Lattice-preferred orientation (LPO) of olivine and amphibole in amphibole peridotites and neighboring hornblendites from Gapyeong, South Korea and implications for seismic anisotropy

IF 2.1 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Jaeseok Lee, Haemyeong Jung
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引用次数: 1

Abstract

Amphibole peridotites and neighboring hornblendites are often found in subduction zones. To understand the effect of amphibole-rich rocks on seismic anisotropy in subduction zones, we studied the lattice-preferred orientation (LPO) of olivine and amphibole in amphibole peridotites and neighboring hornblendites in Gapyeong, South Korea. The major minerals of amphibole peridotites were olivine (31–51% in volume), amphibole (28–47%), and orthopyroxene (7–16%). Amphibole in amphibole peridotites showed relatively high SiO2 and low TiO2 and Na2O contents (S-type amphibole), indicating that it was formed under supra-subduction conditions. Amphibole in amphibole peridotites showed the type-I, type-II, and type-IV LPO, whereas amphibole in neighboring hornblendites showed the type-III and type-IV LPO. In the case of olivine, most samples showed a mixture of A- and B-type LPO, and one sample showed a mixture of B- and C-type LPO. Many serpentine inclusions were found in olivines. Fourier-transform infrared (FTIR) analysis of the samples showed that the olivines contained a large amount of water (∼29000–45000 ppm H/Si). We also found many dislocations in olivines. These observations indicate that samples showing a mixture of A- and B-type LPO and a mixture of B- and C-type LPO of olivine were deformed under water-rich conditions by dislocation creep. In amphibole peridotites, the P-wave anisotropy of olivine was relatively low (0.9–4.8%), whereas the P-wave anisotropy of amphibole was high (6.5–17.7%). The maximum S-wave anisotropy of olivine was also relatively low (0.87–2.89%), whereas the maximum S-wave anisotropy of amphibole was high (3.81–15.19%). In hornblendites, the P-wave anisotropy and maximum S-wave anisotropy of amphibole were high (6.9–13.6% and 4.27–10.61%, respectively). The P-wave anisotropy and maximum S-wave anisotropy of the amphibole peridotites were in the range of 2.6–8.4% and 1.73–7.30%, respectively. The seismic velocity and anisotropy pattern of amphibole peridotites were more similar to those of amphibole than those of olivine, indicating that the seismic properties of amphibole peridotites were more strongly affected by amphibole than by olivine. Furthermore, the seismic anisotropy of the mixture of amphibole peridotite and hornblendite in subduction zones was also found to be significantly affected by the amphibole LPO in hornblendite.

韩国加平地区角闪岩橄榄岩和角闪岩中橄榄石和角闪岩的格优选取向(LPO)及其地震各向异性意义
角闪石橄榄岩和邻近的角闪岩经常出现在俯冲带中。为了了解富含角闪石的岩石对俯冲带地震各向异性的影响,我们研究了韩国Gapyeong角闪石橄榄岩和邻近角闪石中橄榄石和角闪石的晶格优先取向(LPO)。角闪橄榄岩的主要矿物为橄榄石(体积百分比为31-51%)、角闪岩(体积百分比28-47%)和斜方辉石(体积百分比7-16%)。角闪石橄榄岩中的角闪石显示出相对较高的SiO2和较低的TiO2和Na2O含量(S型角闪石),表明它是在超俯冲条件下形成的。角闪岩橄榄岩中的角闪石显示出I型、II型和IV型LPO,而相邻角闪岩中的角闪岩显示出III型和IV类LPO。在橄榄石的情况下,大多数样品显示a型和B型LPO的混合物,一个样品显示B型和C型LPO混合物。在橄榄石中发现了许多蛇纹石包裹体。样品的傅立叶变换红外光谱(FTIR)分析表明,橄榄石含有大量的水(~2900–45000 ppm H/Si)。我们还在橄榄石中发现了许多位错。这些观察结果表明,显示橄榄石的a型和B型LPO的混合物以及B型和C型LPO混合物的样品在富水条件下通过位错蠕变变形。在角闪石橄榄岩中,橄榄石的P波各向异性相对较低(0.9–4.8%),而角闪石的P波异性较高(6.5–17.7%)。橄榄石的最大S波各向异性也相对较低,为0.87–2.89%,而角闪岩的最大S波各向异性较高(3.81–15.19%),角闪石的P波各向异性和最大S波各向异性较高(分别为6.9~13.6%和4.27~10.61%)。角闪橄榄岩的P波各向异性和最大S波各向异性分别在2.6–8.4%和1.73–7.30%之间。角闪岩橄榄岩的地震速度和各向异性模式与角闪岩相比橄榄石更相似,表明角闪岩比橄榄石对其地震性质的影响更大。此外,俯冲带角闪橄榄岩和角闪岩混合物的地震各向异性也受到角闪岩中角闪LPO的显著影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Geodynamics
Journal of Geodynamics 地学-地球化学与地球物理
CiteScore
4.60
自引率
0.00%
发文量
21
审稿时长
6-12 weeks
期刊介绍: The Journal of Geodynamics is an international and interdisciplinary forum for the publication of results and discussions of solid earth research in geodetic, geophysical, geological and geochemical geodynamics, with special emphasis on the large scale processes involved.
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