Syneruptive magma mixing is widespread in volcanic eruptions, affecting explosivity and composition of products, but its evidence in basaltic systems is usually cryptic. Here we report direct evidence of mixing between basanitic and tephritic magmas in the first days of the 2021 Tajogaite eruption of Cumbre Vieja, La Palma. Groundmass glass in tephritic tephra from the fifth day of the eruption is locally inhomogeneous, showing micron-scale filamentary structures of Si-poor and Fe-, Mg-rich melt, forming complex filaments attached to bubbles. Their compositional distribution attests the presence of primitive basanitic magma, with compositions similar to late-erupted melts, interacting with an evolved tephritic melt during the first week of the event. From filament morphology, we suggest their generation by dragging and folding of basanitic melt during bubble migration through melt interfaces. Semi-quantitative diffusion modelling indicates that the filamentary structures are short-lived, dissipating in timescales of tens of seconds. In combination with thermobarometric constraints, we suggest a mixing onset by sub-Moho remobilization of a tephritic reservoir by basanite input, followed by turbulent ascent of a mingled magma. In the shallow conduit or lava fountain, bubble nucleation and migration triggered further mingling of the distinct melt-phases. This phenomenon might have enhanced the explosive behaviour of the eruption in such period, where violent strombolian explosions were common.

共喷岩浆混合在火山喷发中广泛存在，影响爆炸性和产物成分，但其​​在玄武岩系统中的证据通常是神秘的。在此，我们报告了 2021 年拉帕尔马岛 Cumbre Vieja 塔乔盖特火山喷发的最初几天，玄武岩浆和泰火山岩浆混合的直接证据。喷发第五天的火山灰中的基质玻璃局部不均匀，显示出贫硅和富铁、镁熔体的微米级丝状结构，形成附着在气泡上的复杂丝状结构。它们的成分分布证明了原始巴萨尼岩浆的存在，其成分类似于晚喷发的熔体，在事件发生的第一周与演化的软熔岩熔体相互作用。从细丝形态来看，我们建议它们是通过在气泡通过熔体界面迁移过程中拖动和折叠红硅质熔体而产生的。半定量扩散模型表明，丝状结构的寿命很短，在数十秒的时间尺度内消散。结合温压约束，我们建议通过红硅石输入对软熔岩储层进行亚莫霍面再活化，然后混合岩浆湍流上升，从而开始混合。在浅管道或熔岩喷泉中，气泡成核和迁移引发了不同熔体相的进一步混合。这种现象可能增强了该时期火山喷发的爆炸行为，剧烈的斯特龙博式爆炸很常见。