Abstract
AbstractThe Dabie–Sulu orogenic belt in east-central China contains one of the largest ultrahigh-pressure (UHP) metamorphic terranes in the world. The UHP eclogites are associated with gneiss, peridotite and marble. But all these rocks underwent in situ UHP metamorphism during the continental collision in the Triassic. Although fluid action is not significant during cold subduction, it becomes prominent during hot exhumation of UHP slices. Whereas the composition of UHP metamorphic rocks is primarily inherited from their protoliths, they were locally modified by partial melting to varying extents. The partial melting of UHP rocks is highly heterogeneous along the collisional orogen, and achieves a maximum during rifting orogeny at the post-collisional stage. This paper outlines the petrographical features and geochemical compositions of UHP metamorphic rocks, and presents an overview of collisional modification and post-collisional reworking of the subducted continental crust. Further discussions are devoted to continental subduction tectonics, as well as to subduction style, subduction polarity and exhumation mechanism. The results also provide insights into the initiation of continental rifting in a Wilson cycle. Consequently, studies of the Dabie–Sulu orogenic belt have contributed greatly to our understanding of tectonic processes, fluid regime and chemical geodynamics in continental subduction zones.
Highlights
The present study found that the composition of UHP metamorphic rocks in the Dabie–Sulu orogenic belt is nearly bimodal in lithochemistry, being mainly felsic and minorly mafic (Fig. 8)
The arc-like trace element distribution patterns are prominent for the UHP gneisses and eclogites in the Dabie–Sulu orogenic belt, which are characterized by an enrichment in lithophile elements (LILEs), Pb and light rare earth elements (LREEs), but a depletion in Nb and Ta relative to heavy rare earth element (HREE) in the primitive mantle-normalized diagram (Figs 11 & 12)
UHP metamorphic slices were detached from the subducting continental lithosphere and exhumed along subduction channels to crustal levels due to the relative buoyancy of low-density continental crust
Summary
The Dabie–Sulu orogenic belt is located between the South China Block and the North China Block (Fig. 1). Except for UHP metasedimentary rocks that have Archean–Paleoproterozoic protoliths, UHP metaigneous rocks in the Dabie–Sulu orogenic belt have Neoproterozoic protolith ages of 780–740 Ma (Zheng et al 2009; Liu & Liou 2011) Partial melting of the UHP metamorphic rocks during exhumation is widespread in the Dabie–Sulu orogenic belt (Zheng et al 2011b; Chen et al 2017; Gao et al 2017a; Xia & Zhou 2017). There are three stages of exhumation for the Dabie–Sulu UHP rocks: (1) early exhumation of the HP blueschist- to eclogite-facies rocks in the Middle Triassic (247–235 Ma) from lower crust depths to upper crust depths; (2) peak exhumation of the UHP eclogite-facies rocks in the Late Triassic (235–220 Ma) from the subarc depths to forearc depths of 40–80 km; and (3) late exhumation of the UHP terranes to upper crust depths in the Early Cretaceous
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
