JAMSTEC-R IFREE Special Issue, November 2009 ― Original Paper ― Precise Pb isotope analysis of igneous rocks using fully-automated double spike thermal ionization mass spectrometry (FA -DS- TIMS) Takashi Miyazaki1*, Nobuyuki Kanazawa2, Toshiro Takahashi1, Yuka Hirahara1, Bogdan Stefanov Vaglarov1, Qing Chang1-XQLFKL.LPXUD1, Yoshiyuki Tatsumi1 $IXOO\DXWRPDWHG )$ WHFKQLTXHDSSO\LQJ2073E2043EGRXEOHVSLNH '6 WRWKHUPDOLRQL]DWLRQPDVVVSHFWURPHWU\ 7,06 KDVEHHQGHYHORSHG )$'67,06 $ORQJWHUPEDVHOLQHLVPHDVXUHGSULRUWRWKHVDPSOHPHDVXUHPHQWUXQVDQGLVDSSOLHGWR DOORIWKHDFTXLUHGVDPSOHGDWDDYRLGLQJVDPSOHZDVWLQJFDXVHGE\IUHTXHQWEDVHOLQHPHDVXUHPHQWVGXULQJVDPSOHUXQV)$'6 7,06RIIHUVUHOLDEOHIXOO\DXWRPDWHGVHTXHQWLDODQDO\VHVRIVDPSOHVLQRQHEDWFKLQFOXGLQJQDWXUDOUXQVDQGUXQVGRSHG with a spike enriched 2073EDQG2043E7KLVFXWVRSHUDWLQJODERUFRVWVDOWKRXJKWKHPHDVXUHPHQWWLPHLVORQJHUWKDQDFRQYHQWLRQDO 7,06RUDQLGHQWLFDOUXQXVLQJPXOWLFROOHFWRULQGXFWLYHO\FRXSOHGSODVPDPDVVVSHFWURPHWU\ 0&,&306 The isotopic ratios of the 2073E2043EGRXEOHVSLNHXVHGLQWKLVVWXG\DUH 2063E2043E 2073E2043E DQG 2083E2043E ZKHQQRUPDOL]HGWR1,676502083E2063E $YHUDJHYDOXHVIRU1,67650FRQWDLQLQJ DQGQJ3EDUH2063E2043E 2073E2043E 2083E2043E HUURUVDUH 6'Q 7KHVHDUHZLWKLQHUURURIUHFHQWO\UHSRUWHGYDOXHVREWDLQHGE\'67,06DQG'60&,&3067KHUHSURGXFLELOLW\ of 2083E2043ELQWKLVVWXG\LVXVLQJQJ3EDQGXVLQJQJ3E7KHVHDUHVLPLODUWRRUEHWWHUWKDQWKRVH UHSRUWHGE\YDULRXVRWKHUPHWKRGV7KHDYHUDJHYDOXHVIRU-%FRQWDLQLQJQJ3EDUH2063E2043E 2073E2043E = 15.5622 ± 0.0026, 2083E2043E HUURUVDUH6'Q DQGDUHFRPSDUDEOHWRWKRVHUHSRUWHGLQUHFHQWVWXGLHV 7KHVHUHVXOWVVKRZWKDWWKHQHZWHFKQLTXHLVUHOLDEOHLQWHUPVRIERWKDFFXUDF\DQGSUHFLVLRQ Keywords3ELVRWRSH2073E2043EGRXEOHVSLNHIXOO\DXWRPDWHG7,061,67650-% 5HFHLYHG)HEUXDU\$FFHSWHG-XQH ,QVWLWXWHIRU5HVHDUFKRQ(DUWK(YROXWLRQ-DSDQ$JHQF\IRU0DULQH(DUWK6FLHQFHDQG7HFKQRORJ\ 7KHUPR)LVKHU6FLHQWL¿F.. &RUUHVSRQGLQJDXWKRU Takashi Miyazaki ,QVWLWXWHIRU5HVHDUFKRQ(DUWK(YROXWLRQ-DSDQ$JHQF\IRU0DULQH(DUWK6FLHQFHDQG7HFKQRORJ\ 1DWVXVKLPDFKR<RNRVXND-DSDQ +81-46-867-9635 [email protected] &RS\ULJKWE\-DSDQ$JHQF\IRU0DULQH(DUWK6FLHQFHDQG7HFKQRORJ\ 73 3UHFLVH3ELVRWRSHDQDO\VLVXVLQJIXOO\DXWRPDWHG'67,06 1. Introduction analytical procedure of this method and report its results for 3ELVRWRSHVDUHDIXQGDPHQWDODQGSRZHUIXOWRRO 3ELVRWRSHDQDO\VHVRQ1,67650DQG-%VWDQGDUGV in understanding geodynamic processes such as material recycling in the Earth’s interior, or in surface environments, 2. 