Petrology
Ahmad Khaiatzadeh; Ahmad Abbasnejad; Hojjatolah Ranjbar; Hamid Ahmadipour; Behnam Abbasnejad
Abstract
Damavand is one of the most potential volcanoes of Iran for future eruption. Such indicators as having a slightly- eroded cone, presence of many thermal springs, eruption activity in Late Quaternary, as well as the progression of the generating tectonic regime, all, attest this claim. The intensity of ...
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Damavand is one of the most potential volcanoes of Iran for future eruption. Such indicators as having a slightly- eroded cone, presence of many thermal springs, eruption activity in Late Quaternary, as well as the progression of the generating tectonic regime, all, attest this claim. The intensity of eruption is anticipated to be about 3-5 in Volcanic Explosivity Index (VEI) scale. As a result, such hazards as tephra (ash), nuee ardente, lava flow and lahar may pose problems. Thus, this study deals with zoning these hazards. For zoning, Digital Elevation Models (DEM= 30 m), Landsat ESTM+ pictures as well as Arc GIS, ENVI and VORIS softwares were employed, and for construction of nuee ardente- hazard zoning, Malin and Sheridan (1982) model were used. Atmospheric data for the spread of ashes were taken for NCER/NCAR center. Lava flow routes were determined using a simulation model which is based on the assumption that topography plays the main role on the route of flow, and lavas flow from a point to the nearby one if their differences are positive. In order to construct lahar hazard map, locations of main troughlines on the cone and around the volcano were determined and lahar invasion areas were determined using a proper buffer zone. Based on this study, volcanic ash plume will form at the east of volcano and a number of towns and villages would be threatened. Lava flows and nuee ardentes would threaten some villages around the cone. Lahars would flow via throughlines on the cone and arrive the main vallies around it (Hezar and Delichai). They would threaten many residential areas in their route. The prepared hazard maps are useful and necessary for management of these hazards.
Petrology
Maryam Daieparizi; Hamid Ahmadipour; Abbas Moradian
Abstract
In the Pariz area, (Kerman province), there are special deposits and in the geological maps, they have introduced as detrital unconsolidated Neogene Conglomerates (Ng). Detailed field observations of these deposits in this study showed that they are pyroclastic deposits from the post Eocene unknown explosive ...
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In the Pariz area, (Kerman province), there are special deposits and in the geological maps, they have introduced as detrital unconsolidated Neogene Conglomerates (Ng). Detailed field observations of these deposits in this study showed that they are pyroclastic deposits from the post Eocene unknown explosive eruptions. Stratigraphically, these units overlie the Eocene basaltic rocks, and their clasts are dacitic and rhyolitic in compositions, which means that they are completely different from the Eocene rocks. Genetically, these deposits are pyroclastic surges and flow deposits in association with the laharic units. Lithological features of these pyroclastics along with the absence of ducite or rhyolite lava flows and the relatively large dispersion of these deposits indicate that they have been formed by water bearing explosive eruptions. The clasts of these pyroclastic deposits contain plagioclase, amphibole, biotite and quartz and they are geochemically belong to the calcalkaline magmatic series. The geochemical characteristics of these rocks show that they formed in a post-collision environment and their geochemical nature are similar to the continental magmatic arc associations. These results are consistent with other studies on the post Eocene magmatic rocks of the Dehaj-Sardouieh belt.
Petrology
Shirin Behpour; Abbas Moradian; Hamid Ahmadipour
Abstract
The studied area is located in the SE of Bam and Urumieh-Dokhtar Magmatic Arc. Based on petrographical and geochemical characteristics, studied rocks contain tonalite, granodiorite, granite and alkali granite. These rocks are metaluminous, weakly peraluminous, high-K, and calc-alkaline. The behavior ...
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The studied area is located in the SE of Bam and Urumieh-Dokhtar Magmatic Arc. Based on petrographical and geochemical characteristics, studied rocks contain tonalite, granodiorite, granite and alkali granite. These rocks are metaluminous, weakly peraluminous, high-K, and calc-alkaline. The behavior of Y, Ba, Ce and Zr vs. SiO2 display the properties of the high temperature I-type granites. These granitoids plot in the field of VOG. Enriched LREE and LILE with depleted HFSE show characteristics of subduction related active continental margins. The ratios of Nb/U and Nb/La and Sm/Yb indicate the crustal contamination. Isotopic data and La vs. La/Sm diagram show the role of the lower crust and the old continental crust in magma evolution. According to the phenocrysts assemblage, REE pattern with negative Eu anomaly and La/Yb ratio to crustal thickness, studied rocks are fractionated from relatively dry magma which has undergone from shallow depths. Sm/Yb and La/Yb ratio display the mantle source is garnet-free source. The low to moderate degree of partial melting of garnet-free amphibolite is the source of the studied granitoids. Volatiles that is driven from subduction slab and melt of the subducted sediments play a significant role in the generation and evolution of their magma source.
Petrology
Hamid Ahmadipour; Hamideh Salehinejad; Seyed Hesam-Aldin Moeinzadeh; Abbas Moradian
Abstract
Shan Abad–Raviz basic intrusions from the West of Rafsanjan (Kerman province), represent a part of Dehaj-Sarduyieh belt and intruded into the Eocene volcano-sedimentary rocks as dykes and apophyses. Thicknesses of the dikes and the diameters of the patches reach up to 4 and 10 meters respectively. ...
