【作者】 范景辉；

【导师】 马胜利； 刘力强； 杨晓松；

【作者基本信息】 中国地震局地质研究所 ， 固体地球物理学， 2002， 硕士

【摘要】 壳内低速层可能对应着力学上的软弱带从而有利于地震的发生；它还可能作为大陆活动块体的一种底边界而存在。虽然前人在实验岩石物理学方面的研究表明角闪岩熔融和角闪岩中含水矿物脱水是中地壳内低速层的可能成因，但在这些工作中仍存在有待深入之处。有必要在无自由水封闭条件下对角闪岩开展岩石学实验研究，并由此探讨某些壳内低速层的成因。 本文研究内容包括以下四个方面。 (1)在四川省康定地区进行了野外地质调查工作。采集了康定杂岩中部分变泥质岩(康定群)、混合岩、岩浆岩，并观察记录了典型的野外地质现象。在后期室内工作中，对岩石标本和野外地质现象做了进一步的研究。 (2)整理、分析了关于康滇构造带的大量地震测深资料、地热资料及大地电磁资料。 (3)对野外采集的康定群斜长角闪岩样品开展岩石学实验，研究了矿物脱水反应和岩石脱水熔融反应的条件、现象及产物等。全部实验是在中国地震局构造物理开放实验室的活塞-圆筒式固体介质实验装置上完成的。在本文设计的样品组装方案中，传压介质以食盐为主，以叶蜡石为辅；样品封套材料为紫铜。 (4)根据前人有关实验岩石物理学的工作(主要为高温高压岩石波速工作)和构造单元的地热资料，对代表康滇构造带上、中地壳主要组成的花岗质岩石和角闪岩进行了其原位条件下物理性质(主要为波速)的讨论。然后将其结果与地震测深资料和大地电磁资料对比研究，讨论了康滇构造带某些壳内低速层的成因。 本文得到的主要结论如下。 (1)康滇构造带上曾有过多次地质事件，至少包括了区域变质作用、岩浆侵入和构造运动。具体而言，变泥质岩(康定群)的广泛分布说明相对早期的区域变质作用已达到了角闪岩相阶段。混合岩的存在则说明深熔作用已经发生：含斑块混合岩化斜长角闪岩的手标本和镜下结构特征表明，该岩石应代表了局部重熔及熔浆重结晶作用的开始；角砾状角闪混合岩中角砾可拼接这一现象可能表明，角闪岩发生部分熔融在其内部形成了熔体，从而促使岩石发生了脆性破裂，并且熔体应基本未发生大规模迁移。基性岩脉和花岗质岩体侵入变泥质岩和混合岩显示出，在区域变质作用之后，构造区地壳乃至地幔内曾有过强烈的岩浆活动。切断基性岩脉的断层则代表了相对后期的构造活动。以上地质事件说明，康滇构造带在地质历史时期曾是地质作用异常活跃的地区。 (2)在本文4个岩石学实验中，样品内部分别发生了脱水反应和脱水熔融反应。①在实验Run4(400MPa、800℃、7h)，Run5(400MPa、700℃、36h)，Run6(250MPa、700℃、24h)的样品中，角闪石和黑云母光性特征发生了明显变化，推测其中的角闪石和黑云母均发生了脱水反应。含水矿物在无自由水封闭条件下的脱水温度低于在饱和水封闭条件下的脱水温度。②在实验Run7(1.1GPa、800℃、24h)的样品中，出现了熔体、新生石榴石和另一种新生矿物，这表明样品中发生了脱水熔融反应，其反应式应为：Hb(角闪石)+Pl(斜长石)=Melt(熔体)+Pyroxene(?)+Ga(石榴石)。③Run4和Run7实验结果的差异表明，康定群斜长角闪岩的固相线的确有在相对高压下向低温方向偏转的特征。这一特征意味着，角闪岩很可能会在具有较高热异常地区的中、下地壳发生脱水熔融。摘要 (3)在康滇构造带中地壳分布的低速层有两个重要特征:其下部与下地壳之间常有高速夹体;其自身与壳内高导层基本吻合。对花岗质岩石和角闪岩的波速模拟与分析表明，仅仅从温度和压力对岩石波速的影响出发难以解释上述壳内低速层;基于实验岩石学和实验岩石物理学研究结果的分析则表明，角闪岩脱水熔融可以对该类低速层的两个重要特征给予解释。对康滇构造带地热资料和本文实验结果的综合研究显示，康定群斜长角闪岩至少可以在构造带部分地区的中地壳下部条件下发生脱水熔融;进一步的分析说明，角闪岩在康滇构造带中地壳条件下发生脱水熔融的可能性很大。总之，在康滇构造带上，角闪岩脱水熔融与中地壳内低速层具有很强的成因联系。以上工作表明，实验岩石学和实验岩石物理学研究可以为地震测深资料的合理解释提供有关物质组成和状态的约束信息。更多还原

