Damavand volcano trachyandesites and basalts: radiometric ages and radiogenic isotopes

Abstract:
      Damavand volcano (elevation 5671m above see level), is mainly built from trachyandesites but minor volumes of olivine trachybasalts and basanites are present in the southern and eastern margins. Age and genetic relationships between the two rock suites have been debated. This study aims at resolving the dispute by providing radiometric ages and radiogenic isotope ratios. Trachyandesites eruption ages are from about 1.8 Ma to 7300 ka. The Poloor basalt has been dated at 1.53 ? 0.10 Ma which indicates that basalts do not represent the oldest eruptions. Trachyandesites are less enriched in certain large ion lithophile elements compared to the basalts. Therefore, fractional crystallization cannot be the only mechanism to derive trachyandesites from the basalts. The two rock suites yield different Sr and Nd isotopic ratios, suggesting involvement of extensive crustal assimilation along with fractional crystallization.