Geochronology Analysis Of Zhanjin Formation In Ya Dan, Tibet

The Zhanjin Formation of Yadan area, North Tibet, is a part of Longmocuoshuanghu complex, comprising a series of middle to outer fan sequence of turbidites and minor litharenite and bioclastic limestone lens.The rock of Zhanjin Formation is immature and poorly sorted, defined by high portion and sub-angular detritus, indicating short distance transportation and nearby provenance. The components of detritus are mainly basaltic and minor rhyolitic. And the lack of volcanic and intrusion detritus suggests that Zhanjin formation may sourced directly from the nearby andesitic or mafic magma intrusion and from oceanic mafic island or sea-mountain.U–Pb age data was collected by LA-ICP-MS from detrital zircon in Zhanjin formation. One age group yielding ages between ca. 252.8~314.7 Ma with a ~283 Ma peak can be identified. The age distribution indicates a unimodal source. And the magma event can be constrained in the Permian period. In addition, the 176Hf/177 Hf value of zircons from Zhanjin formation yielded a range between 0.28205 and 0.28259 and the εHf(T) values range between-19.6 and-0.1. The TDM age of the sample yielded a range between 928 Ma and 1721 Ma. The TDM age is much larger than the zircon crystallization age, indicating a reworking with crust material or a rich mantle source, which is also supported by the Epsilon Hf(εHf) plot analysis.The sync-sedimentary fossil of fusulinida and the U–Pb age data within Zhanjin formation show a early Permian age.Above all, given our analysis and the early research about regional mafic magma and ice sea conglomerate, we drew the conclusion that the Zhanjin formation of Ya Dan is not the regional Zhanjin formation and the most likely to Qudi formation involved in proliferation of complex curved block.