Petrology
Seyed Ali Akbar Asadi; Habibollah Ghasemi; Mohsen Mobasheri
Abstract
Sargaz-Abshur (Sikhoran) ultramafic-mafic complex, which is situated in Esfandagheh area, SE Sanandaj-Sirjan metamorphic- magmatic zone, intruded into Upper Paleozoic- Triassic metamorphic rocks and covered by Jurassic sedimentary rocks. This complex consists of harzburgite and porphyroclastic ...
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Sargaz-Abshur (Sikhoran) ultramafic-mafic complex, which is situated in Esfandagheh area, SE Sanandaj-Sirjan metamorphic- magmatic zone, intruded into Upper Paleozoic- Triassic metamorphic rocks and covered by Jurassic sedimentary rocks. This complex consists of harzburgite and porphyroclastic dunites of the residual mantle (tectonites), layered ultramafic-mafic cumulates, large isotropic gabbro intrusion and scattered microgabbroic to diabasic dykes. It does not have extrusive and sedimentary parts of a topical ophiolite sequence (e.g., diabasic swarm dykes, massive and pillow basalts, hyaloclastites, chert, radiolarite and pelagic limestone). The complex is like a large pluton that caused the intensive contact metamorphism of Upper Paleozoic- Triassic rocks through the widespread partial melting of amphibolites, thus it is not an ophiolite sequence. The pluton is mainly comprised of porphyroclastic dunites and layered ultramafic-mafic cumulates. Cr-spinel is enriched or depleted in Cr, having magmatic to residual origins and found in the layered ultramafic (mantle) part of the pluton. The Euhedral Cr-spinel crystalized between olivine grains or as inclusion with massive and layered cumulative textures. It is chromite, magnesiochromite, hercynite in composition, corresponding to Cr-spinels of depleted peridotites from the supra-subduction zone (SSZ), especially those magmas of SSZ that reacted with boninitic magmas. Detailed field works together with previous and new geochronological ages of pegmatite veins related to partial melting of host amphibolite show the alpine type Sargaz-Abshour ultramafic-mafic pluton was ascended as a astenospheric mantle diaper in extensional intra/fore-arc basin of the Andyan type of Sanandaj-Sirjan metamorphic- magmatic zone during the Late Triassic-Early Jurassic (187.2 ± 2.6 Ma).
Petrology
Habibollah Ghasemi; Mahbubeh Arabzadeh Baniasadi; mojtaba rostami hosuri
Abstract
The Abbasabad Eocene volcano-sedimentary belt in the east of Shahrood includes of basaltic-andesitic rocks and related pyroclastics along with interlayers of sedimentary rocks. The volcanic rocks include olivine basalt, trachybasalt, trachy andesybasalt, trachyandesite and andesite with various textures ...
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The Abbasabad Eocene volcano-sedimentary belt in the east of Shahrood includes of basaltic-andesitic rocks and related pyroclastics along with interlayers of sedimentary rocks. The volcanic rocks include olivine basalt, trachybasalt, trachy andesybasalt, trachyandesite and andesite with various textures such as hyallomicrolitic porphyry, microlitic porphyry, glomeroporphyry, trachytic and sieve textures. The main minerals of the rocks are clinopyroxene and feldspar. Pyroxene composition ranges from diopside to augite and feldspar composition is in the ranges of orthoclase and oligoclase to bytownite. The 87Sr/86Sr(Initial) and 143Nd/144Nd(Initial) ratios of these rocks, taking into account the age of 40 Ma for them, range from 0.7042 to 0.7047 and 0.5127 to 0.5130 respectively. Also, the values of ԐNd(0) and ԐNd(t=40Ma) of them range between 2.67 to 7.72 and 3.8 to 8.8, respectively, indicate an enriched mantle source for them. Whole rock, isotopic and clinopyroxene chemistry indicate arc-related calc-alkaline-alkaline nature and basaltic composition of the parental magma originated from partial melting of an enriched OIB source in an extensional intra-arc setting. Geothermobarometry calculations on clinopyroxene indicate a temperature range of 1100-1150 Cº and pressures of 2-13 kb for crystallization of the magma.
