Age, trace elements and Hf-isotope composition of zircon in eclogites from the sulu UHP belt, East-Central China: Neoproterozoic intrusion and subsequent Paleozoic and Early Mesozoic metamorphism

Abstract

The Sulu (苏鲁)-Dabie (大别) orogen in East-Central China formed during the subduction and collision of the Yangtze block with the North China block in Early Mesozoic (240–225 Ma). Constraints on the nature and derivation of eclogites, which are a significant component of the orogen, can provide useful information about subduction-zone metamorphism and crust-mantle interaction. The U-Pb ages, Hf-isotope ratios and trace-element compositions of zircons in eclogites from the Jiangzhuang (蒋庄) (Jiangsu (江苏) Province) and Rongcheng (荣成) (Shandong (山东) Province) areas indicate that the protoliths of the eclogites derived from ultramafic-mafic complexes or mafic intrusion in the subducted continental lithosphere. The upper intercept age of 852±10 Ma and high ɛHf (up to 14.7) of the Neoproterozoic zircons in a Jiangzhuang sample indicate that the protoliths represent products of the Neoproterozoic addition of juvenile materials to the older (i.e., Paleo-Mesoproterozoic) continental crust. The zircon ages of eclogites from both localities mainly record the Triassic (230–220 Ma) metamorphism, consistent with the formation of the Sulu orogen in Early Mesozoic. The lower intercept age of 316±4 Ma in a Jiangzhuang sample suggests that thermal activity relating to the paleo-Tethyan in Late Carboniferous also affected the eclogitic protolith.