Use of the elastic recoil detection analysis (ERDA) microbeam technique for the quantitative determination of hydrogen in materials and hydrogen partitioning between olivine and melt at high pressures

Details Use of the elastic recoil detection analysis (ERDA) microbeam technique for the quantitative determination of hydrogen in materials and hydrogen partitioning between olivine and melt at high pressures Use of the elastic recoil detection analysis (ERDA) microbeam technique for the quantitative determination of hydrogen in materials and hydrogen partitioning between olivine and melt at high pressures

Jan 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61..101s&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 61, Issue 1, p. 101-113.

Computer Science

8

Scientific paper

A nuclear microbeam technique called elastic recoil detection analysis (ERDA) or forward recoil spectroscopy which is capable of yielding bulk H in silicates at ppm sensitivities is described. This technique is nondestructive and uses a 4He+ beam which may be routinely focused to dimensions less than 5 × 5 μm. The technique is suitable for the analysis of both materials of appreciable H content (e.g., amphiboles) and materials with trace H content. The technique is calibrated in the range 0 2 wt% H2O using a set of mineral standards of known H2O concentration with sensitivities of 0.04 wt% H2O achieved. There is a good correlation between H2O contents derived by spectra simulations and concentrations derived by empirical calibration, although the former yield data 10 20% lower when compared to known values. The equilibration of olivine with a potassic silicate melt at high pressures (1.5 to 10 GPa) in experiments shows more H is accommodated in the mineral with increasing pressure. The olivine-melt KH2O (expressing H as wt% H2O concentration in mineral/concentration in melt) at 1.5GPa (1400°C) was ca. 0.04 ± 0.015. At 5.8 6 GPa (1740°C), olivine-melt KH2O increased to 0.13 ± 0.03. A single experiment at 10 GPa (ca. 2000°C) yielded a minimum KH2O of 0.12. The amount of H which minerals accommodate is also highly correlated with bulk system composition (which controlled melt composition). In alkali-absent bulk systems, the KH2O for olivine equilibrated with a MgSi melt was 0.30 at 1 GPa (1400°C), an order of magnitude increase over the alkali-bearing system at this pressure. This reflects the reduced facility of a wholly MgSi melt to accommodate H2O relative to an alkali-bearing melt. The increase in KH2O with pressure for olivine-melt, combined with data for KH2O of natural olivine (and orthopyroxene) in basaltic glass at P < 0.3 GPa (<0.005), implies that a deep residual mantle would be more H-rich than the shallow mantle for the same degree of melt extraction.

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