土参数对桩基水平响应影响的研究

桩基的水平响应由桩土间的相互作用决定,通过采用p-y曲线来表示桩土间的非线性相互作用。通过算例,讨论分析了粘性土参数的变化对p-y曲线中土体的极限强度和刚度、桩基水平位移和弯矩分布及最大弯矩和水平荷载关系的影响。     

The method of design for seismic data database system based on tree structure

Introduction In recent years, with the development of earthquake observation technology, increasing ofobservation stations and improvement of observation instruments which are digitalized and con-nected by network, a great deal of data is recorded, to some extend, which brings difficulty for usto manage and store them. It leads to traditional methods, which use the file system to managemass data, could not satisfy our requirement, and it is necessary to find a new method in place oftradit…     

Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions

Using arrival data of the body waves recorded by seismic stations, we reconstructed the velocity structure of the crust and upper mantle beneath the southeastern edge of the Tibetan Plateau and the northwestern continental margin of the South China Sea through a travel time tomography technique. The result revealed the apparent tectonic variation along the Ailao Shan-Red River fault zone and its adjacent regions. High velocities are observed in the upper and middle crust beneath the Ailao Shan-Red River fault zone and they reflect the character of the fast uplifting and cooling of the metamorphic belt after the ductile shearing of the fault zone, while low velocities in the lower crust and near the Moho imply a relatively active crust-mantle boundary beneath the fault zone. On the west of the fault zone, the large-scale low velocities in the uppermost mantle beneath western Yunnan prove the influence of the mantle heat flow on volcano, hot spring and magma activities, however, the upper mantle on the eas     

Deep Mechanical Background for the Cenozoic Volcanism in the Tibetan Plateau

INTRODUCTION Volcanoesaremostlyobservedinoceanicridges,hotspotsandcontinentalriftzones(Hongetal.,2003),andarerarelyobservedincontinentalinteri ors.However,sincethevolcanoeswithintheconti nentinteriorscannotbeattributedtotheplate/block marginprocess,theydr…     

Variability in the vertical hyporheic water exchange affected by hydraulic conductivity and river morphology at a natural confluent meander bend

River confluences and their associated tributaries are key morphodynamic nodes that play important roles in controlling hydraulic geometry and hyporheic water exchange in fluvial networks. However, the existing knowledge regarding hyporheic water exchange associated with river confluence morphology is relatively scarce. On January 14 and 15, 2016, the general hydraulic and morphological characteristics of the confluent meander bend (CMB) between the Juehe River and the Haohe River in the southern region of Xi'an City, Shaanxi Province, China, were investigated. The patterns and magnitudes of vertical hyporheic water exchange (VHWE) were estimated based on a one‐dimensional heat steady‐state model, whereas the sediment vertical hydraulic conductivity (K_v) was calculated via in situ permeameter tests. The results demonstrated that 6 hydrodynamic zones and their extensions were observed at the CMB during the test period. These zones were likely controlled by the obtuse junction angle and low momentum flux ratio, influencing the sediment grain size distribution of the CMB. The VHWE patterns at the test site during the test period mostly showed upwelling flow dominated by regional groundwater discharging into the river. The occurrence of longitudinal downwelling and upwelling patterns along the meander bend at the CMB was likely subjected to the comprehensive influences of the local sinuosity of the meander bend and regional groundwater discharge and finally formed regional and local flow paths. Additionally, in dominated upwelling areas, the change in VHWE magnitudes was nearly consistent with that in K_v values, and higher values of both variables generally occurred in erosional zones near the thalweg paths of the CMB, which were mostly made up of sand and gravel. This was potentially caused by the erosional and depositional processes subjected to confluence morphology. Furthermore, lower K_v values observed in downwelling areas at the CMB were attributed to sediment clogging caused by local downwelling flow. The confluence morphology and sediment K_v are thus likely the driving factors that cause local variations in the VHWE of fluvial systems.     

