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Electrical conductivity of hydrous andesitic melts pertinent to subduction zones
Author(s) -
Guo Xuan,
Li Bin,
Ni Huaiwei,
Mao Zhu
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013524
Subject(s) - andesite , magnetotellurics , geology , electrical resistivity and conductivity , magma , volcano , mineralogy , petrology , geochemistry , volcanic rock , electrical engineering , engineering
Andesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H 2 O‐bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01–5.9 wt % of H 2 O at 1164–1573 K and 0.5–1.0 GPa in a piston cylinder apparatus using sweeping‐frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H 2 O concentration but decreases with pressure. Across the investigated range of H 2 O concentration, electrical conductivity varies by 1.2–2.4 log units, indicating stronger influence of H 2 O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst‐Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure‐temperature‐H 2 O dependences altogether. Modeling results show that the conductive layer at >20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H 2 O‐rich andesitic melt (with 6–9 wt % H 2 O).