Dehydration of phengite inferred by electrical conductivity measurements: Implication for the high conductivity anomalies relevant to the subduction zones

Research Article| October 31, 2017 Dehydration of phengite inferred by electrical conductivity measurements: Implication for the high conductivity anomalies relevant to the subduction zones Sibo Chen; Sibo Chen 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 430074 Wuhan, China2Institute of Geophysics and Geomatics, China University of Geosciences, 430074 Wuhan, China Search for other works by this author on: GSW Google Scholar Xinzhuan Guo; Xinzhuan Guo * 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 430074 Wuhan, China *E-mail: gxzhuan@cug.edu.cn Search for other works by this author on: GSW Google Scholar Takashi Yoshino; Takashi Yoshino 3Institute for Planetary Materials, Okayama University, 682-0193 Misasa, Japan Search for other works by this author on: GSW Google Scholar Zhenmin Jin; Zhenmin Jin 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 430074 Wuhan, China Search for other works by this author on: GSW Google Scholar Ping Li Ping Li 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 430074 Wuhan, China Search for other works by this author on: GSW Google Scholar Geology (2018) 46 (1): 11–14. https://doi.org/10.1130/G39716.1 Article history received: 07 Jul 2017 rev-recd: 15 Sep 2017 accepted: 24 Sep 2017 first online: 31 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Sibo Chen, Xinzhuan Guo, Takashi Yoshino, Zhenmin Jin, Ping Li; Dehydration of phengite inferred by electrical conductivity measurements: Implication for the high conductivity anomalies relevant to the subduction zones. Geology 2017;; 46 (1): 11–14. doi: https://doi.org/10.1130/G39716.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Phengite is a critical carrier of water and potassium (K) in sediment as well as in the basaltic layers of subducted slabs. However, although phengite dehydration can potentially be used to interpret high conductivity in the mantle overlying such slabs at depths between 250 km and 300 km, no experimental constraints on the electrical conductivity of this mineral have so far been performed. We investigated the electrical conductivity of natural phengite before and after dehydration at pressures (P) as high as 12 GPa and at temperatures (T) as high as 1200 K. The results of this study confirm positive T and negative P effects on the electrical conductivity of phengite before its breakdown; subsequently, at 12 GPa and 850 K, electrical conductivity dramatically increased from 10−4 S/m to 100.5 S/m. Characteristic impedance spectra, as well as postexperimental textural observations and sample chemical analyses, show that these abrupt conductivity changes are due to K-rich fluids released by phengite dehydration. These high conductivities of K-rich fluids are in close agreement with geophysical observations at depths of between 250 km and 300 km in backarcs beneath the North Philippine Sea and central Argentina. Comparisons between the geotherms of these areas and the stability field of phengite defined by phase equilibrium experiments suggest that the descending crust is almost completely dehydrated and should not cause further K-metasomatism subsequent to the breakdown of phengite at depths of ∼300 km. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.