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| Titel |
Geochemical models of melting and magma storage conditions for basalt lava from Santorini Volcano, Greece |
| VerfasserIn |
Ioannis Baziotis, Jun-Ichi Kimura, Avgoustinos Pantazidis, Stephan Klemme, Jasper Berndt, Paul Asimow |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141206
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| Publikation (Nr.) |
 EGU/EGU2017-4687.pdf |
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| Zusammenfassung |
| Santorini volcano sits ∼150 km above the Wadati-Benioff zone of the Aegean arc, where the
African plate subducts northward beneath the Eurasian continent (Papazachos et al. 2000).
Santorini volcano has a long history: activity started ca. 650 ka (mainly rhyolites and
rhyodacites), with active pulses following ca. 550 ka (basalt to rhyodacite) and ca. 360 ka
(large explosive eruptions of andesite to rhyodacite and minor basalt), culminating in the
caldera-forming Bronze-age Minoan event (Druitt et al. 1999). As in many arc volcanoes,
scenarios of fractional crystallization with or without mixing between felsic and mafic
magmas have been proposed to explain the compositions, textures, and eruptive
styles of Santorini products (e.g., Huijsmans & Barton 1989; Montazavi & Sparks
2004; Andújar et al. 2015). Here we focus on a basalt lava from the southern part of
Santorini volcano (Balos cove, 36˚ 21.7’N, 25˚ 23.8’E), one of the few basaltic
localities in the Aegean arc. The goals are to infer constraints on the magma chamber
conditions which lead to mafic eruption at Santorini Volcano and to evaluate the
slab and mantle wedge conditions via geochemical and petrological mass balance
modelling.
We collected and characterised 20 samples for texture (SEM), mineral chemistry
(FE-EPMA) and whole-rock chemistry (XRF). The basalts contain phenocrystic olivine (Ol)
and clinopyroxene (Cpx) (<600 μm diameter) in a fine groundmass (<100 μm diameter) of
Ol, Cpx, plagioclase (Pl) and magnetite (Mt) with minor glass and rare xenocrystic quartz.
Santorini basalts exhibit a pilotaxitic to trachytic texture defined by randomly to
flow-oriented tabular Pl, respectively. The predominant minerals are calcic Pl (core An78−85
and rim An60−76; 45-50 vol.%), Cpx (En36−48Wo41−44Fs11−21; 10-15 vol.%) and Ol
(Fo74−88; 10-12 vol.%). Idiomorphic to subidiomorphic Mt (<10μm diameter) with variable
TiO2 contents (1.9-16.5 wt%) is a minor constituent (∼1-2 vol.%) in the less mafic
samples.
Observed mineralogy and major element chemistry suggest fractionation in a shallow
magma chamber. Using the major element chemistry and PRIMACALC2 (Kimura & Ariskin
2014) back-calculator, inferred crystallization conditions are P=0.02 GPa, oxidized
(fO2=QFM+2), and ∼1 wt% H2O in the primary basalt. The source mantle conditions are
estimated at P=2.1 GPa, T=1350˚ C, and degree of melting F=8%. We also used trace
elements to estimate the incompatible element budget of the primary basalt using the
forward trace-element mass-balance model of ARC BASALT SIMULATOR ver.4
(Kimura et al. 2014). Preliminary results suggest that the slab flux was derived from
∼150 km depth, and fluxed mantle melting occurred at P=2.3 GPa, T=1380˚ C,
F=8%. The estimated slab depth is consistent with the seismic observations and
mantle conditions are consistent with the PRIMACALC2 major element modelling.
Our intent is to extend our analytical data with precise trace element and isotope
analyses in order to reveal more detailed source conditions and richer information
about processes from the slab through the mantle and up to the shallow magma
chamber.
References
Andújar, J. et al. (2015). JPET, 56 (4), 765–794.
Druitt, et al. (1999). Geological Society Memoir, 19.
Huijsmans, J. P., & Barton, M. (1989). JPET, 30(3), 583-625.
Kimura, J. I., & Ariskin, A. A. (2014). G3, 15, 1494-1514.
Kimura, J. I. et al. (2014). G3, 15, 691–739.
Mortazavi, M., & Sparks, R. S. J. (2004). Con Min Pet, 146(4), 397-413.
Papazachos, et al. (2000). Tectonophysics, 319(4), 275-300. |
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