摘要
选取内蒙古额尔古纳红水泉地区奥陶系乌宾敖包组石英砂岩进行碎屑锆石U-Pb年龄、原位Lu-Hf同位素研究,尝试限定该地层形成时代及碎屑物质来源,并探讨其沉积大地构造环境。结果显示,采自该地层的2个砂岩样品中的碎屑锆石多数发育典型的岩浆振荡生长环带,呈自形–半自形且具有较高的Th/U值(0.12~1.63),均暗示它们多数为岩浆成因。结合微量元素特征及稀土元素配分模式图,认为碎屑锆石寄主岩石应为花岗质杂岩体。2个砂岩样品具有相似的年龄和Hf同位素组成,锆石年龄分布大致可分为3个主要年龄区间:(1)440~540 Ma,主峰值年龄约为492 Ma和506 Ma,次峰值年龄为447 Ma;ε_(Hf)(t)值介于−2.77~+11.73之间,Hf的两阶段模式年龄为680~1636 Ma;(2)750~950 Ma,主峰值年龄为805 Ma,次峰值年龄为825 Ma和961 Ma;ε_(Hf)(t)值介于−1.14~+11.43之间,Hf的两阶段模式年龄为1100~1824 Ma;(3)1700~2000 Ma,峰值年龄为1787 Ma;ε_(Hf)(t)值介于−9.18~−2.75之间,Hf的两阶段模式年龄为2682~3016 Ma。所有样品碎屑锆石ε_(Hf)(t)值为−9.18~+11.73,Hf的两阶段模式年龄为680~3016 Ma,大部分锆石的Hf同位素组成集中于球粒陨石与亏损地幔标准线之间,表明沉积物源以早古生代和新元古代新增生地壳物质为主,同时存在少量中元古代晚期古老地壳物质的活化改造。结合前人已报道的邻区相关岩体年代学及地球化学资料,研究区乌宾敖包组的沉积时代不早于晚奥陶世,沉积物主要来自额尔古纳和兴安地块的近缘碎屑物,其形成与早古生代时期古亚洲洋演化过程中额尔古纳与兴安地块碰撞拼贴以及随后的伸展垮塌相关。
We present U-Pb ages and Lu-Hf isotope data of detrital zircons from quartz sandstones of the Ordovician Wubinaobao Formation in the Hongshuiquan area,Erguna,Inner Mongolia,in an attempt to constrain the formation age and provenance,and to further discuss the sedimentary tectonic setting.Thet majority of studied detrital zircons are euhedral-subhedral in shape and display typical oscillatory zoning in Cathodoluminescence images,and have higher Th/U ratios(0.12 to 1.63),which suggested to be magmatic.Combined with trace element characteristics and chondrite-normalized Rare-earth element patterns,it is concluded that the host rock of detrital zircons should be granitoids.Two sandstone samples have similar age and Hf isotope compositions and show three dominant populations of:(1)440 to 540 Ma,with two dominant age peaks at ca.492 Ma and 506 Ma,subordinate age peak at ca.447 Ma;ε_(Hf)(t)values between−2.77 to+11.73 with Hf isotopic model ages(tDM2)range from 680 Ma to 1636 Ma;(2)750 to 950 Ma,with dominant age peak at ca.805 Ma,two subordinate age peaks at ca.825 Ma and 961 Ma;ε_(Hf)(t)values between−1.14 to+11.43,with Hf isotopic model ages(tDM2)range from 1100 Ma to 1824 Ma;(3)1700 to 2000 Ma,with major age peak at ca.1787 Ma;ε_(Hf)(t)values between−9.18 to−2.75,with Hf isotopic model ages(tDM2)range from 2082 Ma to 3016 Ma.All detrital zircons displayε_(Hf)(t)values between−9.18 to+11.73,with Hf isotopic model ages(tDM2)ranging from 680 to 3016 Ma.Most zircon Hf isotope compositions are between chondrites and depleted mantle standard lines,indicating that the sedimentary provenance is mainly new crustal materials from Mesozoic and Neoproterozoic,and a small amount of ancient crustal materials from late Mesoproterozoic.In this paper,we suggest that the depositional age of Wubinaobao Formation was Late Ordovician,and that the provenances were dominantly derived from the Erguna and Xing’an terranes,which was probably attributed to the collision of Erguna and Xing’an blocks and the subsequent extensional collapse of orogen during the evolution of Paleo-Asian Ocean in Early Paleozoic.
作者
黄泽涛
梁新权
梁细荣
宋天骄
王策
HUANG Zetao;LIANG Xinquan;LIANG Xirong;SONG Tianjiao;Wang Ce(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;School of Marine Sciences,Sun Yat-sen University,Zhuhai 519082,Guangdong,China)
出处
《地球化学》
CAS
CSCD
北大核心
2022年第1期98-122,共25页
Geochimica
基金
国家自然科学基金(41576040,41072081,40872080)
广东省自然科学基金(2017A030313250)联合资助。
