基于激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)的锆石微区U-Pb精确定年
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摘要
激光剥蚀电感耦合等离子体质谱(LA-ICP-M_S)为锆石U-Pb年代学提供了快速、精确的测试技术。文中利用Agilent 7900型四极杆电感耦合等离子体质谱仪(Q-ICP-M_S)和ResolutionM50-LR型193nm Ar F准分子激光剥蚀系统联机,建立了完整的锆石U-Pb年龄测试流程。在激光束斑直径40μm、能量密度3. 5J/cm2的条件下,用标准玻璃NIST 612对测试系统进行调谐,使238U的灵敏度高于30 000cps/s。对5个锆石标样(年龄为4～1 064Ma)进行了详细的定年研究,所获得的91500、GJ-1、Plesovice、FCT和蓬莱锆石的U-Pb年龄与前人报道的年龄在误差范围内是一致的,3个国际标样(91500、GJ-1、Plesovice)的测试精度优于3%,2个二级标样(FCT和蓬莱)测试精度较低,仅优于15%,结果表明该实验流程是可行的。锆石U-Pb年龄的分析误差主要来自3个方面:同位素比值测定误差、仪器灵敏度漂移和同位素分馏校正系数误差、标样推荐值误差。与国际标样相比,影响FCT和蓬莱锆石的分析误差除了以上3个因素外,还有以下3个方面:放射性成因Pb*含量过低,测试误差增大;普通Pb对其年龄影响加剧,不易精确地扣除;样品与标样匹配程度降低。因此,样品的测试精度取决于绝对年龄、普通Pb含量和标样与样品匹配程度。
LA-ICP-M_S( laser ablation-inductively coupled-mass spectrometry) has been recently used for rapid,accurate and precise U-Pb geochronology on zircon grains. In this paper,we adopted an Agilent 7900 quadrupole ICP-M_S coupled with a Resolution M50-LR 193 nm excimer laser system to establish integrated measurement procedures. Before analysis, the system is tuned to achieve sensitivities better than 30 000 cps/s for238 U with a 40μm spot size,at ～ 3. 5 J/cm2. Detailed parameters for laser system and ICP-M_S are presented here. Then,we analyzed five reference zircons( 91500,GJ-1,Plesovice,FCT,Penglai) with a wide range in age from ～1 064 to ～4. 4 Ma. Two standard zircons,91500 and GJ-1,are employed as external reference standards. Generally,second zircon standard is analyzed in an effort to ensure accuracy and evaluate reproducibility. A typical analysis sequence includes one international glass standard( NIST 610), two external reference standards,five grains of unknown zircon with every eight ablations. Laser induced time-dependent elemental fractionation is corrected using the intercept method,whereas instrument drift,mass bias and elemental fractional caused by ionization differences are corrected by external reference standard91500 or GJ-1. Compared with 91500 and GJ-1,common Pb content of Plesovice,FCT,Penglai can't be ignored. Thus,we did common Pb correction for the above three standard zircons. The performance of the established procedure was assessed by analyzing zircon range in age from ～ 1 064 to ～ 4 Ma. The results show that the ages of these five references are consistent with the ages of published studies with accuracy for three international references( 91500,GJ-1,Plesovice) better than 3% and two young secondary references( FCT,Penglai) lower than 7% at the 2 sigma level,which indicates that our analytical procedure is reliable. For individual laser analysis, the uncertainties are mainly from three sources: Measurement error of isotope ratio,error of correction factors for instrument drift and element fractionation,and error of recommended age of external references. Compared to three international references,there are three extra uncertainties for young reference zircons, including: 1) little radioactive isotopes closing to blank level increase the measurement error of isotope ratio; 2) effect of common lead becomes more significant; 3) the nonhomogeneous samples couldn't match references well. Therefore, accuracy and precision of measurement depend on absolute age, content of common lead and matching degree between references and samples. In summary, the accuracy and precision obtained using the technique presented in this study are similar to those of other LA-ICP-M_S laboratories.
