华北克拉通地壳结构及动力学机制分析

本文对布设在华北克拉通三个陆块的199个宽频带台站记录的远震数据进行了接收函数计算.利用H-κ迭代方法获得了该区域基岩地区的地壳结构,平滑处理后作为背景结构模型中的基岩地区地壳结构;利用相邻算法对沉积层地区的接收函数进行了波形拟合计算,获得了沉积层结构,平滑后作为背景结构模型中的沉积层结构;结合前人的研究成果,完善了研究区域的背景结构模型.以此模型为基础,对接收函数进行了CCP（Common Conversion Point,共转换点）叠加成像,获得了Moho面成像结果,对比沉积层的成像结果发现：西部陆块中鄂尔多斯块体东部地区地壳厚度较大,约为42 km,泊松比较低,小于0.24,为长英质含量较多的地壳层;位于中部陆块的山西地堑地壳厚度小于鄂尔多斯块体,且变化较大,西侧地壳厚度约为40 km,东侧重力梯度带附近地壳厚度迅速减薄至36 km左右,张家口-怀来-大同一带出现了地壳的局部抬升,地壳厚度等值线基本以北北东方向为主,与构造带方向基本一致,地堑内泊松比约为0.26~0.28,前人对此区域的层析成像研究结果表明太行山隆起和阴山隆起存在壳内低速层,推测为地壳部分熔融以及上地幔物质上涌造成的;东部陆块中渤海湾盆地的地壳厚度较薄,约为32 km,部分地区小于30 km,其中冀中坳陷带地壳厚度最薄,约为28 km,沉积层基底分布与Moho面分布呈镜像对称趋势,沉积层较厚地区的地壳较薄,推测东部陆块在太平洋板块俯冲作用下,存在北西-南东向的拉张作用,使其内发育了大量断陷盆地.     

A BRIEF INTRODUCTION TO THE NEW METHOD FOR RIVER PROFILE ANALYSIS: Integral Approach

The topography and geomorphology of active orogens result from the interaction of tectonics and climate. In most orogens, a fluvial channel is most sensitive to the coupling between tectonics, lithology, and climate. Meanwhile, the related signals have been recorded by both the drainage geometry and channel longitudinal profile. Thus, how to extract tectonic information from fluvial channels has been a focused issue in geologic and geomorphologic studies. The well known stream-power river incision model bridges the gap between tectonic uplift, river incision and channel profile change, making it possible to retrieve rock uplift pattern from river profiles. In this model, the river incision rate depends on the rock erodibility, contributing drainage area and river gradient. The steady-state form of the river incision model predicts a power-law scaling between the drainage area and channel gradient. Via a linear regression to the log-transformed slope-area data, the slope and intercept are channel concavity and steepness indices, respectively. The concavity relates to lithology, climatic setting and incision process while the channel steepness can be used to map the spatial pattern of rock uplift. For its simple calculation process, the slope-area analysis has been widely used in the study of tectonic geomorphology during past decades. However, to calculate river slope, the coarse channel elevation data must be smoothed, re-sampled, and differentiated without any reasonable smooth window or rigid mathematical fundamentals. One may lose important information and derive stream-power parameters with high uncertainties. In this paper, we introduce the integral approach, a procedure that has been widely used in the latest four years and demonstrated to be a better method for river profile analysis than the traditional slope-area analysis. Via the integration to the steady-state form of the stream-power river incision equation, the river longitudinal profile can be converted into a straight line of which the independent variable is the integral quantity χ with the unit of distance and the dependent variable is the relative channel elevation. We can calculate the linear correlation coefficient between elevation and χ based on a series of concavity values and find the best linear fit to be the reasonable channel concavity index. The slope of the linear fit to the χ value and elevation is simply related to the ratio of the uplift rate to the erodibility. Without calculating channel slope, the integral approach makes up for the drawback of the slope-area analysis. Meanwhile, via the integral approach, a steady-state river profile can be expressed as a continuous function, which can provide theoretical principle for some geomorphic parameters (e.g., slope-length index, hypsometric integral). In addition, we can determine the drainage network migration direction using this method. Therefore, the integral approach can be used as a better method for tectonogeomorphic research.     