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Shan Abad–Raviz basic intrusions from the West of Rafsanjan (Kerman province), represent a part of Dehaj-Sarduyieh belt and intruded into the Eocene volcano-sedimentary rocks as dykes and apophyses. Thicknesses of the dikes and the diameters of the patches reach up to 4 and 10 meters respectively. In the field, they appear as dark intrusions contain sporadic euhedral pyroxene crystals with up to 5 mm in size. They are gabbro and diorite and their main minerals are plagioclase and pyroxenes set in a fine-grained matrix and show intergranular and porphyroid textures. These rocks have low-K calc-alkaline affinities and their geochemical characteristics tend to the subduction zone settings. In these rocks, 87Sr/86Sr and 143Nd/144Nd ratios vary between 0.70403 to 0.70409 and 0.5128 to 0.5129 respectively and εNd(i) values change between 3.52 to 6.6. These evidences along with the special textures show that their parent magmas affected by fractionation, assimilation and magma mixing processes. Considering that these rocks have intruded into the Eocene volcanics, we suggest that they represent the last stages of Eocene magmatism in the Cenozoic Kerman magmatic belt and intruded into the crust after the intiation of Neo-Tethys subduction beneath to Central Iranian block, probably in a continental margin tectonic setting.
Petrology
Sima Peighambari; Mahdieh Mohammadi; Hamid Ahmadipour
Abstract
Podiform chromitite bodies of various sizes associated with dunite envelopes found at several localities in the Ab-bid ultramafic massif in the southeast of the outer Zagros ophiolite belt. The chromitites occur as layered and lenticular bodies and veins which show different magmatic textures such as ...
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Podiform chromitite bodies of various sizes associated with dunite envelopes found at several localities in the Ab-bid ultramafic massif in the southeast of the outer Zagros ophiolite belt. The chromitites occur as layered and lenticular bodies and veins which show different magmatic textures such as massive, disseminated, and banded features. The Ab-Bid chromitites display a variation in Cr# from 65.36 to 58.43. The Al2O3 and TiO2 contents of chromites range from 18.03% to 22.58 % and 0.20 % to 0.39 %, respectively. The Al2O3, TiO2 and FeO/MgO values, calculated for parental melts of Ab-Bid chromitites, are within the range of melts which are similar to tholeiitic melts. Structural features such as sharp contacts between chromitites and their dunite envelope with host harzburgites, no correlation between chromitite size and dunite thickness, and various textures may be related to magmatic-metasomatic processes through interconnected dunitic channels. The mineralogical and chemical compositions of the chromitites as well as calculated parental melt compositions of Ab-Bid chromitites are consistent with the idea that the Ab-Bid massif was part of mantle section of an ophiolite from a suprasubduction zone. Harzburgites was influenced by hydrous partial melts; variable melt/rock interaction caused the formation of dunitic channels and allowed the chromitite parental melt to percolate through them. Middle partial melting degrees and other mineral chemistry of chromites could be representative of back-arc oceanic spreading environments. Therefore, Ab-Bid harzburgites are parts of mantle wedge above the subducting Neo-Tethys oceanic plate which is under a probably Upper Triassic-Cretaceous back-arc spreading centre.
P Ahmadi Moghadam; H Ahmadipour
Abstract
A part of the Hezar volcanic complex (Urmia-Dokhtar Volcanic Belt), Eocene in age, has been cropped out in the CheheltanMountain at southwest of the Bardsir town, in the Kerman province. This part consists of alternation of lava flows, pyroclastics and epiclastics that are cut by several gabbroic and ...
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A part of the Hezar volcanic complex (Urmia-Dokhtar Volcanic Belt), Eocene in age, has been cropped out in the CheheltanMountain at southwest of the Bardsir town, in the Kerman province. This part consists of alternation of lava flows, pyroclastics and epiclastics that are cut by several gabbroic and dioritic intrusions and dykes. The lava flows can be divided into andesites and basalts and the pyroclastics consist of volcanic breccias, agglomerates, ignimbrites and fine-grained tuffs. The epiclastics consist of several layers of volcanic sandstones and conglomerates that cover a vast area. Alternation of lava flows, pyroclastics and epiclastics show that the volcanic activities in the area have been done periodically from stratovolcanoes and when intensive volcanic eruptions were ceased epiclastics were deposited. It seems that lava flows and pyroclastics have been formed by volcanian and in some cases, plinian eruptions, and continuous basin subsidence during volcanic eruptions have led to the formation of thick layers of pyroclastics and epiclastics. The field evidences such as lacking of unconformities and paleosols show that there is no great interval between volcanic eruptions. The geochemical characteristics indicate that the lava flows probably have the same origin. It seems that fractional crystallization was the main process in the evolution of parental magmas, while crustal contamination played a minor role, so that the andesitic lava flows were produced by fractional crystallization of the basalts and the magmas had no very long stops en rout to the surface.
A. Zahedi; H. Ahmadipour
Abstract
The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous ...
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The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous mineralogy, field and textural evidences such as sieve texture in plagioclase, resorption rims in crystals, oscillatory zoning in plagioclase, high normative quartz and rounded enclaves suggest that the primary magma undergone magmatic evolution including fractionation, contamination, and magma mixing during ascending. The Y/Rb ratio and AFC (assimilation and fractionational crystalization) petrogenetic models confirm the occurrence of evolution in primary magma. Concentration of elements such as K, Pb, P, Zr, Sr, Ba, Rb shows that these rocks belong to the calcalkaline series. Similarity between the andesitic lava and dykes shows a considerable similarity with the calcakaline andesite from Turkey and from this point of view; these rocks belong to the post - collisional arcs. In this tectonic setting, magma ascent is controlled by strike - slip faulting and associated pull- apart extensional tectonics. This post - collisional magmatism may have been occurred due to the Arabian- Iranian collision events.
