PETROLOGY
Year:2018 | Volume:9 | Issue:35 |Papers Count:6

The Almogholagh plutonic body with about 10 km2 is located 15 km of West of Hamedan city and on the Sanandaj-Sirjan zone. The Almogholagh pluton consists of diorite and gabbroic diorite, monzodiorite, quartz monzodiorite, monzonite, quartz monzonite, syenite, quartz syenite and alkali granite. Intergranular and granular are common textures of these rocks. The igneous rocks of the Almogholagh pluton were injected in two periods in the Cretaceous (from 138 to 95 Ma). Syenites, Quartz syenites and alkali granites were infused in the second phase and the remaining rocks have developed in the first stage. The igneous rocks of the Almoghlagh pluton have the A-type granitoids creteria. The magma generating the Almogholagh igneous rocks is formed by low degree partial meting (~7%) from depleted mantle with a garnet-spinel lherzolite composition. Results of the amphibole and plagioclase in the quartz syenite and quartz monzonite thermobarometry show that the mean temperature of the Almogholagh pluton formation is ~715 oC and the mean of its pressure is 2.18 Kb. Textural and thermobarometry evidences suggest a shallow-level (~5 km) emplacement for the Almogholagh pluton.

The Golgohar iron mine is located at 55 km southwest of Sirjan in the Sanandaj-Sirjan structural zone. The host rocks of the ore deposit include metamorphosed rocks in green schist and amphibolite facies. The mineralization is massive or disseminated in adjacent rocks. The metabasic rocks are classified into amphibolite, epidote amphibolite, epidote-biotite amphibolite and biotite amphibolite types. Base on major, trace, and rare earth elements, the protoliths of these rocks are basic igneous rocks varying from basalt, basaltic andesite, trachy basalt, basaltic trachy andesite compositions. The trace elements pattern shows enrichment in large-ion lithophile elements and depletion in high field strength elements, suggesting their island arc signatures. LREEs enrichment and relatively flat HREEs patterns further support this interpretation. According to geochemical data these rocks were derived from depleted mantle that was contaminated by the melts of subducted sediments. The relative age of these rocks does not match with the tectonic setting. It seems that the Neo-Tethyan subduction along the northern subduction zone caused the emplacement of the study rocks in the Upper Triassic time. In this case, geochronological data may be helpful.

The Hanar granitoids, geographically located 155 km south of Birjand in the east of Iran. Geologically, It belongs to the Lut block volcanic–plutonic belt and occurs near to the Lut block-Sistan suture zone border. The granitoid rocks consist of tonalite, granodiorite, quartz-diorite, diorite and microdiorite. The predominant textures are granular, porphyritic and myrmekitic. Geochemical evidence reveals that they are co-genetic and have features typical of calk-alkaline to high-K calk-alkaline, metaluminous with I-type nature. Enrichment in LILE (i.e. Cs, K, Rb, U and Th) rather than HFSE (eg., Nb, P, Zr and Ti), typical negative anomalies of Nb and Ti and LREE enrichment in comparison to HREE, are important characteristics indicating that these rocks were formed in a magmatic belt in a subduction zone. Positive anomalies of Pb and K demonstrate the involvement of continental crust in evolution of parental magma. Trace element ratios and adakitic discrimination diagrams point to the non adakitic nature of the magma. Tectonic discrimination diagrams show formation of these rocks in an immature continental arc setting with less than 45 Km crustal thickness in pre-plate collision event. Primitive magmas should have formed by low degree melting (less than 8%) of an eneriched mantle wedge peridotite (spinel lherzolite). During magma ascent, fractional crystallization and crustal contamination (AFC) took place simultaneously. Field observation and petrography studies support this hypothesis.

A thick sequence of Upper Cretaceous volcano-sedimentary rocks are cropped out on the northern edge of Central Iran, southwest of Sabzevar. The volcanic rocks are dacite/rhyolite and are associated with pyroclastic rocks, including agglomerate, breccia and tuff. Dacites are the thickest felsic volcanic unit. They show felsitic porphyry, glomero-porphyry and microlitic-porphyry textures and are composed of clinopyroxene, plagioclase and quartz. Plagioclases show sieve and zoning textures. Whole-rock and clinopyroxene chemistry reveal the tholeiitic nature of these rocks. Primitive mantle-normalized spider diagrams of the investigated rocks show negative anomalies of Nb, Ti and positive anomalies of Pb and K, which are characteristic features of the subduction environment magmas. Plot of the samples on different tectonic setting discrimination diagrams indicates their close relationship to island arc subduction environments. The results of the clinopyroxene chemistry also indicate their augitic composition. Application of geothermobarometry diagrams show temperature ranges between 850oC to 950oC and pressures less than 5 kb for crystallization of these rocks. The results of the present study show that the tholeiitic magma that formed the rocks studied has been generated by partial melting of a spinel lherzolitic mantle source in an island arc subduction zone during the closure of the Sabzevar Neo-Tethyan oceanic basin in the late Cretaceous.

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The studied area is located in the SE of Heris (Eastern Azerbaijan province) and the Alborz-Azerbaijan structural zone. The Eocene volcanic rocks in the area of under study show various compositions ranging from olivine basalt, hornblende basalt, basaltic andesite and andesite to trachy andesite. The studied basaltic rocks, except for amphibole types, which show calc-alkaline affinity, mainly have shoshonitic and the andesitic rocks are adakitic composition. According to primitive mantle and chondrite normalized spider and REE diagrams, the studied rocks are characterized by LILE and LREE enrichment and pronounced depletion in HFS elements. Based on geochemical data the basaltic rocks have been originated from different degrees partial melting of a heterogeneous lithospheric mantle that metasomatized by subduction agents. The adakitic rocks have been generated from partial melting of thickened potassic mafic lower crust that have been metamorphosed in eclogitic facies.