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.
S. Shekari; M. Sadeghian; M. Zhai; H. Ghasemi; Y. Zou
Abstract
Metamorphic - igneous Shotor-Kuh complex is located in the 80 km of SE Shahrood and in the northern edge of the central Iran structural zone. This complex includes a wide lithological composition range such as metapelite (micaschists and gneisses), metapsammites, metabasites (amphibolite and garnet amphibolite), ...
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Metamorphic - igneous Shotor-Kuh complex is located in the 80 km of SE Shahrood and in the northern edge of the central Iran structural zone. This complex includes a wide lithological composition range such as metapelite (micaschists and gneisses), metapsammites, metabasites (amphibolite and garnet amphibolite), metacarbonate (limestone and dolomitic marbles) and metrhyolites. Protolith of metabasites have been basaltic lavas, diabasic swarm dikes and small scale gabbro-dioritic intrusions. With respect to abundance and importance of metamorphosed basaltic intercalations and diabasic swarm dikes in comparison to the other basic rocks, this article specially advocated to investigation of their evolution. Based on the field evidence and petrography, increasing the degree of metamorphism of metabasites resulted in producing of amphibole schist, amphibolite, garnet amphibolite and eventually amphibolitic migmatites. Thermobarometery based on the chemical analysis of garnet, amphibole and plagioclase of the metabasites indicates that the thermal range of 602-711 °C and 9-11 Kbar pressure for their formation, stop of exchange and final equilibrium, which accommodate with P-T condition of amphibolite and upper amphibolites facies. From the geochemical points of view, the magmas forming of these metabasites have tholeitic to calc-alkaline nature. These magmas originated from the subcontinental lithospheric mantel source. Submarine basaltic lava flows and diabasic swarm dikes originated during extensional tectonic regimes which affected Late Neoproterozoic Iranian Gondwanan terrains. These extensional tectonic regimes are associated with producing of intracontinental sea to oceanic basins (riffitic or back arc). The mentioned basins closed in a short time and lead to generate tectonic melange or accretionary prisms on the continental crust. Based on the U- Pb age dating of the Zircons extracted from these metasbasites, these metamorphism event occurred in the interval time of 526-577 Million years (corresponds to the late Neoproterozoic and Cadomian orogeny in the Iranian Gondwanan landforms).
F Yousefi; M Sadeghian; S Samyari; H Ghasemi
Abstract
In Ahmadabad Khartouran region located in 175 Km southeast of Shahrood, A significant number of adakitic domes crop out, which intruded into the Paleocene- Eocene volcanosedimentary rocks. Lithological compositions of these domes include andesite, trachyandesite, trachyandesite and dacite. Pyroxene (augite), ...
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In Ahmadabad Khartouran region located in 175 Km southeast of Shahrood, A significant number of adakitic domes crop out, which intruded into the Paleocene- Eocene volcanosedimentary rocks. Lithological compositions of these domes include andesite, trachyandesite, trachyandesite and dacite. Pyroxene (augite), green hornblende and plagioclase are typical mafic and felsic rock forming minerals. With respect to low HREE and high LREE along with other characteristic such as silica content (58.91- 63.41), Na2O more than 3%, Al2O3 more than16%, Yb less than 1.8 ppm, Y less than 18 ppm and K2O/Na2O ratio between .98- 2.3, these rocks can be classified as the high silica adakite. Enrichment of LREE relative to the HREE and depletion of Nb, Ti, and high concentration of Rb, Ba, K and Th, which imply crustal contamination of the mentioned adakitic domes. Enclaves with different size and composition have been seen in these domes which indicate contamination and magma mixing with continental crust. The evidence of petrographic and geochemical show that the magma forming of these rocks originated from melting of subducted metamorphosed Neotethys oceanic slab (Sabzevar – Darouneh branch) in P-T conditions of amphibolite facies.
