Recycling and recharge at Hasandağ stratovolcano, Central Anatolia: insights from plagioclase textures and zoning patterns

We explore crystal growth and magma recharge during the formation of intermediate lavas using bulk rock compositions and zoning patterns and textural variation in plagioclase feldspars from Hasandağ volcano in south-central Turkey. Hasandağ intermediate lavas formed primarily through fractionation of the observed mineral phases, and also show abundant evidence for magma mixing and thermochemical disequilibrium. Sparse basaltic andesites originated through mixing of observed mafic and felsic lavas rather than fractionation. Plagioclase phenocrysts from all lava types have uniform core (An_~39) and variable rim (An_39–64) compositions, suggesting plagioclase feldspars from a common magma reservoir are present in all erupted lavas. An-rich crystal rims are regularly enriched in Mg, Fe and Ti, indicating mafic recharge and magma mixing. Mixing timescales determined by diffusion modeling of Mg profiles across core-rim boundaries suggest recharge to eruption occurs on the order of up to ~ 45 days. Thermobarometric calculations constrain shallow crustal storage of dacite to 1.5–2 kbar (~ 5 km) and 800–890 °C, with deeper reservoirs for more mafic magmas (up to 35–40 km for basalts). Abundant disequilibrium textures (sieve-textured zones, oscillatory zoning, resorbed and patchy-zoned cores) indicate mobilization of a homogeneous crystal-rich dacitic reservoir by injection of mafic magma. We suggest that incomplete and dynamic physical mixing at shallow crustal levels results in distinct crystal morphologies, some of which record punctuated ascent and storage, while others are erupted rapidly after the influx of new magma.