Eocene melting of subducting continental crust and early uplifting of central Tibet: Evidence from central-western Qiangtang high-K calc-alkaline andesites, dacites and rhyolites

Changes in oceanic O–Sr isotopic compositions and global cooling beginning in the Eocene are considered to have been caused by the uplift of the Tibetan Plateau. The specific timing and uplift mechanism, however, have long been subjects of debate. We investigated the Duogecuoren lavas of the central-western Qiangtang Block, which form the largest outcrops among Cenozoic lavas in northern-central Tibet and have widely been considered as shoshonitic. Our study demonstrates, however, that most of these lavas are high-K calc-alkaline andesites, dacites and rhyolites. Moreover, they are characterized by high Sr (367–2472 ppm) and Al₂O₃ (14.55–16.86 wt.%) and low Y (3.05–16.9 ppm) and Yb (0.31–1.48 ppm) contents and high La/Yb (27–100) and Sr/Y (48–240) ratios, similar to adakitic rocks derived by partial melting of an eclogitic source. They can be further classified as either peraluminous and metaluminous subtypes. The peraluminous rocks have relatively high SiO₂ (> 66 wt.%) contents, and low MgO (< 1.0 wt.%), Cr (4.94–23.3 ppm) and Ni (2.33–17.0 ppm) contents and Mg^# (20–50) values, while the metaluminous rocks exhibit relatively low SiO₂ (55–69 wt.%) contents, and high MgO (1.41–6.34), Cr (25.7–383 ppm), Ni (14.13–183 ppm) and Mg^# (46–69) values, similar to magnesian andesites. ⁴⁰Ar/³⁹Ar and SHRIMP zircon U–Pb dating reveal that both peraluminous and metaluminous adakitic rocks erupted in the Eocene (46–38 Ma). Paleocene–Early Miocene thrust faults and associated syn-contractional basin deposits in the Qiangtang Block suggest that this region was undergoing crustal shortening within a continent during the Eocene. The low ε_Nd (− 2.81 to − 6.91) and high ⁸⁷Sr/⁸⁶Sr (0.7057–0.7097), Th (11.2–32.3 ppm) and Th/La (0.23–0.88) values in the Duogecuoren adakitic rocks further indicate that they were not derived by partial melting of subducted oceanic crust. Taking into account tectonic and geophysical data and the compositions of xenoliths in Cenozoic lava in northern-central Tibet, we suggest that the peraluminous adakitic rocks were most probably derived by partial melting of subducted sediment-dominated continent of the Songpan-Ganzi Block along the Jinsha suture to the north at a relatively shallow position (the hornblende + garnet stability field), but the metaluminous adakitic rocks likely originated from the interaction between peraluminous adakitic melts generated at greater depths (the garnet + rutile stability field) and mantle. Because the Duogecuoren adakitic rocks must have originated from a garnet-bearing (namely, eclogite facies) source, Eocene continental subduction along the Jinsha suture caused the thickening of the Qiangtang crust. Given that crustal thickening generally equates with elevation, the uplift of the Central Tibetan Plateau probably began as early as 45–38 Ma, which provides important evidence for tectonically driven models of oceanic O–Sr isotope evolution during global cooling and Asian continental aridification beginning in the Eocene.     

河流相砂泥岩薄互层地震反射特征研究

A sedimentary geological model is established in order to study the seismic reflection characteristics of channel sand bodies. Synthetic seismic shot gathers are simulated using the acoustic wave equation and then are prestack time migrated. On the imaged data, the reflection characteristics and instantaneous attributes are analyzed and log-constrained impedance inversion is tested. Because of wave field interference, the experimental results show that seismic events do not definitely correspond to the channel sand bodies and that seismic modes of occurrence do not represent the actual ones. The seismic events formed by wave interference may lead to errors and pitfalls in sand body interpretation. The corresponding relations between instantaneous seismic attributes and sedimentary sands are not well established. Log-constrained impedance inversion improves the resolution of channel sands. However, if the inverted resolution is forced to be too high, artifacts related to the initial model may occur.     

(Exergy)在湖泊生态系统建模中的应用

基于达尔文“适者生存”理论的热力学表述，本文把热力学概念“（Exergy）”作为一些重要模型参数的目标函数引入湖泊生态动力学模型．应用拥控制下的参数组合模拟程序实现了参数随时间的变化，并通过变化的模型参数来反映湖泊生态系统中物种组成和生态结构随时间的变化．这一改进克服了以往模型刚性较强、适应性差和生态系统特性考虑少的缺陷，该改进的湖泊生态动力学模型被成功用于滇池生态系统的模拟．     

强震空带现象机制和应用研究

对中国大陆地震的空间分布进行了仔细的探讨，发现6级以上强震在西部（东经105°线以西）有三组近似是对称分布的空带现象，每组平行空带相邻带间距为5°，带宽约为1°；而东部则有两组NE、NW向空带将其分割成若干强震块体，相邻空带宽约700km，带宽约为150km。6级以下地震在空间上几乎随机分布。理论推导证明：强震空带现象其实质为一些不连续块状分布的强震区在空间的有序排列，且控制东西两部分构造运动的构造波波长均约1000km，并在同一机理下还统一地解释了强震等间距及构造带等间距现象。应力场反演表明，大陆西部受三组主次不同的边界力源作用。在研究过程中还发现气、油等轻而易于流动的物质的聚集区多分布在强震空带内，而金属矿藏多分布在强震块体内，同时从空带分布图即简单的地震危险区划图上可以看到，千百年来已发展建设成的大型城市多位于“安全岛”内。     

青海湟水盆地地壳稳定性的动力学基础

通过对湟水盆地区域震源机制、断层水平运动方式、地层褶皱形态分别反映的现代、第四纪晚期、第三纪构造应力场的对比研究，同时分析1990年以来地震活动图象，得出汉水盆地地壳介质强度可分为三个不同的，为各区未来地震活动强度的预测以及地壳稳定性研究奠定了基础。     

用二相介质有限元方法对共和7.0级地震前兆的数值模拟

利用固液二相介质平面应变问题的有限元程序对共和７．０级地震的前兆现象的时空分布进行了数值模拟．研究中不仅考虑了固相的非线性、硬化及膨胀等效应，也充分考虑了水对前兆的影响，因此模拟结果与实际的前兆分布特征符合较好．     

地震活动的逾渗模型及临界状态的研究

利用现代非线性物理理论及震源理论,结合地震活动的特点,建立了地震活动的逾渗模型．把一次大地震孕育发展的过程看做一次逾渗相变过程,应用重正化群方法处理了逾渗相变．把逾渗相变中的相关长度为无穷大作为重正化群变换中的不动点,在不动点下计算系统的临界性质,得到了逾渗概率指数、相关长度指数等临界指数．利用1975年海城地震以及1976年唐山地震前后的地震活动资料,对两次地震的逾渗相变过程进行了讨论．     

全国地震速报信息共享服务系统

文中对全国地震速报信息共享服务系统（EQIM）进行了简要的介绍,该系统实现省级测震台网与国家测震台网之间的地震速报信息的快速通报、汇集与共享服务,进而对这些数据信息进行进一步的分析处理,以得到更为精确、合理的结果,为防震减灾特别是大震应急服务。其主要功能有地震速报数据的采集输入,发送手机短信,IP数据传输,数据接收存储,数据库查询管理,系统配置管理,WEB服务,地震报警,地震定位和地震分布的图形化展示等。     

长江三峡工程水库蓄水后旅游景观变化预测

本文论述了长江三峡工程建成后库区旅游景观的淹没和“高峡出平湖”的新景观。据预测,水库蓄水后,受淹没影响的景点39处,峡区峡谷气势有所减弱,但雄姿犹存;水库正常高水位达175m 时,将新增湖泊11处、岛屿14处,支流上可提高旅游开发利用价值的峡谷37条、溶洞15个,许多世界级的自然奇观可望得到开发。届时,三峡工程库区将成为观光游乐、度假休闲、科考探险及从事水上运动的多功能旅游区。      

裂变径迹定年法中国际标样的年龄测定

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