Island-arc basalt alkali ratios: Constraints from phengite-fluid partitioning experiments

Research Article| July 01, 2000 Island-arc basalt alkali ratios: Constraints from phengite-fluid partitioning experiments Stefan Melzer; Stefan Melzer 1GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Bernd Wunder Bernd Wunder 1GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (7): 583–586. https://doi.org/10.1130/0091-7613(2000)28<583:IBARCF>2.0.CO;2 Article history received: 01 Dec 1999 rev-recd: 24 Mar 2000 accepted: 03 Apr 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Stefan Melzer, Bernd Wunder; Island-arc basalt alkali ratios: Constraints from phengite-fluid partitioning experiments. Geology 2000;; 28 (7): 583–586. doi: https://doi.org/10.1130/0091-7613(2000)28<583:IBARCF>2.0.CO;2 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 In order to constrain the large ion lithophile (LIL) element distribution for subduction-zone environments, exchange coefficients \(Kᵖʰᵉ⁻ᶠˡᵘⁱᵈD\ {=}\ (XᵖʰᵉRb,Cs\ {·}\ XᶠˡᵘⁱᵈK){/}(XᵖʰᵉK\ {·}\ XᶠˡᵘⁱᵈRb,Cs)\) for K, Rb, and Cs between aqueous fluids and phengite (phe) have been determined experimentally at 2.0 and 4.0 GPa. Derived KD values for the Rb-K exchange slightly increase from 1.62 ± 0.10 at 2 GPa, 600 °C, to 1.84 ± 0.15 at 4 GPa, 700 °C. For the Cs-K exchange, much lower KD values of 0.22 ± 0.06 (at 2 GPa, 600 °C) and 0.37 ± 0.10 (at 4 GPa, 700 °C) were determined. The results show that, for the pressure-temperature range investigated, Rb preferentially fractionates into phengite, whereas Cs partitions into the fluid.Assuming a one-step model of perfect Rayleigh fractionation for continuous decomposition of phengite during subduction, varying alkali ratios observed for island-arc basalts as a function of slab depth may be explained by the LIL-fractionation behavior between fluids and phengites determined in this study. Our data indicate that previously derived models for metasomatic mass transfer during subduction processes need to be reconsidered. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.