TY - JOUR

T1 - Water contents of felsic melts

T2 - Application to the rheological properties of granitic magmas

AU - Holtz, Francois

AU - Scaillet, Bruno

AU - Behrens, Harald

AU - Schulze, Frank

AU - Pichavant, Michel

N1 - Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 1996/1/1

Y1 - 1996/1/1

N2 - New experimental determinations of water solubility in haplogranitic melts (anhydrous compositions in the system Qz-Ab-Or and binary joins) and of the viscosity of hydrous Qz2/Ab38Or34 melts (normative proportions) and natural peraluminous leucogranitic melt (Gangotri, High Himalaya) are used to constrain the evolution of viscosity of ascending magmas, depending on their P-T paths. At constant pressure, in the case of fluid-absent melting conditions, with water as the main volatile dissolved in the melts, the viscosity of melts generated from quartzo-feldspathic protoliths is lower at low temperature than at high temperature (difference of 1-2 log units between 700 and 900°C). This is due to the higher water contents of the melts at low temperature than at high temperature and to the fact that decreasing temperature does not counterbalance the effect of increasing melt water content. In ascending magmas generated from crustal material the magma viscosity does not change significantly whatever the P-T path followed (i.e. path with cooling and crystallisation; adiabatic path with decompression melting) as long as the crystal fraction is low enough to assume a Newtonian behaviour (30-50% crystals, depending on size and shape). Comparison of the properties of natural and synthetic systems suggests that both water solubility and the viscosity of multicomponent natural felsic melts (with less than 30-35% normative Qz) can be extrapolated from those of the equivalent synthetic feldspar melts.

AB - New experimental determinations of water solubility in haplogranitic melts (anhydrous compositions in the system Qz-Ab-Or and binary joins) and of the viscosity of hydrous Qz2/Ab38Or34 melts (normative proportions) and natural peraluminous leucogranitic melt (Gangotri, High Himalaya) are used to constrain the evolution of viscosity of ascending magmas, depending on their P-T paths. At constant pressure, in the case of fluid-absent melting conditions, with water as the main volatile dissolved in the melts, the viscosity of melts generated from quartzo-feldspathic protoliths is lower at low temperature than at high temperature (difference of 1-2 log units between 700 and 900°C). This is due to the higher water contents of the melts at low temperature than at high temperature and to the fact that decreasing temperature does not counterbalance the effect of increasing melt water content. In ascending magmas generated from crustal material the magma viscosity does not change significantly whatever the P-T path followed (i.e. path with cooling and crystallisation; adiabatic path with decompression melting) as long as the crystal fraction is low enough to assume a Newtonian behaviour (30-50% crystals, depending on size and shape). Comparison of the properties of natural and synthetic systems suggests that both water solubility and the viscosity of multicomponent natural felsic melts (with less than 30-35% normative Qz) can be extrapolated from those of the equivalent synthetic feldspar melts.

KW - Aluminosilicate melts

KW - Crystallisation paths

KW - Granites

KW - Viscosity

KW - Water solubility

UR - http://www.scopus.com/inward/record.url?scp=84871213734&partnerID=8YFLogxK

U2 - 10.1130/0-8137-2315-9.57

DO - 10.1130/0-8137-2315-9.57

M3 - Article

AN - SCOPUS:84871213734

VL - 315

SP - 57

EP - 64

JO - Special Paper of the Geological Society of America

JF - Special Paper of the Geological Society of America

SN - 0072-1077

ER -