Zq. Zhong et al., Major constituents of the dabie collisional orogenic belt and partial melting in the ultrahigh-pressure unit, INT GEOL R, 43(3), 2001, pp. 226-236
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.