ИСТИНА

Most magmas experience a tortuous and complex journey from their source regions to the surface with the suspended crystals acting as the primary recorders. However, while all crystals are part of the same system, each individual crystal provides a unique record of the sequence of events; crystals arrive in the system at different times and stages, rest in rheologically and thermodynamically (P-T-X) diverse environments, and are not stationary relative to each other. Their stories can be compared to spectators at a sporting event. While all spectators watched the same match in the same venue, each individual leaves with a unique story. Some were close and had a direct view of a specific action, some arrived late and missed a critical play, and some were distracted by local events; but all mixed on exit of the stadium. As petrologists, we piece together magmatic events by conducting crystal exit interviews. In this context, olivine with its inclusions is a special type of spectator; one that shows up early to the game, but potentially forgets quickly -through diffusion- earlier events. Thus, studying olivine populations provides a unique view into the space-time assembly of different parts of a magmatic system. Here, we synthesize our findings from olivines and their inclusions from a number of arc volcanoes to understand how magmas travel through the crust and retain information regarding the key aspects of storage and transport. Some volcanic systems show prolonged storage in chemically buffered conditions predominantly at lower crustal and Moho levels with ensuing fast delivery to the surface, while other systems carry magnesian olivine with preserved dendritic growth features best reconciled with minimal storage in the crust and rapid transport (on the order of the duration of the eruption). When these individual crystal accounts are seen in the context of populations they show that magma systems are open systems that get assembled on eruption and draw from a complex plumbing system at depth – just like spectators from the bleachers, the upper ranks, or the front rows leave the stadium together and mix on exit. Each population may then provide a unique fingerprint for the eruption and potentially the volcano similarly to the differences seen in a Brazilian, an English or a German crowd.