【作者】 欧新功；

【导师】 金振民；

【作者基本信息】 中国地质大学 ， 构造地质学、岩石物理学， 2003， 博士

【摘要】 大别-苏鲁地区出露的超高压变质岩石是研究大陆造山带根部和深部岩石圈的天然实验室，引起了地质学家的广泛关注。地球物理调查显示在苏鲁东海地区深度3.2-4.3km存在相对较高地震波速度（>6.8km/s）、高密度（>3.2g/cm3）、高电阻率（>6000Ωm）的地质体（简称“三高”地质体）。中国大陆科学钻探(Chinese Continental Scientific Drilling, 简称CCSD)的5000米钻孔可能穿过这个地质体。因此，CCSD的主要科学目标之一就是查明该地质体的成分和组成特征。对钻孔岩心及其周围岩石物理性质的研究可以为地球物理资料的解释提供必要的约束，为建立结晶岩地区的地球物理模型和解释标尺提供直接依据。本次研究通过对中国大陆科学钻探先导孔2000米岩心及钻孔周围地表样品岩石物理性质的研究，尤其是通过对超高压变质岩石的弹性性质和热物理性质的大量测试和分析，初步查明了东海地区不同超高压变质岩的物理性质及其相互关系，探讨了本区岩石物理性质的地质和地球物理意义，解释了该区地震深反射的可能成因，并初步阐明了“三高”地质体可能的物质组成。本次研究主要获得以下四方面的成果：一、建立了CCSD先导孔2000米的岩石物理性质连续剖面，为建立精细地球物理模型和钻孔测井成果的合理解释提供了岩石物理学的重要约束。在常温常压条件下初步查明了各类岩石的密度、地震波速度（Vp、Vs、饱水Vp、饱水Vs）以及岩石热导率随2000米先导孔深度的变化关系，建立了本区超高压变质岩的弹性性质和热物理性质数据库，为建立和检验各种地质和地球物理模型提供了岩石物理数据基础。此外，根据先导孔的岩性分布特征和岩石物理学的分类需要，把所研究的样品划分为7类（1-金红石榴辉岩、2-多硅白云母榴辉岩、3-角闪石化榴辉岩（弱退变榴辉岩）、4-强退变榴辉岩（石榴角闪岩）、5-副片麻岩、6-正片麻岩、7-蛇纹石化石榴石橄榄岩），并讨论和对比了它们的物理性质随岩石退变质程度、矿物组成、温度和压力的变化关系。二、查明了先导孔主要类型的岩石在常温常压和高温高压条件下地震波速度及其各向异性的变化特征，探讨了影响岩石波速的主要因素。通过对CCSD先导孔2000米共350余块样品的弹性波测量得知，钻孔新鲜榴辉岩的地震波速度最大（平均Vp=7.86km/s），但退变质作用显著降低榴辉岩的地震波速度。片麻岩地震<WP=6>波速度最小(正负片麻岩的平均Vp分别为5.53km/s和5.71km/s)。先导孔中出现的超基性岩由于蛇纹石化而使地震波速度降低，Vp介于5.96-6.66km/s，与退变质榴辉岩的地震波速度比较接近。从2000米垂向分布上看，先导孔100~1200m具有高波速的特点，平均Vp为6.37km/s，该段主要由榴辉岩夹片麻岩和超基性岩组成。1200~2000米以花岗片麻岩和部分榴辉岩为主，这段的平均Vp为5.91km/s。这两段的速度与地球物理的探测结果（100-1200米Vp≈6.4km/s，1200-2000米Vp≈5.8km/s）相吻合。先导孔2000米岩心具有明显的地震波各向异性。平均而言，根据对岩心的测量，地震波速度在水平方向上比在竖直方向上传播快，Vp各向异性为7.04%，饱水后降低到3.92%。岩石面理所引起的各向异性平均为10.79%，片麻岩的各向异性最为明显。饱水状态可以改变岩石的弹性性质。通过对近700件样品的统计，Vp在饱水后平均增加19.8%，Vs平均增加6.4%（个别样品饱水后Vs反而降低）。不同岩石在饱水后波速增加的幅度不同，片麻岩增加的最大，正片麻岩饱水后Vp增加33.64%，副片麻岩Vp增加26.74%，榴辉岩平均增加10%。蛇纹石化石榴橄榄岩饱水前后速度基本不变。此外，实验表明饱水后岩石的泊松比增加，这是粒间自由水对岩石泊松比的影响。Gao等的研究表明岩石泊松比随岩石中H20+含量的增加而增加，这是结构水对岩石泊松比的影响，二者有类似之处。测试结果表明地震波Vp、Vs随着岩石密度的增加而增加，自然条件下满足方程：Vp=2.636ρ-2.540，相关系数r=0.71；饱水条件下满足方程：Vp=2.076ρ+0.004，相关系数r=0.85；在高压600MPa条件下满足方程：Vp=2.685ρ-1.324，相关系数r=0.94。由不同条件下的相关系数可见，饱水状态可以部分消除裂隙的影响，高压（600MPa）可以基本闭合微裂隙，所以地震波速度和密度的相关性最大。高温高压条件下弹性波的测定结果表明，随压力的增大，在小于200Mpa的条件下，岩石的地震波速度和各向异性都快速非线性变化，速度明显增大，各向异性降低。在压力大于250MPa之后，地震波速度及其各向异性基本上线性变化。该过程是岩石内部微裂隙闭合的过程。岩石在大于250MPa以后的地震波各向异性主要受矿物LPO的控制。根据对苏鲁地区的相关超高压变质岩进行岩石地震波速度（Vp、Vs）随压力（最大到600MPa）和温度(最大为600℃)变化的测试，在600MPa近原位条件下，P波波速介于5.08km/s～8.6km/s，S波波速介于2.34km/s～4.93.6km/s。其对应的密度为2.34g/cm3～3.68g/cm3。与大别地区相应的超高压变质岩石相比，苏鲁地区的榴辉岩具有明显的高P波波速和高Vp/Vs(泊松比)。Vp与泊松比和Vp与SiO2的关系证明，由化学组成和变质程度所控制的矿物学是影响原位岩石物性的最重要因素。本次研究中得到的Vp和V更多还原

