SEISMIC VELOCITY STRUCTURE AND COMPOSITION OF THE CONTINENTAL-CRUST - A GLOBAL VIEW
SEISMIC VELOCITY STRUCTURE AND COMPOSITION OF THE CONTINENTAL-CRUST - A GLOBAL VIEW
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DOI：
10.1029/95jb00259
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发表时间：
1995-06-10
影响因子：
3.9
通讯作者：
MOONEY, WD
中科院分区：
文献类型：
--
作者：
CHRISTENSEN, NI;MOONEY, WD
地震技术提供了地壳结构的最高分辨率测量，并已在全球范围内进行。我们根据地震折射曲线的结果总结了大陆地壳的结构，并通过将这些结果与高压实验室测量的地震速度进行比较来推断地壳成分，以构成深度的函数。地壳的外壳，地壳的厚度和速度结构与构造省良好相关，延伸的外壳显示平均厚度为30.5 LAN，牛根型平均为46.3 km。盾牌和平台的平均地壳厚度几乎等于全球平均水平。我们已经通过估计每种主要地壳类型的全局面积来纠正地震折射曲线的非均匀地理分布。基于这些值的加权平均地壳厚度为41.1 km。该值比以前估计不足的盾牌，平台和Orogens的估计值高10％至20％。外壳的平均压缩波速度为6.45 km/s，最高地幔（PN速度）的平均速度为8.09 km/s。我们以形式以5公里的深度间隔总结了地壳的速度结构。直方图和平均速度深度曲线的平均速度，并将这些确定与压缩波速度的新测量和密度的新测量值相比，超过3000个火成岩和变质岩石核心与1 GPA的压力相比。根据岩石学研究和化学分析，岩石已分为29组。每组以5公里的深度间隔向每三个不同地热的地壳深度以5公里的深度间隔呈现平均速度，密度和标准偏差。这使我们能够开发一个模型，以构成大陆地壳的组成。上大陆壳的速度与许多岩性的速度相匹配，包括许多低级变质岩石和相对硅质的闪石相坡度。在中期区域，速度梯度似乎源于变质级的增加以及二氧化硅含量的降低。音调片麻岩，花岗岩片麻岩和闪石是大量的中心岩性。由于首选矿物方向引起的各向异性在上层和中期区域可能是显着的。下部大陆地壳的大部分在化学上等同于Gabbro，速度与镁铁质颗粒的实验室测量一致。石榴石随着深度而变得越来越丰富，镁铁质石榴石颗粒是正上方不连续性上方的主要岩石类型。公共地壳类型的平均压缩波速度与密度相关。根据我们的模型计算得出的平均地壳密度为2830 kg/m（3），平均SIO2含量为61.8％。
Seismic techniques provide the highest-resolution measurements of the structure of the crust and have been conducted on a worldwide basis. We summarize the structure of the continental crust based on the results of seismic refraction profiles and infer crustal composition as a function of depth by comparing these results with high-pressure laboratory measurements of seismic velocity for a wide range of rocks that are commonly found in the crust, The thickness and velocity structure of the crust are well correlated with tectonic province, with extended crust showing an average thickness of 30.5 lan and orogens an average of 46.3 km. Shields and platforms have an average crustal thickness nearly equal to the global average. We have corrected for the nonuniform geographical distribution of seismic refraction profiles by estimating the global area of each major crustal type. The weighted average crustal thickness based on these values is 41.1 km. This value is 10% to 20% greater than previous estimates which underrepresented shields, platforms, and orogens. The average compressional wave velocity of the crust is 6.45 km/s, and the average velocity of the uppermost mantle (Pn velocity) is 8.09 km/s. We summarize the velocity structure of the crust at 5-km depth intervals, both in the form. of histograms and as an average velocity-depth curve, and compare these determinations with new measurements of compressional wave velocities and densities of over 3000 igneous and metamorphic rock cores made to confining pressures of 1 GPa. On the basis of petrographic studies and chemical analyses, the rocks have been classified into 29 groups. Average velocities, densities, and standard deviations are presented for each group at 5-km depth intervals to crustal depths of 50 km along three different geotherms. This allows us to develop a model for the composition of the continental crust. Velocities in the upper continental crust are matched by velocities of a large number of lithologies, including many low-grade metamorphic rocks and relatively silicic gneisses of amphibolite facies grade. In midcrustal regions, velocity gradients appear to originate from an increase in metamorphic grade, as well as a decrease in silica content. Tonalitic gneiss, granitic gneiss, and amphibolite are abundant midcrustal lithologies. Anisotropy due to preferred mineral orientation is likely tb be significant in upper and midcrustal regions. The bulk of the lower continental crust is chemically equivalent to gabbro, with velocities in agreement with laboratory measurements of mafic granulite. Garnet becomes increasingly abundant with depth, and mafic garnet granulite is the dominant rock type immediately above the Mohorovicic discontinuity. Average compressional wave velocities of common crustal rock types show excellent correlations with density. The mean crustal density calculated from our model is 2830 kg/m(3), and the average SiO2 content is 61.8%.