Gcochemical characteristics and the (Ecological significance of oil shales from the youganwo formation,maoniing basin. China北大核心CSCD

Geochemical elements of oil shale in the Maoniing Basin were analyzed to discuss provenance attribute and depositional environment of the Youganwo formation. Experimental date of the major elements, trace elements and rare earth elements of 24 samples from the Maoye I well were examined. The analyzed oil shale samples were characterized by enrichment of Tb, U, Kb and LREE, depleted of Zr, Cr and Hf, negative Eu and Ce anomalies, indicating that these samples were originated from continental crust. The chemical index of alteration( CIA) values and the ZrZSc-Th/Sc diagrams indicate that source rooks had undergone intense chemical weathering and deposition recirculation. Based on the La/Th-Hf and La/Yb-^REE diagrams and the negative anomaly of Eu element, the oil shale in the Maoniing Basin has diverse sources, which mainly came from felsic source region of the upper crust or the mixture of felsic volcanic rocks, granite and sedimentary rocks. Ratios of the SrZCu, MgO/CaO suggest that oil shale was formed in fresh water under warm and humid climate, shallow water column became deeper during the middle and late sedimentary period. The depositional environment is interpreted to be limnetic with weak reduction at the early stage and gradually turned into semi-deep to deep lacustrine.     

Geochemical characteristics and petrogenesis of the Dashipo-Heishantuo batholith in Beijing and its geological significanceEI北大核心CSCD

The early Jurassic Dashipo-Heishantuo batholith in Beijing, which consists of the Dashipo hornblende-biotite syenite and Heishantuo granite, exposed in the western Yanshan orogenic belt, eastern North China Craton. The Dashipo syenite is magnesian potassic intermediate rock enriched in large ion lithophile elements such as Rb, Ba, Sr, Pb and LREE, and relatively depleted in high field strength elements such as Nb, Ta, U, Th, Zr, Hf as well as P and Ti, with εNd(t) values from -12.1 to -12.2 and ISr values of 0.70506-0.70464. The Heishantuo granite is magnesian peraluminous high K calc-alkaline, with an enrichment of large ion lithophile elements and radioactive elements such as Rb, Ba, Th, U and Pb, and a depletion of HREE and high field strength elements such as Nb, Ta, Zr and Hf as well as Sr, P and Ti, with εNd(t) values from -15.5 to -18.0 and ISr values of 0.70516-0.70593. The magma of the Dashipo syenite is produced by fractional crystallization of mantle-derived K-rich mafic magma under high pressure. The partial melting of the lower crust, which was heated and metasomatised by the mantle-derived magma, produced granitic magma that intruded into the unconsolidated Dashipo syenite to form the concentric batholith. The petrology and geochemistry of the Dashipo hornblende-biotite syenite indicate that the water weakening was important for the lithospheric destruction within the interior part of the North China Craton. Meanwhile, the partial melting related to the double-diffusion of energy and chemical composition between mantle-derived magma and crustal rocks was an important mechanism for the Mesozoic calc-alkaline felsic magmatism occurred in the interior of the North China Craton. ©, 2015, Science Press. All right reserved.     

Rb-Sr dating of sphalerites from the bingdongshan Pb-Zn deposit in the northern margin of the yangtze bloek and its geological significance北大核心CSCD

In order to discuss the source of ore-forming materials of the Bingdongshan lead-zinc deposit, Rb-Sr isotopes of the main ore-stage sphalerites have been analyzed by using the full dissolution method and fluid inclusions leaching method in this paper, with yielded isochion ages of 507. 7-507. 8 Ma, initial 87Sr/86Sr values of 0. 709193-0. 709220.These isoch-ron ages, representing the age of the main mineralization stage of the deposit, indicate that the deposit was formed in Early Ordovician, or the mineralization occurred in the middle Caledonian. The characteristics of initial strontium isotopic ratios of sphaleritess how that the ore-forming materials or the ore-forming fluid were provided by both of basement rocks and the Sinian carbonates. Combining with geological characteristics of the deposit and regional Pb-Zn metallogenic geological background, it is believed that the Caledonian tectonic movement played important role for the formation of lead-zinc deposits in the northern margin of the Yangtze Block. The Bingdongshan lead-zinc deposit was probably formed under the Caledonian extensional environment, through the precipitation of sulfides, in certain physic-chemical condition, from the ore-forming hydrothermal fluids which were associated with dome structure activities.     