Geophysical constraints on mesozoic disruption of North China Craton by underplating‐triggered lower‐crust flow of the Archaean lithosphere

The mechanism of the disruption, both lithospheric thinning and oceanization of the commonly accepted long‐term‐stable Archaean craton, is still an open question. The available models, all imply a bottom to top process. With the construction of a 1660‐km‐long transect across the eastern North China Craton (NCC), we demonstrate that both the P‐wave velocity and density in the lowermost crust beneath the central section are significantly higher than in the corresponding parts of the south and north sections on the transect. These features are interpreted as geophysical signature of lower crustal underplating, which supplies sufficiently high gravitational potential energy to trigger lateral flow of the lower crust. This magma underplating‐triggered bilateral lower crust flow may facilitate the lithospheric thinning by means of asthenosphere upwelling and decompression melting, which infill the gap produced by the lower crust flow. The underplating‐triggered lower crustal flow can provide an alternative mechanism to explain the NCC lithosphere disruption, which highlights the crustal feedback to Archaean lithosphere disruption, from top to bottom.     

湖南宝山矿床花岗岩类硫-铅同位素和流体包裹体研究及其成因意义

宝山铜铅锌多金属矿床是湖南重要的铅锌生产基地。矿床内矽卡岩型铜(钼)矿化受侏罗纪花岗闪长斑岩的控制,而主要的铅锌矿体则产于远离岩体的碳酸盐地层中,且缺乏可靠的矿化年龄限制。为了查明宝山铅锌矿体与花岗闪长斑岩之间的成因关系,文章对宝山花岗岩类中浸染状黄铁矿的硫同位素和钾长石的铅同位素,以及铅锌矿石萤石脉石的流体包裹体进行了测试和研究,并与前人报道的铅锌硫化物矿石的硫、铅同位素进行了对比,尝试为宝山铅锌矿化的物质来源及成因提供依据。研究表明,花岗闪长斑岩中浸染状黄铁矿的δ34S值为+1.5‰~+3.5‰,与铅锌矿石硫化物(方铅矿、闪锌矿及黄铁矿)相一致;同时,花岗岩类中钾长石的铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.4789~18.7668、15.6835~15.7220和38.7903~39.1035,具有壳源的特征,且与铅锌矿石硫化物的铅同位素分布范围相吻合。宝山矿床的硫、铅同位素特征表明,花岗闪长斑岩应是铅锌矿化的主要硫源及金属来源。宝山矿床铅锌矿石萤石中的流体包裹体具有低温(130~150℃)、低盐度(8%)的特征,可能是岩浆热液演化到晚期的产物。结合已有的有关资料加以对比和分析,研究认为,宝山铅锌矿床的成矿物质应来源于花岗闪长岩的岩浆期后热液,在热液演化晚期迁移到远端地层中沉淀,形成了宝山的主要铅锌矿体。     

内蒙古敖汉旗七家金矿闪长玢岩锆石U-Pb年代学、地球化学及地质意义

内蒙古敖汉旗七家金矿构造位置上处于兴蒙造山带与华北克拉通北缘的结合部位, 靠近兴蒙造山带一侧, 是近年来新发现的石英脉型金矿床.区内岩脉以闪长玢岩为主, 且与石英脉型矿体空间关系密切.根据岩脉与矿体的穿插关系, 将其分为成矿前闪长玢岩和成矿后闪长玢岩.LA-ICP-MS锆石U-Pb年代学表明, 成矿前闪长玢岩加权平均年龄为166.3±3.4 Ma, 成矿后闪长玢岩加权平均年龄为128.6±4.5 Ma, 与区域上两期构造-岩浆活动时间(分别为160 Ma左右和128 Ma左右)近似吻合.主量元素特征显示: 二者均属于准铝质, 高钾钙碱性系列; 微量元素特征显示: 二者均富集轻稀土元素、大离子亲石元素(Rb、K)和活泼的不相容元素(U、Pb), 相对亏损重稀土元素和高场强元素(Nb、Ta、Ti), 反映出岩浆来源具壳源特征.主微量元素特征均显示出二者具有岛弧岩浆岩的地球化学属性.另外, 成矿后闪长玢岩有较高的Nb/Ta(18.66~20.27)和Zr/Hf(37.16~39.23)比值, 暗示其岩浆来源具明显的幔源特征.岩石地球化学特征表明, 成矿前闪长玢岩可能起源于太平洋板块俯冲导致的下地壳部分熔融岩浆; 成矿后闪长玢岩可能起源于俯冲流体交代的地幔楔熔融岩浆, 并在其演化侵位过程中伴有地壳物质的混染.结合闪长玢岩成岩时代、岩石成因及区域构造演化, 反映出七家金矿的形成与太平洋板块的西向俯冲密切相关, 矿床在地壳由挤压增厚向伸展减薄的转换过程中形成.