SIMS锆石U-Pb定年方法-中国科学院地质与地球物理研究所

SIMS锆石U-Pb定年方法

用于U-Pb年龄测定的样品（号码）用常规的重选和磁选技术分选出锆石。将锆石样品颗粒和锆石标样Plésovice (Sláma et al., 2008) (或TEMORA, Black et al., 2004）和Qinghu (Li et al., 2009）粘贴在环氧树脂靶上，然后抛光使其曝露一半晶面。对锆石进行透射光和反射光显微照相以及阴极发光图象分析，以检查锆石的内部结构、帮助选择适宜的测试点位。样品靶在真空下镀金以备分析。

U、Th、Pb的测定在中国科学院地质与地球物理研究所CAMECA IMS-1280二次离子质谱仪（SIMS）上进行，详细分析方法见Li et al. (2009)。锆石标样与锆石样品以1:3比例交替测定。U-Th-Pb同位素比值用标准锆石Plésovice (337Ma, Sláma et al., 2008（或TEMORA (417Ma, Black et al., 2004)）校正获得，U含量采用标准锆石91500 (81 ppm, Wiedenbeck et al., 1995) 校正获得，以长期监测标准样品获得的标准偏差（1SD = 1.5%, Li et al., 2010）和单点测试内部精度共同传递得到样品单点误差，以标准样品Qinghu (159.5 Ma, Li et al., 2009) 作为未知样监测数据的精确度。普通Pb校正采用实测204Pb值。由于测得的普通Pb含量非常低，假定普通Pb主要来源于制样过程中带入的表面Pb污染，以现代地壳的平均Pb同位素组成(Stacey and Kramers, 1975)作为普通Pb组成进行校正。同位素比值及年龄误差均为1σ。数据结果处理采用ISOPLOT软件（文献）。

参考文献

Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R., Campbel, I.H., Korsch, R.J., Williams, I.S., Foudoulis, Chris., 2004.

Improved 206Pb/238U microprobe geochronology by the monitoring of a

trace-element-related matrix effect; SHRIMP, ID-TIMS, ELA-ICP-MS and

oxygen isotope documentation for a series of zircon standards. Chem. Geol.,

205: 115-140.

Jiří Sláma, Jan Košler, Daniel J. Condon, James L. Crowley, Axel Gerdes, John M.

Hanchar, Matthew S.A. Horstwood, George A. Morris, Lutz Nasdala, Nicholas Norberg, Urs Schaltegger, Blair Schoene, Michael N. Tubrett , Martin J.

Whitehouse, 2008. Plešovice z ircon —A new natural reference material for U

–Pb and Hf isotopic microanalysis. Chemical Geology 249, 1–35

Li, Q.L., Li, X.H., Liu, Y., Tang, G.Q., Yang, J.H., Zhu, W.G., 2010. Precise U-Pb and Pb-Pb dating of Phanerozoic baddeleyite by SIMS with oxygen flooding

technique. Journal of Analytical Atomic Spectrometry 25, 1107-1113.

Li, X.-H., Y. Liu, Q.-L. Li, C.-H. Guo, and K. R. Chamberlain (2009), Precise determination of Phanerozoic zircon Pb/Pb ageby multicollector SIMS without external standardization, Geochem. Geophys. Geosyst., 10, Q04010,

doi:10.1029/2009GC002400.

Ludwig, K.R., 2001. Users manual for Isoplot/Ex rev. 2.49. Berkeley Geochronology Centre Special Publication. No. 1a, 56 pp.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet. Sci. Lett., 26, 207-221.

Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., V onquadt, A., Roddick, J.C., Speigel, W., 1995. Three natural zircon standards for U-Th-Pb,

Lu-Hf, trace-element and REE analyses. Geostand. Newsl. 19: 1-23.

SIMS U-Pb dating methods

Samples XXX for U-Pb analysis were processed by conventional magnetic and density techniques to concentrate non-magnetic, heavy fractions. Zircon grains, together with zircon standard 91500 were mounted in epoxy mounts which were then polished to section the crystals in half for analysis. All zircons were documented with transmitted and reflected light micrographs as well as cathodoluminescence (CL) images to reveal their internal structures, and the mount was vacuum-coated with high-purity gold prior to secondary ion mass spectrometry (SIMS) analysis.