General characteristics and research progress of tellurium mineralizationSCIEI北大核心CSCD

碲作为稀散元素,很少形成独立矿床,主要以共伴生形式产出于多个类型矿床中,包括铜镍硫化物和铂族矿床、铁氧化物铜金(IOCG)矿床、块状硫化物(VMS)矿床、斑岩矿床、矽卡岩矿床、造山型金矿、卡林型金矿和浅成低温热液矿床等。研究表明,碲元素可以形成上百种碲矿物,除了自然碲之外,多与Au、Ag、Pb、Bi、Cu等形成碲化物,与S或者Se形成碲的硫化物或硒化物,也可以形成碲酸盐、硅酸盐、磷酸盐、硫酸盐等矿物;此外Te还可以以类质同象形式替换寄主矿物中的元素。在成矿带尺度、矿床尺度及其矿石中碲均表现出极不均匀的分布特征,与主矿种Cu、Au、Ag等具有成因关系。碲具有多来源特征,可以源自地幔,也可以是浅部壳源岩浆或是围岩地层提供。碲矿化一般发生在成矿的中晚阶段,流体可通过混合作用、水岩反应、沸腾作用等改变体系的物理化学条件(如pH值、硫逸度、氧逸度、碲逸度、温度等),导致流体pH值升高、硫逸度和氧逸度降低,碲逸度升高,这是诱发碲矿物富集和沉淀的主要机制。碲由于其受控成矿条件较为特殊,需要着重加强碲富集成矿的关键控制因素、成矿物质来源和富集沉淀机制的研究。     

Distribution characteristics and differential enrichment mechanism of rhenium in molybdenite in the Dexing copper ore fieldSCIEI北大核心CSCD

世界上绝大部分Re赋存在斑岩型矿床的辉钼矿之中,且分布极不均匀。在矿床-矿石-矿物颗粒等不同尺度上,Re含量均存在较大差异,但造成这些差异的因素目前尚不清楚。本文以德兴矿田中富家坞和铜厂二个矿床的辉钼矿为研究对象,在细致的矿相学研究的基础上,对其开展了EPMA、LA-ICP-MS和XRD分析,同时结合前人研究资料,详细探讨了Re在这两个矿床辉钼矿中的分布规律及差异性富集机制。结果显示:富家坞和铜厂均普遍发育两种形态的辉钼矿(细粒集合体型和粗粒片状型),Re在两种辉钼矿中的分布均极为不均,但细粒集合体型相对更富Re,而同一形态辉钼矿铜厂矿床则具有更高的Re含量;同一矿床中辉钼矿结晶越晚,往往越富集Re;个别辉钼矿可见扭结现象,且扭结部位的Re含量更低,暗示后期构造变形可能导致了Re的丢失;两个矿床高Re辉钼矿和低Re辉钼矿的结构均为2H多型,表明Re含量与辉钼矿晶体结构无关。结合前人资料,本文认为成矿流体性质(如温度、盐度等)是导致铜厂和富家坞辉钼矿Re含量差异的主要因素。     

Zircon U-Pb gcochronology and geochemical characteristics of the reshui monzogranite in the eastern kunlun and their tectonic significances北大核心CSCD

