Geophysical source conditions for basaltic lava from Santorini volcano based on geochemical modeling

Abstract

Santorini volcano sits ~145 km above the Aegean Wadati-Benioff zone, where the African plate subducts northward beneath Eurasia. There are only a few localities in the whole Aegean where basaltic lavas primitive enough to constrain mantle processes beneath the Aegean arc can be found; in this work we analyzed one such locality, a basalt lava from the southern part of Santorini. We apply a suite of petrological tools (PRIMACALC2 and ABS5) in sequence to estimate magma chamber conditions, primary magma composition, mantle melting conditions, and slab dehydration conditions. Back-calculation modeling based on major-element chemistry yields shallow magma chamber conditions of P = 0.02 GPa, fO_2 = QFM + 2, and ~1 wt% H_2O in the primary magma. The estimated major element composition of this primary magma then leads to estimated mantle melting conditions of 2.1 GPa, 1353 °C, and F = 8%; whereas a more precise estimate derived from trace elementmodeling implies 1.7 GPa, 1323 °C, and F = 18%. Furthermore, the trace element model implies a slab flux derived from 4.6 GPa (~150 km slab depth). The estimated slab depth, magma segregation conditions, and magma chamber depth are all consistent with seismic observations, supporting slab dehydration in the seismically imaged steep slab interval and flux melting in a relatively hot mantle wedge.