Variation of Moho depth in the central part of the Alborz Mountains, northern Iran

Abstract : The Alborz Mountains of northern Iran form a belt of active crustal deformation along the southern side of the Caspian Sea within the broad Arabian-Eurasia continental collision zone. Although the range has an average elevation of about 3000 m with the volcanic peak Damavand reaching an elevations of 5671 m, early gravity studies found that the crust beneath the range is no thicker than that beneath the surrounding region suggesting the range is not supported by a crustal root. We determine a model for the crust of the central Alborz Mountains using teleseismic receiver functions from data recorded on a network of broad-band seismographs temporarily deployed across the central part of the range. The receiver functions from these recordings have been inverted simultaneously with fundamental-mode Rayleigh wave group velocity measurements in the 10-100 s period range. Our analysis shows a thickening of the crust from ~48 km beneath the northern part of the Central Iranian Plateau to 55-58 km below the central part of the Alborz Mountains, then a thinning of the crust to ~46 km north of the Alborz Mountains beneath the coastal region of the South Caspian Sea. Our seismological results show that the central Alborz Mountains have a moderate crustal root but of insufficient thickness to compensate the elevation of the range. The analysis of free-air gravity shows that the elevation of the Alborz Mountains is largely supported by the elastic strength of the Iranian Plate, the South Caspian Plate, or both.