LA-ICP-M_S( laser ablation-inductively coupled-mass spectrometry) has been recently used for rapid,accurate and precise U-Pb geochronology on zircon grains. In this paper,we adopted an Agilent 7900 quadrupole ICP-M_S coupled with a Resolution M50-LR 193 nm excimer laser system to establish integrated measurement procedures. Before analysis, the system is tuned to achieve sensitivities better than 30 000 cps/s for238 U with a 40μm spot size,at ～ 3. 5 J/cm2. Detailed parameters for laser system and ICP-M_S are presented here. Then,we analyzed five reference zircons( 91500,GJ-1,Plesovice,FCT,Penglai) with a wide range in age from ～1 064 to ～4. 4 Ma. Two standard zircons,91500 and GJ-1,are employed as external reference standards. Generally,second zircon standard is analyzed in an effort to ensure accuracy and evaluate reproducibility. A typical analysis sequence includes one international glass standard( NIST 610), two external reference standards,five grains of unknown zircon with every eight ablations. Laser induced time-dependent elemental fractionation is corrected using the intercept method,whereas instrument drift,mass bias and elemental fractional caused by ionization differences are corrected by external reference standard91500 or GJ-1. Compared with 91500 and GJ-1,common Pb content of Plesovice,FCT,Penglai can't be ignored. Thus,we did common Pb correction for the above three standard zircons. The performance of the established procedure was assessed by analyzing zircon range in age from ～ 1 064 to ～ 4 Ma. The results show that the ages of these five references are consistent with the ages of published studies with accuracy for three international references( 91500,GJ-1,Plesovice) better than 3% and two young secondary references( FCT,Penglai) lower than 7% at the 2 sigma level,which indicates that our analytical procedure is reliable. For individual laser analysis, the uncertainties are mainly from three sources: Measurement error of isotope ratio,error of correction factors for instrument drift and element fractionation,and error of recommended age of external references. Compared to three international references,there are three extra uncertainties for young reference zircons, including: 1) little radioactive isotopes closing to blank level increase the measurement error of isotope ratio; 2) effect of common lead becomes more significant; 3) the nonhomogeneous samples couldn't match references well. Therefore, accuracy and precision of measurement depend on absolute age, content of common lead and matching degree between references and samples. In summary, the accuracy and precision obtained using the technique presented in this study are similar to those of other LA-ICP-M_S laboratories.
引文
侯可军,李延河,田有荣.2009.LA-MC-ICP-MS锆石微区原位U-Pb定年技术[J].矿床地质,28(4):481-492.HOU Ke-jun,LI Yan-he,TIAN You-rong.2009.In situ U-Pb zircon dating using laser ablation-multi ion countingICP-MS[J].Mineral Deposits,28(4):481-492(in Chinese).
柳小明,高山,第五春容,等.2007.单颗粒锆石的20μm小斑束原位微区LA-ICP-MSU-Pb年龄和微量元素的同时测定[J].科学通报,52(2):228-235.LIU Xiao-ming,GAO Shan,DIWU Chun-rong,et al.2007.Simultaneous in situ determination of U-Pb age and trace elements in zircon by LA-ICP-MS in 20μm spot size[J].Chinese Science Bulletin,52(2):228-235(in Chinese).
谢烈文,张艳斌,张辉煌,等.2008.锆石/斜锆石U-Pb和Lu-Hf同位素以及微量元素成分的同时原位测定[J].科学通报,53(2):220-228.XIE Lie-wen,ZHANG Yan-bin,ZHANG Hui-huang,et al.2008.In situ simultaneous determination of trace elements,U-Pb and Lu-Hf isotopes in zircon and baddeleyite[J].Chinese Science Bulletin,53(2):220-228(in Chinese).
Amelin Y,Zaitsev A N.2002.Precise geochronology of phoscorites and carbonatites:The critical role of U-series disequilibrium in age interpretations[J].Geochimica et Cosmochimica Acta,66(13):2399-2419.
Andersen T.2002.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,192(1-2):59-79.
Carpéna J,MailhéD.1987.Fission-track dating calibration of the fish canyon tuff standard in French reactors[J].Chemical Geology,66:53-59.
Chang Z,Vervoort J D,McClelland W C,et al.2006.U-Pb dating of zircon by LA-ICP-MS[J].Geochemistry,Geophysics,Geosystems,7(5):Q05009.
Chew D M,Petrus J A,Kamber B S.2014.U-Pb LA-ICP-MS dating using accessory mineral standards with variable common Pb[J].Chemical Geology,363:185-199.
Crowley Q,Heron K,Riggs N,et al.2014.Chemical abrasion applied to LA-ICP-MS U-Pb zircon geochronology[J].Minerals,4(2):503-518.
Dobson K J,Stuart F M,Dempster T J,et al.2008.U and Th zonation in fish canyon tuff zircons:Implications for a zircon(U-Th)/He standard[J].Geochimica et Cosmochimica Acta,72(19):4745-4755.
Eelhlou S,Belousova E,Griffin W L,et al.2006.Trace element and isotopic composition of GJ red zircon standard by laser ablation[J].Geochimica et Cosmochimica Acta,70(18):A158.
