A special feature of the composite Coastal Batholith of Peru is the presence of ring complexes, which suggests a very high-level crustal environment and a direct connection between the magmas of the constituent plutons and caldera-centred volcanicity. The nature of four such complexes is commented on in detail, especially the high degree of structural control of emplacement, the association of mylonites and tuffisites with ring-fractures, the roles of stoping, fluidization and entrainment during the intrusion of ring-dykes, the co-existence of highly mobile magmas, their pulsatory injection, and the connection between these and volcanics of the same general age. Such mechanisms of cauldron subsidence located at the plutonic–volcanic interface operated throughout much of the 70 m.y. history of the batholith.

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