U-Pb dating for detrital zircons from the Jiejunazhuo Formation in Xuru Co area and its geological significances

The newly identified Jiejunazhuo Formation in Xuru Co area,Tibet,is mainly composed of semi-consolidated to consolidated coarse clastic rocks. In order to reveal its sedimentary time and sediment provenance,we carry out the U-Pb dating for detrital zircons of one sandstone sample from the Jiejunazhuo Formation. The results indicate that the effective ages obtained can be roughly divided into 4 groups:10.1~17.2 Ma (10 zircons),41.7~72.2 Ma (43 zircons),77.9~87.8 Ma (4 zircons),463~1610 Ma (8 zircons). Combining the lithological characteristics,ESR age of sandstone and previous age data in the region,it is believed that the Jiejunazhuo Formation was most likely formed in the Pliocene. Provenance analysis shows that the volcanic rocks of the Linzizong group and the Bugasi Formation in Chazi areas and neighboring regions in the south of Xuru Co,were the main sediment sources of the Jiejunazhuo Formation,and the Paleocene-Miocene intrusive rocks and Late Paleozoic strata also provided a small amount of sedimentary materials. The Jiejunazhuo Formation,which developed in the Xuru Co NS-trending graben basin,was the sedimentary response of the uplifting of Tibetan plateau during the Pliocene,and it was also the result of differential uplifting of the Gangdise areas during that time.