Peralkaline rhyolites, associated with extensional tectonic settings, are medium to low viscosity magmas that often produce eruptive styles ranging from effusive to highly explosive eruptions. The role of pre-eruptive conditions and crystallization kinetics in influencing the eruptive style of peralkaline rhyolitic magmas has been investigated and debated considering equilibrium conditions. However, experimental constraints on the effect of disequilibrium in crystallization in such magmas are currently lacking in the literature. Therefore, we performed isobaric cooling experiments to investigate alkali feldspar crystallization kinetics in peralkaline rhyolitic melts. Experiments were performed under water-saturated, water-undersaturated, and anhydrous conditions between 25 and 100 MPa, at 670–790°C and with experimental durations ranging from 0.5 to 420 h. Here we present the first data on crystallization kinetics of alkali feldspar, which is the main crystal phase in peralkaline rhyolitic melts, in order to improve our understanding of the evolutionary timescales of these melts and their ability to shift between effusive and explosive activity. Our experimental results indicate that the alkali feldspar nucleation delay can range from hours to several days as a function of undercooling and H₂O content in the melt. Thus, a peralkaline rhyolitic magma can be stored at the pre-eruptive conditions for days without important variations of its crystal fraction. This suggests that crystallization may not necessarily play the main role in triggering fragmentation during explosive eruptions of peralkaline rhyolitic magmas.

与伸展构造环境相关的高碱性流纹岩是中等至低粘度的岩浆，经常产生喷发样式，从喷发性到高度爆炸性喷发。在平衡条件下，对喷发前条件和结晶动力学在影响碱性碱性流纹岩浆喷发样式中的作用进行了研究和辩论。然而，目前在文献中缺乏对这种岩浆中结晶中不平衡作用的实验约束。因此，我们进行了等压冷却实验，研究了碱性长石流质熔体中的长石结晶动力学。实验在670–790°C的水饱和，水不饱和和25至100 MPa之间的无水条件下进行，实验持续时间为0。5至420小时。在这里，我们提供了关于碱性长石的结晶动力学的第一个数据，该碱长石是高碱性流纹体熔体的主要晶体相，目的是增进我们对这些熔体的演化时间尺度以及它们在喷射和爆炸活性之间转移的能力的理解。我们的实验结果表明，碱金属长石成核的延迟时间从数小时到数天不等，这是过冷和高温的函数。熔体中₂ O的含量。因此，碱性碱流变岩浆可以在喷发前的条件下保存数天，而其晶体分数没有重要变化。这表明在高碱性流纹岩浆岩的爆发性爆发期间，结晶未必在触发破碎中起主要作用。