WHAT BROUGHT THEM UP - EXHUMATION OF THE DABIE-SHAN ULTRAHIGH-PRESSURE ROCKS

Metamorphic coesite and diamond in the Dabie Shan, eastern China, test ify to subduction of continental crust to >100 km depth. Exhumation of these ultrahigh-pressure rocks through the crust encompassed two stag es. (1) South-dipping foliation, southeast-plunging stretching lineati on, lineation-parallel isoclinal folds, and boudins indicate extreme s ubhorizontal shortening and subvertical extension during top-to-northw est shearing at 200-180 Ma. Syntectonic recrystallization occurred at eclogite and amphibolite facies temperatures and at pressures below co esite stability. (2) Northwest-southeast subhorizontal extension from 133 to 122 Ma was concentrated within an asymmetric structural dome in a magmatic complex that forms the northern half of the Dabie Shan. Pl uton cores at deep structural levels have weak hypersolidus fabrics, a nd pluton carapaces are mylonitic gneisses formed at upper amphibolite facies conditions. Deformation is concentrated in greenschist facies mylonites and ultramylonites along the Xiaotian-Mozitang detachment fa ult at the northern topographic limit of the Dabie Shan. Our preferred exhumation model involves two stages: Triassic indentation-vertical e xtrusion and erosion-followed by Cretaceous plate margin transtension.