Petrological Journal

Geochemical variations of the Eocene volcanic rocks from Kahak area (south of Qom): Evidence for different different conditions of mantle melting in the Urumieh-Dokhtar magmatic arc

Morteza Delavari; Alireza Damghani

Volume 13, Issue 2 , August 2022, , Pages 91-120

https://doi.org/10.22108/ijp.2022.132106.1261

Abstract

IntroductionThe volcanic outputs of the Paleogene are the most conspicuous magmatic products in Iran and the Urmieh-Dokhtar magmatic belt (UDMB) and as the main manifestations of this ... Read More IntroductionThe volcanic outputs of the Paleogene are the most conspicuous magmatic products in Iran and the Urmieh-Dokhtar magmatic belt (UDMB) and as the main manifestations of this magmatism (Verdel et al., 2011). They are part of the southern Eurasian active continental margin formed by the Neotethyan subduction beneath the Central Iranian microcontinent. Geochemically, the magmatism of UDMB is mostly calc-alkaline (especially in the Eocene), although, towards the Oligocene and younger times, alkaline magmatism is also observed (Verdel et al., 2011). The magma origin, partial melting conditions, homogeneity/heterogeneity of mantle sources, evolutionary processes, and tectonic setting of the magma formation are some debatable issues. The purpose of the present study is to investigate field relations, geochemical diversity, and mantle source characteristics of the volcanic units exposed in the south of Qom (Kahak area).Materials and MethodsThe bulk rock major and trace elements contents were obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively, at Zarazma laboratory in Tehran, Iran. The sample powders were melted using lithium metaborate, dissolved and the final solution were analyzed by ICP-OES. To obtain rare earth and trace element contents, the sample powders were dissolved using multi-acid procedure and then the solution has been analyzed by ICP-MS. The detection limit for rare earth and trace elements is between 0.01 to 1 ppm.Field Evidence and PetrographyThe Eocene eruptive products in Kahak region are shown by broadly exposed lava flows and pyroclastics alternated with volcaniclastic and carbonaceous sediments. They are somewhere overlain by clastic sediments of the Lower Red Formation (Early Oligocene) allowing us to deduce their relative age. The thickness of lava units varies from <10 to several tens of meters. The basic lavas, the subject of this study, are dark gray to brownish-colored and aphyric to porphyritic. They show various textures of hyalopilitic, hypocrystalline, intersertal to intergranular, and ophitic. Some of the samples contain plagioclase- to clinopyroxene-phyric, in which the size of phenocrysts may reach up to 1 cm. Plagioclase, clinopyroxene, and Fe-Ti oxides are the common phenocrystic to microphenocrystic phases. Plagioclase is the most abundant phase (up to 40 vol.%). Clinopyroxene (5-10 vol.%) is the common ferromagnesian phase in most of the samples occurring as phenocrystic or interstitial phase. Olivine is rarely observed (<5 vol.%), and when present, it is almost altered to secondary products such as chlorite, serpentine, and iddingsite. Fe-Ti oxides are <0.5 to 0.2 mm-sized and form <5% of the mode.GeochemistryThe SiO2 content in the study samples ranges from 50.5 to 53 wt.% and in Zr/TiO2 versus Nb/Y diagram, they fall in subalkaline basalt field. The TiO2 amount varies from 0.42 to 1.92 wt.%. Also, the CaO, FeOt, and Na2O+K2O show relatively wide variation from 2.3 to 13.8, 4.9 to 12.7, and 3.2 to 9.3 wt.%, respectively.Mg# [(MgO/MgO+FeOT)*100] ranges from 34 to 52.6. Based on variation diagrams, normalized rare earth elements (REE), and multi-element patterns, the samples can be divided into four distinct groups (Fig. 1A). Group 1 rocks have a lower LREE/HREE ratio than the others and are characterized by (La/Yb)N values of 2.5-4.7. Group 2 rocks are Eu-depleted in which the (La/Yb)N ratio ranges from 3.7 to 4.6. Group 3 rocks display steeper REE patterns with (La/Yb)N ratio of 8.7-9.7. In Group 4 rocks, HREE display lower concentration, and the patterns are relatively steeper [(La/Yb)N= 8.4-10.4]. In the normalized multi-element diagrams, all the samples display relative depletion of high field strength elements (HFSE) such as Nb, Ta, Ti, Zr, Y, and Hf with respect to large ion lithophile elements (LILE) (i.e. Rb, K, Sr, and Ba). Despite the overall similarity of multi-element diagrams, there are some geochemical distinctions between them, for example, Group 1 and Group 4 rocks show Sr enrichment or a more pronounced P negative anomaly than the others.DiscussionVariations in the major and trace element contents and the different REE and multi-element patterns are all indicating of geochemical distinction between the studied volcanic rocks (Groups 1 to 4) of the Kahak area. In the major and trace element versus MgO variation diagrams, the scattered plots are also inconsistent with cogenetic relationships among different rock groups. The varied REE values or variously-sloped REE patterns can be attributed to heterogeneous mantle sources or different partial melting conditions. In the studied samples, the Nb/La ratio of 0.20 to 0.58 suggests a lithospheric mantle origin. To model the mantle source and partial melting condition, Sm/Yb versus Sm plot has been used, by which, it is inferred that:All the samples of the Kahak region were derived from a spinel-garnet-lherzolite mantle source with spinel: garnet ratio of 50:50.Geochemical differences between the samples under study are more probably the result of different degrees of partial melting. Accordingly, the primitive magma of Group 3 rocks was derived from the lower degree of partial melting (<10%), while those of the Group 1 rocks resulted from a higher degree of partial melting (10 to 20%). The Groups 2 and 4 rocks fall between these two ranges.Geochemical differences of the Kahak volcanic rocks is most likely the result of partial melting conditions rather than distinct mantle sources. Fig. 1. A) Chondrite-normalized REE patterns of the Kahak volcanic rocks; B) The proposed tectonic model for the Eocene magmatism of UDMB. Relative depletion of HFSE (such as Zr, Ti, Nb, and Ta) in normalized multi-element diagrams is commonly attributed to subduction zone geochemical signature. Also, in the tectonic discrimination diagrams (e.g. Th-Hf/3-Ta diagram), all samples plot in the field of calc-alkaline basalts of arc environment. Therefore, based on our geochemical data, the volcanic rocks of the Kahak region related to arc magmatism. The structural evidences like normal faulting and sedimentary basins with thickened Eocene volcanic-volcanoclastic associations point to an extensional environment. It is probable that the Neotethyan slab-rollback was responsible for the intra-arc (or back-arc) extensional environment in which asthenospheric upwelling led to partial melting of the metasomatized lithospheric mantle and voluminous Eocene magmatism of UDMB (Fig. 1B).

