关于远震Pn波列的实验研究

借助地震模型实验,讨论了深部的低速层力学性质及高速层厚度对地震波水平传播的影响;指出由软弱的低速层和坚硬的高速薄层组成的下部岩石层结构,有利于地震能量沿水平方向传播,是解释远距离上出现强的 Pn 及高速续至波的很可能的结构模式;也阐述了这种解释同已有的关于大洋中脊及大陆裂谷区域内岩石层下部流变学分层的研究结果相一致.      

大陆弹性岩石层有效弹性厚度对岩石层形变和大地水准面的动力影响

用岩石层－地幔力学、热学耦合模型,以俯冲带为例,研究大陆岩石层不同的有效弹性厚度对岩石层形变和大地水准面起伏的动力影响。数值结果显示大陆岩石层有效弹性厚度的作用象一低通滤波器,它抑制岩石层形变和大地水准面起伏的高频分量。随着有效弹性厚度的增加,岩石层的形变和大地水准面起伏不仅幅度减小,其形状变化也被平滑。模拟结果表明,在进行大陆岩石层动力学过程的研究中,只有充分考虑大陆弹性岩石层有效弹性厚度的动力     

球层岩石层模型对表面荷载的响应

本文给出了在球层模型下,地球岩石层对表面荷载响应的解析解。计算了地球岩石层对圆盘形荷载和正弦型荷载的响应,及由此产生的重力异常。结果表明:1.岩石层弯曲不仅与其厚度有密切关系,而且与荷载尺度有关。当岩石层厚度与荷载尺度相比很小时,其弯曲与厚度关系不大,并呈现薄板效应。2.弹性模型岩石层在外加荷载下能承受数千巴的弯曲应力。3.弯曲应力在岩石层中的分布较为规则。由于大尺度荷载下岩石层出现薄板效应,传统的由弯曲刚度估算等效岩石层厚度的部分结果需要重新估价。     

岩石层,软流层和外围层（续一）

3 富集地幔人们曾经用大陆地壳拼凑和原始的下地幔柱解释所有非大洋中脊玄武岩(即富集玄武岩或来自所谓原生储层的玄武岩)。上地幔被看作是枯竭地幔和洋中脊玄武岩的储层,而仅是洋中脊玄武岩的储藏,它是     

海洋板块俯冲作用下上覆大陆岩石层减薄机制的动力学模拟

几乎所有大陆岩石层的减薄现象,可能都与海洋板块的俯冲作用相关,但是两者之间的内在联系迄今仍不十分明确,为此,我们设计了一系列包含洋-陆俯冲系统的二维数值模型,来探讨海洋板块的俯冲作用对上覆大陆岩石层变形行为的影响,尤其对大陆岩石层减薄效应的制约.模型结果表明,海洋板块俯冲过程中的地幔楔熔体对大陆岩石层地幔的热侵蚀以及由熔体上升所诱发的地幔局部对流的强烈扰动会导致上覆大陆岩石层的减薄效应.这种效应不仅表现在横向上的向陆内蔓延,还表现在垂向上的向浅部发展.且多类动力学参数都能制约大陆岩石层的减薄效应.具体地,随着汇聚速率和洋壳厚度的增加,上覆大陆岩石层在横向上的减薄范围越大,在垂向上的减薄程度也越深;而随着俯冲海洋板块年龄的增加,上覆大陆岩石层在横向上的减薄范围增大,但在垂向上的减薄程度会减小;随着上覆大陆岩石层厚度的增加,其横向减薄范围会减小,但在垂向上的减薄程度会加深.本文研究成果能为揭示华北克拉通减薄/破坏的动力学过程提供一定的理论参考依据.     

