Details
| Original language | English |
|---|---|
| Article number | 98JB02469 |
| Pages (from-to) | 27257-27266 |
| Number of pages | 10 |
| Journal | Journal of Geophysical Research: Solid Earth |
| Volume | 103 |
| Issue number | B11 |
| Publication status | Published - 1998 |
| Externally published | Yes |
Abstract
By using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at ∼ 104.5 Pa s, irrespective of their temperature and level of emplacement. Magmas crystallizing as granitic plutons are not water-poor and thus not more viscous than their extrusive equivalents. Instead, comparison between pre-eruption magma viscosities of extrusive silicic-intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous. Given the typical strain rates in silicic magma chambers, magma rheological behavior is expected to be dominantly Newtonian, bubbles having a minor rheological influence at depth although exceptions can exist. Thus whether a silicic-intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors, but not on the rheology of the magma itself. However, preeruptive viscosities of extrusive magmas rarely exceed 106 Pa.s, which suggests that crystal-melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes. The narrow range of viscosities displayed by silicic-intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas. Considerations of the relationships between magma crystallinities, bulk SiO2, and preeruptive melt H2O contents show that the higher the melt H2O content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted. An empirical correlation is proposed that enables us to estimate preeruptive melt H2O contents of erupted magmas by knowing their crystallinity and bulk SiO2.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Earth and Planetary Sciences (miscellaneous)
- Earth and Planetary Sciences(all)
- Space and Planetary Science
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In: Journal of Geophysical Research: Solid Earth, Vol. 103, No. B11, 98JB02469, 1998, p. 27257-27266.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Phase equilibrium constraints on the viscosity of silicic magmas 1. Volcanic-plutonic comparison
AU - Scaillet, Bruno
AU - Holtz, François
AU - Pichavant, Michel
N1 - Copyright: Copyright 2018 Elsevier B.V., All rights reserved.
PY - 1998
Y1 - 1998
N2 - By using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at ∼ 104.5 Pa s, irrespective of their temperature and level of emplacement. Magmas crystallizing as granitic plutons are not water-poor and thus not more viscous than their extrusive equivalents. Instead, comparison between pre-eruption magma viscosities of extrusive silicic-intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous. Given the typical strain rates in silicic magma chambers, magma rheological behavior is expected to be dominantly Newtonian, bubbles having a minor rheological influence at depth although exceptions can exist. Thus whether a silicic-intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors, but not on the rheology of the magma itself. However, preeruptive viscosities of extrusive magmas rarely exceed 106 Pa.s, which suggests that crystal-melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes. The narrow range of viscosities displayed by silicic-intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas. Considerations of the relationships between magma crystallinities, bulk SiO2, and preeruptive melt H2O contents show that the higher the melt H2O content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted. An empirical correlation is proposed that enables us to estimate preeruptive melt H2O contents of erupted magmas by knowing their crystallinity and bulk SiO2.
AB - By using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at ∼ 104.5 Pa s, irrespective of their temperature and level of emplacement. Magmas crystallizing as granitic plutons are not water-poor and thus not more viscous than their extrusive equivalents. Instead, comparison between pre-eruption magma viscosities of extrusive silicic-intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous. Given the typical strain rates in silicic magma chambers, magma rheological behavior is expected to be dominantly Newtonian, bubbles having a minor rheological influence at depth although exceptions can exist. Thus whether a silicic-intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors, but not on the rheology of the magma itself. However, preeruptive viscosities of extrusive magmas rarely exceed 106 Pa.s, which suggests that crystal-melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes. The narrow range of viscosities displayed by silicic-intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas. Considerations of the relationships between magma crystallinities, bulk SiO2, and preeruptive melt H2O contents show that the higher the melt H2O content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted. An empirical correlation is proposed that enables us to estimate preeruptive melt H2O contents of erupted magmas by knowing their crystallinity and bulk SiO2.
UR - http://www.scopus.com/inward/record.url?scp=0032455301&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0032455301
VL - 103
SP - 27257
EP - 27266
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - B11
M1 - 98JB02469
ER -