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Northward extrusion of the ultrahigh-pressure units in the southern Dabie metamorphic belt, east-central China

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Abstract

The Dabie orogenic belt in central China extends along the Triassic suture between the Sino–Korean and Yangtze cratons. The structure of the metamorphic rocks have been investigated in the Shima–Wumiao area near the southeastern end of the Dabie orogenic belt. Detailed mapping revealed that the metamorphic sequence in this area can be subdivided into four subhorizontal lithotectonic units. These units are denoted by I, II, III, and IV in the order of structural bottom to top. Unit I is composed of felsic gneiss, eclogite, and minor pelitic gneiss. Unit II consists of felsic gneiss and eclogite with coesite pseudomorphs. Unit III consists of felsic gneiss, pelitic gneiss, metacarbonate, and eclogite with occasional coesite inclusion. Unit IV is composed of felsic gneiss, amphibolite, and minor pelitic gneiss. Those metamorphic rocks underwent penetrative ductile deformation which is denoted by gently south-dipping or subhorizontal foliation and NNW-trending mineral lineation. Deformation microstructures in oriented samples from Units I and II indicate consistent northward displacements of the hanging wall and those from Units III and IV indicate southward displacements. The subhorizontal structure and opposite shear directions between Units I–II and Units III–IV suggest northward extrusion of UHP metamophic units (II and III). The subduction polarity could be opposite to the extrusion trend. The UHP metamorphism in the Dabie orogenic belt is attributable to southward subduction of the Sino–Korean craton beneath the Yangtze craton.

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