中国东部海域及邻区岩石层地幔的P波速度结构与构造分析

利用中国大陆东部及台湾地区、日本和琉球群岛的地震观测数据,通过体波地震层析技术反演了中国东部海域及其邻近地区的P波速度结构.以此为依据分析了不同地区的岩石层性质和深部动力学条件,探讨了中朝与扬子块体、扬子与华夏块体在海区的深部边界及其构造属性,揭示出菲律宾海板块与欧亚大陆的碰撞以及板片俯冲下沉、弧后扩张作用对中国东部海域岩石层结构的影响.结果表明,中国东部海域的岩石层地幔存在明显的横向非均匀性,它们与区域构造的形成演化有一定的联系.中国大陆东部的五莲－青岛断裂与朝鲜半岛西缘断裂、济州岛南缘断裂共同构成中朝和扬子块体的边界,江绍断裂向东延伸至朝鲜半岛南端成为分隔扬子和华夏块体的边界;东海陆架与冲绳海槽的岩石层结构差异明显,东海陆架具有中国东部地区的岩石层特征,属于欧亚大陆向海域的延伸;冲绳海槽的岩石层强烈减薄,为大陆向大洋过渡的区域;沿着日本－琉球－台湾俯冲带,菲律宾海板块俯冲下沉引起的地幔扰动对中国东部海域产生了较大的影响,欧亚大陆与菲律宾海板块之间的相互碰撞导致台湾地区岩石层明显增厚.     

青藏高原物质东流的岩石层力学背景探讨

利用地表大地球热流观测资料、岩石生热率及热导率数据研究了三江和四川盆地6个地区的岩石层平均温度结构及强度分布。结果表明，整个三江地区岩石层温度较高，而四川盆地温度较低；在岩石层强度分布上，四川盆地为高强度区，而三江地区则为低强度区；整个三江地区构成了一条青藏高原物质流的低强度通道；由于四川盆地高强度块体的阻挡，青藏高原向东的物质流在此转向近南向，沿三江地区流逸；不同岩石层块体的强度差异可能是控制高原物质流动态势的重要力学背景之一。     

海洋转换断层的热结构

用三维有限元模拟方法研究了海洋转换断层下部的温度结构。我们说明,使用岩石层脆性弱化的流变可以沿着转换断层形成地幔强烈上涌和温度升高的区域;推测邻近转换断层中心部位的岩石层温度最高、厚度最薄。以前采用简化的流变定律模拟岩石层及其下部软流层的行为,推测海洋转换断层底部地幔温度比相邻板内的地幔温度低很多,在其中心处岩石层最厚。由于考虑了更真实的脆性流变,所以本研究计算得到了相对高温的热结构。此温度结构与洋脊-转换断层环境中的大量观测结果相符。这些观测资料包括地震活动的深度、沿洋脊临近部位的地球化学异常以及在板块运动变化过程中长的转换断层有分裂为小的内部扩张中心的趋势。     

智利三联点南部含洋脊海洋板块俯冲过程的数值模拟

"三联点"是全球板块运动系统的重要组成部分.扩张的智利洋脊向南美板块俯冲形成了智利三联点,并造成了智利三联点以南数百千米范围内剧烈的地形变化.智利三联点区域的初始板块俯冲角度、洋脊扩张速率等因素的差异对南美板块岩石层热结构及地形起伏造成了显著影响.本文采用有限差分方法,构建了智利三联点区域洋脊俯冲的二维数值模型,模拟洋...     

