Subduction of Continental Crust in the Early Palaeozoic North Qaidam Ultrahigh-Pressure Metamorphic Belt, NW China:Evidence from the Discovery of Coesite in the Belt

Coesite was discovered as inclusions in zircon separates from pelitic gneiss associated with a large eclogite body in the North Qaidam ultrahigh-pressure (UHP) terrane. Some graphite inclusions were also found. This finding suggested the occurrence of in-situ UHP metamorphism and that the terrane was most likely recrystallized at pressures below the diamond stability field. It supported other previous indirect UHP evidence, such as polycrystalline quartz inclusions in eclogitic garnet, quartz lamellae in omphacite and P-T estimates for both eclogite and garnet peridotite. The U-Pb and Sm-Nd ages of the North Qaidam eclogite indicated that subduction of continental crust occurred in the Early Palaeozoic, which probably recorded a collision between the Sino-Korean and Yangtze plates.     

NORTH QAIDAM ULTRAHIGH PRESSURE METAMORPHIC (UHPM) BELT ON THE NORTHEASTERN QINGHAI-TIBET PLATEAU AND ITS EASTWARD EXTENSION

NORTH QAIDAM ULTRAHIGH PRESSURE METAMORPHIC (UHPM) BELT ON THE NORTHEASTERN QINGHAI-TIBET PLATEAU AND ITS EASTWARD EXTENSION1　YangJS ,XuZQ ,LiHB ,etal.DiscoveryofeclogiteatnorthernmarginofQaidambasin ,NWChina[J] .ChineseScienceBulletin,1998,4 3:1755～ 176 0 . 2　ZhangJX ,ZhangZM ,XuZQ ,etal.TheagesofU PbandSm NdforeclogitefromthewesternsegmentofAltynTaghtectonicbelt—theevidencesforexistenceofCaledonianorogenicroot[J] .ChineseScienc…     

Hydrologic modeling of the Heihe watershed by DLBRM in Northwest China

Water shortage is a chronic problem in arid Northwest China.The rapid population growth and expanding urbanization as well as potential climate change impacts are likely to worsen the situation,threatening domestic,irrigation,and industrial supplies and even the survival of the ecosystems in Northwest China.This paper describes the preliminary work of adapting the Distributed Large Basin Runoff Model(DLBRM) to the Heihe watershed(the second largest inland river in arid Northwestern China,with a drainage area of 128,000 km2) for understanding distribution of glacial-snow melt,groundwater,surface runoff,and evapotranspi-ration,and for assessing hydrological impacts of climate change and glacial recession on water supply in the middle and lower reaches of the watershed.Preliminary simulation results show that the Qilian Mountain in the upper reach area produces most runoff in the Heihe watershed.The simulated daily river flows during the period of 1990-2000 indicate that the Heihe River dis-charges about 1×109 m3 of water from the middle reach(at Zhengyixia Station) to lower reach,with surface runoff and interflow contributing 51 and 49 percent respectively.The sandy lower soil zone in the middle reach has the highest evapotranspiration rate and also contributes nearly half of the river flow.Work underway focuses on the DLBRM model improvement and incorporation of the climate change and management scenarios to the hydrological simulations in the watershed.     

Early warning indicators for river nutrient and sediment loads in tropical seagrass beds: a benchmark from a near-pristine archipelago in Indonesia

In remote, tropical areas human influences increase, potentially threatening pristine seagrass systems. We aim (i) to provide a bench-mark for a near-pristine seagrass system in an archipelago in East Kalimantan, by quantifying a large spectrum of abiotic and biotic properties in seagrass meadows and (ii) to identify early warning indicators for river sediment and nutrient loading, by comparing the seagrass meadow properties over a gradient with varying river influence. Abiotic properties of water column, pore water and sediment were less suitable indicators for increased sediment and nutrient loading than seagrass properties. Seagrass meadows strongly responded to higher sediment and nutrient loads and proximity to the coast by decreasing seagrass cover, standing stock, number of seagrass species, changing species composition and shifts in tissue contents. Our study confirms that nutrient loads are more important than water nutrient concentrations. We identify seagrass system variables that are suitable indicators for sediment and nutrient loading, also in rapid survey scenarios with once-only measurements.     

Rheological properties of deep subducted oceanic lithosphere and their geodynamic implications

According to the experimental studies on the rheology of two important mantle rocks (eclogite and harzburgite), the rheological properties of the deep subducted oceanic lithosphere are investigated by assuming a simplified harzburgite type slab model with moderate thickness of basaltic layer. When the mantle convergence rate is small or the subducting slab has been trapped in the mantle for an enough long time, the strength profile of the slab is characterized by a strong subducting crustal component lying on a weak subducting upper mantle. However, if the convergence rate is large enough, the subducting slab will be featured only by a rigid cold center. Our study suggests that the detachment of the subducting crust component from the underlying upper mantle is only likely to happen in hot slow subducting slabs, but not the cold fast subducting lithosphere. Rheological properties of the harzburgitic and the eclogitic upper mantle vary with depths. The eclogitic upper mantle is stronger than the peridotitic upper mantle across the upper mantle. Transition zone is the high strength and high viscosity layer in the upper mantle except the lithosphere.     

测绘业高级人才知识结构合理化研究

一、高级人才在测绘业发展中的地位和作用 所谓人才是指具有一定文化素养、掌握某种专业知识和技能的人。高级人才是具有专科和专科以上规定学历的人。本文所研究的高级人才限于大学本科文化程度以上。 测绘是采集、量测、处理、分析、解译、描述、分发、利用和评价与地理及空间分布有关的数据的一门科学、工艺、技术和经济实体,