In order to probe the genesis and tectonic significance of the granite in the Reshui area, geoehronologicai and geochemical studies of the Reshui monzogranite have been carried out in this paper. The results show that the Reshui monzogranite has LA-1CP-MS zircon U-Pb age of 231 ±1 Ma, indicating that it was formed in late Triassic. It has high contents of Si()2(68. 74%-7l.69%) , Al,(),( 14. 78%-15. 18%). and k,()( 3. 78%-4. 32% ) , with k,()/Na,() ratios ranging from 1. 05 to 1. 32 ,r Rttmann indexes ranging from 1. 87 to 2. 21 . and A/CNk values varying from 1. 03 to 1. 07, respectively. Thus, the Reshui monzogranite belongs to the high k calc-Alkaline weak peraluminous granite. In addition, it has total REE contents(ΣREE) of I 18. 28x 10-6 - 148. 1 x 10-6, with right declined REE distribution patterns showing strong enrichment of LREE and relative depletion of HREE. Its large ion lithophile elements( L1LE) , including Rb. Ra, Th, and l.REE are enriched, while its high field strength elements( HESE) , including Nh, Ta, P. and Ti, are relatively depleted. It has characteristics of the 1-Type granite. It could be mainly sourced from the partial melting of the subducted slab or basic rocks of the lower crust, mixed partly with mantle materials. Combining with regional geological background, it is believed that the Reshui monzogranite was formed by the interaction of the crust and mantle under the tectonic environment of collision-post collision.     

Structural characteristics and active time of the Kangmar detachment,southern TibetEI北大核心CSCD

The Kangmar gneiss dome, typical of the north Himalayan gneiss domes, is composed of three tectono- lithologic units separated by an upper and a lower detachment fault (Kangmar detachment fault). The low-grade metamorphic Tethyan Himalayan sedimentary sequence formed the upper unit above the brittle upper detachment fault. The mylonitic granites and two-mica granites made up the lower unit beneath the ductile lower detachment fault. The mylonitc middle-grade garnet two-mica schist and biotite-plagioclase gneiss constituted the middle unit inbetween the two detachment faults and were involved in the ductile deformation of the Kangmar detachment fault. The meso- and micro-scale structural analyses on the tectonites from the detachment fault zone indicated that the Kangmar detachment fault experienced a top-down-to-north shear. Integrating macro-/micro-analyses of petrology and mineralogy, this study adopts 40Ar/39Ar dating method to constrain the active time of the Kangmar detachment fault. Analyses of the syn-deformation muscovite from the mylonitic garnet two-mica schist yield a 40Ar/39Ar plateau age of 13.23±0.15 Ma, representing the active time of the Kangmar detachment fault. The chronological result hints that the Kangmar detachment was synchronous with the south Tibet detachment systems to the south and was probably part of the south Tibet detachment systems exposed in the Tethyan Himalayan sedimentary sequence. However, this hypothesis needs from the supports of more geological and geophysical evidence. ©, 2015, Science Press. All right reserved.     

Pyrite characteristics and shale gas significance of the Niutitang Formation in Cengong area,Guizhou ProvinceSCIEI北大核心CSCD

黄铁矿特征研究可为页岩沉积环境恢复与页岩气富集保存规律预测提供依据。以贵州岑巩地区岑页1井牛蹄塘组为研究对象,基于岩心、薄片、扫描电镜及微量元素、硫同位素地球化学,确定牛蹄塘组页岩沉积环境及页岩气富集地质条件。研究表明,牛蹄塘组页岩黄铁矿发育为草莓状、自形-半自形及他形(主要为胶状他形)三种形态,不同形态的黄铁矿形成于不同沉积环境,草莓状黄铁矿形成于缺氧还原环境,自形-半自形黄铁矿形成于贫氧环境,胶状他形黄铁矿指示沉积过程有热液活动的参与。测试井牛蹄塘组整体处于较开放的沉积水体,上段为含氧-贫氧环境,硫同位素整体变轻且发生负漂;中段为较缺氧环境,硫同位素跨度大且发生正漂;下段为还原性更强的沉积环境,硫同位素小幅度负漂。黄铁矿含量与有机质富集密切相关,与黄铁矿有关的孔隙为页岩气吸附、保存及运移提供载体,且草莓状黄铁矿指示的缺氧硫化环境更利于有机质保存。研究工作系统梳理了黄铁矿对牛蹄塘组页岩沉积环境及储层页岩气富集的指示作用,为页岩气勘探提供指示。     

