同济大学Jiaji Xi团队在研究倒塌碎片落入浅下地幔的南非太古代克拉通的改造中取得新进展。相关论文于2024年3月19日发表在《地质学》杂志上。

研究展示了非洲南部第一个P波径向各向异性层析成像(使用模型SA-RAnis2024)，揭示了保留的西北和修改的东南Kalahari克拉通根的对比特征。据研究人员推断，经过改造的克拉通岩石圈的碎片落入了下地幔浅层，并在那里观察到孤立的高速异常的地震证据。

研究人员在Kalahari克拉通的西南边缘探测到了一个高速异常，基于板重构Kalahari克拉通可能在大约ca.60Ma从津巴布韦克拉通东南部分离。通过大规模的地幔对流作用，部分破碎板块被带回到浅层，并有助于较年轻岩石圈的地球化学非均质性。

据悉，近30年以来，人们已经在下地幔中探测到了俯冲板块，但对下地幔中是否存在倒塌的克拉通板块仍然知之甚少，研究也不充分。

附：英文原文

Title: Modification of Archean cratons in southern Africa with foundered segments dropped into the shallow lower mantle

Author: Jiaji Xi, Youqiang Yu, Dapeng Zhao, Jiashun Hu

Issue&Volume: 2024-03-19

Abstract: Subducted slabs have been detected in the lower mantle for almost 30 years, yet the presence of foundered cratonic segments in the lower mantle is still unclear and inadequately investigated. We present the first P-wave radial anisotropy tomography of southern Africa (our model SA-RAnis2024), which reveals a contrasting feature of preserved northwest and modified southeast Kalahari cratonic root. Segments from the modified cratonic lithosphere are inferred to have dropped into the shallow lower mantle where seismic evidence of isolated high-velocity anomalies are observed. We detect such a high-velocity anomaly under the southwest margin of the Kalahari craton, which possibly detached from the southeast Zimbabwe craton at ca. 60 Ma based on plate reconstructions. Foundered segments can be partially brought back up to shallow depths, and contribute to the geochemical heterogeneity of younger lithosphere, through large-scale mantle convection.

DOI: 10.1130/G52023.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52023.1/636592/Modification-of-Archean-cratons-in-southern-Africa