Petrogenesis of Cretaceous Peraluminous Granite Suites with Low Initial Sr Isotopic Ratios, Kyushu Island, Southwest Japan Arc

Cretaceous granitic rocks are widely distributed in the northern to central parts of Kyushu Island, southwest Japan arc, and are divided into two types, granite and tonalite-granodiorite. These rocks are clearly defined by their mineral assemblage, that is, the granite contains mostly muscovite and/or garnet and does not have hornblende, whereas the tonalite-granodiorite is always observed with hornblende. Many workers suggest that most of the granite has low initial Sr isotopic ratios (SrI_{90 Ma}: 0.7052-0.7059) whose values are similar to those of tonalite-granodiorite (SrI_{90 Ma}: 0.7050-0.7056).

The SiO₂ contents of the granite (67.9 to 78.0 wt.%) are higher than that of tonalite-granodiorite (54.2 to 68.2 wt.%). The granite is characterized by peraluminous compositions, while the tonalite-granodiorite shows metaluminous to peraluminous compositions. The petrogenetic relation between granite and tonalite-granodiorite is examined by a modal batch melting model, which referred to results of already published experiments. The result of the model suggests that the petrogenesis of the peraluminous granitic magma can be explained by an anatexis of metaluminous tonalite in the tonalite-granodiorite under lower to middle crustal conditions and variable fH₂O.

Rocks of tonalite to granodiorite in a subduction system generally have low initial Sr isotopic ratios (<0.705), which imply that the magma derived from a highly metaluminous origin such as mafic magma, mafic lower crust and/or subducting slab. In this study, it is regarded that the peraluminous granitic magma can be directly produced by an anatexis of metaluminous tonalite. Therefore, peraluminous granite with low initial Sr isotopic ratios may imply to a first step of recycling of the granitic layer in an active plate margin.     

关于线性奇异向量和条件非线性最优扰动差别的一个注记

奇异向量(singular vectors,SVs)和条件非线性最优扰动(conditional nonlinear optimal perturbation,CNOP)已广泛应用于研究大气—海洋系统的不稳定性以及与其相关的可预报性、集合预报和目标观测问题研究。本文首先回顾了SVs和CNOP的发展历史,并简单描述了它们的基本原理;然后针对二维正压准地转模式,使用不同的范数组合,分析了第一线性奇异向量(first singular vector,FSV)和CNOP之间的异同。结果表明,当优化时间较短时,度量SVs和CNOP大小的范数不同也将导致FSV和CNOP相差很大,而当度量SVs和CNOP大小的范数相同时,FSV和CNOP之间的差别则主要是由非线性物理过程作用的结果。因此,针对不同的物理问题,应该选取合适的度量范数研究FSV和CNOP以及其所引起的大气或海洋动力学的异同,从而揭示非线性物理过程的影响机理。     

Assessing the Impacts of Initial Snow Conditions over the Tibetan Plateau on China Precipitation Prediction Using a Global Climate Model

Two ensemble experiments were conducted using a general atmospheric circulation model. These experiments were used to investigate the impacts of initial snow anomalies over the Tibetan Plateau（TP） on China precipitation prediction. In one of the experiments, the initial snow conditions over the TP were climatological values; while in the other experiment, the initial snow anomalies were snow depth estimates derived from the passive microwave remote-sensing data. In the current study, the difference between these two experiments was assessed to evaluate the impact of initial snow anomalies over the TP on simulated precipitation. The results indicated that the model simulation for precipitation over eastern China had certain improvements while applying a more realistic initial snow anomaly, especially for spring precipitation over Northeast China and North China and for summer precipitation over North China and Southeast China. The results suggest that seasonal prediction could be enhanced by using more realistic initial snow conditions over TP, and microwave remote-sensing snow data could be used to initialize climate models and improve the simulation of eastern China precipitation during spring and summer. Further analyses showed that higher snow anomalies over TP cooled the surface, resulting in lower near- surface air temperature over the TP in spring and summer. The surface cooling over TP weakened the Asian summer monsoon and brought more precipitation in South China in spring and more precipitation to Southeast China during summer.     

基于高分辨率中尺度气象模式的实际雷暴过程的数值模拟试验

雷暴数值预报的实际应用离我们还有多远？本文对此进行了尝试, 即利用一个复杂的高分辨率中尺度气象模式驱动一个三维雷电模式, 在只采用常规气象观测资料的条件下, 对北京的一次实际雷暴过程进行模拟试验, 分析了雷暴云的宏观动力、 微物理过程及电结构的时空变化特征以及其可能的相互作用机制。结果表明: 利用高分辨中尺度模式预报出的三维气象场作为雷电模式的初始场, 完全可以不需添加虚假的扰动来触发雷暴云的发展, 高分辨中尺度模式的预报场本身所包含的水平非均匀、 垂直强非静力性及较强的对流不稳定信息足够促发雷暴云的剧烈发展; 用较为真实的三维气象场作为初始场模拟产生的电场分布特征与云微物理分布特征及环境气象要素的分布结构非常协调, 得到的雷暴云的电荷结构特征以及电结构随时间的演变特征更为复杂, 更真实的体现了实际雷暴云本身发展的复杂性, 同时, 模式能够模拟出合理的云闪及正负云地闪, 且模拟的闪电频数随时间发展演变趋势基本与观测实况基本吻合, 从而表现了对雷电天气潜在的预报能力。本次模拟的北京雷暴云在发展过程中, 水物质霰的最大质量比、 最大正电场强度及闪电频数随模拟时间的演变发展趋势非常相似。     

