The Applicationof Inductively Coupled Plasma-quadrupole Mass Spectrometryto Fossil Teethfor U‐TH Isotope Analysis
详细信息
- 责任者：Shao Qingfeng(Département de Préhistoire du Muséum National d’ Histoire Naturelle ; UMR 7194 CNRS ; 1 rue René Panhard ; F-75013 Paris ; France) ; E. Douville
- 刊名：Quaternary Sciences
- 出版年：2012
- 卷期：32(3)
- 页码：p.484-491
- issnNo：ISSN1001-7410
- isbnNo：CN11-2708/P
摘要
Over the past two decades TIMS and MC-ICP-MS have become the main techniques used for high-precision of 230 Th/U dating studies.Recently,a relatively simply and cheap technique for U-Th isotopic analysis was developed by using Inductively Coupled Plasma-Quadrupole Mass Spectrometry(ICP-QMS).With precisions about 0.3 % and 1 % for U and Th isotope analyses,this technique has the ability to estimate sample’s 230 Th/U age with 1 % ~10 % uncertainty.In this work,we use this new technique analyzed four fossil teeth coming from the Acheulian site of Venosa Loreto,southern Italy,where the faunal remains indicate an early Middle Pleistocene age.The previously published purification procedure of U and Th by UTEVA resins was modified for the fossil teeth.The UTEVA resins can efficiently extract U but not Th from the HNO3 solution of dental samples,in the presence of large amount of phosphates.In the present work,Th was allowed to co-precipitate with iron,then was loaded on anion exchange resin column in 7N HNO3 condition.In such strong HNO3 solution Th will be fixed onto the column,and can be diluted by 6N HCl.The U-Th isotope analysis with ICP-QMS was carried out on each dental tissue(enamel,dentine and cementum)of fossil teeth and yielded data with precision on average of 0.3 % and 0.6 % for 238 U and 232 Th contents,and of 0.3 % and 0.8 % for activity ratios of 234 U/238 U and 230 Th/238 U at 2σ uncertainty level,respectively.Our results show that U-contents in fossil teeth can be as high as 1000 ppm,but may differ from tissues by 1~2 orders of magnitude.On the other hand,for each tooth,dental tissues show substantial dispersion( >2σ)in their activity ratios of 234 U/238 U and 230 Th/238 U,consequently leading to scattered 230 Th/U dates,ranging from 139±2ka to 425±48ka.Fossil teeth thus are not ideal targets for 230 Th/U dating because of their open-system behavior,but the measured present-day U-Th isotopic information is useful for simulation of U-uptake histories experienced by dental tissues,and a combination of U-series and ESR analyses on fossil teeth seems a better way for age estimation.