Seismic evidence for stratification in composition and anisotropic fabric within the thick lithosphere of Kalahari Craton
Seismic evidence for stratification in composition and anisotropic fabric within the thick lithosphere of Kalahari Craton
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DOI：
10.1002/2013gc004955
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发表时间：
2013-12
期刊：
影响因子：
3.7
通讯作者：
F. Sodoudi;X. Yuan;R. Kind;S. Lebedev;J. Adam;E. Kästle;F. Tilmann
中科院分区：
文献类型：
--
作者：
F. Sodoudi;X. Yuan;R. Kind;S. Lebedev;J. Adam;E. Kästle;F. Tilmann
基于对S接收函数和面波各向异性的联合考虑，我们提出了在卡拉哈里沙漠下存在厚的层状岩石圈的证据。我们的研究结果表明，冻结的各向异性和成分变化可以分别在85和150-200 km的深度产生尖锐的岩石圈中部不连续性（MLD）。我们发现，一个50 km厚的各向异性层，包含3%的S波各向异性，并具有与下面的层不同的快速度轴，可以解释约85 km深度处的第一个MLD。显着的相关性之间的深度明显的边界分离的耗尽和交代岩石圈，从化学层析成像推断，和我们的第二个MLD导致我们将其描述为一个组成的边界，最有可能是由于修改的地幔岩石圈的岩浆渗透。从150到200公里的边界加深与Thabazimbi-Murchison线性（TML）的表面表达在空间上相关，这意味着TML将林波波河的岩石圈与古Kaapvaal河的岩石圈隔离开来。最大的速度对比度（3.6-4.7%）是在位于太古代域和更古老的元古代带之下的260-280 km深处的边界处观察到的。这个边界最有可能代表岩石圈-软流圈边界，它在较年轻的元古代带之下变浅约200公里。因此，喀拉哈里岩石圈可能在其数十亿年的历史中经历了多次强烈的岩浆活动和碰撞裂谷，并在其内部分层中留下了印记。
Based on joint consideration of S receiver functions and surface‐wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen‐in anisotropy and compositional changes can generate sharp Mid‐Lithospheric Discontinuities (MLD) at depths of 85 and 150–200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast‐velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi‐Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The largest velocity contrast (3.6–4.7%) is observed at a boundary located at depths of 260–280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphere‐asthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering.