摘要
平顶山砂岩是华北陆块晚古生代地层上部的一个显著的标志层,以其广泛的分布、特殊的岩性,以及对晚古生代地层的分划性而著称,暗示了平顶山砂岩可能是一次地质事件的记录,但有关平顶山砂岩的沉积时代和沉积环境一直是争论的焦点。本项研究选取华北陆块南部平顶山砂岩的创名地点---平顶山地区,及其北部巩义地区和宜阳地区的平顶山砂岩样品,进行碎屑锆石LA-ICP-MS U-Pb测年,并辅以Hf同位素测定,分析平顶山砂岩的最大沉积年龄和沉积物源区,在此基础上,进一步分析平顶山砂岩的沉积时代和沉积环境。研究表明,华北陆块南部平顶山、巩义和宜阳地区平顶山砂岩4个样品的碎屑锆石主要为古生代岩浆锆石和前寒武纪变质锆石。其中,古生代锆石占13%,具有~259Ma、~318Ma和~435Ma的峰值年龄;前寒武纪锆石占87%,具有显著的~1871Ma和~2459Ma峰值年龄,还有两个仅由3颗锆石组成的不明显的峰值~812Ma和~976Ma。采用最年轻单颗粒年龄(YSG)限定地层最大沉积年龄的方法,确定出三个地区4个样品YSG年龄分别为249±8Ma、260±7Ma、252±7Ma和248±7Ma,与二叠系-三叠系沉积界线年龄251.0±0.4Ma相接近,推测平顶山砂岩的底界可能是二叠纪与三叠纪的接触界线,即华北陆块南部平顶山砂岩的地质时代应归属于早三叠世。根据平顶山砂岩的沉积和构造背景分析,以及与潜在物源区年龄图谱和值的对比,平顶山砂岩的主要物源区为华北陆块北部内蒙古隆起上的晚古生代侵入岩体和华北陆块的变质基底,次要物源区为北秦岭造山带加里东期的中-酸性花岗质侵入岩和~1000Ma花岗岩或被侵入的该地区的主要变质地层(秦岭群、二郎坪群和宽坪群)。根据平顶山砂岩最大沉积年龄和沉积物源区分析,结合平顶山砂岩下伏地层(山西组、下石盒子组和上石盒子组)沉积物几乎全部来源于华北陆块北部的内
Pingdingshan sandstone is a prominent symbol in the upper part of Late Paleozoic strata of North China Block.It is well known for its extensive distribution,special lithology and significant division of sedimentary lithology for the Late Paleozoic strata,suggesting that Pingdingshan sandstone may record a remarkable geological event,however,its sedimentary age and sedimentary environment have always been the focus of controversy for a long time.In this study,samples are selected from the named place of Pingdingshan sandstone in the southern part of North China Block(i.e.Pingdingshan area,Gongyi area and Yiyang area)for LA-ICP-MS U-Pb dating of detrital zircons,assisted by Hf isotopes analysis,with the attempt to determine the maximum sedimentary age and the material source area,expecting to provide basis for confirming the sedimentary age and sedimentary environment.The results show that the detrital zircons from four samples of the Pingdingshan sandstone in Pingdingshan,Gongyi and Yiyang areas in the southern part of North China Block,are mainly from the Palaeozoic magmatic zircons and the Precambrian metamorphic zircons.Among them,the Paleozoic zircons account for 13%with the peak age of^259Ma,~318Ma and^435Ma,while the Precambrian zircons account for87%with distinct peak ages of^1871Ma and^2459Ma,along with two very inconspicuous peak age of^812Ma and^976Ma which is composed by only three zircons.By using the youngest single detrital zircons ages(YSG)of four samples,249±8Ma,260±7Ma,252±7Ma and 248±7Ma,respectively,which is close to the Permian/Triassic boundary age 251±0.4Ma,we limit the maximum sedimentary age of the stratum and presume that the bottom of Pingdingshan sandstone may be a contact boundary between Permian and Triassic,i.e.,the geological age of the Pingdingshan sandstone in the southern part of North China Block should belong to Early Triassic.Based on analysis of the sedimentary and tectonic setting of Pingdingshan sandstone,accompanied by the comparison with age spectrum andεHf(t)of the
作者
曹高社
方磅磅
孙凤余
余爽杰
徐海亭
CAO GaoShe;FANG BangBang;SUN FengYu;YU ShuangJie;XU HaiTing(Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo 454000, China;Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Henan Province, Jiaozuo 454000, China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第8期2518-2544,共27页
Acta Petrologica Sinica
基金
中国地质调查局地质调查项目(1211302108023-1)资助