全球地球科学大断面与地球动力学（Ⅰ）

全球地球科学断面（ＧｌｏｂａｌＧｅｏｓｃｉｅｎｃｅＴｒａｎｓｅｃｔｓ，简称ＧＧＴ）是当今世界岩石层计划的重要组成部分，也是深化岩石层研究的科学前沿。本文阐明全球ＧＧＴ断面计划的内涵和要求，给出其在全球范围内的分布格局和中国１１条断面的地理位置，在板块构造和地体概念的指导下，依据地球物理、地球化学和地质构造资料相结合的原则进行综合编图。从全球构造出发，对世界上的几条典型断面：北美胡安德富卡－阿尔伯塔（ＪｕａｎｄｅＦｕｃａＡｌｂｅｒｔａ）平原大陆－大洋的ＧＧＴ断面（简称Ｂ＿２断面），欧洲地学断面计划（ＥＧＴ）的“挪威北角－阿尔卑斯－地中海－南突尼斯”断面，中国地学断面计划ＧＧＴ中的“亚东－格尔木”断面，“满都拉－响水”断面和“广州－巴拉望”海洋断面等进行了阐述和讨论，同时对其它一些断面也进行了概述。在各条断面分布的地理位置和构造部位各异的条件下，对其地球物理场和岩石层结构进行了综合研究，探讨了其地球动力学机制并给出了地球科学解释的概念性模式。     

Heat flow and thickness of the oceanic lithosphere

Existing thermal models of the oceanic lithosphere predict too sharp an increase of heat flow towards the ridge axis. A new mathematical model of a thickening lithosphere is presented. The temperature distribution is computed by the use of observed surface heat flow as a boundary condition. If observed heat flow values represent flow of heat from the mantle, the model predicts a rather rapid growth of the lithosphere within the first 30 m.y. and a nearly steady state after 100 m.y. Heat flow from the asthenosphere to the lithosphere shows a minimum near the ridge axis, suggesting a down-going convective flow in the asthenosphere at both sides of a spreading center.     

Electrical Structure in Marine Tectonic Settings

This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations, (2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle. The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab) are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent. Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity patterns in the depth range of 60–200 km.     

Effect of the oceanic lithosphere velocity on free convection in the asthenosphere beneath mid-ocean ridges

The paper presents results obtained in experiments on a horizontal layer heated from below in its central part and cooled from above; the layer models the oceanic asthenosphere. Flow velocity and temperature profiles are measured and the flow structure under boundary layer conditions is determined (at Rayleigh numbers Ra > 5 × 10⁵). The flow in the core of a plane horizontal layer heated laterally and cooled from above develops under conditions of a constant temperature gradient averaged over the layer thickness. The flow core is modeled by a horizontal layer with a moving upper boundary and with adiabatic bounding surfaces under conditions of a constant horizontal gradient of temperature. Exact solutions of free convection equations are found for this model in the Boussinesq approximation. Model results are compared with experimental data. Temperature and flow velocity ranges are determined for the boundary layer regime. Based on the experimental flow velocity profiles, an expression is found for the flow velocity profile in a horizontal layer with a mobile upper boundary heated laterally and cooled from above. Free convection velocity profiles are obtained for the asthenosphere beneath a mid-ocean ridge (MOR) with a mobile lithosphere. An expression is obtained for the tangential stress at the top of the asthenosphere beneath an MOR and the total friction force produced by the asthenospheric flow at the asthenosphere-lithosphere boundary is determined.     

Approximate solutions for the formation of the lithosphere

The lithosphere is interpreted as a thermal boundary layer. Approximate solutions of the boundary layer cooling problem are developed which include mantle radioactivity, partial melt in the asthenosphere, a temperature gradient in the asthenosphere, and a non-zero lithospheric thickness at the ridge crests. The cooling history of oceanic lithosphere is found to be remarkably insensitive to assumptions about the amount of radioactivity in the upper mantle and the extent of melting in the asthenosphere. Determinations of the thickness of oceanic lithosphere and the depths of oceans as a function of age are in excellent agreement with boundary layer predictions which include a heat flux from the asthenosphere. However, the determinations do not resolve how much of the total asthenospheric heat flux might be caused by a temperature gradient in the asthenosphere. Simple thermal arguments indicate that the initial lithospheric thickness, L₀, at ridge crests should depend on the local half-spreading rate, V, as L₀ = 3 km/V(cm/year).     

