Distribution characteristics and its influencing factors of active layer thickness in Tanggula area on the Qinghai-Tibet Plateau北大核心CSCD

多年冻土区活动层的冻融过程显著影响地-气间的水热交换、地表水文过程、冰缘地貌演变及寒区工程建设。活动层厚度的空间分异规律及其空间分布的准确模拟计算是冻土学研究的基础和核心问题之一。作为青藏高原中部东西走向最大的山脉和青藏高原多年冻土的主要分布区,唐古拉地区是青藏高原南部湿润区与北部干旱区的过渡区,该地区的活动层厚度空间分异规律研究对于揭示青藏高原多年冻土区活动层厚度整体空间分布规律具有重要意义。利用唐古拉地区南、北坡两个区域野外实测活动层厚度分布数据,分析了该区域活动层厚度的空间分异特征及其主要影响因素。结果表明,活动层厚度分布的突出特点是空间分异巨大,最小值仅为1.2 m,最大值达到5.6 m。以不同植被类型区活动层的平均厚度为对比标准,其分布特征为：沼泽草甸<高寒草甸<高寒荒漠<高寒草原,高寒草原的平均活动层厚度最大。对比南、北坡,南坡活动层厚度普遍大于北坡。Stefan方程的计算结果表明,活动层厚度的变化速率随土壤含水率的变化最大,其次为土壤热导率,而随地表融化指数的变化最小。实测土壤含水率、探坑数据及地表融化指数与活动层厚度分布关系表明,影响活动层厚度空间分异的最为敏感的因素为土壤含水率,其次为土壤热导率,地表融化指数的敏感性最小。     

Simulation and assessment of soil temperature and moisture in seasonally frozen soil regions of the Tibetan Plateau based on SHAW model北大核心CSCD

In recent years,more and more attention has been paid to the problem of the cryosphere changes on the Tibetan Plateau,and it has gradually become a hot issue for scholars. Known as the“water tower of Asia”,the Tibetan Plateau is the source of many major rivers in Asia. Under the combined influence of climate change and human activities,water resources on the Tibetan Plateau have undergone profound changes,especially soil water,as an important component of water resources,which plays an important role in regulating vegetation and crop growth,rainfall and runoff. However,global warming leads to the degradation of permafrost and seasonal⁃ ly frozen soil,which affects the original water cycle process and the spatial and temporal pattern of water re⁃ sources by changing the properties of soil water storage and water transport. In the Tibetan Plateau,where there are few data,it is difficult to directly study the soil water cycle process under freezing-thawing by using original data. Therefore,it is an important means to simulate the variation characteristics of soil water and temperature under freezing-thawing in seasonally frozen soil regions of the Tibetan Plateau by using coupling model of soil water and heat. Aiming at the key problem of the difference of soil temperature and moisture characteristics in typical seasonally frozen soil regions under different meteorological conditions,this paper simulated the charac⁃ teristics of soil moisture and temperature change in Maqu,Naqu（Nagqu）and Shiquanhe from 2017 to 2018 by using SHAW（Simultaneous Heat and Water）model and three soil moisture characteristic curve models. The simulation effect and variation characteristics of soil moisture and temperature under different meteorological conditions were analyzed,and the influence of soil moisture characteristic curve model on the simulation effect was studied. The results show that SHAW model can well simulate the temporal variation and vertical distribu⁃ tion of soil temperature and moisture under different meteorological conditions. The simulation effect of soil tem⁃ perature is better than that of soil moisture. The average NSE,R2 and RMSE of soil temperature are 0. 88,0. 96 and 2. 20 ℃,respectively. The mean NSE,R2 and RMSE of soil moisture are 0. 60,0. 72 and 0. 03 m3·m-3,respec⁃ tively. In terms of different meteorological conditions,the simulation effect of soil temperature in relatively dry region was significantly better than that in humid region,while the simulation effect of soil water in relatively hu⁃ mid region was significantly better than that in arid region. From different depths in soil,the simulation effect of soil temperature decreases gradually with the increase of depth,while the simulation effect of soil moisture in the middle and lower layers is better than that in the surface layer. From the view of different soil moisture character⁃ istic curve models,different soil water characteristic curve models have no significant effect on soil temperature simulation effect,but there are significant differences in soil moisture simulation effect. In addition,there are great differences and uncertainties in simulating soil temperature and moisture in different freezing-thawing stag⁃ es. With the increasing trend of climate warming,permafrost and seasonally frozen soil on the Tibetan Plateau may continue to degrade,may change the current water resources pattern,resulting in frequent extreme weather events. Therefore,from the perspective of numerical simulation,this paper verified the applicability of soil moisture and heat coupling model in soil temperature and moisture simulation under different meteorological con⁃ ditions,revealed the influence of precipitation and temperature on soil temperature and moisture simulation at different depths in seasonally frozen soil regions,and analyzed the differences in simulation effects of different soil moisture characteristic curve models. The results provide reference for the study of soil water resources vari⁃ ation under freezing-thawing conditions. © 2023 Chinese Journal of General Practitioners. All rights reserved.     

