GEOTECTONIC OF NAMCHE BARWA SYNTAXIS IN EAST TIBET, CHINA

GEOTECTONIC OF NAMCHE BARWA SYNTAXIS IN EAST TIBET, CHINA     

西藏中冈底斯带措勤地区则弄群熔结凝灰岩锆石LA—ICP—MS U—Pb年龄

对措勤地区则弄群熔结凝灰岩进行了LA—ICP—MS锆石U—Pb定年．所测的2件熔结凝灰岩样品的LA-ICP—MS锆石U—Pb年龄分别为112．7Ma±1．0Ma和108．6Ma±1．6Ma。根据已有的年代学数据、地球化学资料和最新的1：25万区域地质调查成果,认为中冈底斯北部的则弄群火山岩很可能与班公湖一怒江特提斯洋向南的俯冲作用有关。     

中亚与邻区盆地群构造演化及含油气性

基于中亚及其邻区大地构造和盆地构造演化,利用古板块再造、地理信息软件等对中亚盆地群的构造演化及含油气性进行探讨。中亚与邻区盆地群在早古生代分属不同陆块,这些陆块于早石炭世开始汇聚,早二叠世完成拼合,形成中亚盆地群。汇聚前该区受到海西期构造影响,在中生代伸展构造和新生代挤压构造的作用下形成的众多盆地类型为叠合盆地。该区主要烃岩源发育于海西期早期和中-新生代伸展背景的裂谷事件。油气主要集中在侏罗系(41%)和石炭系(37%)中,主要的勘探目的层是碳酸盐岩、礁灰岩、膏岩和泥岩。阿姆河、费尔干纳、图尔盖和阿富汗-塔吉克等盆地的油气主要集中于前陆冲断带和凹陷断阶带。滨里海、北乌斯丘尔特和曼各什拉克等克拉通盆地油气集中于盆地边缘的隆起带和断阶带,具有自生自储特征。     

Age and Tectonic Setting of Mesothermal Magmatic Hydrothermal Vein‐Type Pb–Zn–(Ag) Mineralization in the Xiaohongshilazi Deposit,Central Jilin Province,Northeast China

The Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium‐scale Pb–Zn–(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two‐stage mineralization has been identified in this deposit. Stratiform volcanic‐associated massive sulfide (VMS) Pb–Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous–Early Permian Daheshen Formation was controlled by the premineralization E–W‐trending faults. Vein‐type Pb–Zn–(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major‐mineralization N–S‐trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein‐type Pb–Zn–(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA–ICP–MS U–Pb dating on zircon from the ore‐bearing granodiorite and diorite porphyries and Rb–Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U–Pb weighted‐mean ²⁰⁶Pb/²³⁸U ages of 203.6 ± 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 ± 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein‐type ore samples yield a Rb–Sr isochron age of 195 ± 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein‐type Pb–Zn–(Ag) mineralization. The granodiorite associated with vein‐type mineralization has high SiO₂ (68.99–70.49 wt.%) and Na₂O (3.9–4.2 wt.%; Na₂O/K₂O = 1.07–1.10) concentrations, and A/CNK values of 0.95–1.04; consequently, the intrusion is classified as a high‐K, calc‐alkaline, metaluminous I‐type granite. The granodiorite porphyry is enriched in large‐ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high‐field‐strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction‐related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31–34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore‐bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross‐cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb–Zn mineralization that produced stratiform orebodies within the Late Carboniferous–Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein‐type Pb–Zn–(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo‐Pacific Plate beneath the Eurasia Plate during the Late Triassic–Early Jurassic.     

绍兴中心城区工程地质特征及场地工程建设适宜性评价

根据时代、成因类型、物理力学性质,绍兴中心城区岩土层可划分为10个工程地质层。以地貌、岩土层性质与结构组合类型及是否存在第二硬土层、砂砾土或基岩等桩基持力层为依据,划分出1个低山丘陵区基岩岩组、1个山麓沟谷区低压缩松散岩组、1个平原区高压缩松散岩组及其4个亚组。采用"点面结合、由点到面"的定量评价方法,开展建筑地基(场地工程建设)适宜性评价,划分出场地工程建设适宜区、较适宜区和适宜性差区。     

