Lithological interpretation of crustal composition in the Fennoscandian Shield with seismic velocity data
Lithological interpretation of crustal composition in the Fennoscandian Shield with seismic velocity data
复制标题
利用地震速度数据对芬诺斯坎迪亚地盾地壳成分进行岩性解释
DOI：
10.1016/j.tecto.2006.01.014
复制
发表时间：
2006
期刊：
影响因子：
2.9
通讯作者：
L. Pesonen
中科院分区：
文献类型：
--
作者：
M. Kuusisto;I. Kukkonen;P. Heikkinen;L. Pesonen
在这项研究中，我们报告了使用地震广角速度模型和不同岩石类型的纵波和横波速度的实验室测量对芬兰芬诺斯坎地盾中部地壳岩性解释的调查结果。将广角速度模型所采用的速度与根据研究区地壳PT条件校正的不同岩石类型的实验室速度进行了比较。宽角速度模型表明，纵波速度不仅在主要地壳层边界处呈阶梯增长，而且在地壳层内也呈阶梯增长。另一方面，实验室对速度的测量表明，没有一种岩石类型能够提供逐渐下降的增加趋势。因此，岩石组成在垂直方向上一定有逐渐的变化。速度的向下增加表明地壳的组成随着深度的增加而逐渐趋于基性。我们计算了一系列可能的地壳岩性组成的垂直速度剖面。芬兰的地壳速度剖面需要比平均的全球大陆模型所显示的更多的基性成分。例如，在SVEKA’81样带上，计算模型表明，地壳速度剖面可以用岩石类型混合来模拟，其中上地壳由长英质片麻岩和花岗花岗闪长岩组成，角闪岩和辉绿岩占少量比例。在中地壳，角闪岩比例增加。下地壳由调性片麻岩、基性石榴麻粒岩、角闪岩、辉石岩和少量基性榴辉岩组成。假设这些岩石类型存在于足够广泛和厚的地层中，它们也会有足够高的声反射系数，从而在盾构中部的地壳中产生普遍发育良好的反射率。根据岩性模型计算的密度剖面表明，在莫霍高速下地壳区域几乎没有密度对比。将FIRE-1和FIRE-3样带的反射面与SVEKA'81广角样带的速度模型进行比较，结果表明反射面与速度分层有关，但地壳的三维结构使这种比较复杂化。
In this study, we report the results of an investigation of lithological interpretation of the crust in the central Fennoscandian Shield (in Finland) using seismic wide-angle velocity models and laboratory measurements on P- and S-wave velocities of different rock types. The velocities adopted from wide-angle velocity models were compared with laboratory velocities of different rock types corrected for the crustal PT conditions in the study area. The wide-angle velocity models indicate that the P-wave velocity does not only increase step-wise at boundaries of major crustal layers, but there is also gradual increase of velocity within the layers. On the other hand, the laboratory measurements of velocities indicate that no single rock type is able to provide the gradual downward increasing trends. Thus, there must be gradual vertical changes in rock composition. The downward increase of velocities indicates that the composition of the crust becomes gradually more mafic with increasing depth. We have calculated vertical velocity profiles for a range of possible crustal lithological compositions. The Finnish crustal velocity profiles require a more mafic composition than an average global continental model would suggest. For instance, on the SVEKA'81 transect, the calculated models suggest that the crustal velocity profiles can be simulated with rock type mixtures where the upper crust consists of felsic gneisses and granitic–granodioritic rocks with a minor contribution of amphibolite and diabase. In the middle crust, the amphibolite proportion increases. The lower crust consists of tonalitic gneiss, mafic garnet granulite, hornblendite, pyroxenite and minor mafic eclogite. Assuming that these rock types are present in sufficiently extensive and thick layers, they would also have sufficiently high acoustic reflection coefficients for generating the generally well-developed reflectivity in the crust in the central part of the shield. Density profiles calculated from the lithological models suggest that there is practically no density contrast at Moho in areas of the high-velocity lower crust. Comparison of reflectors from FIRE-1 and FIRE-3 transects and the velocity model from SVEKA'81 wide-angle transect indicated that the reflectors correlate with velocity layering, but the three-dimensional structures of the crust complicate such comparisons.
影响因子：
3.9
作者：
CHRISTENSEN, NI;MOONEY, WD
通讯作者：
MOONEY, WD