Shear‐wave splitting beneath the Galápagos archipelago
Shear‐wave splitting beneath the Galápagos archipelago
复制标题
加拉帕戈斯群岛下方的剪切波分裂
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
P. Silver
中科院分区：
文献类型：
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作者：
F. Fontaine;E. Hooft;P. Burkett;D. Toomey;S. Solomon;P. Silver
加拉帕戈斯群岛的横波分裂测量表明，从一致取向的各向异性迅速转变为不可测量的各向异性。在群岛西缘，延迟时间为0.4~0.9 S，快极化方向为81~10 9°E，与上覆板块剪切软流圈产生的各向异性相一致，在板块扩展方向上未发现古岩石圈各向异性的迹象。相反，在群岛中心以下，上地幔是各向同性或弱各向异性的。各向同性区域与异常低的上地幔速度体积近似重合，表明熔体的存在可能削弱了组构对各向异性的影响，或者熔体择优取向产生了垂直的快速极化方向。或者，与近山脊热点相关的复杂的流场可能导致表观各向同性。
Shear‐wave splitting measurements in the Galápagos archipelago show a rapid change from consistently oriented anisotropy to no measurable anisotropy. At the western edge of the archipelago delay times are 0.4–0.9 s and fast polarization directions are 81–109°E. These directions are consistent with anisotropy resulting from shear of the asthenosphere by the overlying plate; there is no indication of fossil lithospheric anisotropy in the plate spreading direction. In contrast, beneath the center of the archipelago the upper mantle is isotropic or weakly anisotropic. The isotropic region coincides approximately with a volume of anomalously low upper mantle velocities, suggesting that the presence of melt may weaken the effects of fabric on anisotropy or that melt preferred orientation generates a vertical fast polarization direction. Alternatively, the complex flow field associated with a near‐ridge hotspot may result in apparent isotropy.