Permafrost and taliks and their changes on the south and north banks of the Tuotuo River in the Qinghai-Tibet Plateau under the climate warming北大核心CSCD

The distribution of permafrost and taliks is very complex in the Tuotuo River Basin(TRB), which is located in interior of the Qinghai-Tibet Plateau. Characterizing the spatial distribution and the thermal stability of permafrost and taliks is of great significance to community activities and engineering construction in TRB. Based on the zonation of permafrost and talik distribution around TRB conducted in the 1980s, the soil temperature and its variation process of permafrost and taliks in the south and north banks of the Tuotuo River were analyzed by using the observation data of five boreholes(N1~N5)along the Qinghai-Tibet Railway in the north bank and five boreholes(S1~S5)on the first terrace in the south bank. The results showed that, under the climate warming, permafrost and taliks in the north banks experienced significant degradation and warming process. From 2005 to 2020, the permafrost at the N1 borehole has undergone a significant down-draw degradation process, from extremely unstable and high-temperature permafrost to thawed zone. From 2005 to 2013, the annual average ground temperature of the talik at N2 increased at a rate of 0. 3~0. 4 °C·(10a)-1. At Maqutang on the south bank, permafrost prevails from the first-class terrace to the gentle slope of the Kaixinling Mountain, with both through and non-through taliks on the first-class terrace. The spatial distribution and the thermal stability of permafrost and talik in the TRB are further promoted by analyzing the changes in temperatures at boreholes in the basin. However, to meet the requirements of mapping and engineering construction of permafrost and taliks in the TRB, it is still necessary to carry out geological investigation with multiple methods and in-depth research on development mechanism of taliks in the future. © 2022 Nanjing Forestry University. All rights reserved.     

Study on chemical composition of snowpack in southeast and southwest of Tibetan Plateau in winter北大核心CSCD

According to 73 snow samples collected in the southeast and southwest of Tibetan Plateau in January,2021,the characteristics of hydrogen and oxygen stable isotopes（δD and δ18O）fractionation in dry season and the influence of water vapor migration on the chemical composition change of snow profile were revealed by measuring the stable isotopes of hydrogen and oxygen and soluble inorganic ions in snow,and the relationship between stable isotopes of hydrogen and oxygen and climate and the composition and source of soluble inorganic ions were discussed. The results show that the local meteoric waterline of snowpack in the whole study area is δD=7. 86δ18O+11. 8（R2=0. 95）,which is close to the Lhasa winter meteoric waterline,and the slope and inter⁃ cept of the meteoric waterline in the southeast are slightly lower than those in the southwest. δD and δ18O fluctu⁃ ates from -178. 11% to -68. 07% and -23. 80% to -9. 61%,respectively,and the d-excess values fluctuate from 11. 03% to 23. 49%,showing low values of δD and δ18O in winter,and high d-excess values. The surface layer is relatively enriched in heavy isotopes,and the isotope values are higher than those of the lower snow sam⁃ ples,and the water vapor migration inside the snow makes the slope of the relationship between δD and δ18O dif⁃ ferent. The concentration sequence of the main soluble inorganic ions is Ca2+>SO42->Na+>NO3->Cl->K+>Mg2+> NH4+,of which Ca2+（42. 47%）,SO42-（23. 53%）accounted for the largest proportion of cation and anion,re⁃ spectively,and the average concentration of ions in the southeast was higher than that in the southwest. The re⁃ sults of principal component analysis show that terrigenous sources are the main source of ions in snow,and NH4+ and some NO3- are related to human activities. The backward air mass trajectory shows that the source of water vapor is related to the water vapor transport controlled by the upper-altitude westerly circulation,and most of the ions are terrestrial mineral dust carried by westerly winds in winter. © 2023 The Author(s).     

