摘要
由于缺少精确的定年结果与可靠的生物标志化石,青藏高原广泛发育的上白垩统—中新统的多套陆相红层时代与分布混乱不清,影响了对一系列重大问题的认识。本文利用锆石U-Pb测试手段,对双湖—伦坡拉地区红层时代开展研究。根据新发现的斑脱岩与火山岩夹层精确厘定了牛堡组中上部时代(45.41~43.82 Ma)和阿布山组地层时代(101.9~73.09 Ma);根据上覆角度不整合的纳丁错组(35.5~32.59 Ma)与鱼鳞山组(46~28 Ma)火山岩年龄约束了康托组与唢呐湖组的时代上限;结合前人年代学研究,初步建立了K2—N1红层时代格架,主要包括晚白垩世阿布山组与竟柱山组、古新世—始新世牛堡组与康托组、始新世—渐新世唢呐湖组和渐新世—中新世丁青湖组,均可与北部可可西里盆地对比。其中,双湖—多玛主要出露阿布山组,非早期划分的康托组;而康托组多数分布于中央隆起或山顶高处;唢呐湖组则沿双湖周边平缓低地发育;竟柱山组、牛堡组与丁青湖组普遍沿班公湖—怒江缝合带展布,其中牛堡组向北延伸到多玛。精确厘定红层时代与分布,直接推动了对盆地沉积地层系统与逆冲推覆构造活动时代的认识,有利于进一步综合评价逆冲推覆构造对羌塘盆地油气资源的影响,探讨逆冲推覆构造与盆—山演化过程及动力学机制;同时,为以红层为研究对象的高原抬升过程、古环境与古气候演化等提供了良好的基础。
Objectives:The chronostratigraphic framework and distribution of the K2—N1 Red beds in the Shuanghu—Lunpola area of the central Xizang(Tibetan)Plateau has been controversial due to lack of precise age controls and reliable guide fossils,which also affect the understanding of a series of other scientific problems about the red beds.In this study,we briefly discuss the time scale of the K2—N1 red beds in the research area according to geochronological and stratigraphic study of the bentonite and volcanic rocks.Methods:The zircon LA-ICP-MS U-Pb dating is used to make a detailed geochronology of the bentonite and volcanic rocks in the research area.Zircon U-Pb isotope ages of selected samples were performed in the Isotopic Laboratory,Tianjin Institute of Geology and Mineral Resources of China Geological Survey and Continental Tectonics and Dynamics Laboratory of Institute of Geology,Chinese Academy of Geological Sciences.Results:The zircon U-Pb dating of the volcanic rocks establish the Abushan Fm.age from 101.9 to 73.09 Ma,and the Bentonite combining previous ages of the Upper Niubao Fm.age of 45.41~43.82 Ma.Combined with the regional geological data,we establish the geochronologic time scale of the continental deposit from the Late Cretaceous to Miocene.Zircons from the bentonite yield concordant206 Pb/238 U ages between 45.41 and 43.82 Ma,which is interpreted as the formation age of the Upper Niubao Fm.Similarly,zircons from the volcanic rocks yield concordant206 Pb/238 U ages from 101.9 to 73.09 Ma,which is indicative of the formation age of the Abushan Fm.The zircon U-Pb and Ar-Ar dating of the volcanic rocks ranging from 35.5 to 32.59 Ma for the Nadingcuo Fm.,and 46~28 Ma for the Yulinshan Fm.,which unconformably overlie the Kangtuo Fm.and the Suonahu Fm.respectively,indicating the minimum depositional age of these two red beds.Conclusion:According to these data above,combined with previous research,we establish the chronostratigraphic framework of the K2—N1 red beds in the Shuanghu—Lunpola area,consisting of the Upper Cretaceous Abushan Fm.and the Jingshan Fm.,the Niubao Fm.and the Kangtuo Fm.during the Paleocene—Eocene epoch,the Eocene—Oligocene Suonahu Fm.and the Oligocene—Miocene Dingqinghu Fm.,and these formations are also coeval with the red beds of the Hoh Xil basin to the north.The Abushan Fm.,instead of the Kangtuo Fm.suggested by previous research,are mainly distributed within the Shuanghu—Duoma area,while the Kangtuo Fm.predominately outcrops in the Central Uplift of the Qiangtang Basin and other hills.The Suonahu Fm.trends to be located along the gentle depressions near the Shuanghu area.The Jiangzhushan Fm.,the Niubao Fm.and the Dingqinghu Fm.are widely located along the Bangong Lake—Nujiang River suture zone,and the Niubao Fm.extends north to Duoma area.Establishing the chronostratigraphic framework and distribution of the K2—N1 red beds in the Shuanghu—Lunpola area may give us a further understanding of the basin evolution and active time of thrusts from the Late Cretaceous to Miocene in the study area with the purpose to provide a useful basis to the study on sedimentary—tectonic—paleoenvironment evolution in the central plateau.
作者
赵珍
吴珍汉
杨易卓
季长军
ZHAO Zhen;WU Zhenhan;YANG Yizhuo;JI Changjun(Chinese Academy of Geological Sciences,Beijing,100037;Yangtze University,Wuhan,430100;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing,100081)
出处
《地质论评》
CAS
CSCD
北大核心
2020年第5期1155-1171,共17页
Geological Review
基金
中国地质科学院基本科研业务费专项经费资助项目(编号:JKY201903-06)
地质调查项目(编号:DD20190367)的成果。
