John Wakabyashi on the Franciscan Complex

Glossary

accretionary prism – wedge-shaped pile of material, mostly consisting of soft sediment, that is thought to have been scraped off a downgoing plate at a subduction zone.

corner flow model – a simple model for the flow of low-viscosity material in an accretionary prism in which material flows down along the base of the prism, driven by drag of the subducting plate, before turning upwards at the bottom corner of the wedge.

channel flow model – an alternative to the corner flow model in which flow within the prism is confined to a narrow channel adjacent to the subducting plate.

chert - fine-grained, noncrystalline sedimentary rock made up of silicon dioxide; flint.

clastic sedimentary rock - rocks composed of fragments, or clasts, of pre-existing minerals and rock.

eclogite - metamorphic rock containing granular minerals formed at depth, typically including garnet, omphacite (a pyroxene), and glaucophane (an amphibole).

imbricate stack - stacked-up, fault-bounded sections of an accretionary prism.

mega-movement - movements along major faults that bound kilometer-scale blocks of material.

mélange – tracts of chaotic deposits, consisting of a disrupted matrix of either clay or serpentinite with scattered blocks of other sediments, basalts, and metamorphosed oceanic crust.

pelagic sediment - fine-grained sediment (organic and inorganic) that settles in the open sea.

radiolaria - protozoa with intricate mineral skeletons made of silica.

return flow - subducted material that has turned around and flowed back up towards the surface.

subduction erosion - the loss of crust from an overriding tectonic plate at a subduction zone.