Eggins S M,Kinsley L P J,Shelley J M G.1998.Deposition and element fractionation processes during atmospheric pressure laser sampling for analysis by ICP-MS[J].Applied Surface Science,127-129:278-286.
Fryer B J,Jackson S E,Longerich H P.1993.The application of laser ablation microprobe-inductively coupled plasma-mass spectrometry(LAM-ICP-MS)to in situ U-Pb geochronology[J].Chemical Geology,109(1-4):1-8.
Gehrels G.2014.Detrital zircon U-Pb geochronology applied to tectonics[J].Annual Review of Earth and Planetary Sciences,42(1):127-149.
Gehrels G E,Valencia V A,Ruiz J.2008.Enhanced precision,accuracy,efficiency,and spatial resolution of U-Pb ages by laser ablation-multicollector-inductively coupled plasma-mass spectrometry[J].Geochemistry,Geophysics,Geosystems,9(3):Q03017.
Horstwood M S A,Foster G L,Parrish R R,et al.2003.Common-Pb corrected in situ U-Pb accessory mineral geochronology by LA-MC-ICP-MS[J].Journal of Analytical Atomic Spectrometry,18(8):837-846.
Jackson S E,Longerich H P,Duning G R,et al.1992.The application of laser-ablation microprobe-inductively coupled plasma-mass spectrometry(LAM-ICP-MS)to in situ trace-element determinations in minerals[J].Canadian Mineralogist,30:1049-1064.
Jackson S E,Pearson N J,Griffin W L,et al.2004.The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology[J].Chemical Geology,211(1-2):47-69.
Johnston S,Gehrels G,Valencia V,et al.2009.Small-volume U-Pb zircon geochronology by laser ablationmulticollector-ICP-MS[J].Chemical Geology,259(3-4):218-229.
Kltzli U,Kltzli,E,Günes,Z,et al.2009.Accuracy of laser ablation U-Pb zircon dating:Results from a test using five different reference zircons[J].Geostandards and Geoanalytical Research,33:5-15.
Koler J,Sylvester P J.2003.Present trends and the future of zircon in geochronology:Laser ablation ICPMS[J].Reviews in Mineralogy and Geochemistry,53(1):243-275.
Li X H,Liu X M,Liu Y S,et al.2015.Accuracy of LA-ICP-MS zircon U-Pb age determination:An inter-laboratory comparison[J].Science in China(Ser D),58(10):1722-1730.
Li X H,Long W G,Li Q L,et al.2010.Penglai zircon megacrysts:A potential new working reference material for microbeam determination of Hf-O isotopes and U-Pb age[J].Geostandards and Geoanalytical Research,34(2):117-134.
Liu Y,Hu Z,Gao S,et al.2008.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MSwithout applying an internal standard[J].Chemical Geology,257(1-2):34-43.
Ludwig K R.2003.ISOPLOT 3.0:A Geochronological Toolkit for Microsoft Excel[M].Berkeley Geochronology Center,Spec Pub 4.
Nebel-Jacobsena Y,Scherer E E,Münker C,et al.2005.Separation of U,Pb,Lu,and Hf from single zircons for combined U-Pb dating and Hf isotope measurements by TIMS and MC-ICP-MS[J].Chemical Geology,220(1-2):105-120.
Qiu Z.2005.Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China[J].Chinese Science Bulletin,50(22):2602-2611.
Reiners P W.2005.Zircon(U-Th)/He thermochronometry[J].Reviews in Mineralogy and Geochemistry,58(1):151-179.
Schaltegger U,Schmitt A K,Horstwood M S A.2015.U-Th-Pb zircon geochronology by ID-TIMS,SIMS,and laser ablation ICP-MS:Recipes,interpretations,and opportunities[J].Chemical Geology,42:89-110.
Schmitt A K,Chamberlain K R,Swapp S M,et al.2010.In situ U-Pb dating of micro-baddeleyite by secondary ion mass spectrometry[J].Chemical Geology,269(3-4):386-395.
Schmitz M D,Bowring S A.2001.U-Pb zircon and titanite systematics of the Fish Canyon Tuff:An assessment of high precision U-Pb geochronology and its application to young volcanic rocks[J].Geochimica et Cosmochimica Acta,65(15):2571-2587.
Schoene B,Latkoczy C,Schaltegger U,et al.2010.A new method integrating high-precision U-Pb geochronology with zircon trace element analysis(U-Pb TIMS-TEA)[J].Geochimica et Cosmochimica Acta,74(24):7144-7159.
Slma J,Koler J,Condon D J,et al.2008.Pleovice zircon:A new natural reference material for U-Pb and Hf isotopic microanalysis[J].Chemical Geology,249(1-2):1-35.
