METHODOLOGY

A total of 32 polished thin sections were prepared from samples of fresh dacite. In addition, 31 samples of fresh to incipiently altered dacite from the shipboard thin section collection were included in our petrographic analyses. Minerals and glass were analyzed for major element oxide and minor (>0.2%) and trace elements (Table T2). Mineral chemistry on samples from Sites 1188, 1190, and 1191 was determined by electron microprobe at the Texas A&M Department of Geology and Geophysics (College Station, Texas) with the Cameca SX-50 Superprobe using a combination of glass, mineral, and pure metal standards. Phases were analyzed using an accelerating voltage of 15 keV and count times from 20 to 30 s with a 1- to 10-Ám-wide beam. Mineral chemistry on samples from Site 1188 was determined by the JEOL JXA-8600 Superprobe in the Geology Department at the University of Georgia, using 15-keV accelerating voltage, 5- to 10-Ám beam, and well-characterized natural and synthetic mineral standards.

The concentrations of major and trace elements of 28 fresh bulk rock samples were determined. Samples marked "JM" in Table T1 were analyzed by LiBO2 fusion followed by inductively coupled plasma (ICP) spectrometry. Major element oxides were determined by ICP–atomic emission spectrometry and trace elements by ICP–mass spectrometry (MS). These analyses were performed by Acme Analytical Laboratories, Vancouver, British Columbia, Canada. Replicate samples and U.S. Geological Survey standard reference materials were included in the analytical suite as unknowns to ensure accuracy and precision. Samples marked "HP" in Table T1 were analyzed by X-ray fluorescence for major elements and selected trace elements (Ba, Rb, Sr, Y, and Zr). All other trace elements, including rare earth elements (REE) were analyzed by ICP-MS. Solutions were prepared using hydrofluoric and nitric acids under atmospheric conditions. A pair of interlaboratory standards compiled from ground wash core material was submitted during all of these analyses to ensure interlaboratory comparability. Data from these reference material analyses are included in Miller et al. (this volume).

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