seasonality between sites by cluster of all summer groups. Principal component analysis identified that variability in species composition was significantly affected by mud, very fine sand, fine sand, light intensity, and sediment temperature. This study suggests that sediment composition plays an important role in the functioning of intertidal MPB communities in estuarine ecosystems.  相似文献   

Petrologic and geochemical constraints on the petrogenesis of Permian–Triassic Emeishan flood basalts in southwestern China     

Yigang Xu  Sun-Lin Chung  Bor-ming Jahn  Genyao Wu 《Lithos》2001,58(3-4):145-168

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A three-stage identification approach for hysteretic systems     

Chin-Hsiung Loh  Sheng-Tsai Chung 《地震工程与结构动力学》1993,22(2):129-150

This paper deals with the identification of the parameters of a smoothed hysteretic model which was proposed by Bouc and Wen with emphasis on restoring force hysteresis. The problem of estimating the parameters of this system on the basis of input-output data, possibly noise corrupted, is considered. Through the application of various simulated time histories from the hysteretic model, a three-stage systematic method of system identification was proposed. Four different methods of identification are arranged and conducted in this three-stage system identification. The first stage, a sequential regressional analysis is used to identify the equivalent linear system from which elastic or inelastic response can be identified. The identified parameters can be used in the stage when the system is in elastic response. In the second stage, both time domain least-squares method and Gauss-Newton method are applied. The convergence of the Gauss-Newton method can be guaranteed if the identified results from least-squares method are adopted as the initial values for Gauss-Newton method. In the third stage, the extended Kalman filtering technique is needed to identify the noise-corrupt data. Application of this algorithm to a SDOF non-deteriorating system is verified.  相似文献