Anisotropic structure in the mantle wedge beneath southeastern Mexico from shear-wave splitting tomography

IF 2.1 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Samuel Celis , Raúl W. Valenzuela , Marco Calò , Xyoli Pérez-Campos , Gerardo León Soto
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引用次数: 0

Abstract

Cocos intraslab earthquakes were used to make a 3-D tomographic inversion to define a crystallographic orientation model for the mantle wedge beneath southeastern Mexico. This model provided insights regarding the pattern of the mantle wedge flow and its relationship to the geometry of the subducting slab. The mantle wedge was parametrized as a 3-D block model of crystallographic orientations assuming the elastic constants of olivine and orthopyroxene with orthorhombic symmetry (hexagonal symmetry was also tested). A linearized, damped, and iterative least-squares approach was used to account for the nonlinear behavior of the shear-wave splitting, numerically recalculating partial derivatives after each iteration. The best-fitting model is consistent with two main flow regimes: (1) 2-D corner flow in a mantle wedge core made up of A-type olivine fabric northwest of the Tehuantepec Ridge extension, and (2) 3-D trench-parallel mantle flow in a mantle wedge core made up of A-, C-, or E-type olivine fabric southeast of this geological feature. Around the Tehuantepec Ridge extension, a partially serpentinized mantle wedge tip is inferred since olivine a-axis orientations are trench-parallel regardless of whether a 2-D corner flow or a 3-D trench-parallel flow prevails. Right above the Tehuantepec Ridge extension (beyond the 100 km isodepth contour of the subducting slab), a change of well-resolved olivine a-axis orientations from trench-normal to trench-parallel while going from northwest to southeast is observed. It signals an abrupt change in the mantle flow pattern possibly through a vertical tear in the Cocos slab. 3-D toroidal flow could be driving subslab mantle material into the mantle wedge around the deepest slab segment. Lastly, approximately trench-normal olivine a-axis orientations are observed in the mantle wedge tip near the Mexico and Guatemala border region, and they could be explained by assuming the presence of B-type olivine fabric.

墨西哥东南部地幔楔各向异性结构的剪切波分裂层析成像
Cocos实验室内地震被用来进行三维层析反演,以确定墨西哥东南部地幔楔的晶体学方向模型。该模型提供了关于地幔楔流模式及其与俯冲板块几何形状关系的见解。假设橄榄石和正辉石的弹性常数具有正交对称(也测试了六方对称),将地幔楔体参数化为晶体取向的三维块体模型。使用线性化、阻尼和迭代最小二乘方法来解释剪切波分裂的非线性行为,在每次迭代后数值重新计算偏导数。最佳拟合模型符合两种主要的流动模式:(1)特万特佩克岭伸展部西北部由a型橄榄岩组构组成的地幔楔核的二维角流,(2)该地质特征东南部由a型、C型或e型橄榄岩组构组成的地幔楔核的三维槽平行地幔流。在特万特佩克海岭扩展区周围,推断出部分蛇纹石化的地幔楔尖,因为橄榄石的a轴方向与海沟平行,无论其为二维角流还是三维海沟平行流。在特万特佩克岭延伸段上方(在俯冲板块100 km等深等值线之外),观察到从西北到东南方向的高分辨橄榄石a轴方向由海沟正向海沟平行转变。这标志着地幔流动模式的突然变化可能是通过科科斯板块的垂直撕裂。三维环面流可以驱动板块下地幔物质进入最深板块周围的地幔楔。最后,在靠近墨西哥和危地马拉边境地区的地幔楔尖上观察到近似海沟法向的橄榄石a轴取向,可以通过假设存在b型橄榄石结构来解释。
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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