【Abstract】 Low velocity layers in crust may be mechanically weak layers and thus favorable for the occurrence of earthquakes. They also act as a kind of bottom boundary of tectonic blocks in continent. Although previous petrophysical works have displayed that the dehydration of hydrous minerals in amphibolites and the dehydration melting of amphibolites are possible causes for the formation of low velocity layers in mid crust, there are still insufficiencies in these works. It is necessary to perform petrological experiments with rock samples of amphibolites under vapor-absent and closed conditions, and then to discuss the formation cause of some low velocity layers based on geological, petrological, petrophysical, and geophysical data.The contents of this paper comprise the following four parts:(1) Field work in Kangding area, Sichuan province. In the field work, some metapelitic rocks, migmatites and magmatic rocks have been collected, and some typical geological phenomena have been recorded. Later, the rock samples and the recorded phenomena have been analyzed in laboratory.(2) Collections and analyses of a lot of seismic sounding data, geothermal data, and magnetotelluric sounding data.(3) Experimental studies on the plagioclase amphibolite of Kangding group. Based on four petrological experiments, this paper has discussed the conditions, phenomena, and products of the dehydration reaction and the dehydration melting reaction. All the experiments have been run on the piston-cylinder apparatus with solid confining media in Laboratory of Tectonophysics, China Seismological Bureau. In these experiments, pyrophyllite and NaCl composed the solid confining media and the rock samples were sealed in red copper capsules.(4) According to the previous works of experimental petrophysics (mainly rock velocities under high pressure and high temperature) and geothermal data about the tectonic unit, this paper has discussed the in-situ physical properties (mainly the velocities) of granitoid rocks and amphibolites which supposed to be typical rocks in the mid crust in Kang-Dian tectonic zone. The results from the above discussions were then compared with the seismic and magnetotelluric sounding data. At last the formation cause of some low velocity layers in the crust in Kang-Dian tectonic zone was discussed.The conclusions of this paper are:(1) Several geological events, including at least regional metamorphism, intrusion of magma and tectonic movement, had occurred in Kang-Dian tectonic zone. For example, the widespread distribution of metapelitic rocks, i.e. Kangding group, shows that the early regional metamorphism reached amphibolite facies. The existence of migmatites implies the occurrence of anatexis: the partial fusion of crustal rocks and recrystallization of melts are illustrated by the textural features in both rock samples and polished sections of migmatized amphibolites containing coarse-grained blocks; the breccias in the brecciated amphibolite migmatite can be put together into one mass, which implies that the melts produced by the fusion in amphibolites had induced the brittle fracture of the rocks, and that the melts hadn’t move far. The intrusion of mafic veins and granitoid bodies into metapelitic rocks and migmatites is the clues of magmatic activities in crust and even mantle of the tectonic area after the regional metamorphism. The later tectonic movement is displayed by a fault dislocating the mafic vein. The above-mentioned geological events indicate that Kang-Dian tectonic zone had been a geologically active area in geological history.(2) The dehydration reaction and the dehydration melting reaction have occurred in rock samples of the plagioclase amphibolite of Kangding group in four petrological experiments. (1) In the experimental samples of Run4(400MPa 800C 7h), Run5(400MPa 700 C 36h), Run6(250MPa ? 700 C , 24h), the optical characteristics of hornblendes and biotites are changed, which implies that dehydration reactions have occurred. And it seems tha更多还原