Influence of plant on the extractability of estrogen in the rhizospheric soil

Livestock wastes applied to agricultural land are potential sources of steroidal hormones （estradiol （E2）, estrone （E1）, and estriol （E3）） that can adversely affect the aquatic ecosystem as endocrine disruptors. But the effects of plants on the fate of estrogen in the environment are not clearly known. In the present report, the behavior of E1, E2 and E3 added to the rhizospheric soil in various concentrations and its effect on plant growth were examined by estrogen batch sorption test, plant pot test and estrogen extraction test. Trifolium repens was grown on the soil spiked with E2 or a mixture of E1, E2 and E3. Pots without plant were prepared as controls. All pots were watered in 50 ml dose almost every day, and the rhizosheric soil and plant body were collected 7, 19, 26, 33 days after planting. The soil was sequentially extracted with Milli-Q water, and methanol / 1M acetic acid solvent followed by methanol wash at the solid to liquid ratio of 1 ： 4 （g/mL）. Extracts were analyzed for El, E2 and E3 using a Shimadzu GCMS-QP5050. Plant dry weight （4 hours, 105 ℃） was measured as an indicator of plant growth. In batch sorption tests, E1 and E2 concentrations in the liquid phase significantly decreased within 24 hours after the addition of estrogen. The sum of methanol / 1M acetic acid extractable E 1 and E2 in the soil decreased to half of the initial added amount within 7 days. Reduction in total estrogenic activity of the soil extracts （estimated as 0.01CE1＋CE2＋0.1CE3 where CE1, CE2 and CE3 are respective El, E2 and E3 concentrations per unit soil weight） continued for 1 month due to slow oxidation of E2 to E1. Desorption of E2 from soil during the pot experiment was higher than expected from the sorption experiment.     

Characteristics and Zonation of the Cenozoic Volcanic Rocks on the Qinghai-Tibet Plateau

1.IntroductionCenozoicvolcanicrockshavebeenfoundinanumberoflocationsbothintheinteriorofandatthemarginsoftheQinghai-Tibetplateau.TheyhavebeenconsideredtObegeneticallyrelatedtOtheplatCsubduchon.Forexample,cafe-alkalinevolcedcrocksoftheLingzizongFormation(60-50Ma)occultingintheGangdisebelttothenorthoftheYarlungZangbosutUrezonehavebeenregardedtoberelatedwiththenorthwardsubduchonoftheboaplateandthecloseoftheNeo--Tethysocean(Wang,1984).StUdiesalsoindicatethattheseCenozoicvolcwhcrocksaredomina…     

Accuracy verification of MODIS daily cloud-free snow cover products over the Tibetan Plateau北大核心CSCD

