On-fault processes during earthquakes contribute to seismic rupture propagation and slip. Here we investigate clast fragmentation in an experimental pseudotachylyte (solidified seismic melt) produced with a rotary shear machine. We slid for 0.44 m (corresponding to Mw ≥ 6 earthquakes), at slip rates > 1 m/s, pre-cut samples of quartz + phyllosilicates + plagioclase + sillimanite + garnet -bearing ultramylonite, that hosts pseudotachylytes in nature. The ultramylonite minerals extensively preserved as clasts in the experimental pseudotachylyte are quartz, plagioclase, and sillimanite. Garnet is scarcely preserved, despite having a melting temperature similar to plagioclase, probably due to having low thermal shock resistance. This selective clast survival is identical to the one found in the natural pseudotachylytes. Based on these experimental observations and assuming non-equilibrium melting, the preservation of a mineral, as a clast, in the melt appears to be controlled by its thermal shock properties as well as by its melting temperature. Since the mechanical effects of rupture propagation in these experiments were negligible, we conclude that, for Mw ≥ 6 earthquakes, (i) frictional slip and heating of the slipping zone plus (ii) thermomechanical properties of minerals, rather than fault rupture processes, control mineral comminution and clast survival in frictional melts.

地震中的断层过程会导致地震破裂的传播和滑动。在这里，我们研究了用旋转剪切机生产的实验假速溶液（凝固的地震熔体）中的碎裂碎片。我们以大于1 m / s的滑动速率滑动了0.44 m（对应于Mw≥6地震），预先切割了石英+层状硅酸盐+斜长石+硅线石+石榴石+含石榴石的超mylonite样品，这些样品自然含有假速溶质。在实验假速溶物中作为碎屑广泛保存的超ultra石矿物为石英，斜长石和硅线石。石榴石几乎没有保存，尽管其熔化温度与斜长石相似，可能是由于其耐热冲击性较低。这种选择性的碎片生存与在天然假速溶菌中发现的相同。基于这些实验观察结果，并假设非平衡熔融，矿物质作为熔渣在熔体中的保存似乎受其热冲击性能以及熔融温度的控制。由于在这些实验中破裂传播的机械效应可以忽略不计，因此我们得出结论，对于Mw≥6级地震，（i）滑动带的摩擦滑移和加热，以及（ii）矿物的热机械性质，而不是断层破裂过程控制矿物质的粉碎和碎屑在摩擦熔体中的存活。