Boron and B-Sr-Nd isotopes as tracers of FME and volatile enrichments in the mantle source of Kamchatka arc basalts, insights from Kozelsky, Avachinsky and Khangar mafic series

Brennan, E.; Savov, I.P.; Agostini, S.; Churikova, T.; Gordeychik, B.; Morgan, D.J.; Pevzner, M.

Авторы: Brennan E., Savov I.P., Agostini S., Churikova T., Gordeychik B., Morgan D.J., Pevzner M.
Сборник: Continental collision zone volcanism and associated hazards. International conference. Yerevan, Armenia, 3-8 September, 2023
Тезисы
Год издания: 2023
Место издания: Institute of Geological Sciences Yerevan
Первая страница: 50
Последняя страница: 51
Аннотация: The voluminous magmatic outputs from the old, cold, and altered Pacific slab under the Kamchatka Peninsula creates an ideal environment to utilise B and B isotopes to faithfully trace volatile release across subduction zones. Here we report new petrological and geochemical results (XRF, EMPA, SEM, ICP-MS, and TIMS) from the forearc-situated Kozelsky and Avachinsky volcanoes (Avacha Group) with respect to the back arc volcano Khangar. We will present a first geochemical and petrological typification of Kozelsky. The sampled olivinephyric basalts from the Avacha Group record high MgO (5-15 wt%), Ni (15-250 ppm) and Cr (60-800 ppm) abundances. The whole rock 87/86Sr and 143/144Nd ratios of these volcanoes show narrow ranges (~0.70335 and ~0.51305, respectively), revealing dominantly mantle wedge (non-crustal) magma sources. Such isotopic signatures are nearly identical to those of highMgO basaltic lava and tephra from the Tolbachik monogenetic field in the Central Kamchatka Depression (the second volcanic belt with slab depths of ~200km) (Iveson et al., 2021, 2022; Gorbtov et al., 1997]. Kozelsky magmas sample very shallow depths to the slab of less than 90km ( Syracuse and Abers, 2006). New whole rock B and B isotope data reveals serpentiniteforearc mélange influenced outputs [e.g. high B and heavy δ11B (up to >+2 to +5‰ )]; this deviates from the expected deep sourced slab melt contribution (+2‰, Li et al., 2023) which whilst has an influence, alone cannot source these magmas. This is also in contrast to AOC (altered oceanic crust) melt-dominating mantle metasomatism in the arc belts with deeper subducting slabs (i.e. Tolbachik: Iveson et al., 2021, 2022; Gorbtov et al., 1997;EB : Iveson et al., 2021). Therefore, such excess, non-sediment sourced B and enriched δ11B should be derived from dehydrated and with heavy δ11B AOC ( McCaig et al., 2018) or forearc, serpentinite, melange rocks associated with the subducting slabs, supporting the mélange model of slab material transport (Nielsen and Marschall, 2017). Moreover, Khangar, which samples a depth to the slab of ~350km, has the expected dominantly OIB signature with a much lighter δ11B signature (-5 to -10‰, EB, Iveson et al, 2022) and lower B concentrations from a volatile starved slab. We are now focussing on the analysis of δ11B and hydrous contributions in melt inclusions, to further trace the non-crustal, boron-depleted, and isotopically light arc mantle background across the Kamchatka arc. Our results will evaluate if systematic variations in BSr-Nd isotopes and trace element ratios can be linked to across-arc change in depth to a slab of the magma source and/or reveal details about the prevailing geodynamic regime.
Добавил в систему: Гордейчик Борис Николаевич

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Boron and B-Sr-Nd isotopes as tracers of FME and volatile enrichments in the mantle source of Kamchatka arc basalts, insights from Kozelsky, Avachinsky and Khangar mafic seriesтезисы доклада Тезисы

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