Nash瞬时单位线推演河道汇流的完整公式

Nash瞬时单位线是基于零初始条件而得到的,没有反映河道汇流的完整过程。通过拉普拉斯变换和数学归纳,推导出了考虑初始槽蓄量退水过程的完整Nash河道汇流公式。分析讨论了公式各项的物理含义,出口断面的流量应是河槽初始槽蓄量的退水过程与上游入流演算结果的叠加,据此建立了一种具有物理概念的河道洪水演算实时校正模型,通过实例分析验证了公式的实用性和合理性。完整公式是更为一般情形下的Nash河道汇流模型,一定程度上丰富和发展了现有Nash汇流理论,并可适当提高河道洪水演算的精度。     

识别洋陆转换的岩石学思路——洋内弧与初始俯冲的识别

阐述了洋陆转化形成的洋内弧与初始弧的岩石组合序列及其地球化学特征,提出岩浆弧是由洋陆转化以及底侵的壳幔转化共同作用形成的认识,前弧环境是洋陆转化形成初生大陆的场所,由特征的类似洋中脊的洋内弧前弧玄武岩类构成。大陆的形成过程如下:从地幔中生长出洋壳,从洋壳中的洋陆转化生长出不成熟的弧陆壳,最后从弧陆壳底侵的壳幔转化中长出成熟的陆壳。这样,地壳的生长和形成主要通过岩浆增生作用来实现。     

约束稀疏脉冲反演在大庆茂兴地区泉四段储层研究中的应用

笔者从约束稀疏脉冲反演技术的基本原理入手,重点说明稀疏脉冲反演在大庆茂兴地区泉四段储层的应用,其基本步骤和方法,如子波估算、初始模型建立和Lambda取值等,为约束稀疏脉冲反演技术的合理应用提供参考.     

逆散射理论的发展及应用前景

逆散射理论作为量子力学发展的产物,目前在地震数据处理方面得到了较为广泛的应用.逆散射成像是通过散射体外部场的探测来获得散射体内部的信息,它是近年来发展比较迅速的一种成像方法,其突出的应用是运用逆散射序列中的一阶近似项进行深度成像.本文对逆散射理论在国内外的发展历程进行较为系统的概括和总结,在此基础上,对逆散射理论的应用前景进行了分析.逆散射理论在多次波的压制、界面奇性反演、大扰动深度成像等方面具有广阔的应用前景.     

班公湖中特提斯洋打开的时限:来自MOR型辉长岩的年代学制约

班公湖?怒江结合带西段班公湖地区蛇绿岩组合较为完整,由超镁铁质岩、镁铁质堆晶岩、辉绿岩脉、铁镁质熔岩、放射虫硅质岩等组成。这套蛇绿岩所代表的洋盆打开时间一直争论不休。该蛇绿岩中MOR型辉长岩的LA-ICP-MS锆石U-Pb定年显示,18个测点的~(206)Pb/~(238)U加权平均年龄为231.5±2.6 Ma,代表了辉长岩的结晶年龄。地球化学分析表明辉长岩SiO_2含量在46.12%~47.85%之间,TiO_2(1.52%~1.71%),具低的K_2O(0.19%~0.25%)、Al_2O_3(12.97%~13.51%)和Fe_2O_3/FeO比值(0.19~0.24);微量元素蛛网图与洋中脊玄武岩类似,Zr、Nb、Ta、Hf丰度与N-MORB相当或略高,相对富集Ba、Pb、Sr等大离子亲石元素,无Ta-Nb负异常,在基性岩构造环境判别图上显示出洋脊玄武岩的亲合性;REE配分曲线具有平缓型特点,介于E-MORB与N-MORB之间;各种地球化学特征与洋脊玄武岩类似,表明该辉长岩是在班公湖洋盆扩张阶段形成的。结合前人研究成果,本文认为班公湖中特提斯洋盆初始打开时间至少为中三叠世。     

隧洞边界超欠挖的摄动法解析分析

钻爆法施工常造成隧道边界不平整,隧道分析模型一般将开挖界面光滑处理,忽略了边界不平整对围岩应力的扰动作用。将隧道超欠挖值当作中心偏量小参数,利用摄动法得到了静水压力下圆形隧道的弹性应力解。计算分析表明:超欠挖改变了隧道洞壁附近围岩的应力状态,围岩应力随超欠开挖曲线呈波浪状变化,应力变化量与超欠挖曲线幅值及曲线斜率有关;环向应力变化最大值在洞壁处,其应力集中系数分别在超挖及欠挖顶点达到局部极大与极小值,径向应力变化最大值靠近洞壁表面,切应力变化最大值位于超挖与欠挖表面相交处;扰动应力在径向衰减较快,影响范围约为1~2倍的隧道半径。