S Saki; H Ghasemi; M Sadeghian
Abstract
Bouin- Miandashtgranitoid pluton with an area of 40 Km2, outcropped in the north of Bouin Miandasht- Aligoudarz road, was emplaced into Triassic to early Jurassic low to medium grade metapelitic rocks of Sanandaj - Sirjan structural zone. This pluton composed of alkali feldspar granite to leucogranite. ...
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Bouin- Miandashtgranitoid pluton with an area of 40 Km2, outcropped in the north of Bouin Miandasht- Aligoudarz road, was emplaced into Triassic to early Jurassic low to medium grade metapelitic rocks of Sanandaj - Sirjan structural zone. This pluton composed of alkali feldspar granite to leucogranite. For the first time, variation of anisotropy of magnetic susceptibility (AMS) is applied to investigate magnetic fabric of this pluton. The Mean magnetic susceptibility values (Km in µSI) of the different rock groups of Bouin- Miandasht pluton are as follows: alkali feldspar granites (158), fine granites (120), coarse granites (166), and leucogranites (34). The lower Km values for the main compositions of this pluton (< 500 µSI) suggesting the paramagnetic nature of these granites. Biotite is the main carrier of magnetic properties in the studied rocks. The magnetic anisotropy (P %) varies from 1 to 15. Aalkali feldspar granites have the highest P value and show positive correlation with degree of deformation. Shape parameter of magnetic ellipsoid (T) values varies from -0.43 to 0.85 and most of the magnetic ellipsoids are oblate. Seventy five percent of specimens have positive T value. This subject indicates that magnetic ellipsoids are oblate and then foliation is prevailing, and also field evidence confirms this conclusion.
M Sheibi; M Pooralizadeh Moghadam
Abstract
Panj-Kuh granitoid intrusion with an area of 15 Km2 is intruded into the Eocene volcano-sedimentary sequence, in south-east of Damghan city. Syenite is the main composition of the pluton. It has converted to monzonite wherever subjected to sodic-calcic alteration. The presence of albite-scapolite veins ...
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Panj-Kuh granitoid intrusion with an area of 15 Km2 is intruded into the Eocene volcano-sedimentary sequence, in south-east of Damghan city. Syenite is the main composition of the pluton. It has converted to monzonite wherever subjected to sodic-calcic alteration. The presence of albite-scapolite veins (from mm to some hundred meters in width) are the main evidences of the Na-Ca alteration in the mentioned pluton. Present study investigates the result of magnetic fabric in the Panj-Kuh pluton and defines the emplacement mechanism according to the lineation and foliation patterns and microstructural observations. The pluton belongs to the ferromagnetic granites due to high mean bulk magnetic susceptibility (Km>400mSI) and presence of magnetite. The highest anisotropy values were observed in the regions with high deformation. High plunging lineation and foliations associated with negative value of shape parameter show the magma feeder zones. According to the present study, it seems that the pluton has two different types of fabric patterns. The first pattern belongs to the magmatic liniation and foliation that are arranged parallel to the long axis of the pluton with NE-SW trend. The second fabric is related to the regions that were subjected to Na-Ca alteration and cross cutting the first pattern as three parallel corridors. This fact is confirmed by magmatic to low temperature solid state microstructures as well. Compiling all data implies that the mentioned pluton was emplaced in a sinistral shear zone.
M Sheibi; P Majidi
Abstract
The Challu granitoidic pluton composes of two monzodiorite and quart diorite units, injected into the Eocene volcanic rocks in south of Damghan. Emplacement mechanism of this pluton has been investigated by the anisotropy of magnetite susceptibility method. The measured mean value of bulk susceptibility ...
