Articles
Petrological Journal (22285210)15(1)pp. 159-184
Rahmani, F.,
Varas-reus, M.I.,
Marchesi, C.,
Noghreyan, M.,
Makizadeh, M.A.,
Garrido, C.J. International Geology Review (00206814)65(21)pp. 3388-3411
The Sabzevar ophiolite is the most extensive and best-exposed section of oceanic lithosphere in NE Iran. In this study, we examined the mantle section of the eastern part of the Sabzevar ophiolite, where mantle peridotites are the most widespread rock type and are crosscut by pyroxenite veins and mafic dykes. Major and trace element compositions (minerals and whole-rock) of lherzolites are akin to those of abyssal peridotites from mid-ocean ridges (MOR), whereas those of harzburgites evidence formation in a supra-subduction zone (SSZ) setting. Rare-earth element (REE) patterns of whole-rock and clinopyroxene of lherzolites and harzburgites suggest polybaric melting, with initial melting in the garnet peridotite field (~5–6%), followed by ~5–15% melting for lherzolites and ~10–20% for harzburgites in the spinel peridotite field. Harzburgites show LREE enrichment incompatible with partial melting models, indicating significant interaction with SSZ-related melts, whereas analysed lherzolites experienced limited melt-rock interaction. Pyroxene dissolution and olivine precipitation in residual peridotites resulting from reaction with island arc tholeiite and/or boninite melts led to the formation of dunites. These melts eventually intruded as dykes and veins in the mantle and crustal sections of the ophiolite. In addition, boninite melts are inferred to be responsible for forming olivine pyroxenite veins within the harzburgites. We conclude that the mantle section of the Sabzevar ophiolite formed in an intra-oceanic arc setting and experienced a geochemical evolution from a MOR-like to SSZ setting. The intra-oceanic subduction of the Neotethys oceanic lithosphere and shifting conditions of melting during the development of subduction beneath the incipient island arc were responsible for the geochemical heterogeneity of mantle peridotites and the generation of SSZ-related magmas within the Sabzevar oceanic lithosphere. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Indian Journal of Geosciences (22293574)76(1)pp. 59-84
The mantle sequence of Nain ophiolite in Central East Iran Microplate is composed of harzburgite, dunite, chromitite pods and lherzolite with major minerals of olivine, orthopyroxene, clinopyroxene and chromite. The studied chromites were classified as high chromium (Cr#>0.6) and high aluminum (Al2O3 average content ≈ 17.5wt%; Cr#<0.6). The high Cr-chromite plots fall in the boninitic field but the high-Al ones are mostly closer to abyssal peridotites and mid-oceanic ridge fields. The Cr# of chromite in dunite and chromitite varies between 0.77-0.83 and 0.86-0.89 respectively and show a boninitic nature for the parental melts. These characteristics prove that they were generated in an arc setting. High-Al harzburgites seem to have originated or been modified by boninitic magmatism which is taken place in the mid ocean ridge basalt environment due to melt-rock or melt-melt interactions. Also, the studied chromites occupy the field of supra-subduction zone (SSZ) peridotites with a tendency towards a MORB-type setting can be inferred. Hence, hydrous fluids which released from a subducted plate might have played an important role in Nain ophiolite petrogenetic evolution. MORB-like melts sourced from an arc environment and melting associated with a supra-subduction zone are primary factors for chromite occurrences in this area. © 2022 Geological Survey of India. All rights reserved.
Journal of Economic Geology (20087306)12(1)pp. 93-109
In porphyry copper deposits, turquoise is considered to be a supergene oxidation product (John et al., 2010; Chavez, 2000). Based on Rezaian et al., 2003; Zarasvandi et al., 2005 and Eslamizadeh, 2004, the Aliabad index is introduced as a porphyry copper system. The first published report on turquoise events around Ali-Abad was presented by Momenzadeh et al., 1988. This area is located 57 km southwest of Yazd. Alterations often include siricitization, advanced argillization. Kaolinization and silicification have occurred frequently in the arkose and microcan glomerate of the Sangestan formation. The aim of this research study is to try to reconstruct and investigate the formation and origin of turquoise by using the latest mineralogical and geochemical data. Field evidence shows occurrence of turquoise in the form of a veinlet and nodules, with blue-green and blue-white colors. Jarosite, alunite, quartz and iron oxides are found together with turquoise. © 2020 Ferdowsi University of Mashhad. All rights reserved.
Acta Geodynamica et Geomaterialia (12149705)17(1)pp. 61-87
The Mollaahmad pass bentonite deposit occurs within an area of about 10 km2 with Oligo-Miocene age (Isfahan-Iran). This bentonite deposit with two general lenticular and layered forms has extended in the tuff, conglomerates and sandstones (including volcanic fragments). XRD studies are demonstrating that montmorillonite, montmorillonite-illite, nontronite, albite, anorthite and quartz are major and clinoptilolite, heulandite, sanidine, orthoclase, calcite, microcline and actinolite are minor constituent minerals in studied bentonite deposit. Moreover, mineral chemistry indicates that Mollaahmad pass bentonite deposit has intermediate to di-octahedral smectites, so it can be classified as Wyoming bentonite type. Based on geochemical studies, transform process of parent rocks into bentonite was accompanied by enrichment of Cr, Sb, Se and REEs, and also enrichment or depletion of other major and trace elements. More geochemical studies have shown positive to negative Eu and Ce anomalies. This can be related to change in rate of oxidation and alteration intensity in altered system. In addition, study of rare earth elements indicates high differentiation of LREEs from HREEs that related to egress of HREEs from environment in form of carbonate complexes. It seems that six factors including discrepancy in rate of alteration intensity of the source materials, incorporation in crystal lattice, complex-forming ligands, surface adsorption and difference in stability of primary minerals are able to control mobilization, differentiation and distribution of elements in studied bentonites. This bentonite deposits has formed in margin of lacustrine environment. © 2020, Academy of Sciences of the Czech Republic,. All rights reserved.
