Lithospheric geotherm and basalt assemblage beneath Nemrut and Suphan volcanoes (East Anatolia) Inference from integrated geophysical-petrological modeling

Abstract

Understanding volcanic processes including eruption mechanisms depends on knowledge of temperature and chemical compo- sition (thermochemical structure) of the crust and the upper mantle. This study applies an integrated geophysical-petrological modeling constrained by available seismic information to study the crustal and upper mantle thermochemical heterogeneities in two active volcanoes, Nemrut and Suphan (East Anatolia). The results reveal significant assemblage of basalts at depth beneath Nemrut and Suphan volcanoes. The assemblage of basalt is correlated with considerable lithospheric thinning/disappearance. Predicting geoid height anomaly and fitting gravity data including free-air and Bouguer anomalies supports the presence of the basaltic body as well as the modeled thermochemical structure. This study also implies that the crustal density structure can be biased in the presence of the significant sub-lithospheric heterogeneities. The temperature of the Moho is ~1118 °C, while the temperature of the underlying asthenosphere exceeds 1420 °C, beneath Nemrut and Suphan. The intense seismicity and focal mechanism type (strike-slip and thrust) suggests the magma differentiation and ascent of multiple magma intrusions beneath Nemrut and Suphan, which is supported by asthenospheric and extensional tectonics. Magmatism in East Anatolia is likely to be associated with a low-degree of anhydrous melting of the asthenosphere while hydrous melting is unlikely.