Integrated geophysical-petrological model of Damavand volcano, North Iran: Compositional structure of crust and upper mantle from seismic temperature profiling and gravity anomaly fitting

Abstract

Our study employs well-constrained integrated geophysical-petrological modeling to investigate the compositional structure of Damavand volcano, the Alborz mountains in northern Iran. The thermochemical model utilizes high-resolution compressional velocity anomalies to determine temperature, while geochemical data from volcanic rocks further constrain mostly the lithospheric mantle model. By examining density and velocity, we deduce the upper mantle's compositional structure using observed free-air gravity anomalies and shear-wave seismic models. Our results reveal a lower crust density reduction of 150 kg/m3 due to a high-temperature regime (1080 °C) and the presence of melt indicated by a calculated Vp/Vs ≥ 1.8. The magma storage in the lithosphere is characterized by a harzburgite-melt mixture in agreement with shear-wave seismic profiles, and the lithospheric magma reservoir is positively buoyant with a density reduction of ∼75 kg/m3 compared to the ambient lithospheric mantle. The absence of a warm zone beneath the Alborz suggests that a transient mantle flow from the 660 km transition zone beneath Eurasia is responsible for the lateral heating (and possibly hydration) of the lithospheric mantle. This aligns with the high-temperature conditions observed in the Damavand (Alborz) region. Furthermore, the presence of elevated Nb (and high Nb/Yb ratio as well as radiogenic Nd isotope) concentrations in certain volcanic rocks suggests that a portion of the melt may have originated from the Earth's asthenosphere mantle. Moreover, the existence of water and/or volatiles (likely ≥0.64 wt%, as determined through a comparison of predicted and observed seismic velocities, along with previous laboratory analyses) promotes decompression melting of the lithospheric mantle at significantly lower temperatures (1230–1130 °C) in contrast to earlier estimations (1430–1180 °C). Finally, the reductions in velocity observed in the lower crust and uppermost lithospheric mantle beneath Damavand are likely attributed to thermal and compositional factors, respectively. The presence of a hydrated and melt-rich composition within the lithospheric mantle can account for the observed decrease in seismic velocity.