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The origin of high-Ni olivines in Mexican arc magmas revisited with new temperature constraints from olivine-spinel aluminum exchange thermometry

Susanne M. Straub 1, Valentina Batanova2, Alexander Sobolev2, Arturo Gómez-Tuena3, Ramon Espinasa-Perena3, Ilya N Bindeman4, Finlay M. Stuart5, Elisabeth Widom6, Yoshiyuki Iizuka7

  • Affiliations:  1Lamont Doherty Earth Observatory at the Columbia University, 61 Route 9W, Palisades NY 10964, U.S.A; 2Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, ISTerre, 38000 Grenoble, France; 3Instituto de Geología, Universidad Nacional Autónoma de México, Cd. Universitaria, Coyoacán 04510, Mexico City, México; 4Department of Earth Sciences, University of Oregon, Eugene, Oregon, 97403-1272, U.S.A.; 5Isotope Geosciences Unit, Scottish Universities Research and Reactor Centre, East Kilbride G75 0QF, UK; 6Department of Geology and Environmental Earth Science, Miami University, 118 Shideler Hall, 250 S. Patterson Ave, Oxford Ohio 45056, U.S.A.; 7Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec. 2, Nangang, Taipei 11529, Taiwan, ROC 

  • Presentation type: Talk

  • Presentation time: Thursday 09:30 - 09:45, Room S150

  • Programme No: 1.1.5

  • Theme 1 > Session 1

Abstract

High-Ni olivines have higher Ni concentrations than expected for olivines crystallizing in partial peridotite melts. Their discovery in intraplate and arc magmas has caused much controversy concerning their implications for magma genesis. While some studies link high-Ni olivines to Ni-rich melts from secondary mantle pyroxenites, others argue that compositional and thermal variations of peridotite melt sufficiently increase the composition- and temperature-sensitive olivine/melt partition coefficient for crystallizing high-Ni olivine. Here we re-evaluate the origin of high-Ni olivines from the Trans-Mexican Volcanic Belt (TMVB) using olivine crystallization temperatures from olivine-spinel aluminum exchange thermometry. The TMVB olivines crystallize at comparatively low temperatures of ~1147±25°C in hydrous, silicic, and less magnesian (≤10 wt% MgO) primary arc magmas. Despite a moderate melt Ni ≤220 ppm, the  increases sufficiently to crystallize olivines with up to ~3500 to 4000 ppm Ni, which accounts for ~90% of TMVB high-Ni olivines. However, an increased melt Ni still best explains a small population of olivines with very high Ni concentrations of >4000 to 5500 ppm. Crystal-scale data suggest that these Ni-rich melts form by reactive melt/wall rock interaction in peridotite-hosted mantle conduits continuously fluxed by silicic slab melts. Thus, the very high-Ni olivines provide a rare view of the deep mantle plumbing system beneath volcanic arcs, whereby it remains open whether the conditions of their formation only rarely exist, or whether they are only seldom preserved en route to the surface through the overlying crust.