]> Back-arc basins (or retro-arc basins) are geologic features, submarine basins associated with island arcs and subduction zones. They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. [Wikipedia] A forearc is a depression in the sea floor located between a subduction zone and an associated volcanic arc. It is typically filled with sediments from the adjacent landmass and the island arc in addition to trapped oceanic crustal material. [Wikipedia] The remnant arc is what is left on the rear side of the speading zone as athe basin broadens. [Wikipedia] In a Back-arc basin the arc axis is the line where spreading occurs on the overlying plate of the subduction zone. [Wikipedia] Orogeny refers to natural mountain building, and may be studied as (a) a tectonic structural event, (b) as a geographical event, and (c) a chronological event. Orogenic events (a) cause distinctive structural phenomena and related tectonic activity, (b) affect certain regions of rocks and crust, and (c) happen within a specific period of time. [Wikipedia] The process in which mountains begin to collapse under their own weight and spread out laterally.