Tracking halogens through the subduction cycle

Abstract

Research Article| December 01, 2012 Tracking halogens through the subduction cycle Mark A. Kendrick; Mark A. Kendrick 1School of Earth Sciences, University of Melbourne, Victoria 3010, Australia Search for other works by this author on: GSW Google Scholar Jon D. Woodhead; Jon D. Woodhead 1School of Earth Sciences, University of Melbourne, Victoria 3010, Australia Search for other works by this author on: GSW Google Scholar Vadim S. Kamenetsky Vadim S. Kamenetsky 2ARC Centre of Excellence in Ore Deposits and Institute for Marine and Antarctic Studies, University of Tasmania, Tasmania, Australia Search for other works by this author on: GSW Google Scholar Geology (2012) 40 (12): 1075–1078. https://doi.org/10.1130/G33265.1 Article history received: 03 Feb 2012 rev-recd: 08 May 2012 accepted: 27 May 2012 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mark A. Kendrick, Jon D. Woodhead, Vadim S. Kamenetsky; Tracking halogens through the subduction cycle. Geology 2012;; 40 (12): 1075–1078. doi: https://doi.org/10.1130/G33265.1 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 The flux of halogens into the Earth’s mantle at subduction zones is a critical yet poorly constrained parameter in the geochemical evolution of the planet. Here we report the first ever combined high-precision measurements of chlorine, bromine, and iodine for backarc basin basalt (BABB) and ocean island basalt (OIB) glasses. The measurements were undertaken in order to evaluate the depth and extent of the halogen subduction cycle by comparing: (1) melts formed in the Manus Basin (Papua New Guinea) proximal to a modern subduction zone, and (2) melts formed from enriched mantle (EM) reservoirs that have been linked to ancient subduction recycling [EM1 and EM2 sampled by the Pitcairn and Society seamounts (central Pacific Ocean), respectively]. As expected from previous studies, the BABBs are strongly enriched in chlorine relative to other trace elements and mid-oceanic ridge basalts (MORB); however, the combined Br/Cl and I/Cl data provide additional insights. The BABBs have I/Cl weight ratios of up to 5.3 × 10−4, that are up to five times higher than typical MORB; and the BABBs with the highest I/Cl have Br/Cl ratios of 2–3 × 10−3, that are lower than typical MORB, and significantly lower than either iodine-rich sediments or seawater-derived sedimentary pore fluids. The final breakdown of iodine-rich serpentine is considered the most likely source of the halogen enrichment in the BABB, suggesting that subduction of serpentinized peridotites enables transport of strongly incompatible, fluid-mobile, volatile elements, like iodine, beyond zones of arc-magma generation. The Pitcairn and Society melts exhibit a remarkable correlation between K/Cl and 87Sr/86Sr. The K/Cl ratios vary from MORB-like values of ∼15 to maxima of ∼40 in the isotopically most enriched EM end members. The trend reflects the lower subduction efficiency of halogens compared to K and other lithophile elements. Melts formed from EM and MORB mantle reservoirs have very similar Br/Cl and I/Cl weight ratios of 3.6 ± 0.8 × 10−3 and 85 ± 42 × 10−6 (2σ) respectively, that could indicate that subducted volatiles have been mixed throughout the mantle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.