207Pb-204Pb DS-TIMS WKURXJKRXWWKH(DUWK¶VKLVWRU\3ELVRWRSHVDUHDQDO\]HGE\ 7KH'6PHWKRGUHTXLUHVDQLQGLYLGXDOVDPSOHWREH thermal ionization mass spectrometry (TIMS) and multiple VHSDUDWHGLQWRWZRDOLTXRWVRQHRIZKLFKLVGRSHGZLWKD collector inductively coupled plasma mass spectrometry spike enriched in two isotopes (in this case 2073EDQG 2043E 0&,&306 0DVVIUDFWLRQDWLRQRFFXUULQJZLWKLQPDVV 'RGVRQ %RWKDOLTXRWVDUHFRQVHFXWLYHO\DQDO\]HG spectrometers has been a major obstacle preventing the in the mass spectrometer; the ‘natural run’ refers to the PHDVXUHPHQWRISUHFLVH3ELVRWRSHUDWLRVDVQDWXUDOO\ XQGRSHGDOLTXRWWKHµVSLNHGUXQ¶WKHGRSHGDOLTXRW7KUHH3E RFFXUULQJ3EKDVRQO\RQHVWDEOHLVRWRSH 2043E6HYHUDO isotope ratios are measured with a common denominator (i.e., approaches have been developed to correct for this mass either 206,207,2083E2043E 204,207,2083E2063E 204,206,2083E2073ERU fractionation. In the case of TIMS, 1) a conventional 204,206,2073E2083E IRUHDFKUXQDQGWRJHWKHUZLWKWKHNQRZQ fractionation correction using a mass fractionation factor isotope ratios of the spike, derive the mass discrimination determined by analyzing a standard, which is then applied IDFWRURIWKHQDWXUDOUXQDQGFRQVHTXHQWO\WKHWUXHLVRWRSH to all unknowns, 2) a zero-time correction (Kuritani and ratios of the natural and the spiked runs. Several methods Nakamura, 2002), and 3) double, triple or two-double spike have been discussed in the literature to derive these values, PHWKRGV HJ'RGVRQ+RIPDQQ+DPHOLQHWDO RIZKLFKWKHUHDUHWZRW\SHVLWHUDWLYHFDOFXODWLRQV 'RGVRQ :RRGKHDGHWDO*DOHUDQG$ERXFKDPL :RRGKHDGHWDO DQGGLUHFWFDOFXODWLRQV Thirlwall, 2000; Kuritani and Nakamura, 2003) have been +RIPDQQ+DPHOLQHWDO*DOHU DSSOLHG:KLOHIRU0&,&306 DQH[WHUQDOIUDFWLRQDWLRQ Thirlwall, 2000; Kuritani and Nakamura, 2003). The latter correction using Tl (e.g. Thirlwall, 2000; Tanimizu and was applied in this study. Ishikawa, 2006), 2) a combination between double spike $VFKHPDWLFLOOXVWUDWLRQRIWKHGRXEOHVSLNHPHWKRG '6 ZLWK7OH[WHUQDOFRUUHFWLRQ %DNHUHWDO DQG (2073E2043EGRXEOHVSLNH DVSURSRVHGE\+RIPDQQ '6ZLWKRXW7OFRUUHFWLRQ 0DNLVKLPDHWDO KDYHEHHQ is illustrated in Fig. 1. The ‘true’ isotopic compositions applied. RIWKHXQNQRZQDQGGRSHGPL[WXUHVDUHSORWWHGDWSRLQWV These procedures have resulted in a dramatic U and M, respectively, while points u and m correspond LPSURYHPHQWLQWKHSUHFLVLRQDQGDFFXUDF\RI3ELVRWRSHV to the measured isotopic compositions of the