利用多种地球物理观测资料直接反演地幔对流模型

假定地幔为一个均匀的、粘滞系数为常数、同时均匀分布放射性热源的流体球层,其内部存在的对流则由流体力学3个基本方程:运动方程、能量方程和连续性方程确定.如果假定地幔处于低瑞利数的状态（临界瑞利数1.5倍左右）,那么上述方程中的非线性项可以忽略不计.作为一类可能的模型,本文计算一组用6个边界条件确定6个未知数的线性方程组.这些条件包括板块绝对运动极型场、地球大地水准面异常和地震层析结果提供的地幔密度分布横向不均匀相应的“刚性地球”水准面异常等.模型计算表明:1.地幔中流体运动格局不仅受地幔热动力学参数（瑞利数）控制,而且强烈地受边界条件的影响.2.若不限定下边界为等温边界,则上、下地幔之间并不呈现出活动性明显差异;但是在模型瑞利数加大到一定值时,核-幔边界附近将出现一些局部的小尺度对流环.3.当模型瑞利数从很小增加时,对流格局将发生变化,这些格局可能反应由地幔热动力学参数决定的地幔固有特性.4.当瑞利数为50000和80000时,核-幔边界形变与PcP波得到的结果吻合较好.     

区域重力异常和上地幔小尺度对流相关方程及对流拖曳力场

建立了区域重力均衡异常的物理模型,假定区域重力均衡异常源于上地幔密度分布横向不均匀以及由上地幔小尺度对流产生的边界形变．导出了区域重力均衡异常和上地幔小尺度对流之间的相关方程,讨论了该方程在地球动力学研究中的应用．应用几种模型计算上地幔小尺度对流产生的作用于岩石层底部的拖曳力场．结果表明,将这一相关方程用于利用区域重力均衡异常研究地壳及上地幔应力状态,将有广阔的前景．     

三维速度结构的研究现状和展望

本文评述了三维速度图像研究的现状,简要地叙述了在全球尺度、大尺度和区域尺度内三维速度图像重建所取得的主要成果.笔者在介绍了三维速度图像同地球科学其它领域的关系之后,在对未来的展望中认为,为板块构造和地球动力学这样一些基本的地学问题提供直接的地震学的证据将是一个长期的目标,并为此提出了三个要解决的问题,还针对我国现有条件提出了供选择的参考课题.     

Properties of the lithosphere-asthenosphere system in Europe with a view toward earth conductivity

Over the past 20 years the study ofP- andS-wave velocities in the upper mantle of the Mediterranean area and continental Europe has been the subject of intensive research work. We present a summary of results based on the inversion of available surface-wave dispersion data andP-wave trave time observations. For areas characterized by different tectonic settings and very large lateral variations, a discussion is made about structural models based on seismological, geothermal and electrical conductivity data.     

南海北缘琼东南盆地热结构与莫霍面温度

相对于大陆地区,洋壳或海陆过渡区目前较缺乏岩石圈热结构方面的研究.本文依据琼东南盆地现有热流数据和相关岩石热物性参数,沿分布于盆地内不同位置的4条地震测线计算了不同圈层的热流分配关系(即热结构)及莫霍面温度.计算时根据最新的P-波速度变化分析将该区地壳分为四层,分别为沉积盖层、上地壳、下地壳及下地壳高速层.结果表明:琼东南盆地地幔热流由浅水区向深水区逐渐增加,是控制盆地现今海底热流分布的主要因素;其占海底热流平均比例为76.3±7.0%,具有典型的"冷壳热幔"的岩石圈热结构特征;莫霍面温度范围500~700℃,存在一个低温区和两个高温区,其整体分布与盆地基底以下地壳伸展减薄及断裂发育有关.     

基于重力数据特征的东北地区深部动力机制解析

中国东北地区处于古亚洲构造域、蒙古-鄂霍茨克构造域和环太平洋构造域叠加作用最为显著的地区,是地学研究的热点区域.为了探析欧亚大陆下西太平洋板片的俯冲形态以及揭示该区域深部地球动力学机制,利用卫星重力数据通过预处理共轭梯度快速密度反演算法获得了包含东北地区、华北部分地区及日本海海域在内的研究区域上地幔三维密度结构,结合天然地震三维层析成像结果共同揭示太平洋板片的俯冲形态和深部动力机制.俯冲的太平洋板片在日本海沟处呈高密度异常,向西横向持续扩张,深度方向上有逐渐增加趋势.不连续的高密度体俯冲至地幔转换带（410~660 km）后继续水平西向俯冲,部分滞留板片可能进入下地幔;在大兴安岭断裂带下面转换带中同样发现水平分布的高密度体,推断是大兴安岭断裂带下方地幔岩石圈拆沉的结果,横向不均匀分布的俯冲板片边缘已抵至大兴安岭造山带附近,这对于研究东北地区深部动力学机制具有重要的意义.

