Petrology
Seyed Mohsen Kashfi; Saeed Alirezaei; Mohammad Reza Hosseini; Iraj Rasa
Abstract
The Zaghdareh area in the Esfandagheh-Faryab ophiolitic complex, southern Sanandaj-Sirjan belt, embraces extensive outcrops of mafic-intermediate lava flows and a felsic intrusive body. The volcanic rocks are calc-alkaline to tholeiitic, metaluminous, and distinguished by depletions in light rare earth ...
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The Zaghdareh area in the Esfandagheh-Faryab ophiolitic complex, southern Sanandaj-Sirjan belt, embraces extensive outcrops of mafic-intermediate lava flows and a felsic intrusive body. The volcanic rocks are calc-alkaline to tholeiitic, metaluminous, and distinguished by depletions in light rare earth elements and relatively flat patterns for heavy rare earth elements in chondrite-normalized diagram; the (La/Yb)N ratio is lower than unity for most samples. The chemical attributes for the Zaghdareh volcanic rocks are comparable to those developed in suprasubduction zones. The Zaghdareh intrusive body is distinguished by abundant plagioclase and quartz, and subordinate hornblende, phenocrysts in quartz-feldspar rich matrix. Representative samples from the intrusion plot in the trondhjemite-tonalite fields in the normative An-Ab-Or diagram. The intrusion is calc-alkaline to tholeiitic, peraluminous, and marked by enrichments in Na2O and CaO and depletions in K2O, Rb, and most other LILEs, as well as low K2O/ Na2O ratios, very low Rb/Sr ratio, and distinct depletions in light rare earth elements, which are typical of the oceanic plagiogranites. Results from this study and a comparison with other ophiolitic suites in Iran suggest that the occurrence of plagiogranites is a recurring feature associated with the development and evolution of ophiolitic suites in suprasubduction zones.
Leili Fathiyan; farhad aliani; ali akbar baharifar; mohamad hossein zarinkoub
Abstract
Granitoid bodies of west of Zanjan with Precambrian age are located in northwest of central Iranian structural zone. Based on field observations and microscopic studies, these bodies contain tonalite, granodiorite and monzogranite. Tonalite are I-type, calc-alkaline, and peraluminous (206Pb/238U age ...
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Granitoid bodies of west of Zanjan with Precambrian age are located in northwest of central Iranian structural zone. Based on field observations and microscopic studies, these bodies contain tonalite, granodiorite and monzogranite. Tonalite are I-type, calc-alkaline, and peraluminous (206Pb/238U age of 576±13 Ma) which base on isotopic studies (87Sr/86Sr (i) and εNd (i) values equal to 0.710544, -7.01), and geochemistry of major and trace elements, can concluded that they were resulted from melting of amphibolitic crust that generated from thickened mafic crust or under plate basalts (with presence of plagioclase in source area) in low pressures and depth in an active continental margin. Monzogranites are S-type, peraluminous and calc-alkaline, which is plotted in collision zone. These rocks were generated from melting of crustal rocks (melt derived from pelitic rocks with high plagioclase). Granodiorite are I-type, calc-alkaline and Weakly peraluminous (206Pb/238U age of 548±27 Ma). They have value of 87Sr/86Sr (i) more than 0.705, negative value of εNd (i), and geochemical data, which is generated from partial melting of lower to middle crust, because of thickening and shortening due to continental- continental collision. With respect of geographical location of granitoid bodies of Mahneshan and age of their units, it seems that these granitoid rocks have formed in an active continental margin during convergence of Central Iran and Alborz-Azarbayjan with Arabian platform during Precambrian
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.