H Ghasemi; M Rostami Hossuri; M Sadeghian; F Kadkhodaye Arab
Abstract
Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in ...
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Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in Nain, Sabzevar and Sistan in Central Iran during Mesozoic, but little is known about generation of such basins in Cenozoic. The depressed extensional back-arc basin of Central Iran contains sedimentary successions of intracontinental extensional environments associated with alkaline basic magmatic rocks. These magmatic rocks are outcropped in the Oligo-Miocene gypsiferous red marls (red formations), as both intrusive (gabbro) and extrusive (basalt) forms. The present study has focused on the basaltic lava flows in the Oligo-Miocene siliciclastic-evaporitic sedimentary succession extending for about 300 kilometers from Sabzevar to Shahroud along the northern edge of Central Iran. These lava flows are observed as interbedded with the Oligo-Miocene sedimentary units. In the Kalate-Sadat area, located SW of Sabzevar, there are at least five intermittent basaltic lava flows in the red marls. These basaltic rocks (with a composition of olivine-basalt to basalt) show porphyritic, glomeroporphyritic and trachytic textures and are composed of olivine, clinopyroxene and plagioclase phenocrysts in a glassy to microlitic ground mass. On the basis of geochemical data, the parent magma of these rocks had a sodic-alkaline affinity, enriched in LILEs and LREEs and depleted in HREEs, without negative anomalies in HFSEs. The basalts show the geochemical characteristics of the basaltic magmas originated from partial melting of adjusted enriched garnet lherzolite mantle source beneath the continental areas of extensional back-arc basins.
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.
H Ghasemi; Z Kazemi; SH Salehian
Abstract
On the basis of stratigraphical studies, parental rocks of the Gorgan schists have same petrological features and fossil contents as the Ghelli formation in the eastern Alborz Zone and despite to the previous theories, these schists are not Precambrian in age. Also, the mafic igneous rocks of these two ...
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On the basis of stratigraphical studies, parental rocks of the Gorgan schists have same petrological features and fossil contents as the Ghelli formation in the eastern Alborz Zone and despite to the previous theories, these schists are not Precambrian in age. Also, the mafic igneous rocks of these two rock units have considerable petrological and geochemical similarities. These mafic igneous rocks include basalt, trachybasalt and basaltic trachyandesite in association with microgabroic sills, dykes and small intrusions. Investigations on, and comparison of their petrological and geochemical features, indicate similarities in age, petrology, magma sources, geochemistry and tectonic setting. It seems that the parental rock of the Gorgan schists and the rocks forming the Ghelli formation were sedimentary and igneous rocks, deposited during the initial stages of extensional movements and rifting of the Paleotethys ocean during Ordovician in the eastern Alborz. However the, parental rocks of the Gorgan schists were metamorphosed in the greenschist facies in middle-upper Triassic (early Cimmerian orogeny), due to vicinity to the oceanic trench of the Paleotethys subduction zone. Geochemical features of the igneous rocks in these two units indicate 12-16% partial melting of an enriched garnet lherzolite mantle source (such as the Oceanic Island Basalt source) for generation of the original magma in the garnet peridotite stability field at 100-110 Km depth..
M Derakhshi; H Ghasemi; T Sahami
Abstract
The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by ...
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The Soltan Maydan Basaltic Complex indicates the most important, thickest, and most voluminous early Paleozoic magmatic activity in Iran outcropping in the eastern Alborz structural zone, in the north-northeast of Shahrud. This complex overlies the late Ordovician Ghelli Formation and is overlain by the early Devonian Padeha Formation. The field evidences show more than 50 lava flows erupting frequently in the sub-aerial and submarine environments. This complex comprises of a continuous fractional spectrum including basalt, basaltic andesite, trachybasalt and basaltic trachyandesite that has undergone medium to high degrees of alteration. The geochemical data and diagrams signify transitional to alkaline nature of the primary magma, genetic relationship among all rocks of this complex due to fractional crystallization, none or weak role of magmatic contamination in magma evolution, and generation of primary magma by 15-17 percent partial melting of an enriched garnet peridotitic mantle source in an intra-continental extensional rift setting. This tectonic setting is concordant with the known extensional rift setting governed on the Alborz and Central Iran zones during the early Paleozoic, especially late Ordovician-Silurian, primary stages of generation and development of the Paleotethys.