Geochemical characteristics and LA-ICP-MS zircon U-Pb age of the Lanhualing granite in Ningguo,Anhui ProvinceEI北大核心CSCD

The Lanhualing tungsten-molybdenum deposit is a skarn-type deposit located in Ningguo county, Anhui province. This deposit is mainly hosted in the Yinzhubu Formation and the Yanwashan Formation of Ordovician, and genetically related to the Lanhualing granite. The Lanhualing granite belongs to high-K calc-alkaline series with high alkali (Na2O+K2O=4.00%-7.03%), SiO2 (67.87%-74.92%) and MgO (0.62%-1.23%) contents. The granitic rocks show right-dipping chondrite normalized REE patterns with weak δEu anomalies. The granitic rocks are relatively enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). The ore-bearing granite was dated at 148.17±0.94 Ma by LA-ICP-MS zircon U-Pb method. The late Yanshanian is the main tungsten mineralization epoch in the South Anhui-north Jiangxi area; and indeed, the Dongyuan, Zhuxi, Yangchuling, Dahutang and other large and super-large tungsten deposits were formed in this period. Geochemical Characteristics of the Lanhualing granite indicate a crustal source but with mantle input under tectonic regime of compression thickening. ©, 2015, Science Press. All right reserved.     

Comparative analysis of the cold surge characteristics over China before and after 2000北大核心CSCD

Based on the daily minimum temperature data in China from 1961 to 2018, using n-order polynomial fitting, sliding t-test, empirical Orthogonal Function analysis, Morlet wavelet transform and other methods, this paper reveals the temporal and spatial distribution characteristics of the number of cold surge (CS) day, CS frequency and CS intensity by time and region. The results are as follows. On a national level, the number of CS day, CS frequency, and CS intensity decreased from 1962 to 2000. Specifically, the trend of every element of CS has changed from a previous decrease trend to an increase trend, and the inflection point was around 2000. The CS activity occurred more frequently, became more strengthen, and last for longer time after 2000. There are obvious spatial differences in the number of CS days, CS frequency, CS intensity and their changing trends in China. The number of CS days and CS frequency reach the maximum value in northeast China and northern Inner Mongolia. Meanwhile, the CS intensity value is low in the southeast China and high in the northwest China, with the exception of southern Xinjiang. The changes in the number of CS day and the CS frequency are mainly manifested as the “Northeast, Southwest Reverse Pattern”, the CS intensity is mainly manifested as the “Uniform Change Pattern”. The number of CS day, CS frequency, and CS intensity did not change significantly after, but a significant transition point was detected in 1980. On a regional scale, from 1962 to 2018, the number of CS day, frequency and intensity of cold surge in all regions showed a decreasing trend, while they increased after 2000. In the northern and northeastern of China, mean of three elements of cold surge increased after 2000. The transition year was different in different regions. The transition year of three elements of cold surge in Northeast China were the earliest. Mean value of the number of CS day, CS frequency, and CS intensity have an oscillation period of 3~5 years in total China and all regions. In addition, the periodic oscillations of the number of CS day and CS frequency in all regions are basically the consistent. © 2022 Science Press (China).     

