Investigation of Sahand volcanic sequence along with petrology and geochemistry of the volcano
visits:2649
Executorof project: Dr. Jalil Ghalamghash
2016
Sahand volcano is located in Northwestren of Iran and in Eastern Azarbaijan province. Sahand volcano is including Neogene-Quaternary pyroclastic and volcanic rocks. Based on field study ofthis project volcanic sequences of Sanand are divided into Old-, Middle- and Young-Sahand rock units. The Volcanic rocks of Old and Middle Sahand included pyroclastic and lava sequences thatare built the main volume of this volcano. Young sub-volcanic and volcanic domes of Sahand haveintruded the Old and Middle Sahand volcanic succession Lithological compositions of Old Sahand volcanic rocks are basaltic andesite to andesite. The composition of tuff breccias, ignimbrite and volcanic rocks of the Middle Sahand are andesite, trachyandesite to dacite. Young Sahand volcanic has dacitic, rhyolitic and rarely quartz-andesitic compositions.
Abundance of silica in the Sahand volcanic rocks is from 54.81 to 75.28%. Different patterns for various elements in Harker diagrams, difference in LREE/HREE ratios in chondrite–normalized REE patterns and difference in LILE relative to HFSE in primitive mantle normalized multi element diagrams for Old Sahand volcanic rocks relative to Middle and Young Sahand are implying to different magmatic sources for Old Sahand volcanic rocks.Geochemical characteristics of Old Sahand volcanic rocks including distinctive depletion in HREE and Y reveal that these rocks are derived from spinel-lherzolite mantle in mantle-crust boundary; and parental magma of these rocks based on negative anomalies of Nb, Ti, Ta and also low Ba/Th ratios, metasomatized by slab sediment derived melt during the Neo-Tethyan subduction.Volcanic rocks of Middle and Young Sahand have adakitic nature and are derived from crustal garnet bearing (garnet-amphibolite) source rock; extreme depletions in Y and HREE in geochemical characteristics of these rocks implying that garnet is residual mineral in the source region.The age (12 Ma to 140Ka) and geochemical characteristics of Sahand volcano suggest that it formed in continental collision zone of Eurasia-Arabia plates, in the North of suture zone.
Abundance of silica in the Sahand volcanic rocks is from 54.81 to 75.28%. Different patterns for various elements in Harker diagrams, difference in LREE/HREE ratios in chondrite–normalized REE patterns and difference in LILE relative to HFSE in primitive mantle normalized multi element diagrams for Old Sahand volcanic rocks relative to Middle and Young Sahand are implying to different magmatic sources for Old Sahand volcanic rocks.Geochemical characteristics of Old Sahand volcanic rocks including distinctive depletion in HREE and Y reveal that these rocks are derived from spinel-lherzolite mantle in mantle-crust boundary; and parental magma of these rocks based on negative anomalies of Nb, Ti, Ta and also low Ba/Th ratios, metasomatized by slab sediment derived melt during the Neo-Tethyan subduction.Volcanic rocks of Middle and Young Sahand have adakitic nature and are derived from crustal garnet bearing (garnet-amphibolite) source rock; extreme depletions in Y and HREE in geochemical characteristics of these rocks implying that garnet is residual mineral in the source region.The age (12 Ma to 140Ka) and geochemical characteristics of Sahand volcano suggest that it formed in continental collision zone of Eurasia-Arabia plates, in the North of suture zone.