H. Ghasemi; Mojtaba. Garavand; N. Hafezi Moghddas
Abstract
In this paper, the role of Gorgan metamorphic complex, as a geogenic source of the heavy metals has been investigated in the soils of south Kordkoy and Gorgan areas. For this, some important soil chemical parameters such as pH, EC, CEC, and concentrations of the heavy metals in 14 soil samples and 6 ...
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In this paper, the role of Gorgan metamorphic complex, as a geogenic source of the heavy metals has been investigated in the soils of south Kordkoy and Gorgan areas. For this, some important soil chemical parameters such as pH, EC, CEC, and concentrations of the heavy metals in 14 soil samples and 6 rock samples have been determined and interpreted. The enrichment factor, geo-accumulation index, contamination factor and degree of soil contamination for the elements of As, Cd, Co, Cr, Cu, Mn, Mo, Pb, V and Fe, have been studied. Multivariant Statistical methods including Pearson correlation, cluster analysis and principal component analysis were done to study the correlations and paragenetic relations. The results shown that the average concentration of Fe (80502.86 ppm) is higher than maximum allowable concentration (70000 ppm) and located near the threshold (100000 ppm). Also, average values of V (165.09ppm) is higher than maximum allowable concentration (150 ppm) but is very lower than its threshold (450 ppm). Average values of Cr, Ni, Co and Cu are in the range of the background concentration and those for Pb, As, Mo and Cd are lower than background. Calculation of the enrichment factor indicates the low enrichment of As and Fe in these soils. Iron, with the geo-accumulation index of 0.14, is uncontaminant to slightly contaminant. Also, contamination factors of iron, cobalt and vanadium are low and overaly, in the sense of environmental quality, the soil of this area classified among uncontaminated or very low contaminated areas. The results of the statistical analysis of the heavy metal data indicate the lowest concentrations of these elements in the soils derived from pelitic schists, especially in Tuskestan valley, and the highest values of them in the soils derived from the basic igneous rocks, such as Naharkhoran valley. These results show a natural geogenic origin for the heavy metals and the role of chemical composition of the Gorgan metamorphic complex in the entrance of them in the soils of this area.
M. Sadeghian; H. Ghasemi; Z. Farsi
Abstract
Chah Salar granitoidic pluton is located in the N of Chah-Salar village, SW of Neishabour, in the northern margin of structural Central Iran zone. This pluton intruded in Sabzevar ophiolitic Zone and based on the field observations, petrographical and geochemical classification diagrams, its lithological ...
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Chah Salar granitoidic pluton is located in the N of Chah-Salar village, SW of Neishabour, in the northern margin of structural Central Iran zone. This pluton intruded in Sabzevar ophiolitic Zone and based on the field observations, petrographical and geochemical classification diagrams, its lithological composition composed of diorite, quartzdiorite, granodiorite and alkali feldspar granite. Alkali feldspar granites as a much fractionated end-members of this rock association are intruded in this pluton in the form of dikes or apophyse shapes. Granitic pegmatites and their associated quartzolites are the most differentiated end-member of this rock association. Their subvolcanic equivalents such as pyroxene-bearing andesite, andesite, trachyandesite and dacite cut this pluton in the forms of dikes or domes. The studied rocks show variety of textures including granular, myrmekitic, graphic, porphyritic, microlitic porphyry and pilotaxitic. Except alkali feldspar granites which are highly fractionated, the other lithological compositions, on the variations diagrams of major, trace and rare earth elements versus SiO2 or differentiation index show continuous compositional variations. This pluton has calc-alkaline and metaluminous nature and belongs to I-type granitoids. Also tectonic setting discrimination diagrams indicate that the Chah Salar granitoidic pluton belongs to volcanic arc granitoids (VAG) and continental arc granitoids (CAG). Detailed investigations of field geology, petrography and geochemical characteristics indicate that magma-forming of this pluton is resulted from partial melting of subducted oceanic slab (metabasite) or metasomatized mantle wedge and then evolved by fractional crystallization, magma contamination or magma mixing.
