The geology of Damavand volcano, Alborz Mountains, northern Iran

Abstract

Damavand volcano, located in northern Iran, is a large (>400 km^3) composite cone that is currently dormant; it shows fumarolic activity near the summit but no evidence of eruption in the past 1000 yr. The volcano represents an isolated focus of magmatism of uncertain tectonic affinity, although geophysical and geochemical constraints point toward a local hotspot/plume origin, possibly associated with lithospheric delamination, rather than any association with subduction. New (U-Th)/He and ^(40)Ar/^(39)Ar geochronological constraints indicate that the present cone (Young Damavand) has been constructed over ∼600 k.y. on an older, eroded edifice of indistinguishable composition (younger than 1.8 Ma). Damavand activity has been characterized by the eruption of radially directed trachyandesite lava flows, almost exclusively from summit vents. Limited pyroclastic activity has yielded thin fallout pumice lapilli layers and a few pyroclastic flows. Only one significant pyroclastic event is recognized in the remnants of a welded ignimbrite, ponded and preserved along the Haraz River drainage. Relatively short periods of volcanic eruptive activity were interspersed with longer periods of erosion in which volcanic products were transported, particularly as hyperconcentrated flows, into the surrounding drainage systems to be further reworked into epiclastic deposits. Occasional catastrophic events punctuated this interplay between volcanism and erosion. At least one sector collapse is signified by the presence of a large debris avalanche deposit, and the regional drainage systems appear to have been frequently dammed by incursions of volcanic material.