【Abstract】 The UHPM rock slice exposed in the Dabie-Sulu belt provides a natural laboratory for examining the deep parts of the lithosphere and orogenic roots, and has attracted many geoscientists for frontier researches. Geophysical investigations revealed a high-velocity (>6.8km/s), high-density (>3.2g/cm3) and high resistivity (>6000Ωm) layer (3-high body) at depths between 3.2km and 4.3 km in Donghai area, which can be penetrated by a 5000-meter-deep drillhole. Therefore testing the composition and character of this "3-high body" is one of the scientific goals of CCSD project. Petrophysics investigations on the cores from pilot-hole and rocks form the outcrop around the drillsite supplied necessary constrains on the interpretations of geophysical results, and published the direct evidence in establishing geophysical models and interpretation standards for crystalline rocks. Based on the petrophysical measurements on the cores from CCSD 2000m-pilothole and some rocks from the outcrops in Donghai area, especially according to lots of tests and analysis on the elastic and thermal properties of the rocks, the petrophysical properties and their relationship as well as their significances in geology and geophysics are given for different rocks in Donghai area. Possible origins of deep seismic reflection are discussed and the possible composition of 3-high body is given according to the petrophysical results.1. Continuous petrophysical profiles of CCSD 2000m pilothole are established, which gives important constrains on geophysical models and well-logging interpretation.A dataset of densities, seismic velocities (including compressional wave Vp, shear wave Vs, water saturated Vp and Vs) as well as their profile along the depth of 2000m-pilohole are investigated based on the petrophysical measurements under air pressure and room temperature, which supplied the data foundation in verifying different geological and geophysical models. According to the lithological distributions of pilot hole and the requirements of petrophysical studies, all the samples are classified into 7 types: 1-Rutile-bearing eclogite, 2-Phengite-bearing<WP=10>eclogite, 3-Amphibolization eclogite, 4-Strongly retrograde eclogite, 5-Paragneiss, 6-Orthogneiss and 7-Serpentinization garnet Peridotite. The petrophysical properties and their relation to the degree of retrograde, the components of minerals, the temperature and the pressure are discussed and compared for 7 kinds of rocks.2. The characteristics of seismic velocities and their anisotropy of different rocks from pilot-hole are studied. The factors influenced on seismic velocity are discussed and the seismic velocities measurements are performed under high temperature up to 600℃ and high pressure up to 600MPa.About 350 core samples from CCSD 2000m-pilothole are measured on the elastic properties, which shows that among the different rocks, fresh eclogite has the maximum seismic velocity with average Vp=7.86km/s, and the gneiss has the minimum velocity (average Vp=5.53km/s for orthogneiss and 5.71km/s for paragneiss). The retrogression can decrease the seismic velocity of eclogite. The ultra-mafic rocks occurred in pilothole has the Vp velocity varies from 5.96km/s to 6.66km/s. The serpentined garnet-peridotite has the decreased velocity near the level of retrograde eclogite. In the vertical profile, the layers from 100 to 1200m have the high velocity with average Vp=6.37km/s because of the eclogite and ultra-mafic rocks in this layer. From 1200 to 2000 meters are made up of orthogneiss and some eclogites, which induced a lower velocity in average Vp=5.91km/s. The velocities of these 2 layers are consistent with those inferred from geophysical results (Vp≈6.4km/s from 100 to 1200m and Vp≈5.8km/s from 1200 to 2000m).The core samples from 2000m-pilothole have distinct seismic anisotropy under air pressure and room temperature. In average, seismic wave propagates in horizontal direction is faster than that in vertical direction with the anisotropy 7.04%, decreased to 3.92% after w更多还原