Kuritani Takeshi, Xia Qun-Ke, Kimura Jun-Ichi, Liu Jia, Shimizu Kenji, Ushikubo Takayuki, Zhao Dapeng, Nakagawa Mitsuhiro, Yoshimura Shumpei
Graduate School of Science, Hokkaido University, Sapporo, Japan.
School of Earth Sciences, Zhejiang University, Hangzhou, China.
Sci Rep. 2019 Apr 25;9(1):6549. doi: 10.1038/s41598-019-43103-y.
Magmatism at some intraplate volcanoes and large igneous provinces (LIPs) in continental areas may originate from hydrous mantle upwelling (i.e. a plume) from the mantle transition zone (MTZ) at 410-660 km depths in the Earth's deep interior. However, the ultimate origin of the magmatism, i.e. why mantle plumes could have been generated at the MTZ, remains unclear. Here, we study the buoyancy of a plume by investigating basalts from the Changbaishan volcano, beneath which a mantle plume from the hydrous MTZ is observed via seismology. Based on carefully determined water contents of the basalts, the potential temperature of the source mantle is estimated to be 1310-1400 °C, which is within the range of the normal upper mantle temperature. This observation suggests that the mantle plume did not have a significant excess heat, and that the plume upwelled because of buoyancy resulting from water supplied from the Pacific slab in the MTZ. Such a hydrous mantle plume can account for the formation of extremely hydrous LIP magmatism. The water was originally sourced from a stagnant slab and stored in the MTZ, and then upwelled irrespective of the presence or absence of a deep thermal plume.
大陆地区一些板内火山和大火成岩省（LIPs）的岩浆作用可能源于地球深部地幔过渡带（MTZ）在410 - 660千米深度处的含水地幔上涌（即地幔柱）。然而，岩浆作用的最终起源，即为何在地幔过渡带会产生地幔柱，仍不清楚。在此，我们通过研究长白山火山的玄武岩来探讨地幔柱的浮力，通过地震学观测发现该火山下方存在来自含水地幔过渡带的地幔柱。基于对玄武岩含水量的精确测定，源区地幔的潜在温度估计为1310 - 1400℃，这处于正常上地幔温度范围内。这一观测结果表明，地幔柱并没有显著的过热现象，其上升是由于地幔过渡带中太平洋板块提供的水所产生的浮力。这样一个含水地幔柱可以解释极度含水的大火成岩省岩浆作用的形成。这些水最初来源于停滞的板块并储存在地幔过渡带，然后无论深部热地幔柱是否存在都会上涌。
