ONGOING ISOTOPIC CHARACTERIZATION OF USGS STANDARDS: MC-ICPMS AND TIMS DATA FROM THE PACIFIC CENTRE FOR ISOTOPIC AND GEOCHEMICAL RESEARCH, UNIVERSITY OF BRITISH COLUMBIA

The PCIGR at the University of British Columbia has undertaken a systematic analysis of isotopic (Nd, Sr, Hf, Pb) composition and concentration of a broad compositional range of United States Geological Survey standards, including basalt (BCR-1, 2; BHVO-1, 2; BIR-1), dunite (DNC-1), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2) and granite (G-2).  USGS rock standards are geochemically well-characterized,  but there is no systematic methodology nor database for radiogenic isotopic analyses, even for the widely used BCR-I.  Instrumentation at PCIGR, including a Nu MC-ICPMS, a Triton TIMS, and an ElementII HR-ICPMS, permits a rigorous assessment and comparison of precision and accuracy in isotopic analyses.

Our separation technique involves an HF/HNO₃ dissolution in Teflon bombs, standard cation exchange elutriation for Sr and REE separation, and HDEHP Teflon columns for Nd separation.  Samples are unspiked, and elemental concentration is determined by HR-ICPMS.  Isotopic composition is determined by both thermal ionization mass spectrometry (Sr, Nd) and by multi-collector inductively coupled plasma mass spectrometry (Nd, Hf, Pb).  Replicate runs of La Jolla Nd standard demonstrate excellent agreement between MC-ICPMS (¹⁴³Nd/¹⁴⁴Nd=0.511846±14 [n=100]) and TIMS (0.511849±15 [n=42]).

 ¹⁴³Nd/¹⁴⁴Nd values and Sm/Nd ratios of isotopically known standards, such as BCR-1 (¹⁴³Nd/¹⁴⁴Nd=0.512623±2 [Nu; n=2]; 0.512627±7 [Triton; n=8]; Sm/Nd=0.1389) and BHVO-1 (0.512972±5 [N=2]; 0.512973±6 [T=12]; 0.1522-0.1532) are within error of of published values.  Replicate analyses of previously uncharacterized standards, such as AGV-1 (0.512776±4 [N=4]; 0.512781±7 [T=7]) and RGM-1 (0.512800±5[T=1]), and second generation standards, such as BCR-2 (0.512639±6 [T=3]), BHVO-2  (0.512984±3 [T=3]), and AGV-2 (0.512794±2 [T=2]), provide the first reproducible data available for these standards.

 

Strontium isotopic analyses of BCR-1 (⁸⁷Sr/⁸⁶Sr=0.705027±7 [T=4]) and BHVO-1 (0.703482±13 [T=6]) yield ⁸⁶Sr/⁸⁷Sr values that replicate known values.  Replicate analyses of other standards, such as BCR-2 (0.705024±5 [T=3]), BHVO-2 (0.703487±9 [T=4]) and AGV-1 (0.703997±10 [T=6]) provide the first data for these standards.

 

Hafnium and lead isotopic analyses are underway.  This investigation provides the first complete isotopic characterization of USGS standards.