Snow cover is of great hydrological,ecological,and climatic significance in the Tibetan Plateau. MODIS snow products are widely used at present but are seriously affected by clouds. Scholars at home and abroad have developed a variety of cloud removal products for raw MODIS daily snow products,but the accuracy of these products in the Tibetan Plateau has not been evaluated comprehensively. Therefore,this paper uses Landsat-8 data with high resolution as the reference value to conduct systematic verification of three datasets of cloud-free snow products released on a daily basis. The results show that compared with the two sets of products （M*D10A1GL06 and MODIS_Dysno_Cloudfree）,which are produced based on raw MODIS daily snow cover product realized by NSIDC（National Snow and Ice Data Center）,the MODIS CGF SCE product produced based on MODIS surface reflectance data,has a great advantage in snow identification accuracy. The MODIS CGF SCE product optimized the NDSI threshold for different land cover types. Although the accuracy of snow identification was significantly improved,the problem of large snow identification error in forest areas was still not effectively resolved,and there was a high underestimate error. © 2022 Science Press (China).     

Snow avalanche susceptibility evaluation in the central Shaluli Mountains of Tibetan Plateau based on machine learning method北大核心CSCD

Snow avalanches,which are widely and frequently developed at high elevations,seriously threatens the built traffic corridors in the Tibetan Plateau. Susceptibility evaluation of snow avalanche via machine learning model with a high forecast accuracy can be appled to quickly and effectively assess the regional avalanche risk. This paper took the central Shaluli Mountain region as the study area,in which the snow avalanche inventory was established through remote sensing interpretation and field investigation verification. We quantitatively extracted 17 evaluation factors via GIS-based analysis,and these factors were selected through the variance expansion factor（VIF）. Four machine learning models containing SVM,DT,MLP and KNN were used to compile the susceptibility index map of snow avalanches,and kappa coefficient and ROC curve were used to verify the accuracy. The results suggested that the susceptibility indexes obtained from SVM,DT,MLP and KNN were in the range of［0,0. 964］,［0,815］,［0,0. 995］and［0,1］,respectively. The accuracy test results show that these four models all have good prediction accuracy. Among them,the SVM model is the best. The results also indicated that the areas with the high snow avalanche susceptibility mainly distributed in Genie Mountain and Rigong Mountain,most of which were above the planation surface of the Tibetan Plateau. The average altitude of the extremely high snow-avalanche-prone areas is 4 939 m,while the average altitude of the high snow avalanche-prone areas is 4 859 m. The snow avalanche has low perniciousness on the Sichuan-Tibet Highway and the Sichuan-Tibet Railway in the study area. This study can provide theoretical basis and method reference for disaster prevention and mitigation of snow avalanche along Sichuan-Tibet Railway and other major projects across Shaluli Mountains region. © 2022 Science Press (China).     

Effects of tree species and soil depths on ethylene and methane consumption in tropical and temperate forest soils

To date our knowledge is limited with regard to the responses of ethylene and methane consumption by forest soils to tree species and soil types, and to the effect of presence of ethylene on atmospheric methane consumption. The soils at depths from tropical and temperate forests in China were used to study the responses of ethylene and methane consumption to tree species and soil types. The ethylene and methane consumption by soils beneath each forest floor was measured under the same oxic conditions, along with main properties of forest soils. The accumulation of ethylene was studied in the soil slurry （soil/water, 1/2.5）. In temperate soils under spruce and birch forests, maximal consumption rates of ethylene and methane were observed in the 2.5-5.0 cm and 5.0-7.5 cm soil layers, respectively （P〈0.05）. However, a maximal consumption of both occurred in the 0-2.5 cm soil layer under temperate Korean pine forest （P〈0.05）. Contrary to temperate forest soils, there was a significant lower consumption of ethylene and methane in tropical forest soils at less than 20 cm depths under a seasonal rainforest and secondary rubber forest （P〈0.05）. Hence, the potential of ethylene and methane consumption in the 0-20 cm soil profile was variable with tree species and soil types. According to ethylene formation in the soil slurry, there was greater accumulation of ethylene in the 0-2.5 cm soil under temperate forests than under tropical forests, and its accumulation under spruce and birch forests was more than under Korean pine forest （P〈0.05）. The presence of extrinsic ethylene can significantly inhibit the consumption of atmospheric methane by forest soils.     

