美国莱斯大学Brandon Schmandt团队研究了黄石岩浆系统的一个富含挥发性物质的尖顶。这一研究成果于2025年4月16日发表在《自然》杂志上。

危险火山系统的稳定性受到最高岩浆储存深度和挥发性出溶的强烈影响。尽管有大量证据表明黄石火山口下方存在上地壳岩浆储层，但其深度和顶部的性质并没有得到很好的限制。新的可控震源地震成像照亮了东北火山口下方约3.8公里处岩浆储层的一个尖锐反射帽。岩浆上升到如此低的压力预计会驱动挥发性出溶，并可能在储层顶部附近局部积聚气泡，但这一过程通常隐藏在当代火山系统中。

黄石岩浆储层尖锐顶部的纵波和P-to-S波反射表明，超临界流体和岩浆的混合物填充了地震层析成像的约3-8km深的低剪切速度层顶部的孔隙空间。结果与上地壳储层出溶气泡的部分保留一致，该储层有来自挥发性富集地幔源的持续岩浆供应。

气泡积聚最终可能导致储层不稳定，但目前储层顶部地震估计的气泡体积分数低于流纹岩喷发前条件的典型估计，热液系统的测量记录了大量岩浆挥发物逃逸到地表。根据对岩浆储层富含晶体（孔隙度小于30%）的估计，研究组推断岩浆储层处于有效气泡上升到热液系统的稳定状态，动态建模有利于通道化气泡逃逸，防止不稳定。

附：英文原文

Title: A sharp volatile-rich cap to the Yellowstone magmatic system

Author: Duan, Chenglong, Song, Wenkai, Schmandt, Brandon, Farrell, Jamie, Lumley, David, Fischer, Tobias, Worthington, Lindsay Lowe, Lin, Fan-Chi

Issue&Volume: 2025-04-16

Abstract: The stability of hazardous volcanic systems is strongly influenced by the uppermost magma storage depth and volatile exsolution1,2,3. Despite abundant evidence for an upper crustal magma reservoir beneath Yellowstone caldera4,5,6,7, its depth and the properties at its top have not been well constrained. New controlled-source seismic imaging illuminates a sharp reflective cap of the magma reservoir approximately 3.8km beneath the northeastern caldera. Magma ascent to such low pressure is expected to drive volatile exsolution and potentially localized accumulation of bubbles near the top of the reservoir8,9, but this process typically remains hidden in contemporary volcanic systems. P-wave and P-to-S-wave reflections from the sharp top of the Yellowstone magma reservoir indicate that a mixture of supercritical fluid and magma fills the pore space at the cap of the approximately 3–8-km-deep low-shear-velocity layer imaged by seismic tomography6,7. The results are consistent with partial retention of bubbles exsolved from an upper crustal reservoir with ongoing magma supply from a volatile-enriched mantle source. Bubble accumulation can eventually lead to reservoir instability2,8, but the bubble volume fraction seismically estimated at the top of the reservoir today is lower than typical estimates of pre-eruptive conditions for rhyolites1,10,11, and measurements of the hydrothermal system document high fluxes of magmatic volatiles escaping to the surface12,13,14,–15. We infer that the magma reservoir is in a stable state of efficient bubble ascent into the hydrothermal system on the basis of estimates that it is a crystal-rich (less than 30% porosity) reservoir for which dynamic modelling favours channelized bubble escape that prevents instability8.

DOI: 10.1038/s41586-025-08775-9

Source: https://www.nature.com/articles/s41586-025-08775-9