SHRIMP U-Pb Ages of the Abagong Granites in the Altay Orogen and Their Geological Implications

Numerous granitic plutons occur in China's Altay orogen.The authors made zircon SHRIMP U-Pb dating of two gneissic granites in Abagong area,which yielded ages of(462.5±3.6)Ma and(457.8±3.1)Ma respectively.These two ages are consistent with each other within the error limits,suggesting that the two plutons were produced by synchronous magmatism and probably formed a complete pluton in the deep crust.The age of the Abagong pluton indicates that the opinion held by previous researchers that Abagong granite is only a middle-late Variscan pluton seems not correct.The batholithic granite probably consists of plutons formed in different ages.The No.2 Abagong pluton occurs as a small stock that crops out within the volcanic strata of Lower Devonian Kangbutiebao Formation.The nonexistence of intrusive or faulting contact between this pluton and the strata implies that the volcanic strata might be the unconformable cover of the pluton.The pluton crops out locally due to the subsequent denudation and tectonic process.