     

大别苏鲁地区层状地幔反射体及其解释

深反射地震虽然己广泛应用于地壳上地幔调查,然而,来自地幔的反射体在全世界 都还比较少见,尤其是尚未有发现上地幔中多层水平反射体的报道. 近年来,作者用24s 的 深反射地震记录揭示了在大别苏鲁地区岩石圈地幔内存在5组水平的反射体, 表明该区具有 特殊演化作用形成的上地幔组构, 它们可随深度增加分别命名为M1到M5 . 这些反射体不仅 可在地震叠加剖面上看到,有时还可在野外单炮记录上看到. 反射体M1对应Moho面,而M5大 概与现今岩石圈底界对应,根据地热资料,苏鲁热岩石圈厚度约为78km. 其他3个反射体可 能是中生代岩石圈减薄诱发的壳幔作用的结果. 根据岩石学与地球化学的数据,在晚中生代 中国东部岩石圈的厚度约从150km减薄到约60km,在新生代又略微加厚到平均 78km. 这一减 薄作用引起岩浆底侵并在下地壳产生麻粒岩层,而早侏罗纪扬子克拉通向北的陆-陆俯冲又 在上地幔产生榴辉岩层. 在双程走时12s处的反射体M2 则是麻粒岩层与榴辉岩层的边界,它 也是古生代的 Moho面. 反射体 M3 出现在14s 前后,看来是榴辉岩层的底面, 它的下面应 保存有残留的古生代上地幔. 由于新老岩石圈地幔成分不同,其界面产生反射体 M4. 这种 多层岩石圈地幔反射体的存在表明,所研究地区的地幔结构与中国东部中生代岩石圈减薄作 用有关. 同时,由于20世纪80年代以来一直认为上地幔在反射地震上是相对透明的,多层反 射体的发现对这一认识是新的挑战, 表明采用爆炸震源与地震反射新技术有可能揭露岩石圈 地幔内部结构细节,这些细节也是地幔动力学作用的产物.     

Co-existing fluid and silicate inclusions in mantle diamond

We document the compositions of co-existing silicate macro-inclusions and fluid micro-inclusions in the fibrous coats of eight coated diamonds from the Panda kimberlite (Canada). The mineral inclusions in the diamond coats come from either the peridotite suite (Cr-pyrope, orthopyroxene, olivine and Cr-diopside) or the eclogite suite (omphacite). Therefore, fibrous diamonds grow in the same paragenetic environments as octahedral diamonds. The inclusions document a more fertile source composition (lower Mg# and higher CaO) than for equivalent phases in octahedral diamonds from Panda and worldwide. However, moderate to high Cr₂O₃ contents in garnet and clinopyroxene inclusions suggest that this apparent fertility is due to a secondary process. Geothermometry of the silicate inclusions yields low equilibration temperatures of 930 to 1010 °C. The co-existing fluid micro-inclusions are dominated by H₂O, carbonate and KCl. Fluid inclusions in both the peridotitic and eclogitic samples fall along linear arrays between Fe–Ca–Mg carbonate and KCl. Inclusions in the one eclogitic sample also contain quartz. We suggest that the diamonds have trapped both metasomatised minerals and the metasomatic fluid, and so provide a snap shot of a metasomatic event in the mantle.     

Eruption style and petrology of a new carbonatitic suite from the Mt. Vulture Southern Italy/: The Monticchio Lakes Formation

The Monticchio Lakes Formation MLF is a newly identified carbonatite-melilitite tuff sequence which is exposed in the southwestern sector of the Vulture volcano. It is the youngest example ca. 0.13 m.y. of this type of volcanism in Italy, although other carbonatites of smaller volume, but with similar characteristics, have been discovered recently. This volcanic event occurred in isolation after a 0.35 m.y. period of inactivity at Vulture. The eruption produced two maar-type vents and formed tuff aprons mainly composed of dune beds of lapilli. Depositional features suggest that a dry surge mechanism, possibly triggered by CO₂ expansion, was dominant during tuff emplacement. The MLF event involved a mixture of carbonatite and melilitite liquids which were physically separated before the eruption. Abundant mantle xenoliths are direct evidence of the deep-seated origin of the parental magma and its high velocity of propagation towards the surface. Often, these nodules form the core of lapilli composed of concentric shells of melilitite andror porphyritic carbonatite. Coarse-ash beds alternate with lapilli beds and consist of abundant lumps and spherulae of very fine-grained calcite immersed in a welded, highly compacted carbonatite matrix. Porphyritic carbonatite shells of the lapilli and fine-grained spherulae of calcite in the tuff matrix suggest incipient crystallisation of a carbonatite liquid in subvolcanic conditions and eruption of carbonatite-spray droplets. Dark coloured juvenile fragments mainly consist of melilite, phlogopite, calcite, apatite, perovskite, and häuyne crystals in a carbonatite or melilitite matrix. The rocks have an extremely primitive, ultramafic composition with very high Mga) 85. and Cr and Ni content 1500 ppm-. The calcite contains high SrO, BaO and REE of up to 1.5 wt.%. Similar compositions are typical of primary, magmatic carbonates which are found in both intrusive and extrusive carbonatites. The high modal Sr-Ba-REE-rich calcite, the typical mineralogy, and the high amount of Sr-group elements identify the carbonate component as a carbonatite. The very high Mga, mantle debris and C, O, He isotope ratios in the range of mantle values indicate a near-primary character for the carbonatite which is distinctive of a restricted group of extrusive carbonatites only found in continental rift areas.     

层状介质中膨胀圆台体震源模型的应力场、应变场及位移场计算

用两层介质中存在的一膨胀圆台体作为模型以便模拟地幔物质上涌孕震的力源模式．计算了层状介质结构条件下结构底部膨胀圆台模拟力源在不同横向、纵向尺度以及不同锥角时的应力场、应变场及位移场的变化．结果表明，介质中及地表附近的应力场、应变场、位移场不仅与上涌力源的几何参数和物理参数有关，而且也受到层状介质结构参数的制约和影响．这种数值模拟不仅为解释上地幔物质向地壳下部侵入的现象提供了一种有意义的方法，而且表明对于考虑地幔物质上涌孕震过程有关的前兆场分布而言，必须认真考虑介质结构不均匀性问题．