Major constituents of the dabie collisional orogenic belt and partial melting in the ultrahigh-pressure unit

The present constitution and architecture of the Dabieshan orogenic belt is the combined result of Triassic subduction collision, extensional tectonic s postdating the HP and UHP metamorphism, and thermo-tectonic evolution in Mesozoic-Cenozoic time. In addition to Yanshanian and post-Yanshanian magma tic intrusion, volcanic eruption, and basin deposition, lithotectonic const ituents of the Dabie orogenic belt consist mainly of a core complex (CC) un it, an UHP unit, an HP unit, an epidote-blueschist (EBS) unit, and a sedime ntary cover (SC) unit. Minor mafic-ultramafic plutons were intruded into or preserved within the CC. UHP, HP, or EBS units. Slices of UHP HP, and EBS units are progressively sandwiched between the underlying core complex and the overlying sedimentary cover. The distribution of lithotectonic units is controlled by an extensional tectonic framework, which postdates the colli sional event. The tectonic pattern of the Dabieshan orogenic belt as a whol e is characterized by a general doming, with the development of multi-layer ed detachment zones. The study of partial melting associated with decompressive retrogression in the UHP unit during exhumation of the eclogites provides us with a better understanding of the relationship between eclogites and the surrounding cou ntry rock (so-called UHP gneisses). and the foliated garnet-bearing; granit es (the non-HP country rocks). It supports the "in situ" interpretation. An atexis occurred under conditions of amphibolite-facies metamorphism at lowe r to middle crustal levels. This partial melting associated with decompress ion is one of the most important physico-chemical processes that postdate t he collisional event in the Dabieshan. It signaled the evolution of the def ormation regime from compression to extension, and reflected thinning of th e continental crust and rapid uplift of UHP metamorphic rocks to middle to lower crustal levels by regional-scale extension.