Solari L A,Gómez-Tuena A,Bernal J P,et al.2010.U-Pb zircon geochronology with an integrated LA-ICP-MSmicroanalytical workstation:Achievements in precision and accuracy[J].Geostandards and Geoanalytical Research,34(1):5-18.
Sylvester P J,Ghaderi M.1997.Trace element analysis of scheelite by excimer laser ablation-inductively coupled plasma-mass spectrometry(ELA-ICP-MS)using a synthetic silicate glass standard[J].Chemical Geology,141(1-2):49-65.
Tera F,Wasserburg G.1972.U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks[J].Earth and Planetary Science Letters,14(3):281-304.
Eynatten H V,Dunkl I.2012.Assessing the sediment factory:The role of single grain analysis[J].Earth Science Reviews,115(1-2):97-120.
Wiedenbeck M,AllP,Corfu F,et al.1995.Three natural zircon standards for U-Th-Pb,Lu-Hf,trace element and REE analyses[J].Geostandards and Geoanalytical Research,19(1):1-23.
柳小明,高山,第五春容,等.2007.单颗粒锆石的20μm小斑束原位微区LA-ICP-MSU-Pb年龄和微量元素的同时测定[J].科学通报,52(2):228-235.LIU Xiao-ming,GAO Shan,DIWU Chun-rong,et al.2007.Simultaneous in situ determination of U-Pb age and trace elements in zircon by LA-ICP-MS in 20μm spot size[J].Chinese Science Bulletin,52(2):228-235(in Chinese).
谢烈文,张艳斌,张辉煌,等.2008.锆石/斜锆石U-Pb和Lu-Hf同位素以及微量元素成分的同时原位测定[J].科学通报,53(2):220-228.XIE Lie-wen,ZHANG Yan-bin,ZHANG Hui-huang,et al.2008.In situ simultaneous determination of trace elements,U-Pb and Lu-Hf isotopes in zircon and baddeleyite[J].Chinese Science Bulletin,53(2):220-228(in Chinese).
Amelin Y,Zaitsev A N.2002.Precise geochronology of phoscorites and carbonatites:The critical role of U-series disequilibrium in age interpretations[J].Geochimica et Cosmochimica Acta,66(13):2399-2419.
Andersen T.2002.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,192(1-2):59-79.
Carpéna J,MailhéD.1987.Fission-track dating calibration of the fish canyon tuff standard in French reactors[J].Chemical Geology,66:53-59.
Chang Z,Vervoort J D,McClelland W C,et al.2006.U-Pb dating of zircon by LA-ICP-MS[J].Geochemistry,Geophysics,Geosystems,7(5):Q05009.
Chew D M,Petrus J A,Kamber B S.2014.U-Pb LA-ICP-MS dating using accessory mineral standards with variable common Pb[J].Chemical Geology,363:185-199.
Crowley Q,Heron K,Riggs N,et al.2014.Chemical abrasion applied to LA-ICP-MS U-Pb zircon geochronology[J].Minerals,4(2):503-518.
Dobson K J,Stuart F M,Dempster T J,et al.2008.U and Th zonation in fish canyon tuff zircons:Implications for a zircon(U-Th)/He standard[J].Geochimica et Cosmochimica Acta,72(19):4745-4755.
Eelhlou S,Belousova E,Griffin W L,et al.2006.Trace element and isotopic composition of GJ red zircon standard by laser ablation[J].Geochimica et Cosmochimica Acta,70(18):A158.
Eggins S M,Kinsley L P J,Shelley J M G.1998.Deposition and element fractionation processes during atmospheric pressure laser sampling for analysis by ICP-MS[J].Applied Surface Science,127-129:278-286.
Fryer B J,Jackson S E,Longerich H P.1993.The application of laser ablation microprobe-inductively coupled plasma-mass spectrometry(LAM-ICP-MS)to in situ U-Pb geochronology[J].Chemical Geology,109(1-4):1-8.
Gehrels G.2014.Detrital zircon U-Pb geochronology applied to tectonics[J].Annual Review of Earth and Planetary Sciences,42(1):127-149.
Gehrels G E,Valencia V A,Ruiz J.2008.Enhanced precision,accuracy,efficiency,and spatial resolution of U-Pb ages by laser ablation-multicollector-inductively coupled plasma-mass spectrometry[J].Geochemistry,Geophysics,Geosystems,9(3):Q03017.
Horstwood M S A,Foster G L,Parrish R R,et al.2003.Common-Pb corrected in situ U-Pb accessory mineral geochronology by LA-MC-ICP-MS[J].Journal of Analytical Atomic Spectrometry,18(8):837-846.