Late Paleozoic basaltic magmatism of Tarom- Masuleh area (western Alborz): whole-rock chemical characteristics and tectonic implications

Morteza Delavari; Khadijeh Sehhat

Volume 12, Issue 3 , December 2021, , Pages 1-26

https://doi.org/10.22108/ijp.2021.128168.1228

Abstract

The Tarom- Masuleh area (western Alborz) exposes considerable Late Paleozoic volcanic rocks. Stratigraphic relationships indicate that the igneous units are of Carboniferous- Permian ... Read More

The Late- Cretaceous volcanic rocks from Talesh area (western Alborz): chemical variation, crystallization condition, hygrometry and tectonic setting

Khadijeh Amani; Morteza Delavari; Sadraldin Amini; Amir Ali Tabbakh Shabani

Volume 11, Issue 1 , May 2020, , Pages 29-52

https://doi.org/10.22108/ijp.2019.117648.1140

Abstract

In the Talesh area (western Alborz), a thick sedimentary- volcanic association formed in a littoral- deltaic environment during the Late Cretaceous. The extrusives comprise volcanoclastics ... Read More

Paleozoic magmatism in the southwest of Julfa (northwestern Iran): geochemical characteristics, U-Pb dating and tectonic setting

morteza delavari; Fatemeh Arab Asadi; Ali Mohammadi

Volume 10, Issue 2 , September 2019, , Pages 99-120

https://doi.org/10.22108/ijp.2019.117112.1136

Abstract

Extensive sedimentary- igneous rock associations of Paleozoic age crop out in southwest of Julfa (northwest of Iran). Geochemically, the igneous rocks display various basic to acidic ... Read More

