Accretionary orogens form along continental margins where oceanic lithosphere is subducted. They are primary sites of juvenile continental crust production and have been active on Earth since the earliest Archean. Orogen lifetimes expressed as accretion intervals range from 50 to over 300 m.y. The short duration of Late Archean accretionary orogens (<70 m.y.) may reflect the short duration of a global mantle plume event at 2.7 and 2.5 Ga. Although there is no simple relationship between the onset or duration of accretionary orogens and the supercontinent cycle, many postArchean orogens terminate with continent-continent collisions during supercontinent assembly. Average terrane lifespan is typically 100-200 m.y. in post-1 Ga orogens, 50-100 m.y. in pre-1 Ga Proterozoic orogens, and 70-700 m.y. in Archean orogens. Accretionary orogens can be grouped into two end members: simple orogens containing chiefly juvenile terranes with lifespans of <100 m.y., and complex orogens with both juvenile accreted components and exotic microcratons, with terrane lifespans of ≥100 m.y. Terrane lifespan is controlled by (1) terrane tectonic setting, (2) complexity of precollisional terrane history, (3) availability of continental crust on Earth, and (4) plate history of ocean basins adjacent to accretionary orogens. Average accretion rates in accretionary orogens are 70 to 150 km 3/km/m.y. in Phanerozoic orogens and 100 to 200 km 3/km/m.y. in Precambrian orogens. Some orogens at 2.7 Ga have unusually high accretion rates greater than 300 km3km/m.y., which may reflect a global mantle plume event. Production rates of juvenile crust in accretionary orogens are typically 10% -30% lower than total accretion rates, but can be up to 50% lower in Phanerozoic orogens.
- Accretionary orogen
- Juvenile crust