Jackson S E,Longerich H P,Duning G R,et al.1992.The application of laser-ablation microprobe-inductively coupled plasma-mass spectrometry(LAM-ICP-MS)to in situ trace-element determinations in minerals[J].Canadian Mineralogist,30:1049-1064.
Jackson S E,Pearson N J,Griffin W L,et al.2004.The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U-Pb zircon geochronology[J].Chemical Geology,211(1-2):47-69.
Johnston S,Gehrels G,Valencia V,et al.2009.Small-volume U-Pb zircon geochronology by laser ablationmulticollector-ICP-MS[J].Chemical Geology,259(3-4):218-229.
Kltzli U,Kltzli,E,Günes,Z,et al.2009.Accuracy of laser ablation U-Pb zircon dating:Results from a test using five different reference zircons[J].Geostandards and Geoanalytical Research,33:5-15.
Koler J,Sylvester P J.2003.Present trends and the future of zircon in geochronology:Laser ablation ICPMS[J].Reviews in Mineralogy and Geochemistry,53(1):243-275.
Li X H,Liu X M,Liu Y S,et al.2015.Accuracy of LA-ICP-MS zircon U-Pb age determination:An inter-laboratory comparison[J].Science in China(Ser D),58(10):1722-1730.
Li X H,Long W G,Li Q L,et al.2010.Penglai zircon megacrysts:A potential new working reference material for microbeam determination of Hf-O isotopes and U-Pb age[J].Geostandards and Geoanalytical Research,34(2):117-134.
Liu Y,Hu Z,Gao S,et al.2008.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MSwithout applying an internal standard[J].Chemical Geology,257(1-2):34-43.
Ludwig K R.2003.ISOPLOT 3.0:A Geochronological Toolkit for Microsoft Excel[M].Berkeley Geochronology Center,Spec Pub 4.
Nebel-Jacobsena Y,Scherer E E,Münker C,et al.2005.Separation of U,Pb,Lu,and Hf from single zircons for combined U-Pb dating and Hf isotope measurements by TIMS and MC-ICP-MS[J].Chemical Geology,220(1-2):105-120.
Qiu Z.2005.Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China[J].Chinese Science Bulletin,50(22):2602-2611.
Reiners P W.2005.Zircon(U-Th)/He thermochronometry[J].Reviews in Mineralogy and Geochemistry,58(1):151-179.
Schaltegger U,Schmitt A K,Horstwood M S A.2015.U-Th-Pb zircon geochronology by ID-TIMS,SIMS,and laser ablation ICP-MS:Recipes,interpretations,and opportunities[J].Chemical Geology,42:89-110.
Schmitt A K,Chamberlain K R,Swapp S M,et al.2010.In situ U-Pb dating of micro-baddeleyite by secondary ion mass spectrometry[J].Chemical Geology,269(3-4):386-395.
Schmitz M D,Bowring S A.2001.U-Pb zircon and titanite systematics of the Fish Canyon Tuff:An assessment of high precision U-Pb geochronology and its application to young volcanic rocks[J].Geochimica et Cosmochimica Acta,65(15):2571-2587.
Schoene B,Latkoczy C,Schaltegger U,et al.2010.A new method integrating high-precision U-Pb geochronology with zircon trace element analysis(U-Pb TIMS-TEA)[J].Geochimica et Cosmochimica Acta,74(24):7144-7159.
Slma J,Koler J,Condon D J,et al.2008.Pleovice zircon:A new natural reference material for U-Pb and Hf isotopic microanalysis[J].Chemical Geology,249(1-2):1-35.
Solari L A,Gómez-Tuena A,Bernal J P,et al.2010.U-Pb zircon geochronology with an integrated LA-ICP-MSmicroanalytical workstation:Achievements in precision and accuracy[J].Geostandards and Geoanalytical Research,34(1):5-18.
Sylvester P J,Ghaderi M.1997.Trace element analysis of scheelite by excimer laser ablation-inductively coupled plasma-mass spectrometry(ELA-ICP-MS)using a synthetic silicate glass standard[J].Chemical Geology,141(1-2):49-65.
Tera F,Wasserburg G.1972.U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks[J].Earth and Planetary Science Letters,14(3):281-304.
Eynatten H V,Dunkl I.2012.Assessing the sediment factory:The role of single grain analysis[J].Earth Science Reviews,115(1-2):97-120.
Wiedenbeck M,AllP,Corfu F,et al.1995.Three natural zircon standards for U-Th-Pb,Lu-Hf,trace element and REE analyses[J].Geostandards and Geoanalytical Research,19(1):1-23.