Tectonics
Nayyer Bayeste Hasti; Hosein Motamedi; Mahmoud Almasian
Abstract
This study has focused on the result of seismic data. The first stage of basin formation is the opening of Neo- Tethys Sea which is Simultaneous with Dashtak, Kangan and Khaneh kat Formation and after that on the early to middle Triassic sediments an unconformity that can be named as an expansion of ...
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This study has focused on the result of seismic data. The first stage of basin formation is the opening of Neo- Tethys Sea which is Simultaneous with Dashtak, Kangan and Khaneh kat Formation and after that on the early to middle Triassic sediments an unconformity that can be named as an expansion of sedimentary basin in the upper Triassic happened. This stage of basin opening caused the formation of big faults and probably basement faults in the area that studying on this faults and their movements is the main goal of this study. The next stage of evolution of basin starts when the basin began to closure and still there is disagreement about the exact time; but the obvious thing is the four compressional events: first, from Cenomanian- Turonian up to Masstrichtian; second, Late Paleocene- Early Eocene; third, Late Oligocene-Miocene and the forth, Miocene up to Quaternary. All events caused to obduction of Ophiolite and sedimentation of Gurpi with partly erosion and Pabdeh with regional erosion, then disappearing formations such as Asmari and Gachsaran and at the end, the late Zagros orogenic phase which is the compression that is continues to this day.
E. Keshtkar; M. Ghorbani; J. Omrani
Abstract
A gabbro to monzonite sill is injected into the Karaj tuffs at the north of Parachan village, North of Karaj.. The main minerals of these rocks are plagioclase, pyroxene, K feldspar, olivine and biotite. Clinopyroxene mineral chemistry studies carried out on the intrusive bodies, indicate two types of ...
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A gabbro to monzonite sill is injected into the Karaj tuffs at the north of Parachan village, North of Karaj.. The main minerals of these rocks are plagioclase, pyroxene, K feldspar, olivine and biotite. Clinopyroxene mineral chemistry studies carried out on the intrusive bodies, indicate two types of diopside and augite clinopyroxene composition. The chemical composition of the pyroxenes shows that these rocks have been crystallized in a subduction geological setting. The average crystallization temperature of clinopyroxenes is about 1120 to 1170 °C, and it seems that clinopyroxenes crystallized at lower temperature than orthopyroxenes. Plagioclase composition in these rocks is variable, changing from andesine to labradorite. K feldspars are in the orthoclase range and olivine are hyalosiderite. Biotite is one of the most prominent ferromagnesian minerals in the studied bodies. Compositionally, it is plotted between the fields of annite and siderophyllite. Most of these biotites are primary magmatic and some are plotted in the re-equilibrated filed. Petrological evidence represent that fractional crystallization from gabbro to monzonite had main role in genesis of these rocks. Enrichment in LILE) Ba, Rb and Th(and also depletion in HFSE (Nb and Ti) in Rare Earth Elements distribution pattern in spider diagrams, indicate features of subduction-related rocks. Also they are enriched in LREE rather than HREE, the characteristic which is usually observed in the rocks from subduction environments and active continental margins. Chemical and petrological studies, indicate role of fractional crystallization in the evolution of magma, although, minor amounts of assimilation and contamination of magma by crustal rocks occurred. This alkaline magma has been formed by low degree of partial melting of an enriched sub-continental lithospheric garnet-lherzolite mantle source.
E. Keshtkar
Abstract
The Intrusive bodies of the Karaj-Taleghan Axis, situated in the Central Alborz zone have lithological compositions including gabbro, monzogabbro, monzodiorite, monzonite andfelsic dikes of alkali feldspar syenite to syenite. Furthermore, they are accompanied by pyroclastic rocks of the Karaj formation, ...
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The Intrusive bodies of the Karaj-Taleghan Axis, situated in the Central Alborz zone have lithological compositions including gabbro, monzogabbro, monzodiorite, monzonite andfelsic dikes of alkali feldspar syenite to syenite. Furthermore, they are accompanied by pyroclastic rocks of the Karaj formation, for which Oligocene age is considered. Geological surveys, mineralogical and geochemical studies indicated that the parental magma of this complex had shoshonitic and meta-aluminous nature. Petrological evidence show that fractional crystallization from gabbro to monzonite had main role in genesis of these rocks. Enrichment in LILE) Ba, Rb and Th(and depletion in HFSE (Nb and Ti) in Rare Earth Elements distribution patterns of spider diagrams, indicate an subduction-related environment for formation of these rocks. Also they are enriched in LREE rather than HREE, the characteristics which are usually observed in the rocks from subduction environments and active continental margins. Chemical and petrological studies indicate a common source for these igneous rocks and the main role of fractional crystallization in the evolution of magma, although, minor amounts of assimilation and contamination of magma by crustal rocks occurred. The alkaline magma formed by low degree partial melting of an enriched sub-continental lithospheric garnet-lherzolite mantle. Contribution of both the lithospheric and asthenospheric mantles in petrogenesis of the Karaj-Taleghan basic rocks might be attributed to a tensional geodynamic setting with change in subduction dip in the form of roll back, dominated at the final stage of the subduction of Neotethyan plate beneath Iran in upper Oligocene (Chattian).
