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伦坡拉盆地西部丁青湖组新发现凝灰岩锆石U-Pb年龄及其地质意义
投稿时间:2019-06-26  修订日期:2019-08-06  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020017
摘要点击次数: 128
全文下载次数: 112
作者单位E-mail
曾胜强 中国地质调查局成都地质调查中心 zengsq@126.com 
王剑 西南石油大学地球科学与技术学院  
陈文彬 中国地质调查局成都地质调查中心  
付修根 中国地质调查局成都地质调查中心  
孙伟 中国地质调查局成都地质调查中心  
李金锋 核工业二八0研究所  
刘君豪 核工业二八0研究所  
基金项目:国家自然科学基金项目(批准号:41702119)和中国地质调查局项目(编号:DD20190116)联合资助的成果
中文摘要: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。
中文关键词: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
 
Zircon U-Pb age of the newly discovered tuff layers of the Dingqinghu Formation in the West Lunpola Basin and its geological significance
Author NameAffiliationE-mail
ZENG Shengqiang) Chengdu Center of China Geological Survey zengsq@126.com 
WANG Jian) School of Geoscience and Technology,Southwest Petroleum University,Chengdu  
CHEN Wenbin) Chengdu Center of China Geological Survey  
FU Xiugen) Chengdu Center of China Geological Survey  
Sun Wei) Chengdu Center of China Geological Survey  
Li Jinfeng) 280 Institute of Nuclear Industry  
Liu Junhao) 280 Institute of Nuclear Industry  
Abstract:The deposition age of Dingqinghu Formation in the Lunpola Basin is of great importance to study the paleo-elevation and climate of the central Tibetan Plateau. While, due to a lack of absolute age of the Dingqinghu Formation in the Lunpori Basin, weather the Uppermost part of the Formation contain Miocene deposit is still controversial. Two tuff layers in the Lower to Middle Dingqinghu Formation were found during the geological survey in the Ejiazu area of the Lunpola Basin, and LA-ICP-MS zircon U-Pb dating from the tuffs from Middle and Upper part of the Ejiazu profile yielded ages of 24.05±0.24Ma (MSWD=1.07, n=24) and 22.64±0.33Ma (MSWD=0.45, n=17), respectively, with the deposition age of Late Oligocene and Early Miocene, respectively. According to the new zircon U-Pb age and former researches, the clasticSrockSstrata in the Ejiazu profile was Dingqinghu Formation rather than Niubao Formation, and the deposition age of the Dingqinghu Formation is Oligocene to Middle Miocene. Using sedimentation rate and sedimentation thickness of the Dingqinghu Formation, the whole depositon of Dingqinghu Formation was estimates to last about 21 to 23 Ma, and the top of the Dingqinghu Foramtion 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 previous estimates paleo-elevation and climate of the central Tibetan Plateau since the Late Eocene to Oligocene. The recent discovered fossil mammals, climbing perch and palms plants and advanced palynological paleoaltimetry collectively demonstrate that the paleo-elevation of the Lunpola Basin was lower than ~2500-3000m. Hence, during the Late Oligocene to Middle Miocene time, the warm and humid paleoclimate prevail in this area was probably influenced by the airflow from the India Ocean penetrating into the central Tibetan Plateau, and this Indian monsoon prevailed in the Lunpola Basin at the latest in the Middle Miocene, which led to the diversity of organism in the Tibetan Plateau.
keywords:Lunpola Basin  Dingqinghu Formation  Tuff  Zircon U-Pb dating  Oligocene to Middle Miocene
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