Geochemistry, petrography, and tectono-magmatic setting of Eocene volcanic lavas in the south of Mamoniyeh, Urumieh-Dokhtar magmatic arc, Markazi Province, Iran

Author(s): Mohammad Goudarzi, Hassan Zamanian, Urs Klötzli
Abstract: Introduction The study area is located in the Markazi province and south of Mamoniyeh is a part of the Zaviyeh 1:100000 geological map which is located in the middle part of the Urumieh-Dokhtar magmatic arc and terms of the presence of volcanic phases and intrusive masses prone to mineralization. It has been the focus of researchers. Due to various phenomena, including magmatic and tectonic activities have a significant effect on the geological evolution of this region, and so, due to the lack of detailed studies on the volcanic rocks of this area (Mamoniyeh), we aim to link the tectonic setting and the magmatic evolution of rocks. In addition, magma evolution processes, such as fractional crystallization, crustal contamination, and magma mixing may play an important role in the genesis of these rocks. This research presents new petrological and geochemical data from these volcanic rocks, which were formed during the Eocene. The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks that formed during the Late Cretaceous to Early Miocene, approximately 95 to 20 million years ago, and extends for about 2,000 kilometers. The magmatic rocks in the Urumieh Dokhtar Magmatic Arc include a variety of lithologies, such as lavas, pyroclastic deposits, and plutonic rocks like granites and diorites. These rocks were formed as a result of the subduction of the Arabian plate beneath the Eurasian plate, which led to the melting of the mantle and the formation of magma. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Volcanic rocks in the region are more than 4 km thick and include lava flows, pyroclastic layers, tuff, and ignimbrite. Regional Geology The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks that formed during the Late Cretaceous to Early Miocene, approximately 95 to 20 million years ago, and extends for about 2,000 kilometers. The magmatic rocks in the Urumieh Dokhtar Magmatic Arc include a variety of lithologies, such as lavas, pyroclastic deposits, and plutonic rocks like granites and diorites. These rocks were formed as a result of the subduction of the Arabian plate beneath the Eurasian plate, which led to the melting of the mantle and the formation of magma. In this area, the Eocene volcanic units have been completely disrupted due to the influx of intrusive masses and high displacement by shear-compressional faulting. Volcanic rocks in the region are more than 4 km thick and include lava flows, pyroclastic layers, tuff, and ignimbrite. Research methodology Simultaneously with the preparation of a 1:20000 geological map of the area, sampling of surface volcanic units and drilled boreholes was carried out. 50 samples of volcanic rocks were collected based on lithological diversity and then thin sections were prepared after studying petrography, 15 samples with the least amount of alteration were analyzed by ICP-MS and XRF methods and by combining the information obtained from field observations, microscopic studies and analysis of the main and rare elements using the GCDkit software, petrogenesis and the formation of volcanic rocks of the region have been investigated. Petrography According to petrographic studies, the rock types include rhyolite, dacite, trachydacite, trachyte, andesite, trachyandesite, basalt, trachyandesite and trachybasalt. The main rock-forming minerals are plagioclase, K-feldspar, quartz, amphibole, biotite, pyroxene, rarely olivine, apatite, zircon, and Fe-Ti oxides. Microscopic evidence indicates the presence of clastic, porphyritic with trachytic and cryptocrystalline textures, sieve texture, intergranular, intersertal, hyalomicrolitic and hyaloporphyritic, porphyritic, and microgranular cryptocrystalline textures in the samples. Constituent minerals have been altered with different intensities. Minor minerals include opaques, quartz, carbonate, epidote, chlorite, sericite, apatite, sphene, zircon, and sometimes tremolite and actinolite. Fine-grained and idiomorphic apatites are found as inclusions in plagioclase. Zircon is present as small grains in the form of short prismatic crystals and as inclusions in biotite. Geochemistry The amount of SiO₂ varies from 47 to 73% and the amount of Al₂O₃ from 11.6 to 17.8% by weight. The total amount of alkali elements in the samples varies from 4.5 to 10.1 percent by weight. The magmatic series of rocks are placed in the range of basalt-andesite and calc-alkaline series and dacite-rhyodacite of the calc-alkaline series based on different charts of rare elements. The data of rare elements like Nb vs. Nb/Zr, Sr/Zr vs. Ti/Zr, Rb vs. Rb/Sr, and Rb/Sr vs. Ti/Zr shows the effect of crystal segregation and mixing during magma ascent, and the presence of large plagioclase and clinopyroxene crystals also confirm it. In the spider diagram (Primitive Mantle-normalized multi-element spider) samples show enrichment in large ion lithophile elements (LILE), especially Rb, Ba, K, and Cs and depleted of high field strange elements (HFSE), such as Ti, Yb, and Zr. The strongly positive Pb and positive K anomaly can be caused by crustal involvement in magmatic processes. On chondrite-normalized REE diagrams, samples are enriched in LREE and depleted in HREE. The rather flat HREE patterns imply the absence of garnet and/or hornblende in the source of these magmas. The absence of a negative anomaly in Eu in non-altered volcanic rocks explains the high water content or oxygen fugacity and an abundance of hornblende, pyroxene, sphene, and garnet may cause a positive Eu anomaly. Discussion and Conclusion South of Mamoniyeh Volcanic complex are enriched in LILE, enriched in LREE, and depleted in HFSE which is a reason for the origin of the magma that creates these rocks from a metasomatized weak Korean mantle above the subduction zone. The presence of non-equilibrium textures such as sieve texture in plagioclase and opacification of amphiboles can indicate the occurrence of contamination by crustal rocks. Zr/Y > 3 corresponds to continental volcanic arcs and Zr/Y < 3 corresponds to oceanic arcs. Most rocks of the Mamoniyeh area have a ratio of less than 3 and indicate the similarity of the magma tectonic environment of this area with a continental volcanic arc. The available geochemical data show that the magmatism of volcanic rocks in the region is calc-alkaline. It seems that the origin of magma was from a metasomatized mantle with a partial melting degree of 20 to 45% garnet-spinel lherzolite to spinel lherzolite. Trace elements show the contamination with crustal materials and mixing during the ascent of parent magma and the role of fluids released from the subducting plate in the composition of the magma. The subduction process, which was accompanied by the release of water and volatile materials from the subducting spheroid, caused the metasomatism of the mantle wedge and its partial melting by the fluids released from the subducting oceanic spheroid. This pattern is consistent with the results presented in the entire of Urumieh-Dokhtar.
Organisation(s): Department of Lithospheric Research
External organisation(s): Lorestan University, University of Tehran
Journal: Petrological Journal
Volume: 15
Pages: 85-116
No. of pages: 32
ISSN: 2228-5210
DOI: https://doi.org/10.22108/ijp.2024.139861.1315
Publication date: 05-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 105105 Geochemistry, 105127 Geochronology, 105106 Geodynamics
Keywords
ASJC Scopus subject areas: Earth and Planetary Sciences (miscellaneous), Economic Geology, Geochemistry and Petrology, Geology
Portal url: https://ucrisportal.univie.ac.at/en/publications/c6cb8720-1ad7-4e88-94eb-68cc91048967

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