Appendix A4 (ANALYTICAL TECHNIQUES)

Three whole-rock samples were analyzed for whole-rock 40Ar-39Ar ages at the Geological Survey of Japan/AIST on a VG Isotech VG3600 noble gas mass spectrometer fitted with a BALZERS electron multiplier. Complete analytical results are listed in Appendix 3.  We also note that the comparatively large uncertainty on ages for two of the samples (HPD1013 R01 and R8) was caused by the high Ca/K of these samples than HPD1012 sample, which caused a larger error derived from correction for the Ca-derived interfering isotopes. This effect was strongly enhanced by delay of analyzing the irradiated samples as a consequence of damage to the lab caused by the March 11 2011 Tohoku earthquake.   
For whole rock chemical compositions, samples with prefix “HPD” in Appendix Table A5 were analyzed at JAMSTEC.  HPD samples were analyzed using the following procedure:  After sawing and jaw crushing, samples were pulverized in an agate ball mill. Major and selected trace elements (Ba, Ni, Cu, Zn, Pb, Th, Rb, Sr, Y, Zr and Nb) were determined by X-ray fluorescence at IFREE, JAMSTEC. Trace elements were analyzed on pressed powder discs, and major elements were determined on fused glass discs. A mixture of ~0·4 g powdered sample and 4 g of anhydrous lithium tetraborate (Li2B4O7) was used; no matrix correction was applied because of the high dilution involved. Samples with prefix “C7” were analyzed for major elements by Activation Laboratories (Ancaster, Ontario, Canada) http://www.actlabs.com/page.aspx?menu=40&app=183&cat1=489&tp=2&lk=no and at U Texas Dallas for trace elements.  Major elements were analyzed by fusion-ICP techniques.  Each batch of samples contained a method reagent blank, certified reference material and 17% replicates. All were mixed with a flux of lithium metaborate and lithium tetraborate and fused in an induction furnace. Melt was immediately poured into 5% nitric acid solution containing an internal standard, and mixed until completely dissolved (~30 minutes). Sample solutions for major oxides and selected trace elements were analyzed on a Thermo Jarrell-Ash ENVIRO II ICP or a Varian Vista 735 inductively-coupled plasmaphotometer (ICP).  Calibration was performed using 7 prepared USGS and CANMET rock standards.  One of the 7 standards was used during the analysis for every group of ten samples. Trace element analyses at UTD were carried out by inductively coupled plasma mass spectrometer (ICP-MS). Powders were prepared in an alumina ball mill. Samples (~200 mg) were weighed into teflon beakers and digested using HF, HClO4, HCl, and HNO3. Solutions were diluted 250 times in ~10% HNO3 and further diluted 10 times in 4% HNO3 prior to analysis. A typical analytical run of 25 samples consisted of five to six certified reference materials (CRMs), and one to two procedural blanks with the remainder being sample unknowns. CRMs included USGS standards BIR-1, W-2, BHVO-2, BCR-2, AGV-2, RGM-1, GSP-2, and G-2. Acids were distilled in-house or were purchased (Baseline grade) from Seastar Chemicals. All dilutions were prepared using 18.2 MW water from a Millipore system including an Elix reverse osmosis and electrodeionization unit and a Milli-Q Element final purification unit. Trace elements were analyzed on a Perkin Elmer-Sciex Elan 6100 dynamic reaction cell ICP-MS (DR-ICP-MS). External calibration standards were prepared from multi-element ICP standards. Samples were introduced to the ICP via an autosampler at a flow rate of 1 mL min-1. Samples were nebulized using a cross-flow nebulizer and Ryton Scott spray chamber. Typical operating conditions are 0.90 L min-1 nebulizer gas flow, 1.30 L min-1 auxiliary gas flow, 13 L min-1 plasma gas flow at an operating RF voltage of 1,100 W. The ion lens is optimized at the start of each run and the voltage is dynamically modified by the instrument software to optimize analyte signal for masses of In. To monitor drift, a calibration standard and a certified reference material were run after every five unknowns. Procedural blanks were near or below detection for the operating conditions.