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.
S. M. Tabatabaeimanesh; H. Safaei; A. S. Mirlohi
Abstract
In south of Kashan, early Paleozoic volcanic rocks are a part of Ghohrudmountains. In Iran structural- sedimentary division, these volcanic rocks located inUrumieh- Dokhtar zone. These volcanic rocks are basic to semibasic and mostly involved basalt. Geochemical investigations of these rocks show the ...
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In south of Kashan, early Paleozoic volcanic rocks are a part of Ghohrudmountains. In Iran structural- sedimentary division, these volcanic rocks located inUrumieh- Dokhtar zone. These volcanic rocks are basic to semibasic and mostly involved basalt. Geochemical investigations of these rocks show the alkaline nature and the intra-continental rift geotectonic setting in their formation time. The Isfahan fault is a north-trending fault across the Sanandaj-Sirjan zone. This fault is one of the old and basement fault that was active in the early Paleozoic. The unique present of Silurian volcanic rocks in this area can refer to the activation of the north part of this fault that was created by extension phases after Caledonian orogeny.
N. Amel; M. Moayyed; A. Ameri; M. Vosoghi Abedini; M.H. Emami; M. Moazzen
Abstract
The Plio-Quaternary calc-alkaline magmatism in Azerbaijan, northwest Iran, occurs as stratovolcanoes, lava flows and domes consisting of andesitic basalts, andesites, dacites, rhyodacites, and pyroclastic materials. The volcanic rocks unconformably cover the Miocene sedimentary ...
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The Plio-Quaternary calc-alkaline magmatism in Azerbaijan, northwest Iran, occurs as stratovolcanoes, lava flows and domes consisting of andesitic basalts, andesites, dacites, rhyodacites, and pyroclastic materials. The volcanic rocks unconformably cover the Miocene sedimentary formations. The chemistry of the felsic-intermediate volcanic rocks indicates that the parent magmas are medium-K calc-alkaline and metaluminous in nature, and are distinguished by Na2O/K2O> 1. The volcanic rocks are enriched in LILE and LREE, and depleted in Y, Nb, and HREE, and display highly fractionated REE patterns, with no Eu anomaly. They display post-collision and continental margin arcs affinities. The post collision convergence between Arabia and Eurasia continental plates, starting in Miocene, resulted in significant shortening, thickening, and uplift of the crust in northwestern Iran and eastern Turkey, and shaped the present Iran-Turkey Plateau.
The thermal perturbation processes in the underlying asthenospheric mantle led to partial melting at a low degree, producing alkali- basalt magmas, with garnet remaining stable in the source region. The ascent of the basaltic magma and its emplacement in the lower crust resulted in the partial melting of the crustal materials and development of acidic magma. These processes led to the ascent and eruption of the felsic magmas prior to the mafic magmas. Mixing of mantle-derived mafic magmas with felsic magmas of crustal origin, produced hybrid magmas of intermediate composition. The occurrence of inverted volcanic sequences, where olivine-alkaline basalts are underlain by calc-alkaline felsic-intermediate rocks, are typical features of bimodal volcanic activities in the Plio-Quaternary times in Azerbaijan.
There are mineralogical as well as geochemical evidences that AFC-type processes were involved in the evolution of the Plio-Quaternary volcanic rocks in Azerbaijan. A comparison of geological and geochemical characteristics of the Plio-Quaternary volcanic rocks from northwest Iran with those from eastern Turkey indicates that the two areas share similar evolution paths in the petrogenesis of magmatic rocks.