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.
B. Hosseini; M. Mohammadi Siyani; A. R. Ahmadi
Abstract
Quaternary volcanic activities in Alamut Valley occurred in three stages and covered Neogene red sedimentary rocks. The volcanic rocks are intermediate in composition and are classified as hornblende trachyandesite. The SiO2 content of the rocks varies in a range from 55.48-61.88 wt%. Chondrite normalized ...
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Quaternary volcanic activities in Alamut Valley occurred in three stages and covered Neogene red sedimentary rocks. The volcanic rocks are intermediate in composition and are classified as hornblende trachyandesite. The SiO2 content of the rocks varies in a range from 55.48-61.88 wt%. Chondrite normalized REE patterns exhibit a steep arrangement of LREEs and MREEs (La/Ho)N =85 and a relatively flat HREE (Ho/Lu)N =1.3., Large ion lithophile elements (LILE) do not show strong enrichment compared to LREEs in mantle normalized multi-element spider diagrams. Nb andTa are slightly depleted compared to neighboring light rare earth elements. These rocks have high Sr/Y (140-205), La/Yb (113-142) ratios, accompanied by high K2O/Na2O (0.7-0.9) and resemble C-Type adakites. Geochemical evidence suggest that these rocks are resulted from partial melting of thickened eclogitic lower crust in presence of abundant residual garnet. Partial melting of lower continental crust probably triggered by thickening of crust as a result of late Cenozoic orogenic phases especially the Passadenian Orogenic phase.
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
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.
M Aghazadeh
Abstract
The Sar Cheshmeh mine, a world-class porphyry copper deposit, is located in the Kerman metallogenic zone. The rock outcrops in the deposit are Eocene basalt, basaltic andesite and andesite, Oligocene granular and porphyry granodioritic intrusions and Miocene Sar Cheshmeh granodioritic porphyry stock, ...
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The Sar Cheshmeh mine, a world-class porphyry copper deposit, is located in the Kerman metallogenic zone. The rock outcrops in the deposit are Eocene basalt, basaltic andesite and andesite, Oligocene granular and porphyry granodioritic intrusions and Miocene Sar Cheshmeh granodioritic porphyry stock, granitic late fine-grained porphyry and andesitic to dacitic hornblende, plagioclase, and biotite porphyry dykes. In the spider diagrams, studied rocks show LILE enrichment and HFSE depletion pattern similar to volcanic arc rocks. Eocene volcanic rocks and Oligocene granular and porphyry granodioritic intrusions represent typical magmas characteristics of volcanic arcs whereas Miocene intrusions and dykes have adakitic nature. The (La/Yb)N ratio in the volcanic rocks and Oligocene intrusions varies between 1-5 and 7-11 respectively, while Miocene intrusions and dykes show highest amount of this ratio(20-40). Low aboundancy of HREE in the Miocene intrusions and dykes implies that garnet have been in the source, which has been formed due to increasing crustal thickness during Oligocene and Miocene. According to U-Pb dating, the Sar Cheshmeh porphyry stock and granitic late fine grained have been emplaced in 12.97 ± 0.23 Ma and 12.37 ± 0.1 Ma respectively, while hornblende porphyry dykes has been intruded in 12.16 ± 0.8 Ma. According to trace element characteristics in zircon crystals, Miocene intrusions and dykes originated from same source. Middle Miocene intrusions and dykes have been generated in a post collisional tectonic setting from various degree partial melting of amphibolitic mafic lower crust with variable garnet.
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.
M Khalatbari Jafari; P Konani
Abstract
Lava-dome shallow massive bodies located right around Nodeh Engelab, SE Jogatay in Khorasan Razavi province, cutting Eocene volcanic rocks in northern part of Sabzevar ophiolitic belt, are covered by Pliocene-Quaternary deposits. The margin of bodies comprise of lavas of basalt, phyric andesite basalt, ...
