Mantle Source Characteristics of Damavand Volcanic Rocks, Northern Iran; Constraints From New Sr, Nd, Pb and O Isotope Data
Abstract
Continental volcanic rocks can provide important information about the processes controlling the geochemical evolution of the sub-continental mantle. However, no systematic geochemical studies on igneous rocks are available that can be used to delineate the chemical composition of the mantle underlying northern Iran. We present the first Sr, Nd, Pb and O isotope data for the Quaternary Damavand that occurs as a solitary volcano in Central Alborz Mountains, located in northern Iran and southern Caspian Sea. The Damavand volcano is a composite cone consisting of trachyandesite, basaltic trachyandesite and minor alkali olivine basalt. Since the Damavand alkali olivine basalts represent the most primitive rock type in the association and because they have MgO, Ni and Cr abundances similar to near primary magmatic rocks, these basalts have been used here to study the mantle source underlying Damavand. Some geochemical features of the basalts such as slight depletion in Nb, Ta and Ti, enrichment in Ba and Pb, relatively high δ 18O values (+6.5 to +6.8‰ ), and crustal-like Pb isotopic ratios (206 Pb/204Pb 18.76, 207Pb/204 Pb 15.62, 208Pb/204Pb 38.89) suggest that they were contaminated during ascent through the continental crust. This is also reinforced by the presence of embayed and relict quartz and feldspar xenocrysts in the basaltic rocks. In addition, the initial Sr and Nd isotopic compositions of the basalts (0.70450 and 0.51259, respectively), that cluster near bulk silicate Earth (BSE) values and plot within the mantle array on Nd-Sr isotopic diagram, can result from small degree contamination of MORB- or OIB-like magma with crustal material. On Nd-Sr isotopic diagram, the basaltic trachyandesites, and trachyandesites plot on the enriched part of the quadrant indicating higher involvement of crustal materials in the evolution of these lavas. Arc magmatism resulting from subduction of oceanic lithosphere underneath the Alborz Mountains cannot be invoked for the genesis of the Damavand volcanics due to the lack of geological and geophysical evidence. However, the observed geochemical features of the studied samples can be reconciled with crustal contamination of Damavand magmas originated from partial melting of sub-continental mantle source.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.V43A..09M
- Keywords:
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- 1040 Isotopic composition/chemistry