二维速度随机分布逐步迭代射线追踪方法

基于Ｓｎｅｌｌ定理，研究一种新的射线追踪方法──逐步迭代射线追踪法。首先，从一端出发，根据射线路径上任意连续三点均满足Ｓｎｅｌｌ定律，利用一个近似公式逐段迭代，求取中间折射点，从而实现逐步迭代计算。该方法的追踪路径结果符合射线追踪要求，计算速度快，方法精度高，可以克服射线追踪的路径非唯一性；并且在追踪过程中可以给出透射走时，为层析成像方法提供了一种有效的射线追踪过程。     

粘弹介质中高斯束二维理论地震记录的合成

本文对无限空间二维变化粘弹介质中的高斯束及有关过界面的情况进行了讨论。在讨论中发现,利用高斯束法既可不用定点射线追踪,还可保证处处规则,较近年来发展较快的标准射线方法有很大的灵活性,适于处理各种复杂地质情况。并对理论地震记录的合成方法作了简要介绍。     

Stable Strontium Isotopic Fractionation During Chemical Weathering in Drainage Basins: Mechanisms and Applications

The new non-traditional stable strontium (Sr) isotope has aroused great attention from academic scholars in terms of the continental weathering and marine Sr cycle. The analytical precision of stable Sr isotope using mass spectrometry is better than 0.03‰. The compiled δ⁸⁸/ ⁸⁶Sr values vary from -3.65‰ to 1.68‰ in natural reservoirs. Recent findings indicate that multiple processes can cause stable Sr isotope fractionation in Earth surface, including the incongruent dissolution of primary minerals, the formation and adsorption of secondary minerals, the precipitation of calcium carbonate, and the biological cycling. These processes lead to higher δ⁸⁸/ ⁸⁶Sr in the liquid phase and lower δ⁸⁸/ ⁸⁶Sr in the solid phase, and thus result in different geochemical behavior of stable Sr isotopes in water and sediment during the weathering processes. The δ⁸⁸/ ⁸⁶Sr values of river sediment decrease with the increase of weathering intensity, which has the potential to indicate chemical weathering intensity. Meanwhile, further study on the fractionation mechanisms and constraints of stable Sr isotopes in river water plays an important role in tracing chemical weathering processes within the watershed, which will lead to a better understanding of the global ocean Sr cycle.     

用于速度图象重建的层析成象法

本文提出了一种用于速度图象重建的层析成象法。特别注意到地震学上的ST与医学上的CT的不尽相同之处,并处理了由此引起的困难。与速度图象重建有关的正问题的分析表明,不同频率范围的资料其分辨能力是不同的,因此,区域地震与远震资料的解释应予注意。本文有关速度图象重建的讨论不仅涉及到与成象方法有关的反演理论和方法,还给出了进行数值计算的内存量和运算量的分析。关于重建图象的质量评价,还给出了反演解的可靠性分析,为分辨特性的描述提供了一种既简便又形象直观的方案。 本文的方法与现行主要方法的比较表明:1.本文的方法允许存在速度间断面,有利于揭示不同构造区域的地壳厚度的差异;2.在常用的方法中,作为正问题假定的常速度块同反演结果解释时非常速度块之间不协调。由于我们把给定网格点的速度值的插值函数作为速度的空间函数,这一困难已被解决;3.相对于Aki等的一般方法,本文的内存量节省约一个量级、运算量减少约一半;4.相对于ART类方法本身不能给出成象结果的可靠性分析,本文的方法则具有显著的优点。 作者在分析了天然地震资料的状况之后相信,对充分利用我国地震台网的现有观测资料,本文的方法是有效的。     

Geochemical and Nd, Sr Isotopic Study of the Post-Orogenic Granites in the Yidun Arc Belt of Northern Sanjiang Region, Southwestern China