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Lava-dome shallow massive bodies located right around Nodeh Engelab, SE Jogatay in Khorasan Razavi province, cutting Eocene volcanic rocks in northern part of Sabzevar ophiolitic belt, are covered by Pliocene-Quaternary deposits. The margin of bodies comprise of lavas of basalt, phyric andesite basalt, fluidal andesitic compositions but the medial parts and roof of masses composed of phyric andesite-trachy andesite, phyric-aphyric dacites and quartz monzodiorite. No impacts of pyroclastic deposits have been observed around these masses. The sieve texture, oscillatory zoning in plagioclase crystals could be attributed to disequilibrium in magma chamber. The lava from margins of shallow massive bodies has calc alkaline and the rocks from middle parts of the bodies show calc alkaline to high-K calc alkaline affinities. The spider diagrams of margin lavas have substantial compliance with those middle parts of bodies and show enrichment in Rb, Ba, Th, La, Sr, and clear depletion in Nb and Ti. Despite some samples plot in adakitic domain, but they do not display chemical characteristic of index adakites. It seems that the parental magma of the studied shallow intrusions produced from partial melting of mantle wedge which have different enrichment and probably influenced by the components released from subducted slab. The other scenario could be attributed to the partial melting of metamorphosed mafic rocks at the top of subducted slab.
Gh Ghadami; A Moradiane Shahre Babaki; S.M Mortazavi
Abstract
More than 20 tonalitic to granodioritic plutonic domes, Oligo-Miocene in age, have intruded into the older volcanic rocks, in southeast of Urumieh- Dokhtar Magmatic Belt, northwest of Shahr-e-Babak. These rocks have granoporphyritic texture and consist of Phenocrysts of plagioclase, amphiboles and biotites. ...
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More than 20 tonalitic to granodioritic plutonic domes, Oligo-Miocene in age, have intruded into the older volcanic rocks, in southeast of Urumieh- Dokhtar Magmatic Belt, northwest of Shahr-e-Babak. These rocks have granoporphyritic texture and consist of Phenocrysts of plagioclase, amphiboles and biotites. The geochemical data show calc-alkaline affinities of these rocks , which formed in volcanic arc (I type) of an active continental margin. These data also show LILE and LREE enriched normalized multi-element patterns, and depleted of HFSE (Nb, Ta and Ti). Primitive mantle-normalized REE patterns display a dramatic decrease from LREE to HREE without any Eu anomaly. They have higher SiO2, Al2O3 and Sr content and Sr/Y and La/Yb ratios and lower MgO, Y and Yb contents than the normal calc-alkaline rocks, which reveal their adakitic characteristics. The high content of Sr, LREE enrichments, absente of Eu anomaly, HREE depletion, Y and Yb depletion pattern suggest the existence of garnet, amphibole and absence of plagioclase in the source rocks. Our data suggest that the plutons produced by partial melting of amphibole-eclogite or garnet-amphibolite, due to the subduction of Neotethys oceanic slab under the Central Iran continent.
M Nasrabady; F Rossetti; H Moin Vaziri; S.M.H R; M M
Abstract
Some syntectonic tonalitic and trondhjemitic intrusion bodies have been injected into the Soltan Abad (NE Sabzevar) metamorphic complex. The geochemical investigations of these intrusion bodies demonstrated their very obvious adakitic characteristics (very high ratio of Sr/Y and very low contents of ...
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Some syntectonic tonalitic and trondhjemitic intrusion bodies have been injected into the Soltan Abad (NE Sabzevar) metamorphic complex. The geochemical investigations of these intrusion bodies demonstrated their very obvious adakitic characteristics (very high ratio of Sr/Y and very low contents of Y and Yb). According to the field and microscopic evidences and the geochemical characteristics of the whole intrusion bodies, the creation of such adakitic properties originates from the influence of both partial melting and magmatic differentiation processes. The probable scenario is the partial melting of subducted oceanic lithosphere in a hot subduction zone and the generation of adakitic intermediate melt, then amphibole fractionation and enhancing of adakitic indicators of final acidic melt. The resultant residual of partial melting is garnet-hornblenditic blocks that observed adjacent to some intrusion bodies. The primary adakitic intermediate melt accurs as amphibole-rich diorite in the study area. The differentiated cumulate phase and final fractionated melt constitute the hornblenditic dykes and hololococratic tonalitic-trondhjemitic bodies, respectively. The creation of hot thermal regime and partial melting of subducting oceanic lithosphere have been affected by the factors such as subduction velocity variations, mid oceanic ridge subduction or the slab break-off of the subducting oceanic plate and upwelling of the hot asthenosphere.
