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Dynamics, flow and melt content of the Southern East Pacific Rise upper mantle from teleseismic tomography.

机译：远东层析成像技术对东太平洋南部上升上地幔的动力学，流动和熔体含量的分析。

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摘要

The Mantle ELectromagnetic and Tomography (MELT) Experiment at the super-fast spreading Southern East Pacific Rise (SEPR) was designed to distinguish between passive upwelling in response to basal tractions from the lithosphere, and a more diapiric, focussed upwelling resulting from melt-enhanced buoyancy and viscosity reduction. To distinguish between these models I estimate the distribution of melt and temperature anomalies beneath the SEPR using teleseismic P and S phases recorded on the MELT seismic array. The non-linear tomographic inversion for VP, VS and anisotropy variations includes an a priori model for the mantle flow-induced seismic anisotropy, constraints on smoothness, minimum norm, coupling between VP and VS , and a grid search for the best anisotropy. Shear wave splitting measurements also constrain the anisotropy. The best fitting models have anisotropy with the symmetry axis horizontal or dipping shallowly to the west (30°), and magnitudes of VP and VS anomalies approximately 3.7% and 4.7%, respectively. These translate to melt fractions no greater than .013 or temperature variations no greater than 150°C beneath the rise, using relations I estimated for this purpose. The broad distribution (>100 km) of low velocities favors models of passively driven mantle flow. The orientation of the anisotropy favors shallow return flow owing to a 32 mm/yr westward migration of the SEPR and proximity of the South Pacific Superswell.; To best infer melt fraction from seismic velocity, I developed quantitative models of seismic wave propagation through upper mantle partial melts. The elastic effects are estimated with finite element representations of grain-scale laboratory-derived melt geometries. Two- and three-dimensional deformation simulations show that the shear modulus is sensitive to melt inclusion geometry and organization. The anelastic effects are modeled analytically as ellipsoidal pores connected by tubes. Melt moves through the tubes in response to variable compression of the ellipsoids from seismic excitation. The results indicate that the relaxation occurs so rapidly that, in the seismic band, little or no attenuation results. Seismic velocities are reduced by at least 3.6% and 7.9% per percent melt for P and S waves, respectively.; This dissertation contains both my previously published and co-authored materials and unpublished co-authored materials.
机译：在超快速扩展的东南太平洋上升带（SEPR）上进行的地幔电磁和断层成像（MELT）实验旨在区分响应岩石层基础牵引的被动上升流和由于熔融增强而导致的更加尖锐的集中上升流浮力和粘度降低。为了区分这些模型，我使用记录在MELT地震阵列上的远震P和S相估计了SEPR下熔体和温度异常的分布。 VP，VS和各向异性变化的非线性层析成像反演包括地幔流诱发的地震各向异性的先验模型，对光滑度的约束，最小范数，VP和VS之间的耦合以及网格搜索的最佳各向异性。剪切波分裂测量也限制了各向异性。最佳拟合模型具有各向异性，其对称轴水平或向西倾斜（<30°），且VP和VS异常的幅度分别约为3.7％和4.7％。使用我为此目的估算的关系，这些值转化为在上升以下的熔融分数不大于0.013或温度变化不大于150°C。低速的广泛分布（> 100 km）有利于被动驱动的地幔流模型。各向异性的取向有利于浅回流，这是由于SEPR向西迁移32毫米/年以及南太平洋超涌浪的邻近。为了最好地从地震速度推断熔体分数，我建立了地震波通过上地幔部分熔体传播的定量模型。用晶粒度实验室衍生的熔体几何形状的有限元表示来估计弹性效应。二维和三维变形仿真表明，剪切模量对熔体夹杂物的几何形状和组织敏感。非弹性效应被解析为通过管道连接的椭圆孔。熔体在管道中移动，以响应地震激励引起的椭球体的可变压缩。结果表明，弛豫发生得如此之快，以致在地震带中几乎没有衰减，甚至没有衰减。对于P波和S波，地震速度分别降低了至少3.6％和7.9％。本文既包含我以前发表和共同创作的材料，也包含未发表的共同创作的材料。

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  • 作者

    Hammond, William Charles.;

  • 作者单位

    University of Oregon.;

  • 授予单位 University of Oregon.;
  • 学科 Geophysics.; Physical Oceanography.
  • 学位 Ph.D.
  • 年度 2000
  • 页码 151 p.
  • 总页数 151
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地球物理学;海洋物理学;
  • 关键词

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