M Abdetedal; Z.H Shomali; M.R Gheitanchi
Abstract
The Makran zone in southeastern Iran and southern Pakistan is the result of subduction of oceanic crust of the Arabian Plate under the Eurasian Plate. From seismic behavior point of view, there is a distinct segmentation between the western and eastern parts of the subduction zone. The western part of ...
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The Makran zone in southeastern Iran and southern Pakistan is the result of subduction of oceanic crust of the Arabian Plate under the Eurasian Plate. From seismic behavior point of view, there is a distinct segmentation between the western and eastern parts of the subduction zone. The western part of the Makran has an abnormally very low level of deep seismicity with lack of recorded great earthquakes, while the eastern part has experienced many great earthquakes. Another difference between the western and eastern parts of the Makran region is that the distance between the Quaternary volcanic arc and fore-arc setting is larger in the east than in the west. Understanding the nature of unusual behaviors of the Makran subduction zone has long been one of the biggest challenges in seismotectonic investigations of this region. The present study aims at producing high-resolution love-wave velocity structure maps of the crust and the upper mantle in the Makran subduction zone using ambient seismic noise. To achieve this purpose, a large dataset has been provided to produce tomographic maps. Empirical Green’s functions were obtained from cross-correlations of broad-band seismic noise records at different stations inside and outside the region. Love-wave velocity dispersion curves were then extracted from the ambient noise, and finally converted into a 2D group velocity image (or tomography map) for crustal and upper mantle structures of the region.
M. Poormohsen; M. Rahgoshay; I. Azadi; H. Shafaii Moghadam
Abstract
The Siah-Cheshmeh ophiolites at the north-northwest part of the Khoy ophiolites show a dismembered pile of metamorphic units, mantle sequence, and basaltic-andesitic lavas associated with Late Cretaceous pelagic limestones and cherts. The basaltic-andesitic lavas can be divided into alkaline and ...
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The Siah-Cheshmeh ophiolites at the north-northwest part of the Khoy ophiolites show a dismembered pile of metamorphic units, mantle sequence, and basaltic-andesitic lavas associated with Late Cretaceous pelagic limestones and cherts. The basaltic-andesitic lavas can be divided into alkaline and calc-alkaline varieties. The presence of Ti-rich amphibole prisms and Ti-bearing clinopyroxenes is characteristic of these lavas. The calc-alkaline lavas are characterized by enrichment in LREE and depletion in HFSE while the alkaline lavas display positive LREE and HFSE anomalies. The interaction between mantle plumes with a spreading center can be considered for generation of alkaline basalts while a subduction zone is responsible for the genesis of calc-alkaline basalts.
M. Heidarzadeh; M. Dolatshahi Pirooz; N. Zaker; M. Mokhtari
Abstract
This research attempts to assess the history of tsunami occurrences and potential for tsunami generation at the southern coasts of Iran bordering the Indian Ocean by providing a list of historical tsunamis in this region and also, modeling of phases of tsunami generation and propagation. After the December ...
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This research attempts to assess the history of tsunami occurrences and potential for tsunami generation at the southern coasts of Iran bordering the Indian Ocean by providing a list of historical tsunamis in this region and also, modeling of phases of tsunami generation and propagation. After the December 2004 mega-tsunami in the Indian Ocean, wide efforts were devoted to assess hazard of tsunami, and to develop tsunami warning and mitigation systems in the region. To assess the hazard of tsunami in any particular region, the compilation of historical records of tsunami is always the first primary task. Such a list may lead to useful information about the return period of tsunami events, and most vulnerable coastlines to the impact of possible tsunami. Regarding this fact, in the framework of this study, the first list of Makran historical tsunamis is provided. The Makran zone is located offshore Iran and Pakistan and any tsunami in this region would affect coastlines of Iran, Pakistan, Oman, and India. The last major tsunami in this region was produced following the occurrence of an 8.1 magnitude earthquake which took the lives of at least 4000 people all over the Makran coasts. Also, in this research, the potential for tsunami generation in the Makran subduction zone is quantitatively estimated through modeling of tsunami generation phase. In this regard, based on Mansinha and Smylie (1971) formulas a computer program has been developed to predict the ocean floor deformation due to the occurrence of underwater earthquakes in subduction zones. After the verification of model results, it has been employed to predict possible ocean floor deformation after the occurrence of underwater earthquake in the Makran subduction zone. Tsunami generation analysis shows that the risk of tsunami generation from Makran subduction zone can be classified into three main categories, as follows: (1) very little risk for tsunami generation in the case of occurrence of an earthquake having magnitude up to 7; (2) little to medium risk (Magnitude ranging 7 to 7.5); and (3) high risk (Magnitude greater than 7.5). In the next section of the paper, the tsunami propagation in the Makran zone was modeled. The results of tsunami propagation indicate that in the case of tsunami production in this region, the first tsunami waves will hit the nearest shoreline within 15 to 20 minutes. Finally, considering tsunami hazard assessment performed in this paper, the necessity for the development of a tsunami warning system in southern coasts of Iran was emphasized and its components and orderly sequences of tasks are proposed.
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.