Zhou Zhong-Biao, Chen Li-Hui, Huang Zhou-Chuan, Hofmann Albrecht W, Wang Xiao-Jun, Zeng Gang, Bi Ya-Jing, Zhao Jian
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China.
State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China.
Proc Natl Acad Sci U S A. 2025 Jan 7;122(1):e2414632122. doi: 10.1073/pnas.2414632122. Epub 2024 Dec 30.
Subducted plates often stagnate in the mantle transition zone (MTZ), and the fate of the stagnant slabs is still debatable. They may sink into the lower mantle, or remain partially trapped in the MTZ, but it is uncertain whether they can return to the upper mantle. We report geochemical evidence of late-Miocene (~6 Ma) basalts from, and upper mantle seismic evidence beneath Shuangyashan, an area above the slab tear of the stagnant Pacific plate in eastern Asia, to show how the slab returns to the upper mantle from the MTZ. Remarkably high δFe, Gd/Yb and low δMg, Ti/Eu, CaO/AlO values of Shuangyashan basalts suggest that the subducted Pacific oceanic crust had been entrained to their upper mantle source. Therefore, the return of oceanic crust from the MTZ to the upper mantle appears to have been driven by upwelling triggered by tearing of the stagnant slab right beneath this area. Meanwhile, local shear splitting measurements reveal a circular pattern of anisotropy in the upper mantle with delay times diminishing toward the slab tear, suggesting that the slab-fragment-bearing upwelling subsequently turned into lateral flows in the upper mantle, and contributed to a wider intraplate magmatism above the stagnant slab. This finding, together with other widespread intraplate volcanism from eastern Asia, extending for approximately 6,000 km, demonstrates that a subduction-induced tear can lead to the destruction and partial return of stagnant slab material, and thus lead to the cycling of subducted crustal materials and the generation of subduction-induced intraplate magmatism.
俯冲板块常常在地幔过渡带（MTZ）停滞，而停滞板块的命运仍存在争议。它们可能沉入下地幔，或部分滞留在MTZ，但它们能否返回上地幔尚不确定。我们报告了来自东亚停滞太平洋板块板片撕裂上方的双鸭山地区晚中新世（约6 Ma）玄武岩的地球化学证据以及其下地幔地震证据，以展示板块如何从MTZ返回上地幔。双鸭山玄武岩显著高的δFe、Gd/Yb以及低的δMg、Ti/Eu、CaO/Al2O3值表明，俯冲的太平洋洋壳已被卷入其上地幔源区。因此，洋壳从MTZ返回上地幔似乎是由该区域正下方停滞板块撕裂引发的上涌驱动的。同时，局部剪切分裂测量揭示了上地幔中各向异性的圆形模式，延迟时间朝着板片撕裂方向减小，这表明携带板片段的上涌随后在上地幔中转变为横向流动，并促成了停滞板片上方更广泛的板内岩浆作用。这一发现，连同东亚其他广泛分布的板内火山活动（延伸约6000公里），表明俯冲诱导的撕裂可导致停滞板片物质的破坏和部分返回，从而导致俯冲地壳物质的循环以及俯冲诱导的板内岩浆作用的产生。
