Electronic Supplemental Materials
Geochemical Methods
Geochronology. The 40Ar-39Ar ages were determined at Oregon State University using methods described in Koppers et al. (2003) and Duncan and Keller (2004). Holocrystalline matrix material from the interior of the three pillow basalts was hand-picked for age determinations. Samples were finely crushed (<1 mm) with a tungsten-carbide (WC) coated hydraulic press, ultrasonically cleaned in millipore water, dried for 24 hours at 40oC and hand-picked to remove fragments with signs of alteration and phenocrysts. Samples were sent to John Huard at Oregon State University for processing, irradiation and analysis.
Microprobe. Glass major element and S analyses were obtained with the University of Hawai`i JEOL HyperProbe, five-spectrometer electron microprobe using a 15 kV accelerating voltage, 10 nA beam current, and a 10 mm diameter beam. The reported analyses (Table 3) are an average of 10 spot analyses per sample. Accuracy and precision are estimated at <1% for major elements and 2–5% for minor elements (<1 wt.%) based on repeat analyses of a Hawaiian glass standard (A99) from the Smithsonian collection (e.g., Jarosewich et al. 1979).
XRF. Seventeen dive and four dredge samples from Mahukona were analyzed by XRF for major and trace elements (Table 4). Samples were coarsely crushed (1-8 mm) with a tungsten-carbide (WC) coated hydraulic press, ultrasonically cleaned in Millipore water, dried for 24 hours at 40oC and hand-picked to remove fragments with signs of alteration. This procedure ensured only the freshest parts of each sample were analyzed. The efficiency of this process is reflected by the relatively low loss-on-ignition (LOI) values (for methods see Rhodes 1996) for all but two samples (<0.5 wt.%; Table 4). The clean rock fragments were split into two aliquots; one for XRF and the other for ICP-MS and isotopes. Samples for XRF were powdered using a WC-lined mill and analyzed for major and trace elements at the University of Massachusetts (for analytical procedures and precision see Rhodes and Vollinger 2004).
ICP-MS. Matrix material was picked from 13 samples for ICP-MS analyzes to avoid the effects of accumulation of olivine, which is present in some samples (Table 2). The samples were analyzed for trace elements (Table 5) at Washington State University (for analytical methods and estimates of precision see Knaack et al.1994). These samples were powdered in an agate mill. The Kῑlauea rock reference Kil1919 (Pietruszka and Garcia 1999; Rhodes and Vollinger 2004) was analyzed with these samples.
Isotopes. Pb, Sr, Nd and Hf isotopic analyses were made on 12 Mahukona samples (Table 6). Rock chips were powered in agate. A sequential leaching method was used to remove post-eruptive alteration (6 to 14 steps, average 10, with weight losses of 35-67%, average 50%; see Weis et al. 2005; Nobre Silva et al. 2009). For analytical procedures see Weis et al. (2006, 2007); for normalization values see Table 6. During this study, the SRM 987 standard analyses gave 87Sr/86Sr = 0.710250±19 (n=10); La Jolla Nd: 143Nd/144Nd = 0.511852±09 (n=10); JMC 475: 176Hf/177Hf = 0.282150±18 (n=27), and SRM 981: 206Pb/204Pb = 16.9426±23, 207Pb/204Pb = 15.4980±19, 208Pb/204Pb = 36.7181±54 (n=24). The BHVO-2 USGS standard was analyzed together with the samples and the results are within errors of the published values (Weis et al. 2006, 2007). Complete procedural duplicates were analyzed for one Mahukona sample (161-1), yielding an external reproducibility for the isotope ratios of Pb (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) of 22, 32, 7 ppm, and for Sr, Nd and Hf of 10, 33 and 2 ppm, respectively. Column blanks for Sr, Nd, Hf and Pb isotope chemistry were negligible (Sr: 0.63 ng; Nd: 0.67 ng; Hf: 0.01 ng; Pb: 0.05 ng).
Helium abundances and isotopic compositions were analyzed on 10 new samples at Woods Hole Oceanographic Institution using a fully automated, dual collection, statically operated helium isotope mass spectrometer with a Nier-type ion source (for methods see Kurz et al. 2004). All the data reported here were obtained by crushing in vacuo.
References
Duncan RA, Keller RA (2004) Radiometric ages for basement rocks from the Emperor Seamounts, ODP Leg 197. Geochem Geophys Geosyst 5: Q08L03. doi:10.1029/2004GC000704
Jarosewich E, Nelson JA, Norberg JA (1979) Electron microprobe reference samples for mineral analyses. Smithsonian Contr Earth Sci 22:68-72
Kauahikaua J, Hildenbrand T, Webring M (2000) Deep magmatic structures of Hawaiian volcanoes, imaged by three-dimensional gravity models. Geology 28:883-886
Kinoshita WT, Krivoy HL, Mabey DR, MacDonald RR (1963) Gravity survey of the island of Hawaii. US Geol Surv Prof Paper 475C:C114–116
Knaack C, Cornelius SB, Hooper PR (1994) Trace element analyses of rocks and minerals by ICP-MS. Open file report, GeoAnalytical Lab, Washington State Univ
Koopers AAP, Staudigel H, Duncan RA (2003) High-resolution 40Ar/39Ar dating of the oldest oceanic basement basalts in the western Pacific basin. Geochem Geophys Geosyst 4: 8914, doi:10.1029/2003GC000574
Kurz MD, Curtice J, Lott III DE, Solow A (2004) Rapid helium isotopic variability in Mauna Kea shield lavas from the Hawaiian Scientific Drilling Project. Geochem Geophys Geosyst 5: Q04G14. doi:10.1029/2002GC000439
Rhodes JM (1996) Geochemical stratigraphy of lava flows sampled by the Hawaii Scientific Drilling Project. J Geophys Res 101:11,729-11,746
Rhodes JM, Vollinger MJ (2004) Composition of basaltic lavas sampled by phase-2 of the Hawaii Scientific Drilling Project: Geochemical stratigraphy and magma types. Geochem Geophys Geosyst 5: Q03G13. doi:10.1029/2002GC000434
Weis D, Kieffer B, Maerschalk C, Barling J, de Jong J, Williams GA, Hanano D, Pretorius W, Mattielli N, Scoates JS, Goolaerts A, Friedman RM, Mahoney JB (2006) High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS. Geochem Geophys Geosyst 7: Q08006. doi:10.1029/2006GC001283
Weis D, Kieffer B, Hanano D, Nobre Silva I, Barling J, Pretorius W, Maerschalk C, Mattielli N (2007) Hf isotope compositions of U.S. Geological Survey reference materials. Geochem Geophys Geosyst 8: Q06006. doi:10.1029/2006GC001473