H. Ghasemi; M. Rostami Hossuri; M. Sadeghian
Abstract
The Lower Jurassic basin of northern margin of central Iran structural zone and south of eastern Alborz in Semnan province, contains igneous rocks with basic composition, belonging to early stages of occurrence and development of an immature extensional back arc basin at this time. These basic igneous ...
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The Lower Jurassic basin of northern margin of central Iran structural zone and south of eastern Alborz in Semnan province, contains igneous rocks with basic composition, belonging to early stages of occurrence and development of an immature extensional back arc basin at this time. These basic igneous rocks cropped out in at the base of Shemshak Formation and its equivalent in central Iran Structural zone, in the form of extrusive (basaltic rocks) and intrusive (dike, sill and microgabbroic small stocks) rocks. Magma forming of these rocks have had calc – alkaline nature and was enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) and also was depleted in heavy rare earth elements (HREE). The mentioned magmas was, originated from 5 to 30% partial melting of the spinel peridotitic (below the central Iran) and garnet lherzolithic (below the Eastern Alborz) mantle plumes in an immature extensional back arc basin tectonic setting due to oblique subduction of Nneothetyan oceanic lithosphere beneath the central Iran structural zone at late Triassic to middle Jurassic time, and were ascending to upper levels of continental crust by fault and fracture systems and emplaced in shallow sedimentary basins of these zones in different ways. This basin was formed in the behind of the upper Triassic – Lower Jurassic magmatic arc of central Iran and due to initiation of extensional movements in the continental crust of central Iran and Alborz.
F. Tutti; S. Yazdani; K. Bazargani-Guilani
Abstract
South Kahrizak volcanic rocks with Eocene age are located in the north part of Central Iran. These rocks are mainly composed of pyroclastics (tuff and ignimbrites) and lava flows (rhyolite, trachyandesite, basaltic trachyandesite and basalt). Petrographic evidence such as: zoning, ...
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South Kahrizak volcanic rocks with Eocene age are located in the north part of Central Iran. These rocks are mainly composed of pyroclastics (tuff and ignimbrites) and lava flows (rhyolite, trachyandesite, basaltic trachyandesite and basalt). Petrographic evidence such as: zoning, sieve texture and rounded crystals in plagioclase and pyroxene phenocrysts show the non-equilibrium conditions between melt and crystals during magma cooling. Geochemical characteristics indicate that these rocks locate in the subalkaline to alkaline domain. The highly enrichment of LREE compared to HREE, high content of LILE relative to HFSE and significant anomalies of Nb, Ta and Ti reveal the characteristics of a subduction - related volcanism. Whereas, the alkaline affinity of rocks shows that they may have formed in an extentional region, most probably a back-arc basin.
