Atomistic insight into viscosity and density of silicate melts under pressure.
A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates viscosity and affects compressibility. While viscosity of depolymerized silicate melts increases with pressure consistent with the free-volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3-5 GPa, above which it turns over to normal (positive) pressure dependence. Here we show that the viscosity turnover in polymerized liquids corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in high compressibility, continual breakup of tetrahedral connectivity and viscosity decrease with increasing pressure. Above the turnover pressure, silicon and aluminium coordination increases to allow further packing, with increasing viscosity and density. These structural responses prescribe the distribution of melt viscosity and density with depth and play an important role in magma transport in terrestrial planetary interiors.
Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA.
Yanbin
Y
Wang
1] Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA [2].
Tatsuya
T
Sakamaki
Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, USA.
Lawrie B
LB
Skinner
1] Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA [2].
Zhicheng
Z
Jing
Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA.
Tony
T
Yu
HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA.
Yoshio
Y
Kono
HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA.
Changyong
C
Park
HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, USA.
Guoyin
G
Shen
Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA.
Mark L
ML
Rivers
Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA.
Stephen R
SR
Sutton