Analytical approach for sheet flow transport in purely acceleration-skewed oscillatory flow

An instantaneous analytical approach is developed to predict sheet flow transport in purely acceleration-skewed oscillatory flow. The approach is derived from exponential approximations of velocity and concentration profiles above a mobile seabed, and it particularly considers factors of phase lead; phase lag (i.e. phase residual and phase shift); acceleration modification; and asymmetries in shear stress, roughness height, and boundary layer development. The approach can predict net boundary layer flow above a mobile seabed, and can revert to the classical bedload model. Instantaneous and net sediment transport rates are studied using the approach. The instantaneous sediment transport rate in an onshore flow stage can be approximated by a power function of velocity in which the exponent is confirmed to range between 1 and 5 with a decrease in the phase residual. The net sediment transport rate predicted using the approach is validated using a considerable amount of measured data, and compared with existing instantaneous and half-period type models that consider the phase lag or acceleration modification. For the net sediment transport rate in purely acceleration-skewed oscillatory flow, the phase residual is less important than the acceleration-skewed boundary layer difference between onshore and offshore acceleration stages.     

A response spectrum approach for seismic performance evaluation of actively controlled structures

To evaluate and measure the effectiveness of active control schemes in reducing the response of structures subjected to earthquake excitations, it is common to use recorded or artificially generated earthquakes as input motions. This paper introduces the response spectrum analysis to evaluate linear control systems for seismic inputs defined by code‐prescribed or site‐specific ground response spectra. Using such a method one can evaluate a control system in a single analysis for the ensemble of time histories that are represented by the input response spectra. The response spectrum analysis can also facilitate the implementation of comprehensive parametric studies. A generalized response spectrum method is used to analyse systems with non‐symmetrical matrices that are caused by the general nature of the control actions imposed on the structure. The application of the method is demonstrated on several numerical examples of a building structure where the control force is applied through an active tuned‐mass damper. Copyright © 2000 John Wiley & Sons, Ltd.     

Bayesian probabilistic damage detection of a reinforced‐concrete bridge column

A Bayesian probabilistic approach for damage detection has been proposed for the continuous monitoring of civil structures (Sohn H, Law KH. Bayesian probabilistic approach for structure damage detection. Earthquake Engineering and Structural Dynamics 1997; 26 :1259–1281). This paper describes the application of the Bayesian approach to predict the location of plastic hinge deformation using the experimental data obtained from the vibration tests of a reinforced‐concrete bridge column. The column was statically pushed incrementally with lateral displacements until a plastic hinge is fully formed at the bottom portion of the column. Vibration tests were performed at different damage stages. The proposed damage detection method was able to locate the damaged region using a simplified analytical model and the modal parameters estimated from the vibration tests, although (1) only the first bending and first torsional modes were estimated from the experimental test data, (2) the locations where the accelerations were measured did not coincide with the degrees of freedom of the analytical model, and (3) there existed discrepancies between the undamaged test structure and the analytical model. The Bayesian framework was able to systematically update the damage probabilities when new test data became available. Better diagnosis was obtained by employing multiple data sets than just by using each test data set separately. Copyright © 2000 John Wiley & Sons, Ltd.     

高分辨率航空影像建筑物垂直边缘线提取技术研究

高分辨率航空影像建筑物垂直边缘线的提取在获取建筑物高度信息和检测建筑物过程中可以发挥重要的作用。分析建筑物垂直边缘线在遥感影像上的特性,在遥感影像边缘检测和细化基础上,利用带约束条件的Hough变换实现建筑物垂直边缘线的提取,通过实验验证该方法的可行性。     

