Halogen (F, Cl, Br, I) behaviour in subducting slabs: a study of lawsonite blueschists in western Turkey

Lilianne Page, Keiko Hattori, Cees-Jan De Hoog, Aral Okay

Research output: Contribution to journalArticlepeer-review

Abstract

We examined the F, Cl, Br and I abundance of minimally retrogressed lawsonite blueschists from the Tavsanli Zone in northwest Turkey to evaluate the behaviour of halogens in subduction zones, and to determine the role coexisting high pressure minerals may play in transporting the halogens to the Earth's mantle. The blueschists contain sodic amphibole and lawsonite, with variable amounts of phengite and chlorite, and minor apatite. A positive correlation between Cl, Br and I contents in bulk rocks suggests their overall coherent behaviour in subduction zones, although high ratios of I/Cl and Br/Cl compared to altered oceanic crust indicate that Cl is preferentially lost relative to Br and I before or during blueschist metamorphism. Iodine and F are enriched relative to altered oceanic crust, suggesting incorporation from marine sediments. In situ analyses of minerals in thin sections reveal F preferentially concentrates in apatite (avg. 3.13 wt%), over phengite (482 ppm), lawsonite (avg. 413 ppm) and Na-amphibole (257 ppm). Chlorine also preferentially resides in apatite (138 ppm), followed by equal partitioning between phengite (59 ppm) and Na-amphibole (56 ppm), and lower concentrations in lawsonite (27 ppm). Upon apatite decomposition at a depth of ∼200 km, F may redistribute into lawsonite and phengite in slabs, whilst Cl is likely expelled to the overlying mantle wedge. Given the stability of lawsonite and phengite to a depth of 280–300 km in cold subduction zones, they may transport F beyond subarc depths, contributing to the high F in magmas derived from the deep mantle.
Original languageEnglish
Pages (from-to)133-142
JournalEarth and Planetary Science Letters
Volume442
Early online date16 Mar 2016
DOIs
Publication statusPublished - 15 May 2016

Fingerprint Dive into the research topics of 'Halogen (F, Cl, Br, I) behaviour in subducting slabs: a study of lawsonite blueschists in western Turkey'. Together they form a unique fingerprint.

Cite this