Deep mantle structure and origin of Cenozoic intraplate volcanoes in Indochina, Hainan and South China Sea
Deep mantle structure and origin of Cenozoic intraplate volcanoes in Indochina, Hainan and South China Sea
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DOI：
10.1093/gji/ggaa605
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发表时间：
2020-12
影响因子：
2.8
通讯作者：
Dapeng Zhao;G. Toyokuni;K. Kurata
中科院分区：
文献类型：
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作者：
Dapeng Zhao;G. Toyokuni;K. Kurata
印支陆块、南海盆地和雷琼地区（包括雷州半岛和海南岛北方）广泛分布着28.5~<0.1Ma的新生代玄武岩，形成了东南亚玄武岩省（SABP）。这些新生代玄武岩具有共同的岩石学和地球化学特征。然而，关于SABP新生代板内火山作用的成因至今仍存在争议。在这项工作中，我们应用一种新的技术，多尺度全球层析成像研究的全地幔三维P波速度（Vp）结构下的SABP。结果表明，SABP下地幔普遍存在低Vp异常。虽然海南岛下方存在最强的低Vp带，但SABP其他地区的地幔也存在明显的低Vp异常。这些低Vp异常似乎是独立的，而不是来自一个单一的羽。我们认为，在新生代存在一组地幔柱，而不是一个单一的地幔柱，现在可能仍然存在于地幔SABP之下，虽然海南地幔柱可能是最强的。一项地球化学研究表明，海南地幔柱上涌可能正在减缓，并接近耗尽其源区。这一地球化学推断得到了层析图像的支持，显示海南低Vp带在下地幔（700 - 2889 km深度）是弱的和间歇性的。其他SABP新生代火山下的地幔中的低Vp区也很弱，这表明这些地幔柱（如果有的话）也正在死亡或已经死亡。相对于单一的强烟羽，烟羽簇中的每个成员都是弱小的，很难长期存在。SABP被俯冲带包围。SABP之下的热地幔上涌可能是俯冲板片向下塌陷到最低地幔的结果。
Cenozoic basalts with ages ranging from 28.5 to < 0.1 Ma are widely distributed in the Indochina block, the South China Sea basin and the Leiqiong area in South China including the Leizhou Peninsula and the northern Hainan Island, which form the southeastern Asian basalt province (SABP). These Cenozoic basalts share common petrological and geochemical characteristics. However, the origin of the Cenozoic intraplate volcanism in the SABP is still a controversial issue. In this work, we apply a novel technique of multiscale global tomography to study the whole-mantle 3-D P-wave velocity (Vp) structure beneath the SABP. Our results show that low-Vp anomalies prevail in the whole mantle beneath the SABP. Although the strongest low-Vp zones exist beneath Hainan, significant low-Vp anomalies are also visible in the mantle beneath other parts of the SABP. These low-Vp anomalies appear somehow independent, rather than deriving from a single plume. We deem that a cluster of plumes rather than a single plume existed in the Cenozoic and may still exist now in the mantle beneath the SABP, though the Hainan plume may be the strongest one. A geochemical study suggested that the Hainan plume upwelling might be slowing down and close to exhausting its source zone. This geochemical inference is supported by our tomographic images showing that the low-Vp zones under Hainan are weak and intermittent in the lower mantle (∼700–2889 km depths). The low-Vp zones in the mantle beneath other SABP Cenozoic volcanoes are also weak, suggesting that those mantle plumes, if any, are also dying or already dead. As compared with a strong single plume, each member in a plume cluster should be small and weak, and so hard to exist long. The SABP is surrounded by subduction zones. The hot mantle upwelling beneath the SABP might be caused by collapsing of subducted slabs down to the lowermost mantle.