G. Ghorbani; H. Ghasemi
Abstract
Bagho granitoid is located in the southeast of Damghan and has been cut by many quartz-tourmaline veins with about 1 mm to 30 cm thickness. Based on petrography and electron microprobe analyses, these tourmalines show schorl– dravite– foitite composition with a tendency toward schorl end ...
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Bagho granitoid is located in the southeast of Damghan and has been cut by many quartz-tourmaline veins with about 1 mm to 30 cm thickness. Based on petrography and electron microprobe analyses, these tourmalines show schorl– dravite– foitite composition with a tendency toward schorl end member, and located in alkali and vacancy groups. Compared with the ideal composition of schorl– dravite, many of tourmaline samples have high Al contents and alkali – site vacancies. The increase in octahedral aluminum reflects a combination of substitutions in tourmaline involving deprotonation (O–OH exchange) and vacancies in the alkali-site and then they have magmatic origin. In contrast, the presence of zoning, its occurrence as vein form, having high Mg compared with Fe in some samples and tendency away from alkali- deficient and proton– deficient tourmaline vectors, show that these tourmalines have hydrothermal origin. Then, based on these results, it appears that tourmaline veins form by interaction of boron-rich magmatic-hydrothermal fluids of granitic-dacitic provenance with various quartz-tourmaline and metapelitic-metapsammitic host rocks.
H. Ghasemi; A. Ramazani; A. Khanalizadeh
Abstract
Silijerd intrusion with an age of Late Eocene – Oligocene (39.23.2 Ma) is located in Uromeyeh-Dokhtar magmatic arc, central Iran structural zone, northwest Saveh. This intrusion is composed of a continuous compositional range including: diorite/gabbro, ...
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Silijerd intrusion with an age of Late Eocene – Oligocene (39.23.2 Ma) is located in Uromeyeh-Dokhtar magmatic arc, central Iran structural zone, northwest Saveh. This intrusion is composed of a continuous compositional range including: diorite/gabbro, granodiorite, syeno-monzogranite and alkali granite intruded into the Eocene volcanic and pyroclastic rocks.
Variation diagrams showing trends of major and trace elements indicate a continuous compositional range and a comagmatic origin for these rocks. Trends of compatible- incompatible elements indicate the important role of fractional crystallization in the genesis of these rocks. All samples are metaluminous with medium-high K with calc-alkaline nature. High values of Rb, Sr, K, U, Th, Zr and Ba and high ratios of K2O/Rb and FeO/MgO indicate the similarity of the rocks of this intrusion with the rocks of continental margin magmatic arc intrusions. Depletion in Nb,P,Ta and Ti and enrichment in K,Sr,Rb,Cs and Ba are obvious in the spider diagrams of these samples. The enrichment in LILE and depletion in HFSE reveal the I-type metaluminous magmatism of volcanic arcs (VGA). Whole rock 87Sr/86Sr ratios of this intrusion range from 0.704759 to 0.705166 and it can be correlated with the values of these ratios in the mantle and lower crust sources and low contamination of their magmas with upper crust.
Existence of K-feldspar megacrysts and mafic microgranitoid inclusions in this intrusion, high abundances of La and Ce , V enrichement in mafic terms and low whole rock 87Sr/86Sr ratios of this body, suggested a partial melting of mantle wedge, subducted oceanic crust (metabasaltic sources) or lower continental crust (metatonalitic sources) origins for it. The discrimination tectonic setting diagrams also indicate an I-type continental volcanic arc magmatism for this intrusion.