The origin of evolved volcanic rocks in Methana, Greece

Schönhofen M, Wölki D, Haase K, Beier C (2017)

Publication Language: English

Publication Type: Conference contribution, Abstract of a poster

Publication year: 2017

Event location: Palais des Congrès de Paris 2 Place de la Porte Maillot, 75017 Paris, France

Abstract

The formation of evolved andesite to dacite magmas at
subduction zones is an important process on Earth. The
Aegean arc has one of the highest rates of sediment
subduction globally that impacts on the composition of the
erupted melts. Methana peninsula is located at the western
margin of the Aegean arc and consists of numerous effusive
andesitic to dacitic eruptions. These evolved lavas frequently
contain basaltic to basaltic-andesitic enclaves. An origin of
the Methana andesites as a result of melting of mantle
hybridized by sediment melts can be excluded from the
occurrence of basaltic enclaves. Petrological and geochemical
data suggest shallow crustal processes playing a crucial role
in the formation of these rocks. The major element patterns
(e.g. FeO*, Al2O3 or TiO2 vs. MgO) show evidence for
fractional crystallization. Mineral compositions display
oscillatory zonings, disequilibrium textures, secondary rim
overgrowths and different mineral populations indicating
complex mixing of magmas. Plagioclase generations can
mainly be distinguished by their size and phenocrysts display
anortithe contents from 43 to 88, while amphiboles show
evidence for polybaric fractionation. Thermobarometric
calculations using amphibole-plagioclase assemblages imply
that magma mixing occurs in the shallow crust (9-15km)
feeding the volcanic eruptions. We develop a model of a
deep-reaching magma system reaching to the crust-mantle
boundary. This can explain continuous magma mixing along
a range of depths. Fe-Ti oxide thermometry yields partly
higher temperatures than the plagioclase-amphibole
thermometer and possibly resulting from rapid magma ascent.
Explosive volcanism dominates the central and eastern
Aegean islands, e.g., Santorini or Kos [1], while Methana
displays extensive effusive volcanism with lava domes and
flows. We interpret this to result from pre-eruptive re-heating
[2] by recharge of more primitive and hotter magma from the
crust-mantle boundary. The larger crustal thickness in the
western Aegean may influence the eruptive mechanism by
intensive degassing covering a higher distance during magma
ascent than in other parts of the arc.
[1] Druitt et al. (2016), Journal of Petrology 57(3), 461-
494; [2] Ruprecht & Bachmann (2010), Geology, 38(10),
919-922.

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APA:

Schönhofen, M., Wölki, D., Haase, K., & Beier, C. (2017). The origin of evolved volcanic rocks in Methana, Greece. Poster presentation at Goldschmidt 2017, Palais des Congrès de Paris 2 Place de la Porte Maillot, 75017 Paris, France, FR.

MLA:

Schönhofen, Milena, et al. "The origin of evolved volcanic rocks in Methana, Greece." Presented at Goldschmidt 2017, Palais des Congrès de Paris 2 Place de la Porte Maillot, 75017 Paris, France 2017.

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