Petrology
Zohreh Salimi; mohsen moazzen; Robab hajialioghli
Abstract
The ophiolitic-metamorphic complex of Allahyarlu, attributed to pre-Cretaceous, is exposed at the core of Allahyarlu anticline in NW Iran and NE of Meshginshahr. The metamorphic rocks are important constituents of this complex. These rocks include garnet schist, garnet gneiss, amphibolite, marble, associated ...
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The ophiolitic-metamorphic complex of Allahyarlu, attributed to pre-Cretaceous, is exposed at the core of Allahyarlu anticline in NW Iran and NE of Meshginshahr. The metamorphic rocks are important constituents of this complex. These rocks include garnet schist, garnet gneiss, amphibolite, marble, associated with blocks of serpentinite and tectonic slices of gabbro, dunite and diabase. Quartz, garnet, biotite, muscovite and chlorite are the primary minerals in the garnet schists, while zircon, secondary chlorite, opaque minerals and plagioclase make the minor phases. The main minerals in the garnet gneiss samples are K-feldspar, quartz, plagioclase, muscovite, biotite and garnet and tourmaline, zircon and secondary chlorite are the minor phases. Garnet in garnet schists and garnet gneisses is almandine-rich and white mica is muscovite –rich. According to microprobe analyses, brunvigite is the main constituent in chlorite solid-solution. Te average temperature estimated for metamorphism of garnet schists and garnet gneisses, using different methods is 530 to 570 C. Using apetrogenetic grid indicates pressure of ca. 4.5 kbar for the paek of metamorphism. The estimated pressure and temperature are in accordance of Barrovian metamorphic gradient for these rocks, which occurs in crustal thickenning zones such as island arcs, volcanic arcs and collision zones.
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.
F Bakhshizad; Gh Ghorbani
Abstract
The Zanjan-Takab metamorphic complex includes para- and orthogneisses, amphibolites, various types of schists and migmatites along with weakly metamorphosed, young magmatic dikes and lenses. In this study, we are focusing on the Zanjan-Takab metamorphic rocks from three regions including: 1- Almalu-Ghazi ...
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The Zanjan-Takab metamorphic complex includes para- and orthogneisses, amphibolites, various types of schists and migmatites along with weakly metamorphosed, young magmatic dikes and lenses. In this study, we are focusing on the Zanjan-Takab metamorphic rocks from three regions including: 1- Almalu-Ghazi Kandi-Alam Kandi; 2- Qare Naz-Qozlu and 3- Zaki Kandi-Barut Aghasi. Orthogneisses and migmatite leucosomes from these regions show enrichment in light REEs relative to heavy REEs and are characterized by depletion in Nb-Ta. The Almalu-Ghazi Kandi-Alam Kandi orthogneiss zircons show U-Pb ages of 491-516 Ma, but with older inherited cores. Meta-tonalite zircons from this region yield magmatic ages of 24-26 Ma. Migmatite leucosomes, paragneisses and gneissic amphibolite from Qare Naz-Qozlu contains zircons with partial melting evidences at 25-28 Ma. Nd model ages of migmatite leucosomes vary between 466 and 1629, but most of them show Ordovician and late Neoproterozoic Nd model ages (TDM). The epsilon Hf (t) values of zircon rims from migmatites are positive and their Hf model ages vary between 400 and 700 Ma. According to this study, it seems that in addition to the presence of old metamorphic rocks (~500 Ma) in the Zanjan-Takab region, there are weakly (to intensely) metamorphosed, but young (38-24 Ma) magmatic rocks in this area. Furthermore, although the Cadomian magmatism in the Zanjan-Takab region is conspicuous, but this magmatism is younger relative to other Cadomian outcrops of Iran. It seems that the exhumation of gneissic rocks and hence migmatization in this region can be related to core complex formation due to the extensional phases in the Iranian plate, resulted from roll-back of Neotethyan subducted slab beneath Iran.
Behnaz Hosseini; M. Ghorbani; S. M. Pourmoafi; A. R. Ahmadi
Abstract
Kuh-Sefid anticline trends in NW-SE direction and locates in southern Sanandaj-Sirjan zone, and it contains a sequence of Paleozoic metamorphic rocks with facies ranging from greenschist to lower amphibolite. There are granitoid rocks emplaced in the core of this anticline, which based on their facies, ...
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Kuh-Sefid anticline trends in NW-SE direction and locates in southern Sanandaj-Sirjan zone, and it contains a sequence of Paleozoic metamorphic rocks with facies ranging from greenschist to lower amphibolite. There are granitoid rocks emplaced in the core of this anticline, which based on their facies, these rocks are divided into two groups of "augen geneiss " and "metagranitoid". During the course of previous studies, these two rock groups had been attributed to a magmatic phase in Mesozoic, which experienced different degrees of deformation. In this study we proceed to determine the age of these two granitoid rock groups based on U-Pb age dating method applied on Zircon minerals. As a result, the age of orthogneiss rocks is 514±24 million years old and they belong to Cambrian, whereas metagranitoid rocks are 173±9 million years old and attributed to Middle Jurassic. Based on geological and structural evidences, the magmatism occurred in Cambrian was related to tension tectonics in Late Precambrian to Early Paleozoic, while the magmatism in Middle Jurassic associated with dextral transpression tectonics in the studied area.
G. Maleki; A. Saeedi; M.H. Emami; M. Kheirkhah
Abstract
In Sanandaj- Sirjan zone a vast outcrops of volcanic rocks, which founded as high terraces, are covered the Pre-Quaternany rocks. The volcanic rocks are appeared in different shapes and morphological features. Based on the Zagros geodynamical evolution, mentioned rocks assumed ...
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In Sanandaj- Sirjan zone a vast outcrops of volcanic rocks, which founded as high terraces, are covered the Pre-Quaternany rocks. The volcanic rocks are appeared in different shapes and morphological features. Based on the Zagros geodynamical evolution, mentioned rocks assumed to be Post – Collissional, that are formed in an extentional system with a NW-SE trend. Three studied complexes in this paper are Ahmad abad, Tahmures and Nadri. The structural investigation of three the sites are complementary data to the geochemical analysis. In this regards, structural investigation done in those 3 mentioned sites. Studied faults shows different trends and age. Mechanism of faults are normal, and their age are either Post- basalt or syn-basalt, that is, Contemporaneous with the last deposition of late-Miocene marls. The age of the oldest faults is late- Miocene, before basalt intrusion.