Molten core model for Hawaiian rift zones

Abstract

Kilauea volcano's East Rift Zone (ERZ) is extraordinary in that abundant lateral dike intrusions and rift zone widening associated with seaward slip of the south flank over a basal fault may have allowed an extensive molten core to develop. The rift zones of Mauna Loa and the Southwest Rift Zone (SWRZ) of Kilauea do not appear to have such extensive molten cores, perhaps because of a diminished role of flank slip. A molten core may efficiently convey pressure and transport magma to distant sites along the rift zone. This concept helps to explain the long, low profile of Kilauea as viewed along the axis of the ERZ. The combined influence of a molten core and flank slip helps to explain the varied repertoire of magmatic events at Kilauea. I propose that the 1975 M 7.2 earthquake marked a fundamental change of activity at Kilauea, from shallow dike injection above the molten core and largely effusive edifice growth, to chiefly endogenous growth by deep dike intrusion below the molten core. Dike intrusion slowed during the 1983–1991 Pu'u O'o eruption sequence, because inflation of the magmatic system—the engine of intrusion and flank slip processes—was retarded by continuous magma loss via the molten ERZ core to a low-elevation vent site.