IN-SITU TRACE-ELEMENT ANALYSIS OF INDIVIDUAL SILICATE MELT INCLUSIONSBY LASER-ABLATION MICROPROBE INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY (LAM-ICP-MS)

This paper reports the successful application of laser ablation microp robe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) to the in situ analysis of a diverse suite of twenty trace elements including Zr, Hf, Nb, Ta, Y, and REEs, in individual silicate melt inclusions i n phenocrysts from Fantale volcano, Ethiopia. The UV laser, a frequenc y quadrupled Nd:YAG operating at 266 nm, significantly improves the ab lation characteristics of minerals that do not absorb strongly at near -IR wavelengths (e.g., quartz and feldspar). Furthermore, it allows fo r a significant reduction in ablation pit size to ca. 10 mu m, thereby permitting numerous applications that require high-resolution samplin g. Multiple ablations in individual melt inclusions in the size range 10-50 mu m demonstrate both the effectiveness of the technique and the generally homogeneous character of the inclusions. Comparison of the LAM-ICP-MS data for international reference material RGM-1 (a rhyolite ), with recommended values, indicates an analytical precision of < 10% for most of the trace elements determined in this study. The trace el ement abundances of the Fantale melt inclusions, determined by LAM-ICP -MS, are typical of those of pantellerites (i.e., peralkaline rhyolite s), and are consistent with their origin as tiny volumes of melt trapp ed in quartz and alkali-feldspar phenocrysts during the final stage of fractional crystallization of the host peralkaline magma. Copyright ( C) 1997 Elsevier Science Ltd.