Details

Autor(en) / Beteiligte

• Clemens, J. D.
• Stevens, G.
• Mayne, M. J.

Titel

Do arc silicic magmas form by fluid-fluxed melting of older arc crust or fractionation of basaltic magmas?

Ist Teil von

• Contributions to mineralogy and petrology, 2021-06, Vol.176 (6), Article 44

Ort / Verlag

Berlin/Heidelberg: Springer Berlin Heidelberg

Erscheinungsjahr

2021

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Under the right circumstances, fluid-fluxed crustal melting occurs, as demonstrated by some amphibolite-facies migmatites, but the relatively low temperatures involved make this mode of formation an unsatisfactory model for most silicic magma genesis in arcs. The concept of silicic arc magma formation through either partial melting of metabasalts or fractionation of hydrous basaltic parent magmas should also be treated with scepticism, as both these processes produce sodic and moderately to strongly peraluminous liquids that are chemically unlike most arc silicic rocks and glasses. Furthermore, if the silicic magmas are formed in the deep crust, the fractionation model predicts evolved liquids with extreme H 2 O contents. Thus, the answer to the question posed in the title is that neither of these two models, in isolation, seems likely for the formation of the majority of the more silicic magmas in arc environments. Given the totality of the evidence, we favour models in which high- T processes dominate. These could include fluid-absent partial melting of older non-basaltic arc crust, entrainment of source-derived crystal cargos, hybridisation with mantle-derived magmas and, in some cases, crystal fractionation of andesitic magmas at shallow crustal levels.