Meso- and micro-structures of foliated eclogites in Dabie-Sulu UHP belt and implications for the earliest stages of exhumation of UHP metamorphic rocks: An example from Taohang, southeastern Shandong, China

Abstract

The sub-vertical meso- and micro-structures and fabrics developed in coesite-bearing foliated eclogites in the Taohang (桃行) area, southeastern Shandong (山东), China. The diagnostic structures and fabrics, including penetrative foliation or mylonitic foliation containing mineral and stretching lineations, as well as sheath-like folds, appear to be the development of anastomosing UHP eclogite-facies shear belt arrays hosting massive eclogites. Textural relationships and mineral assemblages indicate that the deformation of foliated eclogites developed closely after the formation of the massive eclogite, prior to the development of the granulite/amphibolite-facies symplectites and coronas, occurring over a very wide pressure range of (31−8)×102 MPa. It presents the structural records of the tectonometamorphic processes as being responsible for the earliest stages of exhumation of the UHP metamorphic rocks. Extensive regional field observations show that the meso- and micro-structures and fabrics recognized in the foliated eclogites at Taohang are remarkably similar or consistent in the whole Dabie (大别)-Sulu (苏鲁) UHP metamorphic belt. This article, thus, supports the idea that earliest stages of exhumation of the UHP metamorphic rocks, from mantle depths to the Moho or the mantle-crust boundary layering, may be attributed mainly to a sub-vertical extrusion and ductile flow along the subduction channel, belonging to a syn-collision exhumation at about 235 to 220 Ma.