Abstract
We investigate the conditions under which magma prefers to migrate through the crust via a dike or a conduit geometry. We performed a series of analogue experiments, repeatedly injecting warm, liquid gelatin, into a cold, solid gelatin medium and allowing the structure to evolve with time. We varied the liquid flux and the time interval between discrete injections of gelatin. The time interval controls the geometry of the migration, in that long intervals allow the intrusions to solidify, favoring the propagation of new dikes. Short time intervals allow the magma to channelize into a conduit. These times are characterized by the Fourier number (Fo), a ratio of time and thermal diffusion to dike thickness, so that long times scales have Fo > 102 and short time scales have Fo < 100.="" between="" these="" time="" scales,="" a="" transitional="" behavior="" exists,="" in="" which="" new="" dikes="" nest="" inside="" of="" previous="" dikes.="" the="" flux="" controls="" the="" distance="" a="" dike="" can="" propagate="" before="" solidifying,="" in="" that="" high="" fluxes="" favor="" continual="" propagation,="" whereas="" low="" fluxes="" favor="" dike="" arrest="" due="" to="" solidification.="" for="" vertically="" propagating="" dikes,="" this="" indicates="" whether="" or="" not="" a="" dike="" can="" erupt.="" a="" transitional="" behavior="" exist,="" in="" which="" dikes="" may="" erupt="" at="" the="" surface="" in="" an="" unstable,="" on‐and‐off="" fashion.="" we="" supplemented="" the="" experimental="" findings="" with="" a="" 2‐d="" numerical="" model="" of="" thermal="" conduction="" to="" characterize="" the="" temperature="" gradient="" in="" the="" crust="" as="" a="" function="" of="" intrusion="" recurrence="" frequency.="" for="" very="" infrequent="" intrusions="" (fo=""> 104 to 105) all thermal energy is lost, while more frequent intrusions allow heat to build up nearby.