Basaltic crystal cargoes often preserve records of mantle-derived chemical variability that have been erased from their carrier liquids by magma mixing. However, the consequences of mixing between similarly primitive but otherwise chemically variable magmas remain poorly understood despite ubiquitous evidence of chemical variability in primary melt compositions and mixing-induced disequilibrium within erupted crystal cargoes. Here we report observations from magma–magma reaction experiments performed on analogues of primitive Icelandic lavas derived from distinct mantle sources to determine how their crystal cargoes respond to mixing-induced chemical disequilibrium. Chemical variability in our experimental products is controlled dominantly by major element diffusion in the melt that alters phase equilibria and triggers plagioclase resorption within regions that were initially plagioclase saturated. Isothermal mixing between chemically variable basaltic magmas may therefore play important but previously underappreciated roles in creating and modifying crystal cargoes by unlocking plagioclase-rich mushes and driving resorption, (re-)crystallisation and solid-state diffusion.

玄武岩晶体货物通常保存着地幔衍生的化学变异性记录，这些化学变异性已被岩浆混合从其载液中抹去。然而，尽管无处不在的证据表明初级熔体成分的化学变异性和喷发的晶体货物中的混合引起的不平衡，但对类似原始但化学变化不同的岩浆之间混合的后果仍然知之甚少。在这里，我们报告了对来自不同地幔来源的原始冰岛熔岩类似物进行的岩浆-岩浆反应实验的观察结果，以确定它们的晶体货物如何对混合引起的化学不平衡做出反应。我们实验产品中的化学变异性主要由熔体中的主要元素扩散控制，该扩散改变相平衡并触发最初斜长石饱和区域内的斜长石吸收。因此，化学变化的玄武质岩浆之间的等温混合可能在通过解锁富含斜长石的糊状物和驱动吸收、（再）结晶和固态扩散来产生和改变晶体货物方面发挥重要但以前被低估的作用。