Volcanic eruptions can represent major societal hazards. Placing tighter bounds on the timescales of magmatic processes that precede eruptions is, therefore, important for volcano monitoring and forecasting. Diffusion chronometry, where volcanic crystals that contain chemical gradients are treated as time capsules, allows the timescale of various magmatic processes to be constrained. In this Review, we discuss the basics of diffusion chronometry and describe how re-equilibration via chemical diffusion provides insights into the timescales of magma storage, ascent and eruption. Crystals from mafic volcanoes record timescales of days to years between magma intrusion and eruption, which broadly match those recorded by monitoring data (such as increased seismicity). The timescales recorded in crystals from large silicic calderas, however, are typically longer than those from mafic volcanoes, spanning decades to millennia, but almost two orders of magnitude shorter than the timescales obtained by U-Th isotope disequilibria in zircon. The cause of this discrepancy is debated but likely reflects the protracted magma accumulation and complex thermal history that many crystals experience before eruption. Diffusion chronometry adds the fourth dimension to volcano science (that is, time), and advances in analytical and experimental approaches (such as NanoSIMS) open up new opportunities for understanding magmatic systems.

火山喷发可能代表主要的社会危害。因此，对火山爆发之前的岩浆作用时间范围设置更严格的界限对于火山监测和预报很重要。扩散测年法将包含化学梯度的火山晶体视为时间囊，从而可以限制各种岩浆作用过程的时间尺度。在这篇评论中，我们讨论了扩散年代学的基本原理，并描述了通过化学扩散进行的重新平衡如何提供对岩浆储存，上升和爆发的时间尺度的见解。镁铁质火山的晶体记录了从岩浆侵入到喷发之间几天到几年的时间尺度，这与通过监测数据（例如增加的地震活动）所记录的时间尺度大体上匹配。但是，大型硅质火山口晶体中记录的时间尺度是 它们通常比镁铁质火山的要长，跨越几十年到几千年，但比锆石中U-Th同位素不平衡所获得的时间尺度短将近两个数量级。引起这种差异的原因尚有争议，但可能反映出许多晶体在喷发前经历了长时间的岩浆堆积和复杂的热史。扩散年代计增加了火山科学的第四维度（即时间），分析和实验方法（例如NanoSIMS）的进步为理解岩浆系统开辟了新的机会。引起这种差异的原因尚有争议，但可能反映出许多晶体在喷发前经历了长时间的岩浆堆积和复杂的热史。扩散年代计增加了火山科学的第四维度（即时间），分析和实验方法（例如NanoSIMS）的进步为理解岩浆系统开辟了新的机会。引起这种差异的原因尚有争议，但可能反映出许多晶体在喷发前经历了长时间的岩浆堆积和复杂的热史。扩散年代计增加了火山科学的第四维度（即时间），分析和实验方法（例如NanoSIMS）的进步为理解岩浆系统开辟了新的机会。