Generation of arc rhyodacites through cumulate-melt reactions in a deep crustal hot zone: Evidence from Nisyros volcano

Martijn Klaver*, Jon D. Blundy, Pieter Z. Vroon

*Corresponding author for this work

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The generation of continental crust of intermediate composition occurs predominantly in convergent margin settings, yet the mechanisms by which felsic, calc-alkaline arc magmas are generated remain poorly understood. Magma mixing appears to be a common process in voluminous intermediate arc rocks but the composition of the felsic mixing endmember is typically obscured by the mixing process. We investigate a suite of porphyritic (rhyo)dacitic magmas (65–72 wt.% SiO2) from Nisyros, a young stratovolcano in the Aegean arc, Greece. These magmas are not affected by shallow process such as hybridisation or crystal-melt segregation and thus offer a valuable insight into the origin of felsic melts at convergent margins. We find that the Nisyros (rhyo)dacites form through a reaction in which earlier-formed wehrlite cumulates in the deep arc crust react with melts to form amphibole. This implies that melt major element compositions are effectively buffered by a low-variance mineral assemblage to follow this peritectic boundary such that the silica content of melts extracted from the deep crustal hot zone is controlled by the amount of amphibole crystallised. The resorption of cumulates is pivotal in imparting a distinct trace element signature that is decoupled from major element systematics. For example, high compatible element contents and a strong amphibole signature (low Y and Dy/Yb) cannot be captured by simple crystallisation models and require cumulate resorption. Variable radiogenic isotope systematics indicate minor crustal contamination although assimilation is not proportional to silica content and hence not a main driving force behind the generation of felsic melts. Instead, the Nisyros (rhyo)dacites formed through melt-cumulate reaction processes prior to emplacement as mush bodies at shallow depth and partial eruption. Magma mixing only becomes an important process in the youngest unit on Nisyros. On a global scale, peritectic boundary melts are rarely sampled in the whole rock or melt inclusion record. Conversely, peritectic boundary melts do form a suitable felsic mixing endmember for the generation of voluminous “monotonous intermediate” magmas.

Original languageEnglish
Pages (from-to)169-180
Number of pages12
JournalEarth and Planetary Science Letters
Early online date26 Jun 2018
Publication statusPublished - 1 Sept 2018


Permission for fieldwork and sampling on Nisyros was kindly provided by the Greek Institute of Geology and Mineral Exploration. Roel van Elsas, Bas van der Wagt and Richard Smeets are greatly acknowledged for analytical assistance. Femke van Aken, Tamara Arens and Ellen Schulten are thanked for producing some of the major element data as part of their BSc research projects. Useful discussions with Sarah Fowler helped with the trace element modelling. PZV would like to thank Johan Varekamp for introducing him to the geology of Nisyros in 1985. This manuscript benefited significantly from constructive comments made by Othmar Müntener and an anonymous reviewer and we thank John Brodholt for careful editorial handling. MK acknowledges funding from the STFC through grant no. ST/M007715/1 whilst in Bristol. Appendix A

FundersFunder number
Natural Environment Research CouncilNE/M000419/1
Science and Technology Facilities CouncilST/M007715/1


    • Aegean arc
    • amphibole
    • calc-alkaline (rhyo)dacites
    • magma differentiation
    • melt-cumulate reaction
    • Nisyros


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