Abstract: In the arc (basin)–back area of the Yidun arc belt in the north segment of the Sanjiang tectonic zone, southwestern China, there occurs a post‐orogenic granite belt extending for more than 300 km in NNW direction. It strides across two different tectonic units of the arc (basin)–back area and the subduction area, and is accompanied by extensive Ag‐Sn polymetal–lic mineralizations. More than ten granite bodies have very similar geochemical characteristics: high SiO₂ (73.8–76.3 wt%) and K₂O+Na₂O (7.16‐8.41 %), and low Al₂O₃ (11.9–13.6 %), CaO (0.46‐1.54 %) and MgO (0.16‐0.61 %), as well as high enrichment of Nb, Ta, Ga and Y, and strong depletion of Sr and Eu. Most of these features are peculiar to A‐type granite. Rb‐Sr and ⁴⁰Ar/³⁹Ar isotopic dating results indicate that the formation ages of the granites decrease from 103.7 Ma of the north end to 75.2 Ma near the south end, and that the magmatism became younger from north to south. The tectonic environment analysis clearly reveals that they were formed in post‐orogenic within–plate extension settings. The magma genesis was controlled by a united crustal extension regime after the arc‐continent collision. The granites have low _Nd values ranging from –4.96 to –8.40, whereas the _Sr values vary greatly ranging from –31.7 to 296, reflecting that the source composition transited from mantle – differentiated igneous rocks in the north to basement – dominated metamorphosed sedimentary rocks in the south. Under high temperature and water‐absent conditions, the anatexes of the crustal rocks made a great amount of plagioclase separated from melts and left in magma sources. Through this mechanism, the post‐orogenic granites took geo‐chemical characteristics such as low Al₂O₃ and CaO, and strong depletion of Sr and Eu.     

不同景观区的岩石地球化学勘查方法研究

通过不同景观区岩石测量方法技术研究,提出了以岩屑测量、构造岩石地球化学测量、脉岩地球化学测量和面型岩石地球化学为主体的岩石地球化学测量技术方法系统。在森林覆盖区和风成沙干扰区以及残山戈壁区等浅覆盖区域可采用岩屑测量圈定矿化地段;在岩石裸露区和已开采的矿山采用构造岩石裂隙测量和脉岩测量追踪深部盲矿;面型岩石测量以一定面积的网格采集单元组合样,其具有样品采集和分析数量少、获取信息量大、可圈定不同尺度的找矿靶区的优点。     

CORRECTION FACTORS IN THE DETERMINATION OF MEAN VELOCITY OF OVERLAND FLOW

The velocity of overland flow has been conventionally measured using tracers, but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified. Consequently, previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor α to obtain an estimate of mean velocity. An alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor β to estimate mean velocity. To investigate the controls of α and β and develop predictive models for these correction factors, 40 experiments were performed in a flume with a mobile sand bed. Multiple regression analyses reveal that both α and β vary inversely with slope and directly with Reynolds number. The derived regression equations may be used to calculate the mean velocity of other shallow overland flows, at least within the range of slope and Reynolds number for which the equations were developed. In the experiments, slope ranged from 2.7;° to 10° and Reynolds number from 1900 to 12 600.     

大陆岩石圈深部过程的多元同位素制约研究

本文简述了在大陆动力学新的研究框架中大陆岩石圈深部过程研究的重要意义，主要方法和技术途径，以及作为研究实例的中国东部大陆岩石圈演化的主要特征。本文强调了多元同位素示踪理论与地质学和地球物理学相结合的多维制约研究的重要性和必要性。     

自动化监测电导率在盐示踪试验中的应用--以云南八宝水库盐示踪试验为例

为了了解八宝水库库区地下河的连通性,评价蓄水后是否会发生渗漏,2003年12月底笔者在八宝水库进行了盐示踪试验。以此为例介绍了自动化监测电导率在示踪试验中的应用。实验证明水溶液的电导率直接和溶解盐的浓度成正比,水溶液中电导率的变化反映了溶解的NaCl的变化情况。本次试验通过自动化监测仪器记录水溶液中电导率随时间的变化,反映水中溶解的NaCl随时间的变化情况,根据流量数据换算得出回收量和回收率等数据。