Stratigraphy and Palaeontology
Zahra Khajehjavaran; Gholam Reza Ghadami; Mohammad Poosti; Abbas Moradian; Behrouz Karimi Shahraki
Abstract
Andesites are located in the north of shahr-e-babak , central Iran, Urumieh- Dokhtar belt. The main texture in these rocks is porphyry and their phenocrysts are plagioclase (Andesine to Labradorite), pyroxene (Augite), amphibol (Tschermakite and Magnesiohornblende). These properties are signatures of ...
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Andesites are located in the north of shahr-e-babak , central Iran, Urumieh- Dokhtar belt. The main texture in these rocks is porphyry and their phenocrysts are plagioclase (Andesine to Labradorite), pyroxene (Augite), amphibol (Tschermakite and Magnesiohornblende). These properties are signatures of calc- alkaline series formed in a volcanic arc setting. Based on geochemical studies, the rocks show enrichment in LREE rather than HREE. The lack of significant Eu anomalies in REE pattern indicates oxidation state of magma during crystallization. Based on geochemical studies, the clinopyroxenes are Augite and have been crystallized from magma with almost 10% H2O. Fe3+ values of the clinopyroxenes reveal high oxygen fugacity in the magma. Based on the mineral chemistry data, pressure estimates from the clinopyroxenes in the range of 6-10 Kbr and composition yield the crystalization temperatures that range from 900-1100 OC. Typically, clinopyroxenes occure at calc-alkaline orogenic igneous rocks. The plagioclase composition yield the crystalization temperatures that range from 650-750 OC. According to the present study, the rocks are probably the result of the subduction of the Neo-Tethys oceanic lithosphere below the Sanandaj-Sirjan zone, during the Eocene and in a volcanic arc environment.
Petrology
Marziyeh Abazari; Seyyed Saeid Mohammadi; Malihe Nakhaei
Abstract
Abbas Abad area is located in the northeast of Sarbisheh, in the northern part of Sistan suture zone and southern Khorasan province. In this area, Tertiary volcanic rocks with the composition of intermediate to acid, including basaltic andesite, andesite, and dacite are exposed. Constructive minerals ...
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Abbas Abad area is located in the northeast of Sarbisheh, in the northern part of Sistan suture zone and southern Khorasan province. In this area, Tertiary volcanic rocks with the composition of intermediate to acid, including basaltic andesite, andesite, and dacite are exposed. Constructive minerals of basaltic andesite include of plagioclase, pyroxene and olivine and in andesite consist of plagioclase, hornblende and pyroxene, and in dacite are plagioclase, quartz, biotite and hornblende. The studied rocks have medium to high-K calc-alkaline nature. Most samples show enrichment in LILEs (K, Rb, Sr, Cs) (except Ba) relative to HFSEs (Y, P, Ti, Ta, Nb), which indicates the relation of these rocks to subduction zone and active continental margin. The relatively low (La/Yb)N (7.67 to 13.48) and Dy/Yb (<2) in Abbas Abad lavas indicate that partial melting of mantle occurred in transitional zone of spinel-garnet lherzolite. Based on the concentration of trace elements such as Ce, Yb and Sm, magma originated from a depth of about 95 to 105 kilometers.
Petrology
Maryam Kouchi; Malihe Nakhaei
Abstract
In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The ...
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In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The main texture of these rocks are porphyry with microlitic-glass groundmass, glomeroporphyritic, poikilitic and vesicular. The mineral constituents of andesitic rocks are plagioclase, pyroxene and amphibole with small quantities of biotite and sanidine and in rhyolite and dacite include of quartz, sanidine, plagioclase, amphibole and biotite. Disequilibrium textures such as chemical zoning, sieve texture, rounded and gulf shape margins in phenocrysts of these rocks are observed. Geochemical study results show that these lavas belong to high to medium-K calc alkaline series. Enrichment in LREE and LILE, depletion in HREE and HFSE with negative anomaly of Ti, Nb and P in these rocks indicated active continental margin volcanic arc magmatism. Based on tectonic discrimination diagrams, also support the relation of Zoolesk area lavas with subduction zone and active continental margin. Low ratio of Dy/Yb(<2) in studied lavas, indicated spinel lherzolite mantle source for magma.
Behnaz Barghi; Ali Asghar Calagari; Mohammad Hossein Zarrinkoub; Vartan Simmonds
Abstract
Mn-bearing veins of Jonub -ESehchangi are located 200 km southwest of Birjand, Southern Khorasan province (east of Iran). These veins are hosted by andesitic rocks of Eocene to Oligocene ages. Ore minerals identified by XRD method and mineralographic studies and are Pyrolusite, cryptomelane, psilomelane, ...
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Mn-bearing veins of Jonub -ESehchangi are located 200 km southwest of Birjand, Southern Khorasan province (east of Iran). These veins are hosted by andesitic rocks of Eocene to Oligocene ages. Ore minerals identified by XRD method and mineralographic studies and are Pyrolusite, cryptomelane, psilomelane, hollandite, hematite and goethite, displaying colloform and open-space filling textures. Gypsum, halite, barite, carbonate and silica are the gangue minerals. Alteration zones, specifically argillic alteration zone, are developed along the vein within the andesitic wall rocks. Based on the mineralogical and geochemical data, the primary manganese minerals were Mn oxides and hydroxides, which have gradually been converted to psilomelane and hollandite, and finally pyrolusite. The average grade of Mn within the veins is 38.61%. Considering the average Mn/Fe ratio (about 48.55) in the Mn-bearing veins, as well as the positive correlation of Sr, U and Ba with Mn mineralization in this area show hydrothermal origin.
A. Baharvandi; S. S. Mohammadi; M. Nakhaei
Abstract
In the Boshgaz area in 50 kilometers northwest of Sarbisheh and eastern margin of Lut block, Tertiary volcanic rocks with basaltic andesite, andesite and dacite composition are cropped out. The main texture of these rocks are porphyry with microlithic-glass groundmass, glomeroporphyritic and vesicular. ...
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In the Boshgaz area in 50 kilometers northwest of Sarbisheh and eastern margin of Lut block, Tertiary volcanic rocks with basaltic andesite, andesite and dacite composition are cropped out. The main texture of these rocks are porphyry with microlithic-glass groundmass, glomeroporphyritic and vesicular. The main minerals in andesite lavas are plagioclase, pyroxene, amphibole and biotite and in dacites are plagioclase, quartz, amphibole and biotite. Geochemical investigations show that these rocks have medium to high-K calk alkaline nature. Enrichment of Sr, Zr, Cs, Th, K, depletion of Nb, Ti, P, Ba and enrichment of LREE relative to HREE in the studied rocks show that these rocks are related to a subduction zone and active continental margin setting. On the basis of trace elements diagrams, volcanic rocks of the Boshgaz area are formed in an immature arc or early stage of subdution. Mg# values in volcanic rocks of the Boshgaz area are ~48 indicating the role of mantle constituents in their formation. Low ratio of Sm/Yb(<2.5) in the studied lavas show absence of garnet in the source. Low ratio of Zr/Ba (average 0.34) and high ratio of La/Nb (2.22-3.19) for the studied lavas are characteristics of lithospheric mantle source. MREE/HREE diagrams show that lavas of the Boshgaz area originated from spinel-phlogopite lherzolite. Low ratio of Ba/Rb (<20) and high ratio of Rb/Sr (>0.1), support the existence of phlogopite in the source. The uniform pattern of REEs and medium values of La N /Lu N (8-14)inintermediate and acidic rocks of Boshgaz indicate genetic relationbetween them.
S. Z. Hosseini; M. Arvin
Abstract
Neogene volcanism in the Tel Gorban-Chah Breshk area, north of Shahre-Babak, occurs as dacitic to andesitic lava flows and domes. Petrographically the rocks consist of plagioclase, hornblende ±biotite and quartz phenocrysts setting in porphyritic and hyalopilitic matrix. Opacitization of hornblende ...
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Neogene volcanism in the Tel Gorban-Chah Breshk area, north of Shahre-Babak, occurs as dacitic to andesitic lava flows and domes. Petrographically the rocks consist of plagioclase, hornblende ±biotite and quartz phenocrysts setting in porphyritic and hyalopilitic matrix. Opacitization of hornblende and biotite and zoning and sieve texture in plagioclase are signatures of disequilibrium conditions through the magma cooling. Geochemical data and petrological diagrams show their medium potassic calc- alkaline nature. Enrichment in LILE’s and depletion in HFSE’s (eg. Nb,Ta,Ti) points to a subduction tectonic environment for Tel Gorban-Chah Breshk dacitic to andesitic rocks. Furthermore, their Al2O3>16,Sr/Y>80 and chondrite normalize REE pattern are quite similar to dakites. Distinctive geochemical features such as Rb/Sr< 0.04, La/Yb> 18, Yb< 1, (Sr/Y)n> 80, and Y
A Abedini
Abstract
The Basir-Abad area (northeast of Ahar, East-Azarbaidjan province) is a part of the Cenozoic Ahar-Arasbaran magmatic belt in northwest of Iran. Intrusion of granitic and granodioritic igneous rocks of Oligocene age into the Eocene volcanic rocks (andesite, trachy-andesite, andesi-basalt and basalt) resulted ...
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The Basir-Abad area (northeast of Ahar, East-Azarbaidjan province) is a part of the Cenozoic Ahar-Arasbaran magmatic belt in northwest of Iran. Intrusion of granitic and granodioritic igneous rocks of Oligocene age into the Eocene volcanic rocks (andesite, trachy-andesite, andesi-basalt and basalt) resulted in occurrence of metallic mineralization along with development of widespread alteration zones in this area. Mineralogical studies indicate that these alteration zones include silicic (quartz), intermediate and advanced argillic (kaolinite, smectite, quartz and alunite), and propylitic (chlorite, epidote, albite and calcite). Hypogene ores within veins and veinlets of silicic alteration zone contain pyrite, chalcopyrite and galena accompanied by covellite, copper-carbonate minerals (malachite and azurite) and iron-oxides and- hydroxides (goethite, limonite and hematite) of supergene origin. The distribution patterns of REEs normalized to chondrite display differentiation and enrichment of LREEs relative to HREEs and occurrence of variant negative Eu anomalies in all alteration zones. Mass balance calculations of elements, using isocon method, indicate that during development and evolution of the silicic and the intermediate argillic alteration zones, REEs experienced enrichment in the former and depletion in the latter. Furthermore, development of advanced argillic and propylitic alteration zones was accompanied by enrichment of LREEs and selective depletion of HREEs. Further investigation revealed that occurrence of negative Eu anomaly (0.20-0.23) in silicic alteration zone is related to abundance of chloride ions, increase of oxygen fugacity of hydrothermal system and highly acidic nature of the fluid. The results obtained from geochemical studies (mass balance calculations, changes in values of Eu and Ce anomalies and ratios of REEs) suggest that changes of pH, temperature, oxygen fugacity, difference in abundance and type of complexing ions in solution, fluid/rock ratio, and presence of minerals such as kaolinite, goethite, smectite, hematite and alunite played important role in differentiation, mobilization and distribution of lanthanides in the studied alteration system.
Gh Ghadami; M Poosti; F Babai
Abstract
Few More than 5 dacite to andesite volcanic masses with Mio-Pliocene age are exposed to older volcanic rocksat the south and east of the Mozahem volcano, in south-east of Urumieh- Dokhtar magmatic belt, north-east of Shahre-Babak. These rocks show hyaloporphyritic- trachytic texture and consist of pPhenocrysts ...
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Few More than 5 dacite to andesite volcanic masses with Mio-Pliocene age are exposed to older volcanic rocksat the south and east of the Mozahem volcano, in south-east of Urumieh- Dokhtar magmatic belt, north-east of Shahre-Babak. These rocks show hyaloporphyritic- trachytic texture and consist of pPhenocrysts of plagioclase, amphiboles and biotites. Based on geochemical data and multi elements patterns, these rocks are medium to high K calc-alkaline suite and they show LILE and LREE enriched normalized multi-element patterns, and negative Nb, Ti and Ta anomalies. Chondrite normalized REE patterns display a steep decrease from LREE to HREE without any Eu anomaly. They have higher SiO2 and Sr contents and Sr/Y and La/Yb ratios and low MgO, Y and Yb contents than the normal calc-alkaline volcanic rocks. These volcanic rocks are formed in the a subduction zone in an active margin, and showing full complete of HSA(high SiO2 adakites) characteristics. HREE and Y depleted patterns suggest the existence of garnet and amphibole as a residue in the source. The source of these rocks was probably amphibole-eclogite or garnet-amphibolite possibly generated during subduction or slab break of the Neo-Tethyan oceanic slab beneath the Central Iran microplate in Neogene.
S.Z Hosseini
Abstract
The Eocene mafic lava flows of Sarcheshmehare cropped out in the southwest of Rafsanjan area at the central part of the Urmia – Dokhtar magmatic belt. The rocks are basalt, basaltic andesite and andesite in composition and consist of clinopyroxene + plagioclase ± olivine ± hornblende phenocrysts. ...
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The Eocene mafic lava flows of Sarcheshmehare cropped out in the southwest of Rafsanjan area at the central part of the Urmia – Dokhtar magmatic belt. The rocks are basalt, basaltic andesite and andesite in composition and consist of clinopyroxene + plagioclase ± olivine ± hornblende phenocrysts. The geochemical characteristics show calc-alkaline nature for the lavas that are formed in an active continental margin tectonic environment. Low amounts of MgO, Cr and Ni in the Sarcheshmeh Eocene basaltic lavas points to the role of evolution in their parental magma. The MORB normalized multi-element patterns of the lava flows show enrichment in LILE (e.g. Sr, K, Rb and Ba) and depletion in HFSE (e.g. Ta, Nb and Ti). The Chondrite-normalized REE patterns show moderate enrichments in LREE with (La/Yb)n< 3 for all samples. The geochemical features such as (La/Yb)n
A. Ameri; N. Ashrafi; H. Karimi Gharebaba
Abstract
The study area is located about 20 km to the east of the Heris town in northwest Iran, and lies in the Alborz-Azarbaijan geological zone. The occurrence of lava domes associated with thick lava flows, volcanic breccias, and ignimbrite layers indicate an important eruptive center in the study area. The ...
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The study area is located about 20 km to the east of the Heris town in northwest Iran, and lies in the Alborz-Azarbaijan geological zone. The occurrence of lava domes associated with thick lava flows, volcanic breccias, and ignimbrite layers indicate an important eruptive center in the study area. The investigated volcanic rocks are of lower-middle Eocene time and associated with upper Eocene I-type granitoid intrusions. Hydrothermal fluids derived from the granitoid rocks, considered to be cogenetic with the volcanic rocks, led to local alteration and mineralization in the volcanic rocks. According to chemical classification, the volcanic rocks are andesite, andesitic-basalt and trachy-andesite. The textures vary from porphyry to microlitic porphyry and hyalomicrolitic and the phenocrysts are mostly plagioclase, alkali-feldspar, augite, hornblende and biotite. Sieve texture and selective alteration in some plagioclases, occurrence of biotite and hornblende with opacitic rims, associated with other disequilibrium textures are characteristic features of the rocks. Plots of the samples on the SiO2 vs. Na2O + K2O, AFM, and SiO2 vs. K2O diagrams show that, similar to the associated granitoids, the volcanic rocks are high- to medium- potassium calc-alkaline in nature. Chemical characteristics of the rocks suggest enrichments in a subduction zone or crustal contamination, rather than a within-plate enrichment trend. Plots of Rb/Ba vs. Ti/Y, and Nb/Zr vs. Nb show that the chemical composition of these rocks were controlled typically by fractional crystallization and the role of magma mixing was not significant in the evolution of the rocks. Plots of the samples on tectonic setting discrimination diagrams of basalts and andesites, based on Th, Ti, Zr, Nb, and Sr contents, indicate that the studied rocks belong to calc-alkaline volcanic arcs. Compared to andesitic rocks from typical tectonic environments, the compatible and incompatible elements patterns for the andesitic rocks from the study area are more consistent with a post-collision volcanic arc setting.
A. Zahedi; H. Ahmadipour
Abstract
The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous ...
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The Abaregh area is located in 40 km northwest of Bam city in Kerman province. Rock units of the region consist of lava flows and dikes that crop out along a fault system trending NS. Mineralogically, the rocks contain plagioclase, augite, hypresthen, and minor olivine. Heterogenous mineralogy, field and textural evidences such as sieve texture in plagioclase, resorption rims in crystals, oscillatory zoning in plagioclase, high normative quartz and rounded enclaves suggest that the primary magma undergone magmatic evolution including fractionation, contamination, and magma mixing during ascending. The Y/Rb ratio and AFC (assimilation and fractionational crystalization) petrogenetic models confirm the occurrence of evolution in primary magma. Concentration of elements such as K, Pb, P, Zr, Sr, Ba, Rb shows that these rocks belong to the calcalkaline series. Similarity between the andesitic lava and dykes shows a considerable similarity with the calcakaline andesite from Turkey and from this point of view; these rocks belong to the post - collisional arcs. In this tectonic setting, magma ascent is controlled by strike - slip faulting and associated pull- apart extensional tectonics. This post - collisional magmatism may have been occurred due to the Arabian- Iranian collision events.
K. Kalantari; A. Kananian; A. Asiabanha; M. Eliassi
Abstract
Paleogene basic to intermediate lava flows of Central Alborz, in the northeast of Qazvin city (Zarjebostan), include trachy-andesite, basaltic trachy-andesite and basaltic andesite. These volcanic rocks are high-K calc-alkaline rocks. Based on the high LILE/HFSE and LREE/HREE ratios ...
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Paleogene basic to intermediate lava flows of Central Alborz, in the northeast of Qazvin city (Zarjebostan), include trachy-andesite, basaltic trachy-andesite and basaltic andesite. These volcanic rocks are high-K calc-alkaline rocks. Based on the high LILE/HFSE and LREE/HREE ratios and their similar composition to subduction volcanic rock suites; it seems that they have formed in a subduction zone. The subduction process has little effect on the concentration of Zr, Ta, Hf, Sm, Tb, Nd, Eu and Y elements, while it has strong influence on concentration of Th, U and La elements. Due to high Ba/La, Ba/Ta and La/Ta ratios and low TiO2 content of lavas, they could be attributed to magmatic arc setting. Th/Yb vs. Ta/Yb diagrams and association of study suite with extensive volume of acidic tuffs, indicate that these rocks have been formed in an active continental margin.
