DAMAVAND VOLCANO, NORTHERN IRAN: MORPHOLOGY AND SEDIMENTARY RECORD

Damavand Volcano is an isolated, >350km³ Quaternary composite cone rising 5,670m in the Alborz Mountain Range north of Tehran. Morphological and sedimentological observations, mapping, and U-He dating of apatite phenocrysts have been used to constrain the history of the volcano. The slopes of the volcano comprise trachyandesite lava flows partially overlain by reworked pyroclastic fall deposits. Volcaniclastic sediments are well exposed in cliff-sections and subsidiary valleys along a major N-S drainage, the Haraz River. The exposed sediments consist of fluvial and debris flow deposits, containing mainly clasts of lava and minor basement material. One significant ignimbrite unit has been identified, though pyroclastic eruptions were apparently minor and infrequent. Debris avalanche deposits suggest that one or more sector collapse events shaped the edifice. Local geomorphology has been strongly affected by the formation of the volcano, as erupted products are the main source material for the sediments. A large proportion of the sediments has been eroded into the Haraz River and away from the area towards the Caspian Sea. The sedimentary record of the volcano's growth and evolution is thus greatly fragmented.

Two periods of eruptive activity have been identified (1.78Ma-800ka and 500ka-7.3ka), separated by a period of quiescence. During this time of inactivity, the hydrothermally-altered material in the core of the volcano was exposed and rapidly eroded because of its non-resistant nature. The eruptive style has remained the same throughout the volcano's two million year history despite one or more sector collapse events and the formation of a second cone overlying the old eroded cone.