dd

Accretionary orogens develop at sites of subduction of oceanic
lithosphere and are characterized by tectonic elements including accretionary
wedges, material offscraped from the subducting and overriding
plates, island arc and back-arc assemblages, ophiolites and ophiolitic
fragments, oceanic plateaus, exotic continental blocks, magmatic and
metamorphic rocks related to ridge subduction, post-accretion granitoid
rocks, metamorphic rocks that reach granulite facies and locally UHP and
UHT assemblages, and deformed sedimentary basins (e.g., Kusky and
Polat, 1999; Cawood et al., 2009). The fate of all accretionary orogens is
to ultimately be involved in a collisional phase when the oceans close
and the bounding continents collide, and this phase of collisional orogenesis
significantly modifies the structure of the original accretionary
orogen, even in some cases leading to complete removal of many parts
of the original orogen by deep subduction, thrusting, crustal shortening,
and associated erosion. The challenge is then, how to recognize the early
accretionary orogenic phase of ancient mountain belts, and to precisely
trace the early tectonic history and crustal growth of these belts. Some
convergent margins are characterized by subduction erosion (e.g., von
Huene and Scholl, 1993; Stern, 2011), whereas others are sites of accretion
of material from the downgoing plate to the overriding plate. In
this paper we focus only on the accretionary orogens, where a record
of subduction is preserved in the accreted material.