HR: 15:10h
AN: V43E-07    [Abstracts]
TI: Olivine Phenocrysts Composition and a Role of Non-peridotitic Sources in Mantle Magma Generation
AU: * Sobolev, A V
EM: asobolev@mpch-mainz.mpg.de
AF: Max-Planck Institute of Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: * Sobolev, A V
EM: asobolev@mpch-mainz.mpg.de
AF: Vernadsky Institute of Geochemistry, Kosigin 19, Moscow, 119991 Russian Federation
AU: Hofmann, A W
EM: hofmann@mpch-mainz.mpg.de
AF: Max-Planck Institute of Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Kuzmin, D V
EM: kuzmin@mpch-mainz.mpg.de
AF: Max-Planck Institute of Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Danyushevsky, L V
EM: L.Dan@utas.edu.au
AF: School of Earth Sciences and Centre for Ore Deposit Research, University of Tasmania, Sandy Bay, Hobart, TAS 7001 Australia
AU: Gurenko, A A
EM: agurenko@mpch-mainz.mpg.de
AF: Max-Planck Institute of Chemistry, Postfach 3060, Mainz, 55020 Germany
AU: Kamenetsky, V S
EM: Dima.Kamenetsky@utas.edu.au
AF: School of Earth Sciences and Centre for Ore Deposit Research, University of Tasmania, Sandy Bay, Hobart, TAS 7001 Australia
AU: Krivolutskaya, N A
EM: nakriv@mail.ru
AF: Vernadsky Institute of Geochemistry, Kosigin 19, Moscow, 119991 Russian Federation
AB: Peridotite is not the only possible source of mantle derived magmas. For instance, when the recycled oceanic crust is present within the melting column, it would melt producing a high Si liquid which would generate olivine-free secondary pyroxenite, rich in Ni, Mg and Si, when reacting with the mantle peridotite (Sobolev et al, 2005, Nature 434, 590-597). Further melting of such reaction pyroxenite should yield melts higher in Ni and lower in Mn, Ca and possibly Cr than peridotite-derived melts, as the restite would contain clinopyroxene and thus buffer Ca, Mn and Cr at a lower level in the melt. Olivine in the restite, on the other hand, buffers Ni in the melt. Experimental data show that pyroxenite derived melts have olivine on their liquidus at lower pressures, even though olivine is absent in their source. To resolve inputs of peridotite and reaction pyroxenite sources in composition of mantle derived melts we performed extensive high precision analysis of major (Mg, Fe, Si) and trace elements (Ni, Mn, Ca, Cr) in early olivine phenocrysts in lavas from mantle plumes, large igneous provinces (LIPs) and mid-oceanic ridges. Data for over 10000 high Mg olivine grains from 150 samples from 40 localities manifest much higher variations in concentrations of Ni, Mn and Ca than expected for magmas produced by melting of the peridotite. Specifically, many olivines from mantle plumes and LIPs are too high in Ni and too low in Mn and Ca to be compatible with any peridotitic source. In addition, most of them are too low in Cr to be compatible with harzburgitic sources. Moreover, olivines show strong positive correlations between relative Ni enrichment and depletion in Mn and Ca. These correlations are best explained by common mixing of magmas produced by partial melting of two different lithologies: peridotite and olivine-free pyroxenite. Lavas from mantle plumes and LIPs emplaced on thick lithosphere (Hawaii, Gran Canaria, Karoo, Afar, Emeishan, Etendeka and Siberian Flood basalts), commonly have pyroxenite as a major mantle source. This is consistent with higher melt production of pyroxenite compared to peridotite during decompression at high pressures. In contrast, lavas from mid-oceanic ridges (Atlantic, Pacific and Indian oceans) and mantle plumes emplaced on thin lithosphere (e.g. Iceland, Azores) contain a pyroxenite component highly attenuated by large melting fraction of peridotite. Data obtained suggest that olivine-free secondary pyroxenite rich in Ni, Mg and Si is a common source in the convecting upper mantle and mantle plumes, whenever recycled oceanic crust is present. The estimated amount of recycled oceanic crust is between one to few percents in the convective upper mantle and between few to over 20 percent in the mantle plumes and LIPs mantle sources.
DE: 1025 Composition of the mantle
DE: 1030 Geochemical cycles (0330)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005