Crustal controls on apparent mantle pyroxenite signals in ocean-island basalts

Abstract

Research Article| February 28, 2019 Crustal controls on apparent mantle pyroxenite signals in ocean-island basalts Matthew L.M. Gleeson; Matthew L.M. Gleeson 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK Search for other works by this author on: GSW Google Scholar Sally A. Gibson Sally A. Gibson 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Matthew L.M. Gleeson 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK Sally A. Gibson 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK Publisher: Geological Society of America Received: 29 Oct 2018 Revision Received: 06 Jan 2019 Accepted: 15 Jan 2019 First Online: 28 Feb 2019 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2019 Geological Society of America Geology (2019) 47 (4): 321–324. https://doi.org/10.1130/G45759.1 Article history Received: 29 Oct 2018 Revision Received: 06 Jan 2019 Accepted: 15 Jan 2019 First Online: 28 Feb 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Matthew L.M. Gleeson, Sally A. Gibson; Crustal controls on apparent mantle pyroxenite signals in ocean-island basalts. Geology 2019;; 47 (4): 321–324. doi: https://doi.org/10.1130/G45759.1 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 Ocean-island basalts (OIBs) provide a unique insight into the extent of lithological heterogeneity (peridotite vs. pyroxenite) in Earth’s convecting mantle. However, crustal processing of these mantle melts significantly influences minor-element concentrations in olivine phenocrysts, challenging the suitability of this widely used approach to identify lithological variations in their mantle source. Using a numerical model of magma recharge, mixing, and diffusional reequilibration, we show that this type of crustal processing—which is widely observed in OIBs—results in elevated Ni and lower Ca contents of forsterite-rich olivine, causing erroneously high estimates of the proportion of pyroxenite-derived melt. We applied our model of magma recharge and mixing to several OIBs, including the Galápagos Islands, Canary Islands, and La Réunion. In particular, we critically examined olivine compositional variations in basalts from the eastern Galápagos, which display Sr- and Pb-isotope ratios similar to normal mid-ocean-ridge basalts. While previous interpretations (based on olivine chemistry) argued for a significant contribution from pyroxenite-derived melt, our results indicate that the postulated presence of pyroxenite in the eastern Galápagos mantle is an artifact of processing of magmas and their olivine cargo as they transition through the crust, consistent with major-element and isotopic evidence for a dominantly peridotitic source in this region. This new model for magma recharge and mixing may have important implications for our understanding of lithological heterogeneity beneath OIBs globally, and it highlights the importance of considering crustal processes when attempting to interpret olivine compositions with regard to mantle heterogeneity. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.