A Brillouin scattering study of hydrous basaltic glasses: the effect of H2O on their elastic behavior and implications for the densities of basaltic melts

• Published in: Physics and chemistry of minerals 2017-06, Vol.44 (6), p.431-444
• Main Authors: Wu, Lei, Yang, De-Bin, Liu, Jun-Xiu, Hu, Bo, Xie, Hong-Sen, Li, Fang-Fei, Yu, Yang, Xu, Wen-Liang, Gao, Chun-Xiao
• Format: Article
• Language: English
• Subjects: Basalt; Compressibility; Crystallography and Scattering Methods; Depolymerization; Earth and Environmental Science; Earth models; Earth Sciences; Elastic properties; Elastic scattering; Elasticity; Geochemistry; High temperature; Magma; Melts; Mesozoic; Mineral Resources; Mineralogy; Moisture content; Original Paper; Upper mantle; Water content; Wave velocity
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-017-0870-9

Hydrous basalt glasses with water contents of 0–6.82% were synthesized using a multi-anvil press at 1.0–2.0 GPa and 1200–1400 °C. The starting materials were natural Mesozoic basalts from the eastern North China Craton (NCC). Their sound velocities and elastic properties were measured by Brillouin scattering spectroscopy. The longitudinal ( V P ) and shear ( V S ) wave velocities decreased with increasing water content. Increasing the synthesis pressure resulted in the glass becoming denser, and finally led to an increase in V P . As the degree of depolymerization increased, the V P , V S , and shear and bulk moduli of the hydrous basalt glasses decreased, whereas the adiabatic compressibility increased. The partial molar volumes of water ( ν ) under ambient conditions were independent of composition, having values of 11.6 ± 0.8, 10.9 ± 0.6 and 11.5 ± 0.5 cm 3 /mol for the FX (Feixian), FW (Fuxin), and SHT (Sihetun) basalt glasses, respectively. However, the V H 2 O values measured at elevated temperatures and pressures are increasing with increasing temperature or decreasing pressure. The contrasting densities of these hydrous basalt melts with those previously reported for mid-ocean ridge basalt and preliminary reference Earth model data indicate that hydrous basalt melts may not maintain gravitational stability at the base of the upper mantle.