Mineral chemistry, thermobarometry and tectonomagmatic setting of Late-Cretaceous volcanic rocks from the Kojid area (south of Lahijan, northern Alborz)

Morteza Delavari; Razieh Moradi; Amir Ali Tabbakh Shabani

Volume 9, Issue 1 , June 2018, , Pages 133-164

https://doi.org/10.22108/ijp.2017.104651.1033

Abstract

The volcanic rocks of Kojid area (south of Lahijan) crop out in northern Alborz. They show mainly pillow structure with numerous cross-cutting dykes. Based on lithostratigraphic relationships ... Read More

Geochemistry of volcanic rocks from the south of Gazik (east of Birjand): implications for the evolution of Sistan Ocean (eastern Iran)

Morteza Delavari; Asghar Dolati; Emad Alipoorian

Volume 8, Issue 31 , December 2017, , Pages 21-42

https://doi.org/10.22108/ijp.2017.82010.0

Abstract

The study area is located the south of Gazik (east of Birjand) and along the eastern margin of the Sistan suture zone. The south of Gazic volcanics crop out as a north- south trending ... Read More

The Central Alborz Permian basaltic magmatism: an evidence of southern passive continental margin of Paleo- Tethys

Morteza Delavari; Farzaneh Rostami; Asghar Dolati

Volume 8, Issue 29 , June 2017, , Pages 53-74

https://doi.org/10.22108/ijp.2017.21500

Abstract

The study area is located in the Central Alborz (northeast of Baladeh). The Permianmagmatism in this area occurs as a basaltic unit between Ruteh-Nessen Formation.Petrographically, ... Read More

Mineralogy, thermobarometry and tectonic setting implication of garnet-clinopyroxene amphibolite in the Nain ophiolitic complex

Mohsen Nasrabady; Morteza Delavari; Marjan Partovi

Volume 6, Issue 23 , October 2015, , Pages 181-202

Abstract

The metabasites of the Nain ophiolites consisting of amphibole + plagioclase ± garnet ± clinopyroxene ± epidote rock forming minerals. On the basis of mineralogical ... Read More

Different geodynamic settings for Sistan suture zone ophiolitic units: discussion of textural evidences and mineral chemistry of crustal sequence ultramafic-mafic associations

Morteza Delavari

Volume 4, Issue 16 , February 2014, , Pages 39-58

Abstract

Sistan suture zone ophiolitic rocks are remnants of Tethyan oceanic lithosphere between Lut and Afghan continental blocks. This oceanic basin has been existed at least during the Cretaceous. ... Read More

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Author = Delavari, Morteza

Geochemical variations of the Eocene volcanic rocks from Kahak area (south of Qom): Evidence for different different conditions of mantle melting in the Urumieh-Dokhtar magmatic arc

Abstract

Late Paleozoic basaltic magmatism of Tarom- Masuleh area (western Alborz): whole-rock chemical characteristics and tectonic implications

Abstract

The Late- Cretaceous volcanic rocks from Talesh area (western Alborz): chemical variation, crystallization condition, hygrometry and tectonic setting

Abstract

Paleozoic magmatism in the southwest of Julfa (northwestern Iran): geochemical characteristics, U-Pb dating and tectonic setting

Abstract

Mineral chemistry, thermobarometry and tectonomagmatic setting of Late-Cretaceous volcanic rocks from the Kojid area (south of Lahijan, northern Alborz)

Abstract

Geochemistry of volcanic rocks from the south of Gazik (east of Birjand): implications for the evolution of Sistan Ocean (eastern Iran)

Abstract

The Central Alborz Permian basaltic magmatism: an evidence of southern passive continental margin of Paleo- Tethys

Abstract

Mineralogy, thermobarometry and tectonic setting implication of garnet-clinopyroxene amphibolite in the Nain ophiolitic complex

Abstract

Different geodynamic settings for Sistan suture zone ophiolitic units: discussion of textural evidences and mineral chemistry of crustal sequence ultramafic-mafic associations

Abstract