Lin Shu-Chuan, van Keken Peter E
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA.
Nature. 2005 Jul 14;436(7048):250-2. doi: 10.1038/nature03697.
The hypothesis that a single mushroom-like mantle plume head can generate a large igneous province within a few million years has been widely accepted. The Siberian Traps at the Permian-Triassic boundary and the Deccan Traps at the Cretaceous-Tertiary boundary were probably erupted within one million years. These large eruptions have been linked to mass extinctions. But recent geochronological data reveal more than one pulse of major eruptions with diverse magma flux within several flood basalts extending over tens of million years. This observation indicates that the processes leading to large igneous provinces are more complicated than the purely thermal, single-stage plume model suggests. Here we present numerical experiments to demonstrate that the entrainment of a dense eclogite-derived material at the base of the mantle by thermal plumes can develop secondary instabilities due to the interaction between thermal and compositional buoyancy forces. The characteristic timescales of the development of the secondary instabilities and the variation of the plume strength are compatible with the observations. Such a process may contribute to multiple episodes of large igneous provinces.
单一蘑菇状地幔柱头部能在几百万年内形成一个大火成岩省的假说已被广泛接受。二叠纪-三叠纪边界的西伯利亚暗色岩和白垩纪-古近纪边界的德干暗色岩可能在一百万年之内喷发。这些大规模喷发与大规模灭绝事件有关。但最近的地质年代学数据显示，在绵延数千万年的几个溢流玄武岩中，有不止一次主要喷发脉冲，且岩浆通量各不相同。这一观测结果表明，形成大火成岩省的过程比纯粹的热单阶段地幔柱模型所显示的更为复杂。在此，我们展示数值实验，以证明热地幔柱在幔底夹带致密榴辉岩衍生物质时，由于热浮力与成分浮力之间的相互作用，会产生次生不稳定性。次生不稳定性发展的特征时间尺度和地幔柱强度的变化与观测结果相符。这样一个过程可能导致大火成岩省的多幕形成。
