AN OVERVIEW OF ACCRETIONARY OROGENS

Accretionary orogens form along continental margins where oceanic lithosphere is subducted and they are primary sites of juvenile continental crust production. Orogen lifetimes expressed as accretion intervals range from 50 to over 300 My. The short duration of Late Archean accretionary orogens (< 70 My) may reflect the short duration of one or more global mantle plume events in the late Archean. Although, there is no simple relationship between the onset or duration of accretionary orogens and the supercontinent cycle, many post-Archean orogens terminate with continent-continent collisions during supercontinent assembly. Accretionary orogens are of two types: simple orogens containing chiefly juvenile terranes with lifespans of < 100 My, and complex orogens with both juvenile accreted components and exotic micro-cratons. Terrane lifespans in complex orogens are typically greater than 100 My. Average terrane lifespan is 100 to 200 My in post-1-Ga orogens, 50 to 100 My in pre-1-Ga Proterozoic orogens, and 70 to 700 My in Archean orogens. Terrane lifespan is controlled chiefly by some combination of 1) terrane tectonic setting, 2) complexity of pre-collisional terrane history, 3) availability of continental crust on Earth, and 4) plate history of ocean basins adjacent to accretionary orogens. Average rates of terrane accretion in accretionary orogens are 70 to 150 km3/km/My in Phanerozoic orogens and 100 to 200 km3/km/My in Precambrian orogens. Some orogens at 2.7 Ga have unusually high accretion rates greater than 300 km3/km/My, 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.