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Materials and methods

Fourteen samples from Hole M0008A in the Tiarei area have previously been analyzed for major element contents, except Na2O, by energy dispersive polarized X-ray fluorescence (XRF) at Bremen University (Germany) (see the “Tiarei marginal sites: Sites M0008, M0010–M0014, and M0022” chapter). The contents of some trace elements, including Sr, Ba, Rb, Cu, Ni, and Zn, have also been analyzed. The samples include sand-silt-clay mixtures, pebbles, cobbles, and boulders. For this report, Na2O contents of the previously analyzed samples were determined by inductively coupled plasma–optical emission spectrometry at the Scripps Institution of Oceanography (SIO), University of California, San Diego (USA). The precision of the Na2O analysis based on repeated analyses of the international rock standard AGV-1 is ≤3.5%.

Three additional sand-silt samples from Hole M0008A plus two sand samples from Hole M0010A and one sand sample from Hole M0021B (all in the Tiarei area) were analyzed for major elements and trace elements Ni, Cr, Sc, V, Ba, Rb, Sr, Zr, Nb, Ga, Cu, Zn, Pb, La, Ce, Th, Nd, and U by XRF at the GeoAnalytical Laboratory at Washington State University (WSU) (USA). Information on methods, precision, and accuracy of the XRF analysis at WSU are available at​Geolab/​index.html. All samples previously and newly analyzed for major elements were analyzed for loss on ignition (LOI) values at SIO and WSU, respectively.

All the above samples plus four small amounts of sand-silt samples from Hole M0021B were also analyzed for trace elements, including Rb, Sr, Y, Ba, U, Th, and Pb and the rare earth elements (REE) La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu by high-resolution inductively coupled plasma–mass spectrometry (ICP-MS) at SIO. Samples were prepared by digesting 25 mg of powder using the HF-HNO3 method described by Janney and Castillo (1996). Digested samples were diluted 4000× in a solution containing 2.5 wt% nitric acid and 1 ppb In as an internal standard. Time- and mass-dependent instrumental drift was corrected for by applying a mass-interpolated internal standard correction and correcting measured sample concentrations using values of a well-analyzed in-house mid-ocean-ridge basalt (MORB) standard analyzed repeatedly throughout each run. Duplicate analyses of standards and a number of unknowns were conducted, each analysis in a different run. Reproducibility was generally high (≤3%), except for elements that have low (<0.2 ppm) concentrations.

Four fresh-looking coarse-grained (pebble to boulder size) volcaniclasts were dated by 40Ar/39Ar dating at the Noble Gas Mass Spectrometry Laboratory at Oregon State University (OSU) (USA). These include two large boulders that were originally suspected as parts of a pre-LGM lava flow in the upper section of Hole M0008A (see the “Tiarei marginal sites: Sites M0008, M0010–M0014, and M0022” chapter), a pebble in the lower section of Hole M0008A, and a pebble in Hole M0010A. Information on methods, precision, and accuracy of the 40Ar/39Ar dating method at OSU are similar to those described in Koppers et al. (2004) and are available at​research/​mgg/​chronology.html.

Almost all fine-grained (sand, silt, and clay sized) volcaniclastics were also analyzed for total and inorganic carbon contents (organic carbon contents were calculated by mass balance) at SIO. Total carbon content was determined by combustion with O2 using a Costech elemental analyzer in CHN mode. Inorganic carbon content was determined by reaction with phosphoric acid and measurement with a ThermoFisher Delta XP plus isotope ratio mass spectrometer with associated gas bench. Accuracy for total carbon measurement was 1%, whereas accuracy for inorganic measurement was 2%.