Petrology
Ayoub Veisinia; Mohammad Ebrahimi; Bahman Rahibzadeh; rasoul Esmaeili
Abstract
Kamyaran ophiolitic complex located in the northeast Zagros orogeny along the crush zone between Arabian-Iranian plates. This complex outcropped between the Harsin ophiolites in southeast and Sarwabad ophiolite in northwest. Field observation reveal the fact that the Garmab Ophiolite in the northeast ...
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Kamyaran ophiolitic complex located in the northeast Zagros orogeny along the crush zone between Arabian-Iranian plates. This complex outcropped between the Harsin ophiolites in southeast and Sarwabad ophiolite in northwest. Field observation reveal the fact that the Garmab Ophiolite in the northeast of Kamyaran is a tectonic mélange including peridotites and gabbros cut by microgabbroic dikes. Olivine, clinopyroxene and orthopyroxene with chromian spinel made the peridotites minerals with mesh and porphyroclastic fabrics and Gabbros include plagioclase, clinopyroxene and minor amphibole with intergranular, pegmatoidic and interstitial texture. According to the geochemical results, gabbros have tholeiitic to calk-alkaline nature and show the MORB to island arc characteristics. According to the geochemical and geotectonic results, Garmab peridotites plotted to the abyssal peridotites area that represent from the residual mantle spinel lherzolite after extraction of 15–20% partial melting. The break-off of Neo-Tethyan slab and subduction of this slab branch beneath the oceanic lithosphere during cretaceous led to cessation of the Neo-Tethyan subduction beneath the Sanandaj-Sirjan block, and forming arc-back arc basin (second step of subduction) and related rocks in the Kamyaran ophiolite. Presence of tholeiitic to calc-alkaline magmatism is in response to the slab retreat in the Eurasian continental margin.
Economic Geology
Maryam Honarmand; Ghasem Nabatian; Mahtab Aflaki; Mohammad Ebrahimi
Abstract
Geology, geochronology and tectonic setting of the Moghanlou mylonite gneiss and granite bodies, west of Zanjan Abstract The Moghanlou mylonite gneiss and granite assemblage is located in the west of Zanjan forming a part of the magmatic-metamorphic association in the Takab area. The Moghanlou assemblage ...
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Geology, geochronology and tectonic setting of the Moghanlou mylonite gneiss and granite bodies, west of Zanjan Abstract The Moghanlou mylonite gneiss and granite assemblage is located in the west of Zanjan forming a part of the magmatic-metamorphic association in the Takab area. The Moghanlou assemblage comprises of leucogranite and biotite granite intrusions which have surrounded the gneiss body. The zircon U-Pb dating shows the ages of 563±6.5 Ma for the mylonite gneiss, 576±13 Ma for the biotite granite and 559±6 Ma for the leucogranite intrusions. Moreover, the samples from the Moghanlou assemblage display high-K calc-alkaline and slightly peraluminous affinities, except those from the leucogranite which are low potassium samples due to the sodic alteration and albitization of the K-feldspars. The trace element patterns suggest LILE and LREE enrichment and HFSE and HREE depletion as well negative anomaly of Nb, Ta and Ti. In general, the geochemical features of the Moghanlou intrusions are comparable with the melts formed from crustal partial melting in magmatic arc environment. The Moghanlou assemblage is analogues to other Late Neoproterozoic-Early Cambrian igneous and metamorphic associations in Iran and Turkey which are related to the igneous activity along the Cadomian magmatic arc, in north of Gondwana supercontinent.
Petrology
Abdolsamad pourmohammad; Ahmad Ahmadi khalaji; Masoud Homam; Zahra Tahmasbi; Mohammad Ebrahimi
Abstract
Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature – low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. ...
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Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature – low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. These rocks belong to medium to high potassium calc-alkaline series, low temperature I type granite and are poorly peraluminous. The Chondrite-normalized REE patterns show that the rocks are enriched incompatible elements, with negative anomalies in Nb, Ta, Sr, P, Ti and Ba and strong enrichment in Rb, K and Th. These patterns are in perfect harmony in granodiorite, microgranular enclave (MME) and microgranite specimens. This harmony also has in upper, middle continental crust and greywackes. Positive anomalies in Rb, Th, Sm and negative anomalies in Ba are prominent in the composition of the crust. Based on the integration of these patterns with the pattern of upper continental crust (UCC) elements and greywackes and adaptation to laboratory work, the Geysour granitoid originated from crustal materials and a little mantle component. The temperature of granitoid formation was estimated based on the Zircon saturation temperature of 748-790 ֯C. Microgranular enclaves have rounded and oval shapes, mixed areole around them, fine grained texture, quartz and plagioclase eyes, bladed biotite, needled apatite, oxide phases in biotite, and the presence of a simple mixed – hyperbolic curve between MME and granodiorite. Field, petrography and geochemistry of the major and rare earth elements data suggest mixing/ mingling (partial melting) processes for the origin of enclaves and the rare earth elements patterns indicates the relationship between Geysour granitoid with the subduction system. Analysing its data, based on logarithmic ratios, show collision tectonic environment. Also, the tectonic-chemical distinctive diagrams suggest a syn-collision to post-collision tectonic type that is interpreted in connection with the collision of the Afghan Block with the Lut Block.
Economic Geology
R. Amirkhani; M. Ebrahimi; M. A. A. Mokhtari; A. M. Azimzadeh
Abstract
The study area which is introduced as Homeijan magnetite- apatite mineralization in this paper, is a part of the Posht-e-Badam block in the Central Iranian Zone and is located at ~12Km southwest of Behabad. This area is composed of volcano-sedimentary rocks and acidic- basic intrusions of Precambrian ...
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The study area which is introduced as Homeijan magnetite- apatite mineralization in this paper, is a part of the Posht-e-Badam block in the Central Iranian Zone and is located at ~12Km southwest of Behabad. This area is composed of volcano-sedimentary rocks and acidic- basic intrusions of Precambrian and Cambrian age. Magnetite- apatite mineralizations are present as lenses near the southwestern part of the Homeijan village, which are hosted by acidic- intermediate tuffaceous rocks and dolomites. Magnetite, oligist (hematite), pyrite and chalcopyrite are the main ore minerals and apatite, pyroxene, tremolite- actinolite, calcite and quartz are as gangue minerals in the Homeijan Fe mineralization. Based on field and mineralogical studies, this mineralization texturally includes massive, brecciated, vein- veinlets and replacement textures. Chemical analyses of samples indicate that the mineralization has high concentrations of REEs up to 2.5 % in the apatite crystals. Geochemical studies demonstrate that Fet have high negative correlation with P2O5, SiO2 and ∑REE while there is a high positive correlation between ∑REE and P2O5. SEM-EDS qualitative analyses of apatite crystals indicate two REE bearing minerals including monazite and allanite as inclusions within the apatites. Furthermore, this study demonstrates that the apatite crystals are flour- apatite. Fluid inclusion studies within the apatite crystals indicate that main salinity varies between 7.86-13.9 wt.% NaCl and homogenization temperature is between 240-370°C. Comparing of REE patterns of Homeijan magnetite- apatite mineralization with other iron oxide- apatite mineralizations of Posht-e-Badam Block and Kiruna- type iron ores indicate similarities between these patterns. Generally, based on field and geochemical studies, the Homeijan magnetite- apatite mineralization classified as Kiruna- type Fe deposit.
