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

Time: 2024-03-21Views: 16

Jiaji Xi1;Youqiang Yu1;Dapeng Zhao2;Jiashun Hu3

1State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China

2Department of Geophysics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan

3Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen 518055, China

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.

Full Article:https://doi.org/10.1130/G52023.1