Holtzman B K, Kohlstedt D L, Zimmerman M E, Heidelbach F, Hiraga T, Hustoft J
Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA.
Science. 2003 Aug 29;301(5637):1227-30. doi: 10.1126/science.1087132.
One of the principal means of understanding upper mantle dynamics involves inferring mantle flow directions from seismic anisotropy under the assumption that the seismic fast direction (olivine a axis) parallels the regional flow direction. We demonstrate that (i) the presence of melt weakens the alignment of a axes and (ii) when melt segregates and forms networks of weak shear zones, strain partitions between weak and strong zones, resulting in an alignment of a axes 90 degrees from the shear direction in three-dimensional deformation. This orientation of a axes provides a new means of interpreting mantle flow from seismic anisotropy in partially molten deforming regions of Earth.
理解上地幔动力学的主要方法之一是，在地震快波方向（橄榄石a轴）与区域流动方向平行这一假设下，从地震各向异性推断地幔流动方向。我们证明：（i）熔体的存在会削弱a轴的排列；（ii）当熔体分离并形成弱剪切带网络时，应变在弱区和强区之间分配，导致在三维变形中a轴与剪切方向呈90度排列。a轴的这种取向为解释地球部分熔融变形区域地震各向异性的地幔流动提供了一种新方法。
