Abstract

Crustal-penetrating seismic reflection data across the ultrahigh-pressure (UHP) Dabie Shan orogen show that the Yangtze craton was subducted beneath the Sino-Korean craton, forming a bivergent orogenic fabric strikingly similar to “normal” (non-UHP) collision belts. Hence preservation of UHP minerals (coesite and diamond) may be unrelated to differences between collisional histories, but may be due to opportunities for subsequent intracrustal uplift of material that is routinely returned from mantle depths into the lower crust in most collisional orogens. Only a narrow channel (≤5 km) now exists from the mantle into the crust through which UHP material was returned to lower-crustal depths as thin slabs. We image the Dabie Shan as a crustal-scale dome formed during postcollisional intracrustal uplift by core-complex–type exhumation of the lower crust, tectonically unrelated to the earlier exhumation from >100 km to <35–40 km.

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