期刊
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY
卷 144, 期 4, 页码 397-415出版社
SPRINGER
DOI: 10.1007/s00410-002-0404-3
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An experimental study of H2O exsolution, bubble growth and microlite crystallisation during ascent (decompression) of silicic magmas in the volcanic conduit is presented. Isobaric and decompression experiments were performed on a rhyolitic melt at 860 degreesC, NNO + 1, H2O saturation, and pressures between 15 and 170 MPa. Two sets of decompression experiments* were performed, with decompression rates varying between 0.001 and 960 MPa/min: (1) from 150 to 50 MPa (high-pressure decompression), and (2) from 50 to 15 MPa (low-pressure decompression). The experiments highlight incomplete H2O exsolution for decompression rates > 100 MPa/min, incomplete bubble growth for decompression rates > 0.1 MPa/min, crystal nucleation time lags, and incomplete chemical re-equilibration to final pressures. The observed crystallisation process, i.e. growth versus nucleation, depends on the decompression range. Indeed, decompression-induced crystallisation during high-pressure decompressions is dominated by growth of existing crystals, whereas during low-pressure decompressions crystal nucleation is the dominating process. This study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach.
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