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
204
Pb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 zircon — 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., Vonquadt, 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.
Measurements of U, Th and Pb were conducted using the Cameca IMS-1280
SIMS at the Institute of Geology and Geophysics, Chinese Academy of Sciences in
Beijing. U-Th-Pb ratios and absolute abundances were determined relative to the
standard zircon 91500 (Wiedenbeck et al., 1995), analyses of which were interspersed
with those of unknown grains, using operating and data processing procedures similar
to those described by Li et al. (2009). A long-term uncertainty of 1.5% (1 RSD) for
206
Pb/238U measurements of the standard zircons was propagated to the unknowns (Li
et al., 2010), despite that the measured
206
Pb/238U error in a specific session is
generally around 1% (1 RSD) or less. Measured compositions were corrected for
common Pb using non-radiogenic
204
Pb. Corrections are sufficiently small to be
insensitive to the choice of common Pb composition, and an average of present-day
crustal composition (Stacey and Kramers, 1975) is used for the common Pb assuming
that the common Pb is largely surface contamination introduced during sample
preparation. Uncertainties on individual analyses in data tables are reported at a 1
level; mean ages for pooled U/Pb (and Pb/Pb) analyses are quoted with 95%
confidence interval. Data reduction was carried out using the Isoplot/Ex v. 2.49
program (Ludwig, 2001).