海洋热流与地幔上升流

从洋中脊上升的地慢物质带上来的大量热量,使在洋中脊裂谷处的海底热流及温度最高,向海沟逐渐减小．由于热胀冷缩,海底地势在洋中脊处最高．作者根据板块模型由一维运动物体的热传导方程推出裂谷处上升物体的温度分布公式．用此分布公式作为垂直边的边界条件,严格地求解了运动板块的二维运动物体热传导方程．用此方程研究了各参数与观测量之间的关系．通过改变公式中的参数值,使计算的理论曲线与实测海底热流一年龄及海底深度一年龄曲线拟合,从而求出了板块的厚度Ｌ＝９７ｋｍ,地幔上升速度ｕ＝３．ｇｍｍ／ａ,热膨胀系数ａ＝３．３７×１０－５／℃及温度分布．该方法克服了在洋中脊处理论热流值趋于无限大的问题,并可以计算出地幔上升流的速度及宽度．     

南海西南次海盆的地热流特征与分析

为系统地了解南海西南次海盆的地热流特征,本文通过对研究区及邻域地热流数据的补充采集、收集整理和统计分析,获得了87个有效的地热流数据、一批热导率和生热率的地热参数资料,地热流测点在空间上覆盖了整个区域.研究区的地热流数据分布结果表明,西南次海盆热流密度的平均值为98.1±14.8 mW·m^-2,洋陆过渡带为103.6±19.4 mW·m^-2,南沙岛礁区和西部陆缘分别为79.0±15.5 mW·m^-2和78.3±15.6 mW·m^-2.研究区表层沉积物热导率的平均值0.86±0.06 W·mK^-1,生热率的平均值1.11±0.17 μW·m^-3,海底温度的平均值为2.43±0.01℃.综合海底地形地貌、地质与地球物理资料,认为研究区的热流特征在空间上具有一定的分布规律,表现为：（1）洋盆区测点的热流密度平均值高于两侧陆缘;（2）东南缘洋陆过渡带上测点的地热流密度值高于邻近海盆和南沙岛礁区的测点,而西北缘这种特征不明显;（3）西北翼的热流密度值总体比东南翼高;（4）沿着古扩张中心方向,西南次海盆热流值具有自东北向西南端方向逐步增大的趋势,表明海盆区同时存在着洋中脊与大陆裂谷两种不同的热状态,西南段裂谷热流值比东北段洋中脊高.对西南次海盆沉积物的热导率和生热率值参数的测量及数据空间分析可见,这两种热参数的空间分布无明显规律性,可能与海盆形成之后复杂的沉积环境相关.根据热流-洋壳年龄之间的关系,在西南次海盆东北段26个测站数据中,发现靠近古扩张中心的数据与理论值呈负偏移,而远离古扩张中心的数据呈正偏移,此现象是海盆内地热流数据受不同类型的地下流体影响所致.     

Diapirism of depleted peridotite — a model for the origin of hot spots

A model is proposed for the origin of hot spots that depends on the existence of major-element heterogeneities in the mantle. Generation of basaltic crust at spreading centers produces a layer of residual peridotite ～20–25 km thick directly beneath the crust which is depleted in Fe/Mg, TiO₂, CaO, Al₂O₃, Na₂O and K₂O, and which has a slightly lower density than undepleted peridotite beneath it. Upon recycling of this depleted peridotite back into the deep mantle at subduction zones, it becomes gravitationally unstable, and tends to rise as diapirs through undepleted peridotite. For a density contrast of 0.05 g cm^?3, a diapir 60 km in diameter would rise at roughly 8 cm y^?1, and could transport enough heat to the base of the lithosphere to cause melting and volcanism at the surface. Hot spots are thus viewed as a passive consequence of mantle convection and fractionation at spreading centers rather than a plate-driving force.It is suggested that depleted diapirs exist with varying amounts of depletion, diameters, upward velocities and source volumes. Such variations could explain the occurrence of hot spots with widely varying lifetimes and rates of lava production. For highly depleted diapirs with very low Fe/Mg, the diapir would act as a heat source and the asthenosphere and lower lithosphere drifting across the diapir would serve as the source region of magmas erupted at the surface. For mildly depleted diapirs with Fe/Mg only slightly less than in normal undepleted mantle, the diapir could provide not only the source of heat but also most or all of the source material for the erupted magmas. The model is consistent with isotopic data that require two separate and ancient source regions for mid-ocean ridge and oceanic island basalts. The source for mid-ocean ridge basalts is considered to be material upwelling at spreading centers from the deep mantle. This material forms the oceanic lithosphere. Oceanic island basalts are considered to be derived from varying mixtures of sublithospheric and lower lithospheric material and the rising diapir itself.     