Paleoclimate and Paleoenvironment of Gonghe Basin, Qinghai-Tibet Plateau, During the Lastdeglacial: Weathering, Erosion and Vegetation Cover Affect Clay Mineral Formation

With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin,northeastern Tibet-Qinghai Plateau,clay mineral composition proxies,grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon （EASM） over the northeastern Tibet-Qinghai Plateau during the lastdeglacial.The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies.Smectite/kaolinite and smectite/（illite＋chlorite） ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin.Before 12.9 Cal ka BP,both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase.After 12.9 Cal ka BP,an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate.The beginning of Holocene is characterized by high smectite/（illite＋chlorite） and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae,implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP.The time interval after 5.0 Cai ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin.Comparing variations of clay mineral assemblages with previous pollen results,we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.     

Study on dynamic properties and shakedown behaviors of coarse-grained fillers in Qinghai-Tibet Railway subgrade北大核心CSCD

对冻结路基填料开展一系列恒围压和动围压分级循环加载三轴试验,采用轴向及径向双向同步循环加载方式来模拟原位列车荷载下路基填料的复杂循环应力状态,试验结果表明：轴向累积塑性应变随冻结负温的升高而增大,随粗颗粒含量的增大而减小。体变随冻结负温的降低先减小再增大,而体变在粗颗粒含量增加下的三阶段演化特征被试验确定。最后采用现有的三类路基安定性评估理论对冻结路基填料的累积塑性变形进行评估,Werkmeister-准则和马-准则分别在动围压和恒围压的条件下易进入塑性蠕变阶段,陈-准则在两条件下的评判结果均属于塑性安定范围,后循环压实阶段与二次循环变形阶段间临界点不同的确定方法对安定性的评估结果有不可忽视的影响。     

Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau： Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile

The magnetotelluric (MT) survey along the Zhada (札达)-Quanshui (泉水) Lake profile on the western margin of the Qinghai (青海)-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong (班公)-Nujiang (怒江) sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang (羌塘) terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture,Bangong-Nujiang suture, and the major faults of Longmucuo (龙木错) and Geerzangbu are inferred.     

Study on the Gravity Field and Deep-Seated Crustal Structure at the North Margin of the Qinghai-Tibet Plateau

1.I~ductionThenorthernmarginoftheQinghai-TibetplateauincludestheAltllnMis.,theQilianMis.,KunlunMis.,theQaidambasinandthesouthernTarimbasin.ThisareaistCctonicallycharacterizedbyintensiveCenozoicdeformationwithcomplicateddeformationalmechedsm(Molnaretal.,1987;Zheng,1991;Culetal.,1994;Ding,1995andXuetal.,1996).Thedeformationalmechanismsincludethrust-napping,strike-slipping,extensionandblockrotation,aswellassimultaneousupliftingandtypicalbasin-rangetectonics(CulandXu,1996).IntermsofCenozoi…     

Organic carbon and its oxidation stability characteristics of shallow soil in frozen soil area of Three River Source Region北大核心CSCD

As the most important part of the global carbon cycle,soil carbon pool is the largest carbon pool in terrestrial ecosystems. Soil carbon pool in permafrost regions is the most sensitive carbon pool to climate change. Weak climate change will have a huge impact on the organic carbon production in the shallow soil,and then affect the regional landscape and ecology. As an indicator reflecting the antioxidant capacity of soil organic carbon,oxidation stability affects the quantity and quality of soil organic carbon,and its variation has a certain regularity in the alpine permafrost region under the influence of climatic factors. In order to explore the distribution characteristics of soil organic carbon and its oxidation stability in frozen soil,based on the experimental data and the climatic data from 2011 to 2019,the random forest model was used to conduct multi-factor digital mapping on soil organic carbon content,soil organic carbon components with different oxidation difficulty degrees,and soil organic carbon oxidation stability coefficient and environmental variables（average annual precipitation,average annual sunshine hours,average annual air temperature,and altitude）and analyze the controlling factors. The results showed that the model had an interpretation degree of more than 54% for the shallow soil organic carbon in frozen soil area of Three River Source Region,and the digital mapping could reflect the distribution of soil organic carbon well. Soil organic carbon was mainly affected by precipitation and sunshine duration,and temperature took second place. The spatial distribution of components with different oxidation difficulty is different,but the oxidation stability has the distribution characteristics of high in the north and low in the south. Cold and dry are conducive to improving the oxidation stability of organic carbon in shallow soil of frozen soil area. © 2022 Science Press (China).     

