S Jalalat Vakil-Kandi; M Shahpasand-Zadeh; H Ahmadi-pour; M Honarmand
Abstract
Dehsheikh ultramafic-mafic complex is located in the Esfandagheh ophiolitic mélanges belt of Kerman province. The Dehsheikh complex comprises harzburgite, lherzolite, dunite, chromitite, pyroxenite and layered gabbros. The presence of abundant chromite ore deposits has made this complex important. ...
Read More
Dehsheikh ultramafic-mafic complex is located in the Esfandagheh ophiolitic mélanges belt of Kerman province. The Dehsheikh complex comprises harzburgite, lherzolite, dunite, chromitite, pyroxenite and layered gabbros. The presence of abundant chromite ore deposits has made this complex important. The complex constitutes part of the Neotethys oceanic lithosphere deformed during upwelling from the upper mantle and later emplacement in the upper levels of the Sanandaj-Sirjan continental crust. Microstructural analysis of this complex reveals three deformation mechanisms including intracrystal plasticity, diffusive mass transfer and cataclasis. The microstructures of deformation twins, wavy extinctions, kink bands, exsolution lamellas, dynamic recrystallizations, microboudins, pull-apart microfractures, mineral stretching and elongation, mineral lineations and shear band cleavages formed due to the intracrystal plasticity deformation mechanism. The diffusive mass transfer deformation mechanism was associated with development of indenting, truncating and inter-penetrating grain contacts and micro-veins. The cataclasis deformation mechanism was accommodated by development of micro-fractures and micro-faults. This microstructural study also manifested different generations of olivines, pyroxenes and spinels under upper mantle to crustal conditions.
R Entezari; S.A Alavi; M.R Ghassemi
Abstract
Metamorphic rock assemblage of southern Salmas area is located in the northwestern terminal part of Sanandaj-Sirjan zone, and includes various rock types. This study uses field observations plus mineralogy and petrography of samples to describe and interpret the microstructures in the area. Different ...
Read More
Metamorphic rock assemblage of southern Salmas area is located in the northwestern terminal part of Sanandaj-Sirjan zone, and includes various rock types. This study uses field observations plus mineralogy and petrography of samples to describe and interpret the microstructures in the area. Different rock units are classified into three groups based on their parent rocks, and consist of 1) metabasite, 2) quartz-feldespathic, and 3) marble. Most of these rocks have mylonitic texture but the grade and the intensity of mylonitization are different. Presence of mylonitic foliation and lineation along with other microstructures such as various porphyroclasts, mica fish, S-C fabric, and S-C' fabric demonstrate different mylonitic zones in this area. Due to differences in strain rate, parent rock type, and depth of deformation, we could distinct three mylonitic zones in the metamorphic complex. Most of these mylonitic samples show features characteristic of low to medium grade mylonites, in which mylonitization grade increases from west to east and center of the study area. Presence of ultramylonites in the central part of the area indicates increases in strain rate. Also presence of high-grade mylonites (T> 650 ºC) and migmatite imply that the deformation occurred at depths of middle to lower crust. We could discern two metamorphic phases (M1 and M2) and six deformation phases (D1, D2, D3, D4, D5, D6). Compressional deformation phase D1 occurred after Precambrian magmatism, then a metamorphic phase (M1) impressed these rocks by the Latest Cambrian. During Late Permian to Early Cretaceous, two deformation phases (D1 and D2) with a major simple shear component strongly affected the metamorphic complex, leading to the development of mylonitic zones. Synchronous with the deformation phase D2, a retrograde metamorphic phase (M2) affected the complex. At Late Cretaceous to Early Paleocene, deformation phase (D4) caused obduction of ophiolites over the metamorphic complex. Eventually, two brittle deformation phases (D5 and D6) affected all older rocks.
E Moosavi; M Mohajjel
Abstract
Two main metamorphic events have occurred within Muteh- Golpayegan metamorphic core complexes (including eastern and western complexes) in the Sanandaj-Sirjan zone. Some grain-scale deformations were also happened in relation to these metamorphisms which have produced various deformation microstructures. ...
