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1、,LuHf同位素体系及锆石Hf同位素研究,表1L、Hf元套的同位素组成元素同位素丰度(%)IrHt35.100It has long been recognized that Lu-Hf and Sm-Nd isotopesystems behave analogously during most magmatic processesand that the hf and Nd isotopic compositions should bebroadly correlated in most crustal and mantle rocks/,少常用放射性同位素体系衰变常数半妄期(t半衰期地球
2、年龄年(G48.849.84854.947506.5445.6Lu-Hf isochron dating is more precise than Sm-Nd,Hf同位素分析技术的发展TMS技术 Patchett and Matsumoto,1980)但TIMS方法难以对H实现有效的电离,从而使得实验过程中样品量较大(ug级H含量)。而这又使高质量的纯化(特别是Zr、H的分离)难以进行,并限制了低H含量样品的分析。Hot-SIMS (Salters, 1994)该方法是采用离子束对脱离灯丝的H进行轰击,其,电离效率比TM高几个数量级,样品用量较TMS明显减少。但这一方法的化学分离程序更加复杂,
3、Zr、H的有效分离仍困扰着H同位素的发展。MC-ICPMS(Halliday, 1998)开创H同位素分析新局面,据不完全统计,19992004年间发表的有关Hf同位素方面的文献大约是前20年的两倍Iyu.AN985199019952000图1190年以来国际杂志发表的Hf同位素地球化学文献大致情况(未包含会议摘要,LuHf同位素体系衰变方程76Hf/7HD=76Hf/hFo(7Lu/yHf4(e-1),To define an isochron, all samples in a suitemust meet the following conditions:(1)They must hav
4、e the same initial isotopiccomposition. ( That is, they must have initiallybeen in isotopic equilibrium. This is generallythought to be true for cogenetic igneous rocks ),(2)They must have closed at the same time, and2 3)they must have remained closed systems with 7respect to the parent and daughter
5、 elements beinganalyzedIn addition, the rocks must span a range of parent-daughterratios to provide tight constraints on the slope of the isochron,030sC, BINT 01-50500-12820garnet6H02B5Age=158455MaMSWD- 545Intia6HrH=02810533(e=260)02E07eLu/77Hf,含石榴石变质岩石LuH同位素定年0292 SesiaLanzo zora227Ny(phangtacametl与锆石Uo Dora Maira massifPb、sm(WR-gametgametNd等同位Impure.202的a12M素体系定年(AR,结果较为4致0292E(Duchene et al., 1997),2960136+04Msplex. Locations are shown in Figure 2. MSWD-mean square ofweighted deviatesVery precise ages were obtained by Lu-Hf isotopesystem for Miocene samples(Platt et al., 2006),
