THE LA-ICP-MS U-Pb AGES AND Lu-Hf ISOTOPE OF DETRITAL ZIRCONS FROM THE BAYANKALAANKALA GROUP IN DARI AREA: IMPLICATION FOR THE PROVENANCE

Songpan-Ganzi Orogenic belt is covered by thick Triassic turbidite complex-Bayankala Group. The provenance of Triassic turbidites is still controversial. In order to constrain the provenance of the siliciclastic rocks, we carried out La-ICP-MS zircon U-Pb dating and Hf isotope analyses on 158 detrital zircons obtained from Bayankala group. Analysis on the LA-ICP-MS U-Pb ages of the detrital zircon from Bayankala Mountain Group indicates that the yougest age is 218Ma and it was intruded by the granite (209 M a). Therefore, we suggest that the formation age is 209-218Ma. The detrital zircons from Bayankala group exhibit wide age spectra with three dominant populations of 212-500Ma, I711-2000Ma, and 2200-2500Ma. The epsilon HF(t) range from-11.69- +16.41 and TDM2 age exhibit a wide age spectrum. Generally, three major peaks exist at 3.5-4.5 Ga, 750-1250 Ma, and 290-450 Ma. Combined the geological background, we suggest that the Bayankala Group was mainly derived from Qinling, Qilian, and Kunlun orogens along the southern margin of the North China Craton with minor the South China. In addition, our Lu-Hf isotopic results also reveal that the Phanerozoic magmatic rocks in central China had been the primary products of crustal reworking with insignificant formation of a juvenile crust.