Nonstationary dynamic control of seismic activity of platform regions by mid-ocean ridges

The plot of temporal variation in the seismic activity level in the central and eastern North American platform (NAP) is shown to be similar to that for the Mid-Atlantic Ridge (MAR). This fact was previously noted for Fennoscandia [Skordas et al., 1991]. The characteristic features of the MAR plot recur approximately every three years for Fennoscandia and every four to eight years for the NAP. These data indicate that the mid-ocean ridge largely controls the seismic activity of the adjacent platforms. The control is provided by the ridge push force. As a result of variations in this force due to the nonstationary process of dike intrusion in the axial zone of the ridge, disturbances of the stationary stress-strain state of the lithosphere migrate from the ridge. Using the Elsasser model, the observed time shift can be used for estimating the viscosity of the asthenosphere, amounting to 10¹⁷ Pa s with an accuracy of ±30% in the case considered. The disturbance amplitudes decaying away from the ridge are high enough to change the seismic activity of the adjacent platforms.     

裂谷盆地构造-热演化模拟中几个问题的讨论

裂谷盆地的构造-热演化模拟是在岩石圈尺度计算裂谷盆地形成演化过程中的热历史和沉降史.拉张模型实现了构造和热的完美结合,在描述裂谷盆地沉降和热流演化方面取得了很大的成功.本文使用二维运动学模型,通过有限元方法,在拉格朗日坐标系下进行拉张背景下的构造热演化模拟,探讨了拉张模型中初始地壳、岩石圈厚度、软流圈对流、模型上边界对构造热演化的影响,以及载水和载沉积物两种情况下盆地侧翼抬升的差异.     

Dynamics of the mid-ocean ridge plate boundary: Recent observations and theory

The global mid-ocean ridge system is one of the most active plate boundaries on the earth and understanding the dynamic processes at this plate boundary is one of the most important problems in geodynamics. In this paper I present recent results of several aspects of mid-ocean ridge studies concerning the dynamics of oceanic lithosphere at these diverging plate boundaries. I show that the observed rift valley to no-rift valley transition (globally due to the increase of spreading rate or locally due to the crustal thickness variations and/or thermal anomalies) can be explained by the strong temperature dependence of the power law rheology of the oceanic lithosphere, and most importantly, by the difference in the rheological behavior of the oceanic crust from the underlying mantle. The effect of this weaker lower crust on ridge dynamics is mainly influenced by spreading rate and crustal thickness variations. The accumulated strain pattern from a recently developed lens model, based on recent seismic observations, was proposed as an appealing mechanism for the observed gabbro layering sequence in the Oman Ophiolite. It is now known that the mid-ocean ridges at all spreading rates are offset into individual spreading segments by both transform and nontransform discontinuities. The tectonics of ridge segmentation are also spreading-rate dependent: the slow-spreading Mid-Atlantic Ridge is characterized by distinct bulls-eye shaped gravity lows, suggesting large along-axis variations in melt production and crustal thickness, whereas the fast-spreading East-Pacific Rise is associated with much smaller along-axis variations. These spreading-rate dependent changes have been attributed to a fundamental differences in ridge segmentation mechanisms and mantle upwelling at mid-ocean ridges: the mantle upwelling may be intrinsically plume-like (3-D) beneath a slow-spreading ridge but more sheet-like (2-D) beneath a fast-spreading ridge.