Petrographic and SHRIMP studies of zircons from the Caledonian Xiongdian Eclogite, northwestern Dabie Mountains

The Xiongdian eclogite occurring in the Sujiahe tectonic melange zone at Lu oshan County, Henan Province, in the western Dabie Mountains, is typical hi gh-pressure (HP)-ultrahigh-pressure (UHP) and medium temperature eclogite. The occurrence, internal texture and surface characteristics of zircons in eclogite were studied rather systematically petrographically combined with the cathodoluminescence (CL) and scanning electron microscope (SEM) methods . Zircons are mainly hosted in garnet and other metamorphic minerals with s harp boundaries, have a multifaceted morphology and are homogeneous or exhi bit a metamorphic growth texture in the interior, thus indicating that they are the product of metamorphism. SHRIMP analyses give zircon Pb-206/U-238 ages of 335 to 424 Ma and show a certain degree of radiogenic Pb loss; ther efore it may be inferred that the age of 424+/-5 Ma represents the minimum age of a HP-UHP metamorphic age. From the above analyses coupled with previ ous Sm-Nd, Ar-40-Ar-39, U-Pb and Pb-207/Pb-206 age data, it is suggested th at the peak metamorphic age of the Xiongdian eclogite should be between 424 and 480 Ma. This study further validate the view of the existence of a Cal edonian HP-UHP metamorphic event in the western Dabie Mountains.