The eruption of basaltic magmas dominates explosive volcanism on Earth and other planets within the Solar System. The mechanism through which continuous magma fragments into volcanic particles is central in governing eruption dynamics and the ensuing hazards. However, the mechanism of fragmentation of basaltic magmas is still disputed, with both viscous and brittle mechanisms having been proposed. Here we carry out textural analysis of the products of ten eruptions from seven volcanoes by scanning electron microscopy. We find broken crystals surrounded by intact glass that testify to the brittle fragmentation of basaltic magmas during explosive activity worldwide. We then replicated the natural textures of broken crystals in laboratory experiments where variably crystallized basaltic melt was fragmented by rapid deformation. The experiments reveal that crystals are broken by the propagation of a network of fractures through magma, and that afterwards the fractures heal by viscous flow of the melt. Fracturing and healing affect gas mobility, stress distribution, and bubble and crystal size distributions in magma. Our results challenge the idea that the grain size distribution of basaltic eruption products reflects the density of fractures that initially fragmented the magma and ultimately indicate that brittle fracturing and viscous healing of magma may underlie basaltic explosive eruptions globally.

玄武质岩浆的喷发主导着地球和太阳系内其他行星上的火山爆发。连续岩浆碎裂成火山颗粒的机制是控制喷发动力学和随之而来的危险的核心。然而，玄武质岩浆的碎裂机制仍存在争议，人们提出了粘性机制和脆性机制。在这里，我们通过扫描电子显微镜对七座火山的十次喷发产物进行了结构分析。我们发现被完整玻璃包围的破碎晶体证明了在全球爆炸活动期间玄武岩岩浆的脆性碎裂。然后，我们在实验室实验中复制了破碎晶体的自然纹理，其中可变结晶的玄武岩熔体因快速变形而破碎。实验表明，晶体通过岩浆中裂缝网络的传播而破碎，然后裂缝通过熔体的粘性流动而愈合。压裂和愈合影响岩浆中的气体流动性、应力分布以及气泡和晶体尺寸分布。我们的研究结果挑战了这样一种观点，即玄武岩喷发产物的粒度分布反映了最初破碎岩浆的裂缝密度，并最终表明岩浆的脆性压裂和粘性愈合可能是全球玄武岩爆炸喷发的基础。