Zircon U-Pb Ages and Hf Isotopes of Neoproterozoic Meta-Igneous Rocks in the Liansandao Area,Northern Sulu Orogen,Eastern China,and the Tectonic Implications

The Sulu Orogen preserves the Neoproterozoic tectonic-magmatic events,corresponding to the breaking up of the Rodinia supercontinent. The ages and petrogenesis of meta-igneous rocks in the Liansandao area in the northern Sulu Orogen are not well-constrained. This study reports zircon U-Pb ages and Hf isotopes of these rocks from the Liansandao area. Three meta-igneous rock samples give similar weighted mean 206 Pb/238 U ages of 744±11,767±12,and 762±15 Ma,respectively,indicating the Neoproterozoic crystallization ages. These rocks formed coevally with the Wulian and Yangkou intrusions that located along the Yantai-Qingdao-Wulian fault zone. The Neoproterozoic ages indicate that the meta-igneous rocks from the Liansandao area have affinity to the Yangtze Block. The three samples have εHf(t) values of-7.2–-10.5,-6.0–-17.5,and-6.8–-12.0,respectively. These negative εHf(t) values indicate a primarily crustal source. However,the widely various εHf(t) values that are higher than the continental crust,suggesting magma mixing between mantle-derived materials and the continental crust or source heterogeneity. Combined with the Hf model ages and geochemical characteristics,the monzodiorite(sample LSD-2) is most likely to be mantle-derived magma then interacted with ancient continental crust,and the granitic protolith(samples LSD-1 and LSD-3) in the Liansandao area might derive from the re-melting of a Paleoproterozoic continental crust at ～750 Ma,resulting from the upwelling and underplating of mantle-derived magma formed in an extensional setting due to the break-up of the Rodinia supercontinent.