Composition characteristics and significance of spinel in the kinibcrlite from No. 30 Pipe in the wafangdian area. China北大核心CSCD

The spinel coexisting with diamonds is often used as indicator mineral to evaluate the diamond-bearing potentiality of the kimberlite. In order to figure out the characteristics of spinels in the No. 30 kimberlite pipe, this paper has carried out detailed morphological observation and electron probe analysis on the spinels. The results show that spinels are elliptical and sub-Angular grains, with large particle diameter( 5(H)-1000 μm). A small amount of spinels shows erosional embay men t shape. With high contents of Cr2O3( up to 66. 56% ) and MgO ( 8. 88% - 16. 68% ) , and low TiO2, contents (mostly相似文献   

The geotectonic characteristics and geodynamic evolution of the Red Sea Rift and its adjacent areasSCIEI北大核心CSCD

红海是地球上最年轻的大洋,其板块构造活动正处于威尔逊旋回的幼年期。红海南北两端分别连接着威尔逊旋回的胚胎期和终结期,即东非大裂谷和地中海。这一独特的地理位置和构造部位使其成为板块构造理论研究的圣地。本文通过对已有的地质、地球物理和地球化学资料进行综合分析,了解了红海地区的地形、重磁异常和沿脊的玄武岩地球化学组成等地质构造特征,探讨了红海裂谷的洋壳分布、地幔源区不均一性以及扩张演化历史等问题。红海地形中间深、南北两端浅,可以分为北、中北、中南、南等四段。重磁异常的条带主要出现在中南段,其他段不明显,因而限制了以往对红海扩张历史的认识。目前认为红海全段存在洋壳,红海两岸的沿岸悬崖是共轭扩张陆缘,呈向南开口的喇叭型扩张,而非对应红海岸线的梭子型。红海裂谷沿脊的地幔源区具有明显的不均一性,南段玄武岩显示E-MORB特征,表现为阿法尔地幔柱的影响。红海的发育经历了裂谷前火山作用(31~29Ma)、大陆张裂(29~13Ma)和洋底扩张(<13Ma)三个主要阶段。红海裂谷的形成演化与非洲大陆的裂解、阿法尔地幔柱的活动、新特提斯洋的闭合等密切相关,了解红海的地球动力学过程将为揭示区域大地构造演化以及板块运动规律提供依据。     

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.     

Analysis of water vapor characteristics in snowstorm process on the northern slope of Tianshan Mountains北大核心CSCD

Based on the daily precipitation data of 16 national meteorological observation stations on the north⁃ ern slope of Tianshan Mountains from 2000 to 2020（September to April the following year）,28 blizzard weath⁃ er processes were screened out. Then NCEP/NCAR reanalysis data and HYSPLIT model were used to simulate backward tracking of the water vapor during the snowstorm,analysis of the circulation background of the snow⁃ storm process on the northern slope of the Tianshan Mountains,as well as the main sources and transport of wa⁃ ter vapor and its contribution to the snowstorm. The research showed that the snowstorm area in the northern slope of the Tianshan Mountains was located on the right side of the axis of the southwest jet at 300 hPa high,the southwest airflow in front of the West Siberia trough at 500 hPa,the front convergence of the exit area of the southwest jet at low level at 700 hPa,and the convergence area of water vapor flux divergence and the overlap near the ground cold front area. The water vapor affecting the blizzard on the northern slope of the Tianshan Mountains mainly came from the Mediterranean Sea,the Black Sea and its vicinity,Southwest Asia,Central Asia,the Atlantic Ocean and its coasts,as well as the 850 hPa water vapor in Europe and northern Xinjiang. The water vapor from North America and other places had a relatively small contribution to the blizzard;after each water vapor source reaches the key area with the westerly airflow,under suitable circulation conditions. It mainly entered the blizzard area along the westward（southwest）and the northwest paths. But there were some differences between the layers. Based on the above characteristics,the structure of the source and transport of wa⁃ ter vapor in the snowstorm process on the northern slope of the Tianshan Mountains was established and the char⁃ acteristics of vapor transport at various heights were revealed. © 2023 The Author(s).     

