Accretionary

Accretionary is an adjective relating to accretion, the gradual growth or buildup of material by the addition of external matter. The term is used across disciplines to describe processes, structures, or phenomena that result from such accumulation.

In geology, accretionary refers to features formed at convergent plate boundaries where sediments and rocks are scraped from the subducting slab and added to the overriding plate. The resulting accretionary prisms or wedges, often included with mélange materials, record subduction dynamics and help explain the growth of continental margins and associated seismic activity.

In astronomy and planetary science, accretionary describes processes by which gravity drives matter to accumulate onto a central body, creating accretion disks around young stars or compact objects. Material spirals inward, releasing energy as radiation; accretion is central to star and planet formation, growth of white dwarfs, neutron stars, or black holes, and to the fueling of active galactic nuclei.

The term also appears in other contexts, reflecting the general principle of growth by accumulation. While the specifics differ, accretionary phenomena share a common theme of material addition governed by forces such as gravity, pressure, and angular momentum.