Junction and Evolution of the Qinling, Qilian and Kunlun Orogenic Belts

As the main part of the "central mountain system" in the continent of China, the Qinling, Qilian and Kunlun orogenic belts have been comprehensively and deeply studied since the 1970s and rich fruits have been reaped. However, these achievements were mostly confined to an individual orogenic belt and the study of the mutual relationship among the three orogenic belts was obliged to depend on comparative studies. Different views were produced therefrom. The material composition and structural features of the junction region show that there are several epicontinental and intracontinental transform faults developed in different periods. Restricted by these transform faults, the large-scale lateral movements and, as a consequence, complicated magrnatism and tectonic deformation took place in the orogenic belts. According to these features, the authors put forward a three-stage junction and evolution model and point out that there is not a single junction zone traversing from west to east but that the three     

徐州大屯中心区地面沉降趋势预测

徐州大屯中心区1988年建立了地面沉降观测系统,2005年最大累计沉降量达到600 mm.累计沉降量大于100 mm的地区面积达到11.57 km2.本文根据近20年的沉降观测数据分析了中心区地面沉降的时空分布特征,并采用灰色模型方法,对地面沉降趋势进行了预测,结果表明到2010年最大累计沉降量将达到753 mm,累计沉降量大于100 mm的地区将达到32.86 km2,对中心区的建筑、地下管网将造成较大威胁,应尽快采取防治措施.     

帕米尔中部含刚玉变质杂岩

刚玉矿化位于穆兹科尔(Muzkol)变质杂岩体内.该杂岩体近纬向展布在帕米尔中部阿尔卑斯褶皱带的东部,属蓝晶石—夕线石型阿尔卑斯带变质杂岩.地质填图发现有4个变质岩区:低绿片岩相(白云母—绿泥石)区,高绿片岩相(黑云母—绿泥石)区,绿帘石—角闪岩相区,角闪岩相区,而刚玉矿化集中在绿帘石—角闪岩及周围角闪岩相变质体内的交代蚀变区.交代蚀变区内的刚玉矿化通常与层面或 大型同倾斜褶皱轴面平行.根据母岩成分可将含刚玉交代岩分为3类,分别位于方解石大理岩内、白云石大理岩内及片岩内.在大理岩内,刚玉成粉红色,与白云母、黑云母、方柱石、钙长石、正长石、金红石、电气石、磷灰石、黄铁矿及石墨共生,以Al含量变化大和Fe含量低为特点.在片岩内,刚玉成蓝色,与黑云母、绿泥石、电气石及磷灰石共生各种类型的含刚玉岩石均以K,Na,Mg的含量较高而Fe含量较低为特点.根据P—T—XCO2图估算含刚玉交代岩的稳定范围在610℃相似文献   

近40年西藏“一江两河”流域气候变化特征

利用近40年的降水、气温、小型蒸发量、大风日数和沙尘暴日数等气象资料, 采用现代气候统计诊断和环境综合评价方法, 分析了西藏“一江两河”农业综合开发区域的气候特征。结果表明:该流域呈现气温升高、降水量增加的暖湿化气候特征。区域内年平均气温每10年升高了0.24 ℃, 降水量前20年平均每年减少2.9 mm, 而后20年呈显著的增加趋势, 平均每年增加9.6 mm; 蒸发量、大风日数和沙尘暴日数呈明显的减少趋势; 区域环境综合评价指数提高了5.24%。近期暖湿化的气候变化趋势对干旱半干旱的河谷地带而言, 有利于生态环境的改善, 但因洪涝、冰雹等自然灾害的频繁和人为因素使水土流失和土地沙漠化正在加剧。     

半球形凹陷饱和土半空间对入射平面SV波三维散射问题的解析解

以Biot饱和多孔介质动力学理论为基础,利用Fourier-Bessel级展开法,给出了饱和多孔介质半空间中半球形凹陷地形对入射平面SV波散射问题的解析解.利用这一解析解数值计算地表位移幅值,分析入射角、入射波频率对地表位移幅值的影响,并与现存的单相介质情况下三维半球形凹陷问题解析解进行对比得出如下结论：(1)本文两相介质模型与单相介质模型有很大区别;(2)入射角、入射频率对场地表面位移分量有重要影响;(3)随着入射角、入射频率的增大,地表位移分布变得更复杂,且放大效应比单相介质模拟结果更加显著.