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The Challu granitoidic pluton composes of two monzodiorite and quart diorite units, injected into the Eocene volcanic rocks in south of Damghan. Emplacement mechanism of this pluton has been investigated by the anisotropy of magnetite susceptibility method. The measured mean value of bulk susceptibility (Km in µSI) in fresh quart zdiorites and monzonites are 31608 and 33726, respectively and then the pluton belongs to the ferromagnetite granites. In this granitoidic body, magnetite is the main carrier of magnetic susceptibility and biotite and pyroxene are the other accessory factors of magnetite nature. The field observation along with petrographical and magnetic fabric investigations reveal that the mentioned pluton emplaced at two stages with two different mechanisms. Monzodioritic unit with dominant porphyroidic texture and NS lineation trend and foliation strike parallel to the margin of the pluton emplaced along tensional gash of one dextral shear zone. Quartz dioritic unit at the same time or a time after monzodiorite emplaced as dyke. The magnetic fabric pattern, oblate ellipsoid shape as well as predominance of trachytoidic texture in this unit correspond with the inverse fabric dyking pattern and the orientation of plagioclase show magma flow. The magnetic susceptibility has been decreased in the stations that subjected to the hydrothermal alteration either by reduction of size of magnetite crystals or conversion of magnetite to hematite. The microstructures in the pluton are mainly magmatic and show high melt fraction to crystal during the emplacement or absence of tectonic stress after full crystallization.
M. Sadeghian; M. Sheibi; S. Badallo
Abstract
The Gol-e-Zard granitoidic pluton with an age of ~ 165±5 Ma is located in the north of Aligoudarz city, Lorestan province, in the Sanandaj-Sirjan structural zone. The pluton intruded into the late Triassic-early Jurassic slates, phyllites and micaschists. The granodiorites, dominant rock types ...
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The Gol-e-Zard granitoidic pluton with an age of ~ 165±5 Ma is located in the north of Aligoudarz city, Lorestan province, in the Sanandaj-Sirjan structural zone. The pluton intruded into the late Triassic-early Jurassic slates, phyllites and micaschists. The granodiorites, dominant rock types of the pluton, are cut by the leucogranites, aplitic veins, pegmatites and gabbro-dioritic dykes. The S-type nature of the Gol-e-Zard granite is evidenced by the presence of metaplitic enclaves (surmicaceous and andalusite-sillimanite hornfels), silica enclaves, andalusite and garnet xenocrysts and silica veins relicts. The anisotropy of magnetic susceptibility (AMS) method was used to investigate the mode of emplacement. The total numbers of 868 oriented core samples were analyzed for magnetic susceptibility. The obtained mean susceptibility (Km) in µЅІ was 227, 57 and 585 for granodiorites, leucogranites and gabbrodiorite dykes, respectively. The low Km values (
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 ...
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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.
M. Sadeghian; M. V. Valizadeh
Abstract
Zahedan granitoidic pluton with general NW-SE elongation is located in the middle part of the Zahedan-Saravan granitoidic belt. It includes granites, granodiorites and diorites and it is also cut by numerous of andesitic to dacitic dikes. The regional metamorphic ...
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Zahedan granitoidic pluton with general NW-SE elongation is located in the middle part of the Zahedan-Saravan granitoidic belt. It includes granites, granodiorites and diorites and it is also cut by numerous of andesitic to dacitic dikes. The regional metamorphic rocks of the area, with the age of Eocene, have been intruded by this pluton. In this research, emplacement mechanism of the northern part of Zahedan pluton has been studied with the aid of anisotropy of magnetic susceptibility (AMS) method. The results show that granitic rocks of the Zahedan pluton belong to paramagenitic granites (µSI) while diorites and granodiorites belong to ferromagentic granites (µSI). The magnetic lineations and foliations of the pluton mainly have low dip or sub-horizontal. In contrast, dioritic rocks which cover a small area, have magnetic lineations and foliations with high dip (sub-vertical). Therefore, dioritic rocks are considered as the feeder zone or the ascent location of the magma for this part of the Zahedan granitoidic pluton. Very low dip magnetic lineations and foliations suggest that Zahedan granitoidic pluton has been emplaced as sill. The activity of a very low dip simple shear movement has an important role in preparing a suitable space for emplacement of this granitoidic pluton.
