Details
| Original language | English |
|---|---|
| Pages (from-to) | 1052-1062 |
| Number of pages | 11 |
| Journal | American Mineralogist |
| Volume | 99 |
| Issue number | 5-6 |
| Publication status | Published - 1 May 2014 |
Abstract
Bubble formation during continuous decompression from ∼400 to ∼70 MPa was investigated experimentally in hydrous andesitic melts at T = 1030 °C and at an oxygen fugacity (fO2) of about log(f O2/bar) = QFM+1 (QFM: quartz-fayalite-magnetite buffer). Experiments were carried out at variable decompression rates (r), ranging from 0.0005 to 0.1 MPa/s. The samples were directly quenched after decompression, allowing the investigation of the influence of r on the bubble formation. The effect of variable annealing times (tA) after decompression was also investigated for experiments performed at a decompression rate of 0.1 MPa/s. These samples were annealed for tA = 0 to 72 h at final pressure (70 MPa) to study changes in vesiculation during magma storage at shallow depths after fast ascent. Backscattered electron (BSE) images of the samples were analyzed to determine bubble number densities (BND). The BND values increase strongly with increasing r and vary from about 102.2 mm-3 at 0.0005 MPa/s to about 104.6 mm-3 at 0.1 MPa/s. After fast decompression (r ∼ 0.1 MPa/s), the BND decrease significantly with tA, i.e., from ∼104.6 mm-3 at tA = 0 h to ∼102.9 mm-3 at tA = 72 h. A comparison of the derived BND values with recently published experimental data demonstrates the essential role of the decompression path on bubble formation. The BND are higher in experiments with multi- or single-step decompression when compared to continuous decompression. The new data show that H 2O-undersaturated andesitic melts are characterized by 1 to 2 log units higher BND values than H2O-saturated rhyolitic melts after decompression with the same rate, indicating a strong influence of melt composition on bubble nucleation. This compositional effect is not predicted accurately by existing models and the interpretation of the vesicularity of dacitic to andesitic melts may lead to overestimations of magma ascent rates by about an order of magnitude.
Keywords
- Andesite, Bubble formation, Bubble number density, Continuous decompression
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: American Mineralogist, Vol. 99, No. 5-6, 01.05.2014, p. 1052-1062.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Bubble formation during decompression of andesitic melts
AU - Fiege, Adrian
AU - Holtz, François
AU - Cichy, Sarah B.
N1 - Funding Information: This project was supported by the German Science Foundation (BE1720/25-1). We would like to thank Harald Behrens (scientific discussions), Eric Wolff (electron microprobe), and Otto Dietrich (sample preparation). The valuable comments of the journal editor F. Costa as well as of the reviewers M. Mangan, C. Martel, and A. Toramaru have significantly improved the quality of this manuscript. Copyright: Copyright 2014 Elsevier B.V., All rights reserved.
PY - 2014/5/1
Y1 - 2014/5/1
N2 - Bubble formation during continuous decompression from ∼400 to ∼70 MPa was investigated experimentally in hydrous andesitic melts at T = 1030 °C and at an oxygen fugacity (fO2) of about log(f O2/bar) = QFM+1 (QFM: quartz-fayalite-magnetite buffer). Experiments were carried out at variable decompression rates (r), ranging from 0.0005 to 0.1 MPa/s. The samples were directly quenched after decompression, allowing the investigation of the influence of r on the bubble formation. The effect of variable annealing times (tA) after decompression was also investigated for experiments performed at a decompression rate of 0.1 MPa/s. These samples were annealed for tA = 0 to 72 h at final pressure (70 MPa) to study changes in vesiculation during magma storage at shallow depths after fast ascent. Backscattered electron (BSE) images of the samples were analyzed to determine bubble number densities (BND). The BND values increase strongly with increasing r and vary from about 102.2 mm-3 at 0.0005 MPa/s to about 104.6 mm-3 at 0.1 MPa/s. After fast decompression (r ∼ 0.1 MPa/s), the BND decrease significantly with tA, i.e., from ∼104.6 mm-3 at tA = 0 h to ∼102.9 mm-3 at tA = 72 h. A comparison of the derived BND values with recently published experimental data demonstrates the essential role of the decompression path on bubble formation. The BND are higher in experiments with multi- or single-step decompression when compared to continuous decompression. The new data show that H 2O-undersaturated andesitic melts are characterized by 1 to 2 log units higher BND values than H2O-saturated rhyolitic melts after decompression with the same rate, indicating a strong influence of melt composition on bubble nucleation. This compositional effect is not predicted accurately by existing models and the interpretation of the vesicularity of dacitic to andesitic melts may lead to overestimations of magma ascent rates by about an order of magnitude.
AB - Bubble formation during continuous decompression from ∼400 to ∼70 MPa was investigated experimentally in hydrous andesitic melts at T = 1030 °C and at an oxygen fugacity (fO2) of about log(f O2/bar) = QFM+1 (QFM: quartz-fayalite-magnetite buffer). Experiments were carried out at variable decompression rates (r), ranging from 0.0005 to 0.1 MPa/s. The samples were directly quenched after decompression, allowing the investigation of the influence of r on the bubble formation. The effect of variable annealing times (tA) after decompression was also investigated for experiments performed at a decompression rate of 0.1 MPa/s. These samples were annealed for tA = 0 to 72 h at final pressure (70 MPa) to study changes in vesiculation during magma storage at shallow depths after fast ascent. Backscattered electron (BSE) images of the samples were analyzed to determine bubble number densities (BND). The BND values increase strongly with increasing r and vary from about 102.2 mm-3 at 0.0005 MPa/s to about 104.6 mm-3 at 0.1 MPa/s. After fast decompression (r ∼ 0.1 MPa/s), the BND decrease significantly with tA, i.e., from ∼104.6 mm-3 at tA = 0 h to ∼102.9 mm-3 at tA = 72 h. A comparison of the derived BND values with recently published experimental data demonstrates the essential role of the decompression path on bubble formation. The BND are higher in experiments with multi- or single-step decompression when compared to continuous decompression. The new data show that H 2O-undersaturated andesitic melts are characterized by 1 to 2 log units higher BND values than H2O-saturated rhyolitic melts after decompression with the same rate, indicating a strong influence of melt composition on bubble nucleation. This compositional effect is not predicted accurately by existing models and the interpretation of the vesicularity of dacitic to andesitic melts may lead to overestimations of magma ascent rates by about an order of magnitude.
KW - Andesite
KW - Bubble formation
KW - Bubble number density
KW - Continuous decompression
UR - http://www.scopus.com/inward/record.url?scp=84902507942&partnerID=8YFLogxK
U2 - 10.2138/am.2014.4719
DO - 10.2138/am.2014.4719
M3 - Article
AN - SCOPUS:84902507942
VL - 99
SP - 1052
EP - 1062
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 5-6
ER -