辽北开原地区房木花岗斑岩LA-ICP-MS锆石U-Pb年龄及地球化学特征

研究区位于华北克拉通北缘东段、华北克拉通与兴蒙造山带的交接部位。本文通过对辽北开原地区房木花岗斑岩的岩石学、年代学和地球化学研究,探讨了其形成时代、岩石成因和构造环境,并进一步探讨了华北克拉通东部岩石圈减薄的起始时间。用LA-ICP-MS技术测定了花岗斑岩的锆石U-Pb同位素,获得其锆石²⁰⁶Pb/²³⁸U加权平均年龄为（117±1）Ma,表明花岗斑岩形成于早白垩世。花岗斑岩具有高硅、富碱、贫镁和钙的特征,富集大离子亲石元素（K、Rb）和高场强元素（Th、Ta、Nb）,亏损Sr、Ba、P、Ti元素,稀土配分曲线均呈现右倾海鸥型,具有明显的负Eu异常;显示研究区花岗斑岩为A型（A₁亚型）花岗岩,形成于古太平洋俯冲的后造山伸展环境,其岩浆源于地幔物质上涌而导致的地壳物质重熔。研究区在（156±1）Ma之前,属于挤压造山环境,表明研究区岩石圈减薄时间应处于156~117 Ma之间。     

Ancient deep roots for Mesozoic world-class gold deposits in the north China craton:An integrated genetic perspective

The North China Craton(NCC)hosts some of the world-class gold deposits that formed more than 2 billion years after the major orogenic cycles and cratonization.The diverse models for the genesis of these deposits remain equivocal,and mostly focused on the craton margin examples,although synchronous deposits formed in the interior domains.Here we adopt an integrated geological and geophysical perspective to evaluate the possible factors that contributed to the formation of the major gold deposits in the NCC.In the Archean tectonic framework of the NCC,the locations of the major gold deposits fall within or adjacent to greenstone belts or the margins of micro-continents.In the Paleoproterozoic framework,they are markedly aligned along two major collisional sutures-the Trans North China Orogen and the Jiao-Liao-Ji Belt.Since the Mesozoic intrusions hosting these deposits do not carry adequate signals for the source of gold,we explore the deep roots based on available geophysical data.We show that the gold deposits are preferentially distributed above zones of uplifted MOHO and shallow LAB corresponding to thinned crust and eroded sub-lithospheric mantle,and that the mineralization is located above regions of high heat flow representing mantle upwelling.The NCC was at the center of a multi-convergent regime during the Mesozoic which intensely churned the mantle and significantly en riched it.The geophysical data on Moho and LAB upwarp from the centre towards east of the craton is more consistent with paleo-Pacific slab subduction from the east exerting the dominant control on lithospheric thinning.Based on these results,and together with an evaluation of the geochemical and isotopic features of the Mesozoic magmatic intrusions hosting the gold mineralization,we propose a genetic model that invokes reworking of ancient Au archives preserved in the lower crust and metasomatised upper mantle and which were generated through multiple subduction,underplating and cumulation events associated with cratonization of the NCC as well as the subduction-collision of Yangtze Craton with the NCC.The heat and material input along zones of heterogeneously thinned lithosphere from a rising turbulent mantle triggered by Mesozoic convergent margins surrounding the craton aided in reworking the deep roots of the ancient Au reservoirs,leading to the major gold metallogeny along craton margins as well as in the interior of the NCC.     

华北克拉通西部临县紫金山碱性岩体地球化学特征及地质意义

山西吕梁地区出露的紫金山岩体为我国著名的碱性岩体之一。为了探讨紫金山碱性岩体的物质来源及地质意义,对该岩体主要岩石进行了岩相学及岩石地球化学研究。结果表明: 紫金山岩体各期次岩石具有低硅、富碱、高钾的特点,属钾质碱性岩石; 岩石轻重稀土元素分馏较强烈,具有轻稀土相对富集、重稀土相对亏损、无明显Eu异常的特征; 微量元素总体表现为大离子亲石元素(Rb、Ba、K、Sr等)明显富集、高场强元素(Th、Nb、Ta、La、Ce、Nd、P、Ti等)亏损的特征。紫金山岩体岩浆来源较深,与富集地幔关系密切,岩浆演化机制以部分熔融作用为主且存在陆壳物质混染。结合山西境内多处同时期的碱性、偏碱性岩体特征,推断华北中部早白垩世碱性岩浆活动与古太平洋板块俯冲背景下华北克拉通破坏作用关系密切。