Evidence for a missing crustal root and a thin lithosphere beneath the Central Alborz by receiver function studies

Abstract

The Alborz Mountains build the northern part of the Alpine-Himalayan orogen in western Asia. They are located south of the Caspian Sea and form an east-west range across the north of Iran. This region is one of the most active tectonic areas, as it undergoes extensive crustal deformation and shortening. In the present work, we used data from 11 permanent stations of the Tehran Telemetry Seismic Network to estimate the thickness of the crust and mantle lithosphere beneath the Central Alborz region by P- and S-receiver function methods. Results of both P and S receiver functions revealed a relatively large crustal thickness beneath this region (∼51–54 km), which can be associated with the shortening process related to the orogenic belt. No remarkable crustal thickening has been detected below the high topography of Central Alborz. A thick crust (∼67.5 km) is observed locally in the region beneath the Damavand volcano, which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region. The S receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of ∼90 km, which we interpreted as the base of the lithosphere. The missing crustal root and the relatively thin lithosphere beneath the Alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the Alborz.