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。     

Provenance and tectonic setting of the Gudongjing Group in Beishan OrogenSCIEI北大核心CSCD

增生造山带中陆源碎屑岩物源区特征的研究可为解剖造山带结构甚至大陆地壳的形成和演化提供关键证据。北山造山带中部的古硐井群被认为是前寒武纪稳定沉积盖层,是北山造山带存在微陆块的重要依据。本文围绕古硐井群的物源区特征,进行了碎屑颗粒和重矿物统计、全岩主微量元素地球化学分析、碎屑锆石U-Pb年代学和Hf同位素测试。古硐井群碎屑岩的碎屑颗粒多呈棱角状,主要为石英、长石,同时含大量硅质岩碎屑和一定数量的火山岩碎屑;重矿物组成以褐铁矿、锆石、白钛石、尖晶石为主,角闪石、电气石、辉石次之,暗示物源区可能存在蛇绿岩、增生杂岩。全岩主量元素以高硅、高铝、富碱、低锰为特征,结合REE、Cr、Co、Sc和Th等惰性元素含量特征共同指示了长英质的物源区。最年轻的碎屑锆石年龄为443.9±13Ma,表明古硐井群最大沉积时限为晚奥陶世。碎屑锆石的年龄高度集中于470Ma附近,且该区间锆石ε_Hf(t)值多为正值,指示物源区存在大量新生地壳物质。本文推测古硐井群可能形成于增生楔楔顶盆地;研究结果支持北山造山带是古生代持续增生造山的产物这一认识。     

Morphotectonics and tectonic processes of the Southwest Indian OceanEI北大核心CSCD

The Southwest Indian mid-ocean ridge (SWIR) is an ultraslow spreading ridge. Based on the submarine bathymetric data, we develop a new division principle on submarine morphotectonics and subdivide the SWIR into the seven-order tectonic geomorphologic units. Taking its submarine morphotectonics in the middle segment and adjacent seafloors of the mid-ocean ridge between Discovery II and Gallieni transform faults as a sample, this paper systematically analyzes its tectonic evolution, segmentation, segmentation and propagation mechanism, the formation of the central rift valley, the ridge-plume interactions, and the ocean ridge jumping. The results showed that the mid-ocean ridges can be divided into four three-order morphotectonics units (i.e., one-order segments of mid-ocean ridge), from west to east, which are separated by the Andrew Bain, the Prince Edwards, the Discovery II, and the Gallieni transform faults, respectively, corresponding to ridge landforms associated with a strongly hotspot-affected ridge, a weakly hotspot-affected ridge, and a normal ultraslow spreading ridge. Each segment can be further subdivided into three or four secondary segments. This paper focuses only on the segmentation and division from fourth-order to seventh-order morphotectonics units between the Discovery II and the Gallieni transform faults (i.e., the fourth-order morphotectonics unit of mid-ocean ridges can be subdivided into other three secondary units). Here the seventh-order morphotectonics unit consists of segments of laterally-aligned rifts (shear zone), en echelon rifts, and other transverse-faulting structures. The mid-ocean ridge segment experienced three oceanic ridge jumping at about 80 Ma, 60 Ma and 40 Ma, respectively, which were affected by the Marion and Crozet hotspots, or the Madagascar Plateau, etc. The oceanic processes of the SWIR are related to the Gondwana breakup, and its tectonic processes has been analyzed in detail as the periodic pull-apart extension, domino-style half-graben, graben subsidence, oceanic core complex, etc. in axial mid-oceanic ridge since 20 Ma. ©, 2015, Science Press. All right reserved.     

