Pulsed inflation of pahoehoe lava flows: implications for flood basalt emplacement

Dilated fractures in Hawaiian pahoehoe lava flows contain three zones that show the kinematics of inflation. The upper columnar zone forms through thermal contraction prior to inflation, the middle planar zone reflects inflation-induced tension, and the lower banded zone contains evidence of brittle and ductile deformation. The formation of the lower banded zone requires varying strain rates during fracture propagation and is best explained by a model where small pulses of lava inject beneath the cooled flow crust through a network of preferred pathways. We demonstrate via simple models of pipe flow that this inflation mechanism is incapable of producing areally extensive continental flood basalts on Earth, although it may explain related features on large Martian volcanoes. (C) 1999 Elsevier Science B.V. All rights reserved.