引用本文：曾胜强,王剑,陈文彬,付修根,孙伟,李金锋,刘君豪.2020.伦坡拉盆地西部丁青湖组新发现凝灰岩锆石U- Pb年龄及其地层学意义[J].地质学报,94(8):2354-2366. ZENG Shengqiang,WANG Jian,CHEN Wenbin,FU Xiugen,SUN Wei,LI Jinfeng,LIU Junhao.2020.Zircon U- Pb age and stratigraphic significance of the newly discovered tuff layers in the Dingqinghu Formation, West Lunpola Basin[J].Acta Geologica Sinica,94(8):2354-2366.
Abstract:The depositional age of the Dingqinghu Formation in the Lunpola Basin is of great relevance in studying the paleo- elevation and climate of the central Tibetan Plateau. Due to a lack of absolute age of the Dingqinghu Formation in the Lunpola Basin, it is still controversial if the uppermost part of the Formation contains Miocene deposits. Two tuff layers were found in the Lower to Middle Dingqinghu Formation during the geological survey in the Ejiazu area of the Lunpola Basin. The LA- ICP- MS zircon U- Pb dating of the tuffs from Middle and Upper part of the Ejiazu profile yielded ages of 24. 05±0. 24 Ma (MSWD=1. 07, n=24) and 22. 64±0. 33 Ma (MSWD=0. 45, n=17) respectively, indicating a depositional age of Late Oligocene and Early Miocene respectively. According to the new zircon U- Pb age and previous research, the clasticrockstrata in the Ejiazu profile was the Dingqinghu Formation rather than the Niubao Formation, and the depositional age of the Dingqinghu Formation is Oligocene to Middle Miocene. Using sedimentation rate and sediment thickness of the Dingqinghu Formation, the deposition of the whole Dingqinghu Formation was estimated to have lasted about 21 to 23 Ma, and the top of the Dingqinghu Formation was extrapolated to 11~13 Ma. Therefore, the clastic strata were deposited continually until at least the Middle Miocene, which was much later than the previously estimated paleo- elevation and climate of the central Tibetan Plateau since the Late Eocene to Oligocene. The recent discovery of fossil mammals, climbing perch, and palm plants and advanced palynological paleoaltimetry collectively demonstrate that the paleo- elevation of the Lunpola Basin was lower than ~2500~3000m. The warm and humid climate that prevailed in this area during the Late Oligocene to Middle Miocene was probably influenced by the airflow from the India Ocean penetrating into the central Tibetan Plateau.We conclude that the Indian monsoon prevailed in the Lunpola Basin at the latest in the Middle Miocene, which led to the diversity of organisms in the Tibetan Plateau.