δ30Si and δ29Si determinations on USGS BHVO-1 and BHVO-2 reference materials with a new configuration on a nu plasma multi-collector ICP-MS

We report silicon isotopic determinations for USGS rock reference materials BHVO-1 and BHVO-2 using a Nu Plasma multi-collector (MC)-ICP-MS, upgraded with a new adjustable entrance slit, to obtain medium resolution, as well as a stronger primary pump and newly designed sampler and skimmer cones (B cones). These settings, combined with the use of collector slits, allowed a resolution to be reached that was sufficient to overcome the (14)N(16)O and (14)N(2) interferences overlying the (30)Si and the (28)Si peaks, respectively, in an earlier set-up. This enabled accurate measurement of both delta(30)Si and delta(29)Si. The delta value is expressed in per mil variation relative to the NBS 28 quartz reference material. Based on data acquired from numerous sessions spread over a period of six months, we propose a recommended average delta(30)Si of -0.33 +/- 0.05 parts per thousand and -0.29 +/- 0.11 parts per thousand (2se) for BHVO-1 and BHVO-2, respectively. Our BHVO grand mean silicon isotope composition (delta(30)Si = -0.31 +/- 0.06 parts per thousand) is significantly more negative than the only published value for BHVO-2, but is in very good agreement with the recently established average value of ocean island basalts (OIB), confirming the conclusion that the OIB reservoir has a distinct isotopic composition from the solar reservoir as sampled by chondrites.