Abstract:

The petrogenesis of the extensive Early Cretaceous magmatism in Gangdese Belt and how the tectonic units correlate to the east have long been subjects of debateTo explore these issues, we performed zircon SHRIMP UPb dating and zircon Hf isotopic determination on a dioritic dike from the Ranwu Pluton in Eastern Gangdese, TibetZircons from a diorite sample yield a crystallization age of (1142±09) Ma, identical to the monzogranite of the Ranwu PlutonZircon Hf isotopic compositions of the diorite sample are heterogeneous with  εHf(t) values ranging from -42 to +49, corresponding to the Hf isotopic crustal model ages (TCDM) of 085144 GaThe dioritic sample has εNd(t) value of -47 with twostage model age (TDM2) of 129 Ga, within the range of the zircon Hf isotope model ageThe contemporaneous dioritic dike (and enclave) and the host monzogranite, along with the heterogeneous Hf isotopic compositions indicate the presence of an important magma mixing in Ranwu Area at ~115 MaThis finding, in combination with the Hf isotopic crustal model ages recently reported in other places in the Gangdese Belt, suggest that the Ranwu Area could be correlated with the Middle Gangdese Belt rather than the Northern Gangdese Belt as previously thought.

Key words: zircon U-Pb age; zircon Hf isotope; magma mixing; Ranwu Pluton; Eastern Gangdese; Tibet