unknown PHDVXUHGE\0&,&306DQGWKHVHQRZPDWFKWKRVHRI DQGWKHGRSHGPL[WXUH3RLQWS corresponds to the isotope '67,06 7DQLPL]XDQG,VKLNDZD0DNLVKLPDHW FRPSRVLWLRQRIWKH3EGRXEOHVSLNH$VVXPLQJWKHOLQHDU DO $VDUHVXOWPDQ\ODERUDWRULHVXVH0&,&306 particularly for samples containing relatively large amounts RI3E !QJ EHFDXVHWKHDQDO\WLFDOWLPHUHTXLUHGIRU 208Pb/204Pb 0&,&306LVVKRUWHUWKDQWKDWRI7,06+RZHYHUUHFHQW fu instrumental developments in TIMS have enabled reliable DXWRPDWHGDQDO\VHVRIXSWRVDPSOHVVHWRQRQH¿ODPHQW Unknown sample (U) ● magazine to be performed. This cuts labor costs, although the fm DQDO\WLFDOWLPHUHPDLQVORQJHUWKDQ0&,&306 ○ Measured (u) $W,)5((ZHKDYHEHHQLPSURYLQJWKHFRQYHQWLRQDO ● Doped mixture (M) 7,06WHFKQLTXHUHDFKLQJDUHSURGXFLELOLW\RI ○ Measured (m) 56' 2083E2043EIRUQJRI3E 0L\D]DNLHWDO 207Pb- 204Pb spike (S) 2007). However, the method is not applicable to analyze ● small amounts of sample (< 25 ng) (Miyazaki et al., 2003a). 207Pb/204Pb ,QRUGHUWRDFKLHYHSUHFLVH3ELVRWRSHDQDO\VLVRQVXFKVPDOO 206Pb/204Pb samples, we have developed a fully-automated 2073E2043E Fig.1. Three dimensional graphical representation of the double spike, GRXEOHVSLNH '6 PHWKRGIRU7,06:HEULHÀ\GHVFULEHWKH DIWHU*DOHU )RUGH¿QLWLRQVRIV\PEROVVHHWH[W 74 JAMSTEC-R IFREE Special Issue, November 2009, 73 í80 T. Miyazaki et al., fractionation law, the true isotope ratios of the unknown (Ui) (1985). DQGPL[WXUH Mi FDQEHH[SUHVVHGDV 3. Experimental Ui = ui (1 + İ8¨i) (1) 3.1. Reagents and isotope standard materials ® 7$0$385( $$JUDGH+)+123, Mi = mi (1 + İM¨i) (2) 20 % HBr and 98 % H3324 (Tama Chemicals Co., Ltd) ZHUHXVHGZLWKRXWDQ\DGGLWLRQDOSXULILFDWLRQ:DWHUZDV -1 ® where ui and mi are the measured isotope ratios of the GHLRQL]HGWRDUHVLVWLYLW\RI!0ȍFP by a Milli-Q ® XQNQRZQDQGGRSHGPL[WXUHİ8 and İM are the fractionation system (Millipore DQG¿QDOO\GLVWLOOHGDW&XVLQJDWZR ® IDFWRUVSHU$08RIU and MDQG¨i is the mass difference ERWWOH7HÀRQ VWLOO$QLRQL]DWLRQDFWLYDWRUZDVSUHSDUHGIURP between the numerator and denominator isotopes (subscript silicic acid colloidal solution (Nissan Chemical Industries, iLVIRUWKHWKUHHOHDGLVRWRSHUDWLRV 7KHPL[LQJHTXDWLRQ /WG DVGHVFULEHGLQ0L\D]DNLHWDO $KLJKSXULW\ between the Ui and Si LVRWRSHUDWLRVRI3EGRXEOHVSLNH 3EPHWDO1,67650DQGZKLFKZHUHGLJHVWHGLQ JLYHVWKHLVRWRSHUDWLRVRIWKHGRSHGPL[WXUH Mi and diluted with 0.5 M HNO3 to give a concentration of 10 SSPZHUHXVHGDVD3ELVRWRSHVWDQGDUG Mi (1 + q) = Ui + Si ·q (3) 3.2. DS calibration where q is the ratio between the reference isotope in the spike 2043EDQG 2073EHQULFKHGVSLNHVZHUHREWDLQHGIURP 204 204 207 204 and the unknown ( 3Espike/ 3Eunknown LQWKHGRSHGPL[WXUH WKH2DN5LGJH1DWLRQDO/DERUDWRU\86$ 3E 3EGRXEOH &RPELQLQJHTXDWLRQV DQG JLYHVWKHIROORZLQJ VSLNHFRPSRVLWLRQDQGWKHVSLNHVDPSOHPL[LQJUDWLRKDYH HTXDWLRQ EHHQRSWLPDOO\GHWHUPLQHGE\DQHUURUVLPXODWLRQDIWHU*DOHU (1999). The 2073E2043EGRXEOHVSLNHVROXWLRQZDVGLOXWHG (mi - Si) · q + mi¨i · (1 + q) · İM - ui · İ8¨i = ui - mi with 0.5 M HNO3 to 7 ppm, and calibrated using NIST (4) SRM 982. 2063E2043E 2073E2043EDQG 2083E2043EUDWLRVRI NIST SRM 982, used for this calibration and determined ZKLFKFDQEHH[SUHVVHGLQWHUPVRIWKHPDWUL[HTXDWLRQ following the conventional method (Miyazaki et al. 2003a), were 36.7570, 17.1674 and 36.7629 when normalized to 2083E2063E &DWDQ]DURHWDO 7KHLVRWRSLF (5) composition of the 2073E2043EGRXEOHVSLNHLQFOXGLQJWKH HIIHFWRIWKHORDGLQJEODQN SJRI3E ZHUH2063E2043E 0.10203, 2073E2043E DQG2083E2043E where r = (1 + q DQGWKHPDWUL[A and vector BDUHJLYHQE\ 3.3. Sample preparation $OOWKHFKHPLFDOSURFHGXUHVZHUHSHUIRUPHG (6) in a class 100 clean room. The powdered silicate rock VWDQGDUG -% ZDVGHFRPSRVHGLQDFORVHGPO7HIORQ® DQG SHUÀXRURDONR[\ 3)$ VFUHZFDSYLDOV 6DYLOOH[®) with a 1 PL[WXUHRI0+123 and 20 M HF on a hot plate at &RYHUQLJKW$IWHUUHDFKLQJFRPSOHWHGU\QHVVDW (7) &WKHVDPSOHZDVGLVVROYHGZLWKPORI0+%U7KHQ WKHVDPSOHZDVFRPSOHWHO\GULHGDJDLQWKLVWLPHDW& after which a further 1 ml of 8 M HBr was added. Once more 7KHVROXWLRQWR(T DQGWKHUHIRUHİ 8 , follows by WKHVDPSOHZDVKHDWHGDW&XQWLOFRPSOHWHGU\QHVVZDV PXOWLSO\LQJERWKVLGHVRI(T E\WKHLQYHUVHRIA. The achieved before 1 ml of 0.5 M HBr was added to digest the propagated error for the corrected isotope ratios of the dried sample and it was centrifuged for 20 minutes at 4000 unknown is calculated using a model from Hamelin et al. USP7KHVXSHUQDWDQWZDVWUDQVIHUUHGWRDQRWKHU3)$YLDO JAMSTEC-R IFREE Special Issue, November 2009, 73 í80 75 3UHFLVH3ELVRWRSHDQDO\VLVXVLQJIXOO\DXWRPDWHG'67,06 The remaining precipitate was rinsed with 0.5 ml 0.5 M HBr 3ELVRWRSHPHDVXUHPHQWVZHUHFDUULHGRXWRQD and centrifuged, and the supernatant was then added to the Thermo Finnigan TRITON TI® thermal ionization mass VDPH3)$YLDO7KHVXSHUQDWDQWZDVORDGHGLQWRDQDQLRQ VSHFWURPHWHU 7,06 HTXLSSHGZLWKQLQH)DUDGD\FXS FROXPQFRQWDLQLQJPO%LR5DG$*;UHVLQ ± collectors at the