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Flow banding is a geological term to describe bands or layers that can sometimes be seen in rock that formed frommagma (molten rock).[1]
Flow banding is caused by friction of the viscous magma that is in contact with a solid rock interface, usually the wall rock to an intrusive chamber or, if the magma is erupted, the surface of the Earth across which thelava is flowing.
The friction and viscosity of the magma causesphenocrysts andxenoliths within the magma or lava to slow down near the interface and become trapped in a viscous layer. This forms laminar flow, which manifests as a banded, streaky appearance.
Flow banding also results from the process offractional crystallization that occurs byconvection if the crystals that are caught in the flow-banded margins are removed from the melt. This can change the composition of the melt in large intrusions, leading to differentiation.
Inlayered intrusions, flow banding can occur with crystalaccumulation, forming pseudo-sedimentary structures.
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