| 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 |
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| 引用本文： | 曾胜强,王剑,陈文彬,付修根,孙伟,李金锋,刘君豪.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,2020,94(8):2354-2366. |
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| 作者姓名： | 曾胜强 王剑 陈文彬 付修根 孙伟 李金锋 刘君豪 |
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| 作者单位： | 1) 成都理工大学沉积地质研究院，成都，610059; 2) 中国地质调查局成都地质调查中心，成都，610081;3) 西南石油大学地球科学与技术学院，成都，610500;2) 中国地质调查局成都地质调查中心，成都，610081；4)自然资源部沉积盆地与油气资源重点实验室，成都，610081;5) 核工业二八○研究所，四川广汉，618300 |
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| 基金项目： | 本文为国家自然科学基金项目（项目编号41702119）和中国地质调查局项目（项目编号DD20190116）联合资助的成果。 |
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| 摘 要： | 伦坡拉盆地丁青湖组沉积时代的确定对于研究青藏高原中部的古高度和古气候具有重要的地质意义,但由于没有精确的年龄数据,其顶部是否跨入了新近系,一直以来都存在争论。作者在伦坡拉盆地西部鄂加卒地区开展野外调查过程中,在该剖面中部和上部新发现两套凝灰岩夹层,对凝灰岩进行了LA-ICP-MS锆石U-Pb定年,获得了两件凝灰岩样品的形成年龄分别为24.05±0.24Ma(MSWD=1.07,n=24)和22.64±0.33Ma(MSWD=0.45,n=17),时代分别为晚渐新世和早中新世。根据凝灰岩锆石U-Pb年龄和前人研究成果,将鄂加卒剖面的细碎屑岩地层重新厘定为丁青湖组,并将丁青湖组的沉积时代定为渐新世-中中新世。根据丁青湖组地层厚度及沉积速率估算,该组沉积持续时间在21～23Ma之间,其顶部地层的年龄在11～13Ma左右。由此可见,伦坡拉盆地接受连续沉积一直持续到了中中新世,这比过去普遍认识的晚始新世-渐新世时期青藏高原中部的古高度和古气候变化时间更晚。前人在该地区发现的近无角犀化石、攀鲈鱼化石、棕榈科叶片化石以及孢粉化石等研究结果共同证实,青藏高原中部渐新世晚期的古海拔高度低于～2500～3000 m。因此,该区晚渐新世-早中新世温暖潮湿的气候特征很可能是受到了印度洋气流穿透的影响,而且该影响可能一直持续到了中中新世,从而造就了该时期青藏高原生物的多样性。
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| 关 键 词： | 伦坡拉盆地 丁青湖组 凝灰岩 锆石U- Pb定年 渐新世- 中中新世 |
| 收稿时间： | 2019/6/26 0:00:00 |
| 修稿时间： | 2019/8/6 0:00:00 |
Zircon U- Pb age and stratigraphic significance of the newly discovered tuff layers in the Dingqinghu Formation, West Lunpola Basin |
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| ZENG Shengqiang,WANG Jian,CHEN Wenbin,FU Xiugen,SUN Wei,LI Jinfeng,LIU Junhao.Zircon U- Pb age and stratigraphic significance of the newly discovered tuff layers in the Dingqinghu Formation, West Lunpola Basin[J].Acta Geologica Sinica,2020,94(8):2354-2366. |
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| Authors: | ZENG Shengqiang WANG Jian CHEN Wenbin FU Xiugen SUN Wei LI Jinfeng LIU Junhao |
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| Institution: | 1) Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, 610059;2) Chengdu Center of China Geological Survey, Chengdu, 610081;3) School of Geoscience and Technology, Southwest Petroleum University, Chengdu, 610500;2) Chengdu Center of China Geological Survey, Chengdu, 610081;4) Key Laboratory for Sedimentary Basin and Oil and Gas Resources, Ministry of Natural Resources, Chengdu, 610081;5) 280 Institute of Nuclear Industry,Guanghan, 618300 |
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| 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. |
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| Keywords: | Lunpola basin Dingqinghu Formation tuff zircon U- Pb dating Oligocene to Middle Miocene |
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