Method for calculating the horizontal bearing capacity of segmentally-tapered bucket foundation of offshore wind turbinesEI北大核心CSCD

Because large construction ships cannot enter the shallow sea, traditional configuration foundations, such as gravity-type foundation and pile foundation, are not suited for offshore wind power project in shallow seas. Therefore, a new type of foundation-segmentally-tapered bucket foundation is proposed. Based on the limit equilibrium method, a systematic method is proposed to calculate the horizontal bearing capacity of the segmentally-tapered bucket foundation. The influences of obliquity of wall, foundation height, top diameter of bucket and soil parameters on the horizontal bearing capacity of the segmentally-tapered bucket foundation are analyzed. It is found that the horizontal bearing capacity increases with the increase of the wall obliquity, soil resistance, top diameter of bucket and foundation height, while decreases with the increase of the depth of seabed. Based on the concept of volume compression ratio, the bucket foundation with inclined upper section wall and vertical lower section wall is recommended and demonstrated. An accurate method is proposed to determine the proportional coefficient of soil resistance. The results are helpful in the optimization design of traditional bucket foundation.     

Experimental study on mechanical properties and pore characteristics of the modified lime mortars under freee-thaw cycles北大核心CSCD

石灰土作为路基填料代替宕渣是一种较为经济的方案,但灰土初始强度低、硬化速率慢、碳化时间长,不利于快速施工,需要进行改良研究。利用偏高岭土与石灰发生火山灰反应的原理改良灰土,通过单轴压缩试验和三轴压缩试验,分析改良灰土冻融循环条件下力学参数变化规律,利用图像处理技术提取改良灰土图像表面孔隙,建立孔隙率与强度的关系,并通过研究龄期、石灰含量和含水率变化规律,分析偏高岭土改良灰土的机制。结果表明：偏高岭土能够有效提高灰土材料反应速率,改善灰土力学特性;偏高岭土在一定程度上能够恢复冻融循环导致的灰土力学性能损失,降低冰晶体产生的孔隙;灰土强度达到最优后,其强度随着石灰的增加而降低,而经偏高岭土改良后其强度将继续增加;火山灰反应比灰土碳化过程消耗更多的水分,有效提高了灰土的抗冻性能。     

Comparative study on the geochemical characteristics of rare earth elements in deep-sea sediments from different regions of the Pacific OceanSCIEI北大核心CSCD

太平洋深海沉积物中富集稀土元素(REY,包括钇),被认为是富有潜力的新型稀土资源。(含)沸石粘土、深海粘土和多金属软泥是主要的富含REY的沉积物类型,其中(含)沸石粘土和深海粘土在中、西北太平洋海盆大面积分布,而多金属软泥则多分布于靠近东太平洋洋脊热液活动的深海盆地中。目前关于中、西北太平洋海盆的深海粘土和(含)沸石粘土已有较多的研究,但关于多金属软泥中REY的研究较少。不同区域、不同类型深海沉积物中的稀土元素赋存状态有何差异?影响稀土富集的机制又是什么目前尚不清楚,也就进一步影响了对深海沉积物稀土资源的勘查和开发工作。本文分析对比了太平洋不同区域不同类型深海沉积物的地球化学特征及矿物学特征。结果表明,总体上,中、西北太平洋海盆深海沉积物中,尤其是(含)沸石粘土中的REY含量明显高于东太平洋海盆多金属软泥REY含量,其REY的富集主要与磷酸盐有关。超常富集REY(∑REY>2000×10^(-6))的沉积物中的CaO/P_(2)O_(5)比值趋向于一致(~1.4),几乎接近于磷灰石CaO/P2O5比值(~1.3),因此REY主要赋存载体为磷灰石,该区沉积物中REY的富集可能受到磷酸盐化的影响;东太平洋海盆多金属软泥明显受到热液影响,铁和锰的含量明显增加,但其∑REY含量集中于500×10^(-6)~800×10^(-6),不随铁和锰的增加而变化,REY的富集仍与磷酸盐关系密切,而与铁锰物质和铝硅酸盐关系不大。中、西北太平洋海盆富稀土的深海沉积物形成时处于较强的氧化环境,同时又有充足的含磷物质补给,才造成REY在该区沉积物中的超常富集;而东太平洋海盆多金属软泥虽然处于氧化环境,但缺少足够的磷补给,所以其∑REY含量通常低于中、西北太平洋海盆沸石粘土中∑REY含量。