Zircon Lu-Hf isotopic compositions of ultra-high pressure metamorphic rocks from Dabie Terrain,China

Zircon Lu-Hf isotope analyses were carried out for ultra-high pressure(UHP)eclogite,jadeite quartzite and gneiss from Shuanghe,and eclogite and gneiss from Huangzhen,Southern Dabie Terrain by using LA-MC-ICP-MS technique.The results show that eclogites from Shuanghe and Huangzhen and jadeite quartzite have low ~(176)Lu/~(177)Hf and low ~(176)Hf/~(177)Hf ratio,whereas gneisses from two localities have high ~(176)Hf/~(177)Hf,high and spread ~(176)Lu/~(177)Hf compositions.Zircon Hf isotope distributions are mainly depended on the formation age of metamorphic precursor.Metamorphic zircon succeeded basically Hf isotopes of their protolith.Metamorphic growth zircons have relative low ~(176)Lu/~(177)Hf but high ~(176)Hf/~(177)Hf ratio,inherited and re-crystallized protolith zircons have high ~(176)Lu/~(177)Hf and low ~(176)Hf/~(177)Hf ratio.In some cases Hf isotope compositions of metamorphic and inherited zircons are undistinguishable within the same range.It mainly controlled by origin of protolith and zircon ablation during metamorphism.The low Lu/Hf ratio of metamorphic growth zircons were caused by the decreasing of Lu and increasing of Hf,and the high ~(176)Hf/~(177)Hf ratio originated from the addition of high radiogenic ~(176)Hf from other high Lu/Hf minerals evolution.The initial I-If isotope composition ofe_(Hf)and the model age of depleted mantle T_(DM)indicate that their age and origin are all different for metamorphic precursor.The source material of eclogites from Shaunghe show the mixture of magma derived from depleted mantle of 2.5Ga with at least 2.7Ga late Archean crust.The granitic gneiss from Shaunghe has the same age,but different degree of mantle and crust mixing.The material for eclogite precursor from Huangzhen was formed mainly from the recycling of juvenile crust,which was derived depleted mantle with few crust contamination.The gneiss and eclogite from Huangzhen shares the common source material.The material of gneiss precursor from both localities was derived from mixing of weak depleted mantle and old crust.The zircon Lu-Hf isotope of UHP metamorphic rocks from Dabie orogen mainly reflects magmatic activity character and tectonic setting of north margin of Yantze Craton during 0.7 ~ 0.8Ga and 1.8 ~ 1.9Ga.