Research status and prospect of tensile strength of frozen soil北大核心CSCD

A comprehensive grasp of the research status of tensile strength of frozen soil is the basis for further research. Firstly,the typical methods that can be used to test the tensile strength of frozen soil are introduced,and the test conditions,sample forms and stress mechanism of different test methods are described in detail. The advantages and disadvantages of typical tensile strength test methods are compared and listed. Secondly,the research work and shortcomings based on different test methods are summarized. Then,the latest research progress of the influence of temperature,water content,loading（deformation）rate,soil quality and sample size on the change law of frozen soil tensile strength is comprehensively analyzed. Finally,it is proposed to develop and improve the research method and system of frozen soil tensile strength,and increase the testing research of warm frozen soil tensile strength,so as to obtain the prospect of more accurately simulating the tensile failure behavior of frozen soil. It is pointed out that the internal cause of the formation of the tensile strength and the tensile failure mechanism of frozen soil should be thoroughly revealed by combining the research methods of microstructure and digital image technology of frozen soil. Based on the multi-factor test,a more perfect prediction method of frozen soil tensile strength is explored. Meanwhile,expand the in-situ test research on the tensile strength of frozen soil,and strengthen the parallel research ideas of indoor and outdoor double tracks. Through the analysis of the research status and development trend at home and abroad,it provides reference and guidance for the experimental study of frozen soil tensile strength,the improvement of theoretical model of frost heave,geotechnical engineering design in cold regions and artificial freezing reinforcement engineering. © 2022 Science Press (China).     

Geochemical Evaluation of Soil Quality in Menyuan County of Qinghai Province北大核心CSCD

青海省门源县内林草地面积大于44万公顷,耕地仅不到4.2万公顷,林草地资源丰富。2016年在门源县地区开展了1：25万土地质量地球化学评价工作,是青海省首次在大面积林草地区开展1：25万土地质量地球化学调查工作,具有较好的示范作用。通过评价土壤养分、土壤环境等级划分了土壤质量地球化学综合等级,结果表明：门源县土壤质量一等优质土壤占比92.4%,二等良好土壤占0.8%,三等中等土壤占5.6%,四等差等土壤占0.9%,五等劣等土壤占0.3%。通过项目实施可服务门源县土地资源管理,为门源县土地规划利用、农业种植结构调整及生态环境治理等提供依据,助力门源县绿色有机农畜产品输出地建设。     

Episodes of Cenozoic Gold Mineralization on the Eastern Margin of the Qinghai-Tibet Plateau:~(40)Ar/~(39)Ar Dating and Implication for Geodynamic Events

A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shearzone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new ^40Ar/^39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained ^40Ar/^39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonicmagmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in largescale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.     

Long-term strength attenuation characteristics and yield criterion of frozen soil北大核心CSCD

