南方科技大学史亚男和Morgan, Jason P.近日的研究揭示了冈瓦纳洪水玄武岩与地幔柱诱发的岩石圈不稳定相关。相关论文于2024年3月12日发表于国际顶尖学术期刊《美国科学院院刊》杂志上。

最近的地震层析模型表明，在前冈瓦纳大陆之下，在约600km深度至少存在5个水平快波异常，这些异常似乎与板块俯冲无关，包括与约134Ma的巴拉纳洪水玄武岩事件和约66Ma的德干圈闭事件相关的分层位置的快速构造。这些快波异常通常位于原冈瓦纳地下500至700km深处的宽慢地震波速度主干之上，慢波异常在其周围形成分支。

数值实验表明，脱层的岩石圈在地幔柱上方的过渡带和中地幔中趋于停滞，并在此形成后续的地幔柱上升流。对于热柱而言，受其影响的脱层过程中产生的熔体体积很容易达到约2-4×10⁶km³，与德干圈闭的玄武岩喷发体积一致。

这些地震和数值证据表明，观测到的前洪水玄武岩位置下的高波中地幔异常，是前大陆岩石圈的脱层碎片，而在次大陆热柱存在下的岩石圈脱层事件，诱发了与冈瓦纳大陆多个分裂阶段相关的几个大陆洪水玄武岩。这些地幔柱的持续上升流也可能将中地幔中的次大陆岩石圈卷走，将其独特的地球化学信号带到环绕非洲南部和西部的现代海洋中部扩张中心。

据介绍，大陆岩石圈地幔的分层在几个大陆的下面有很好的记录。然而，不同于在上地幔和中地幔中具相当好地成像的俯冲板块，被移除的大陆岩石圈的命运很少被注意到。

附：英文原文

Title: Gondwanan flood basalts linked seismically to plume-induced lithosphere instability

Author: Shi, Yanan, Morgan, Jason P.

Issue&Volume: 2024-3-12

Abstract: Delamination of the continental lithospheric mantle is well recorded beneath several continents. However, the fate of the removed continental lithosphere has been rarely noted, unlike subducted slabs reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5 horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500 to 700 km depths beneath former Gondwana, with slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone and mid-mantle above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2 to 4×10⁶ km³, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high-wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

DOI: 10.1073/pnas.2320054121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2320054121