Petrology
shirin shahabi; Habibollah Ghasemi; Mehdi Rezaei-Kahkhaei; Zhai Minggou
Abstract
In the Talu area at NE Damghan in the Eastern Alborz Zone, the Permo-Triassic carbonate sequences host several mafic igneous inrusions with olivine gabbro, gabbro and alkali-diorite compositions. The most important rock-forming minerals of these intrusions are olivine, clinopyroxene, amphiboles and plagioclase. ...
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In the Talu area at NE Damghan in the Eastern Alborz Zone, the Permo-Triassic carbonate sequences host several mafic igneous inrusions with olivine gabbro, gabbro and alkali-diorite compositions. The most important rock-forming minerals of these intrusions are olivine, clinopyroxene, amphiboles and plagioclase. These rocks have alkaline nature and their major and trace elements characteristics correspond to OIB-like mantle source. The olivines of these rocks are chrysolite, and the plagioclases are characterized by albite, oligoclase and labradorite. Clinopyroxenes are diopside, augite and salite in composition and characterized with alkaline nature (Non-orogenic). They crystallized in 6-11 Kbar, 1200-1250˚C and high oxygene fugasity conditions. Amphiboles are of calcic and high-Ti kaersutite type and crystallized in igneous conditions with mantle source. The amphiboles were crystallized in temperatures and pressures over than 950˚C and 650-750 MPa (equivalent to 6.5-7.5 Kbar).
Petrology
Marzieh Asadi-Avargane; Mehdi Rezaei-Kahkhaei; Habibollah Ghasemi
Abstract
The Qarah Chay Neogene caldera is located at 30 km SE Quchan in the Binalud Zone. The volcanic rocks of the caldera are mainly dacite in composition and composed of plagioclase and amphibole. The rocks present a variety of porphyry, microlitic porphyry, sieve, trachytic and glomeroporphyritic textures. ...
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The Qarah Chay Neogene caldera is located at 30 km SE Quchan in the Binalud Zone. The volcanic rocks of the caldera are mainly dacite in composition and composed of plagioclase and amphibole. The rocks present a variety of porphyry, microlitic porphyry, sieve, trachytic and glomeroporphyritic textures. Based on the spider diagrams normalized to chondrite and primitive mantle, the study rocks show enrichments in Large Ion Lithophile Elements (LILEs) and depletion in Heavy Rare Earth Elements (HREEs) and High Field Strength Elements (HFSEs). Their’s calc-alkaline affinity and the obvious negative HFSE anomalies (such as Ti, Nb and P), and positive Pb anomaly are similar to those magmas related to active continental margin. Moreover, their high concentrations of Sr, Sr/Y, Na2O/K2O, and low concentrations of K and MgO are the same as high silica adakites. Considering the above points, the parental magma(s) of the Qarah Chay Caldera formed from the partial melting of eclogite during the subduction of oceanic lithosphere of Sabzevar under the southern edge of the eastern Alborz zone in Neogene. It seems that the major Quchan and Dareh Gaz strike slip faults played a main role for the caldera formation.
Economic Geology
Fardin mousivand; Fayeq Hashemi; Mehdi Rezaei-Kahkhaei; Amir Pakizeh
Abstract
The Darreh Amrood Pb (Ag) deposit is located in south of Ghohrood, in the Urumieh-Dokhtar magmatic arc (UDMA). Host rockes to the deposit are Middle to Late Eocene grey-green siliceous tuff and crystal lithic tuff. Geometry of orebodies is stratabound, irregular, and semiconcordant to discordant to layering ...
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The Darreh Amrood Pb (Ag) deposit is located in south of Ghohrood, in the Urumieh-Dokhtar magmatic arc (UDMA). Host rockes to the deposit are Middle to Late Eocene grey-green siliceous tuff and crystal lithic tuff. Geometry of orebodies is stratabound, irregular, and semiconcordant to discordant to layering of the host rocks. Ore structures and textures are dominated by semi-massive to brecciated, banded and vein-veinlets. Main primary minerals are galena, pyrite and chalcopyrite, and secondary minerals are dominated by covelline, goethite and hematite. Gangue minerals are epidote, chlorite, sericite, clay minerals, quartz, calcite and barite. Wall rock alterations are dominated by epidote-chlorite and sericitic. The rare earth element (REE) pattern of ores is not similar to that of volcanic rocks in the footwall and hangingwall that is concordant with sub-seafloor replacement process for ore formation. Also Ce showed negative anomaly that can be attributed to Ce in the seawater. Also based on structural, stratigraphic, petrographic, textures, mineralogical, alteration and geochemical studies, it is inferred that the Pb (Ag) mineralization in the Darreh Amrood area occurred as bimodal felsic- or Kuroko-type volcanogenic massive sulfide (VMS) mineralization, and formed as sub-seafloor replacement. It should be noted that the Darreh Amrood deposit is the first recognition of base metal-rich and poor barite VMS mineralization in the UDMA.
Petrology
Mehdi Rezaei-Kahkhaei; Dariush Esmaeily; Hanieh Sahraei
Abstract
Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve ...
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Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve texture, two generation of fresh and altered plagioclase, reaction rim, corrosion and rounding of phenocrysts. Major and trace element diagrams show, although crystal differentiation was effective in the evolution of the study rocks, the scatter and unusual trends, which are observed in some diagrams in comparing with fractionation trend, reflect magma mixing and contamination were also important during magma generation. Inconsonance and high variations in Sr concentrations together with binary diagrams of Nb/Y-Nb and Rb-Zr/Rb reveal magma mixing role in the evolution of Neshveh volcanic rocks. Considering the above facts, we can conclude that magma mixing and magmatic differentiation were the important processes in formation of the Neshveh volcanic rocks. As well as, the incorporation of new magmatic pulse(s) with differentiation magma is the most effective mechanism for the evolution of volcanic rocks from the study area.