Frozen soil is generally regarded as a strongly rheological geomaterial. The strength attenuation of frozen soil is an important inducement for disease and instability in subgrade engineering, pile engineering and artificial freezing construction. Few efforts have been made to investigate the attenuation characteristics of strength envelope surface for frozen soil under complex stress states experimentally and theoretically. Considering this, at a temperature of -6 ℃, a series of triaxial stress relaxation tests under various confining pressures were carried out on the frozen subgrade soil specimens at strength points. The degeneration of strength parameters and stress attenuation process of frozen soil under complex stress states were systematically studied. The degradation law and mechanism of cohesion and internal friction angle are synchronously revealed in the stress relaxation process. Testing results indicate that the stress relaxation process of compacted frozen soil is significantly influenced by confining pressure. The stress relaxation ratio is increasing linearly with the rise of confining pressure if the confining pressure is beyond 1. 5 MPa. The anti-relaxation ability of frozen soil is greatly reduced during high confining pressure conditions:the stress relaxation ratio of frozen soil is only 41. 94% under 1. 5 MPa, but exceeds 90. 30% under 16 MPa. The strength of frozen soil attenuates linearly with time in the semi-logarithmic coordinate system. When the confining pressure is higher than 1. 5 MPa, the strength attenuation rate of frozen soil increases with the rise of confining pressure. As the development of stress relaxation of frozen soil, cohesion decreases linearly but internal friction angle increases linearly with time in the semi-logarithmic coordinate system. It manifested that the cementation in frozen soil shows evident rheological features and it is a key inducement for strength attenuation. Moreover, the attenuation law and value of cohesion in frozen soil which is measured by triaxial stress relaxation test are similar to the spherical template indenter test results. This may provide a new test method for obtaining the long-term strength and cohesion of frozen soil. On the basis of test results, the stress states of frozen soil in all stress relaxation curves at 12 relaxation durations were captured, and the rate-dependent variation characteristics of strength envelope in p-q stress space were analyzed in detail. Under high confining pressures, the strength envelope of frozen soil shows different geometric features as time goes on. In addition to the decline of level, the strength surface exhibits clockwise rotation with time, and the third stage sharply decreases at first and then becomes flat. Based on the analysis of characteristics of experimental strength surface and evolution law of strength parameters during the stress relaxation process, a rate-dependent strength theory for frozen soil considering the stress relaxation effect is established in this paper. © 2022 Science Press (China). All rights reserved.     

Relationship between pollen assemblages in surface soil and modern vegetation and climate in the western Tianshan Mountains,Xinjiang北大核心CSCD

Based on the pollen spectrum characteristics of 46 surface samples collected in the western Tianshan Mountains of Xinjiang and a plant community quadrat survey, we analyzed the relationship between pollen assemblages and modern climate and vegetation distribution in the region. The results showed the surface pollen assemblages were consistent with the distribution of modern vegetation. Based on the results of cluster analysis, the study area could be divided into three pollen assemblage zones（mountain steppe zone, desert vegetation zone and typical desert zone）. In general, pollen assemblage can roughly reflect the main characteristics of local vegetation, but there are significant differences in the percentage of some pollen types and the coverage of related plants. The pollen of Picea and Pinus in arbor plants, Ephedra in shrub plants, Chenopodiaceae and Artemisia in herb plants were high represented due to the influence of natural wind, water flow and their own pollen yield. While Rosaceae pollen in shrubs and Poaceae in herbs were less representative in a modern plant community with its own dominant species;The Artemisia and Chenopodiaceae（A/C）ratio can distinguish the desert zone from the mountain steppe zone, and could clearly reflect the aridity level. However, when using this indicator to reconstruct the climate environment, it is necessary to combine the characteristics of pollen assemblage and the influence of changes in vegetation composition and other factors to distinguish;Altitude, average annual precipitation, and average annual temperature all affect the distribution of surface pollen in the area. © 2022 The authors.     

Effects of skeleton void ratio on the strength and deformation characteristics of coarse-grained soilEI北大核心

粗粒土强度变形特性与初始级配和制样干密度密切相关。为研究不同级配和密度组合的粗粒料强度变形特性,提出了一种计算简便、易于推广的粗粒土骨架孔隙比计算方法。开展的室内试验结果表明,该计算方法所得的骨架孔隙比与粗粒土力学特性之间存在较为明显的单调性变化规律。当试样尺寸一致时,随着骨架孔隙比减小,破坏剪应力增大,破坏摩擦角增大,黏聚力减小;平均初始切线弹性模量增大,平均初始切线泊松比减小。整体而言,骨架孔隙比越小,粗粒土强度、刚度越大。基于该结论,笔者提出了一种等骨架孔隙比粗粒土缩尺方法。