Read More
Two main metamorphic events have occurred within Muteh- Golpayegan metamorphic core complexes (including eastern and western complexes) in the Sanandaj-Sirjan zone. Some grain-scale deformations were also happened in relation to these metamorphisms which have produced various deformation microstructures. Microfaults are among the microstructures that were formed during brittle conditions. Bulging recrystallization of quartz and rarely feldspar grains, and bookshelf structure of fragmented feldspar porphyroclasts indicate various deformation and formation of shear zones under low-temperature conditions in the eastern complex. Polygonal granoblastic texture of polycrystalline quartz porphyroclasts documents post-mylonitization annealing at medium- grade conditions in shear zones of eastern complex. Chessboard pattern quartz subgrains propose high-grade metamorphic conditions during the first deformation. However, their undulatory extinction reveals low-grade conditions for the second deformation. Polygonal granoblastic texture of chevron folded feldspar grains also accurately supports these conditions during the two mentioned deformations. In general, considering deformation microstructures and conditions, three stages of recrystallization are respectively recognizable in the Muteh-Golpayegan metamorphic complexes including: 1- high-grade static recrystallization subsequent to early metamorphic event, 2- dynamic recrystallization and related mylonitization under low-grade to locally medium-grade conditions, 3-post-mylonitization static recrystallization in medium-grade conditions. The north Golpayegan intrusive bodies can be considered as the heat source for annealing in the western complex but the cause of annealing is not evident in the eastern complex.
M Ramazani; M.R Ghassemi
Abstract
The erosional window of Aghdarband, located in NE Iran and SE of Mashhad is a unique place to study of the Eo-Cimmerian event. This event (Late Triassic-Middle Jurassic) resulted from closure of the PaleotethysOcean and collision between the Iran and Turan plates. In this study, we have tried to analyze ...
Read More
The erosional window of Aghdarband, located in NE Iran and SE of Mashhad is a unique place to study of the Eo-Cimmerian event. This event (Late Triassic-Middle Jurassic) resulted from closure of the PaleotethysOcean and collision between the Iran and Turan plates. In this study, we have tried to analyze the microstructural features of the exposed carbonate units (the Sefid Kuh formation of the Early Triassic age and some Paleozoic units) in the Aghdarband area. The average of ellipticity calculated for the calcite grains is about 0.78 located in the oblate part of the Flinn diagram. The estimated kinematic vorticity number is 0.6 - 0.7. The calcite twining in the carbonate units exposed in the Aghdarband area indicate temperatures of about 180-200˚C and differential stresses of about 180-240 MPa during the main deformational event of the area (Eo-Cimmerian).
A Gourabjeri; M.H Emami
Abstract
Gelmandeh Massive is located north-east of Saghand, in Yazd province. From tectonics point of view it belongs to Central Iran, the Kalmard_Posht-e-Badam Block. The metamorphic complex comprises amphibolites, marble, schist, quartz- feldspatic gneisses. The amphibolites are of three types. Namly: Hornblendite ...
Read More
Gelmandeh Massive is located north-east of Saghand, in Yazd province. From tectonics point of view it belongs to Central Iran, the Kalmard_Posht-e-Badam Block. The metamorphic complex comprises amphibolites, marble, schist, quartz- feldspatic gneisses. The amphibolites are of three types. Namly: Hornblendite (composed of more than 90% hornblende), Garnet-amphibolites and amphibolitic gneiss. Deformations in Gelmandeh metamorphic complex are reflected in 6 types of rocks: 1-deformed igneous rocks, 2- mylonitic series rocks, 3-cataclastic series rocks, 4-regional metamorphic rocks, 5- mylonitic regional metamorphic, 6-cataclastic regional metamorphic rocks. Conspicuous deformational features comprise: tilted feldspars twining, erratic pertite, mirmecite, porphyroblasts, clasts with strain shadows, and strained & fish structure minerals showing right & left lateral sense.
M. Sheibi; D. Esmaeily; J. Luc Bouchez
Abstract
The Lower Cretaceous Shir-Kuh granitic batholith in central Iran intruded to the sandstones and shales of Nayband-Shemshak Formation. The batholith consists of three main granodioritic, monzogranitic and leucogranitic units. The anisotropy of magnetic susceptibility technique (AMS) was used for distinguishing ...
Read More
The Lower Cretaceous Shir-Kuh granitic batholith in central Iran intruded to the sandstones and shales of Nayband-Shemshak Formation. The batholith consists of three main granodioritic, monzogranitic and leucogranitic units. The anisotropy of magnetic susceptibility technique (AMS) was used for distinguishing relative chronology between emplacements of the magma batches in Shir-Kuh batholith. The rather low susceptibility magnitudes (Km<400mSI) call for the dominance of biotite as magnetic carriers, considered as typical of the so-called paramagnetic granites and there is a first-order correlation between magnetic susceptibility and rock-type. The various magnetic data (magnetic lineation and foliation maps, K, P and T parameters), complemented by field and microstractural observations, allow us to propose that the two main feeders of the batholith represent tension gashes that formed at the base of the brittle crust and served as conduits for the magma. The progressive differentiation of magmas associated with petrographic zoning of the Shir-Kuh Batholith is therefore viewed as progressive opening and infilling of the En echelon gashes more or less parallel to the regional dextral shear zone. The filling started with granodiorites, followed with monzogranites and ended with leucogranites and resulted in the construction of the batholith.
