Magmatic Evolution of the Upper Eocene Monzonitic stock in the Kuh-e-Kalut-e-Ghandehari (Northwest of Anarak, Isfahan province)

Document Type : Research Article

Authors

• Marzieh Ghadirpour ¹
• Ghodrat Torabi ²
• Nargess Shirdashzadeh ³

¹ Ph.D. Student, Department of Geology, University of Isfahan, Isfahan, Iran

² Professor, Department of Geology, University of Isfahan, Isfahan, Iran

³ Assistant Professor, Department of Geology, Faculty of Basic Sciences, Tarbiat Modares University, 14115-175, Tehran, Iran

10.22067/econg.2023.84438.1088

Abstract

In central part of the Mesozoic Ashin ophiolite (Northwest of Anarak, Isfahan province, Iran), the Upper Eocene monzonitic stock cross cuts the Ashin ophiolite and Middle Eocene volcanic rocks. Amphibolite xenoliths are enclosed in the stock and associated Eocene volcanic rocks. Xenoliths are more abundant in the margin of the monzonitic stock. Rock-forming minerals of the stock are plagioclase with andesine to labradorite composition (An=34-60%), Alkali-feldspar with orthoclase composition (Or= 70.8 to 96.1%), diopsidic clinopyroxene with (Mg# =0.71-0.90), and phlogopite mica with (Fe#=0.3). Opaque minerals are magnetite and titanomagnetite (TiO₂=1.6-4.4 wt.%). Main textures of samples from this intrusive body are granular, intergranular and poikilitic. Samples from the margin of this stock represent porphyritic texture. 
Geochemistry of minerals and whole rock samples of this stock indicate that they belong to the calc-alkaline magmatic series and are similar to the samples from the continental magmatic arcs.
These magmatic rocks possibly were formed by subduction of the CEIM (Central-East Iranian Microcontinent) confining oceanic crusts (Ashin and Nain oceanic crusts) during Mesozoic and Early Cenozoic eras.
 
Introduction
Iran is a part of the Alpine-Himalayan orogenic system, including the Paleozoic to Cenozoic ophiolites, magmatic and metamorphic rocks (Takin, 1972; Berberian and King, 1981; Berberian et al., 1982; Dercourt et al., 1986; Alavi, 1994; Mohajjel et al., 2003; Shahabpour, 2007). The main pulse of the Paleogene and Neogene magmatic (volcanic and intrusive) activities of Iran can be attributed to the two Cenozoic subduction events, including the western Neo-Tethyan oceanic crust subduction beneath the Sanandaj-Sirjan block in the west and the eastern Neo-Tethyan oceanic crust subduction beneath the Central Iran (e.g., Shirdashtzadeh et al., 2022). The former subduction possibly caused to the formation of the Urumieh-Dokhtar Magmatic Arc, but the later subdution results is not well studied yet. 
In the this research, the target region is located in the west of the Yazd block (Central Iran), where the Eocene volcanic and plutonic rocks represent subduction-related characteristics (Jamshidzaei et al., 2021). The investigated subduction-related monzonitic stock that cross cuts the central part of the Ashin ophiolite in the Kuh-e-Kalut-e-Ghandehari region, in the northwest of Anarak (Isfahan Province, Iran). The main lithologies in the Kuh-e-Kalut-e-Ghandehari are Mesozoic lithologies of Ashin Ophiolite, Paleocene limestone, Eocene volcanic rocks, monzonitic stock, Lower Red Formation, and Akhoreh Formation. Ashin ophiolite was formed in the mesozoic (Shirdashtzadeh et al., 2022) and emplaced in the Late Paleocene (~60 Ma; Pirnia et al., 2020; Shirdashtzadeh et al., 2022), before than Eocene volcanism and plutonism. The studied monzonitic stock of the Kuh-e-Kalut-e-Ghandehari intrudes the Mesozoic Ashin ophiolite and Middle Eocene volcanic rocks.
The calc-alkaline affinity of the volcanic and plutonic rocks of the area, tectonic activity of the Great Kavir fault caused to the crushing and mylonitization of the surrounding rock units, as well as the alteration evidences in the field studies point to suitable conditions for the ore deposit exploration in the area (e.g., copper). In this research, the petrology, mineralogy, and whole rock geochemistry of the Upper Eocene monzonitic stock are considered. This research will expand our understanding of the geochemical nature of subduction-related Cenozoic magmatism in Central Iran.
 
Materials and methods
After detailed field studies and sampling, the selected fresh samples were used for microscopic thin section and polished-thin section studies by the polarizing binocular microscope (Olympus BH-2). The microprobe analyses were performed at the School of Natural Systems, College of Science and Engineering, Kanazawa University (Kanazawa, Japan) using a wavelength dispersive electron probe microanalyzer (EPMA) (JEOL JXA-8800R). The mineral analysis was achieved under an accelerating voltage of 20 kV, a probe current of 20 nA, and a focused beam diameter of 3μm. 14 whole rock samples analyses were performed by Brucker S4 PIONEER XRF in the central laboratory of the University of Isfahan and 3 samples were analyzed in the Isfahan Nuclear Technology Center by neutron activation analysis (NAA).
 
Results
Based on the field relation ships, this gray to light gray pluton intrudes into the Middle Eocene volcanic rocks and belongs to the Upper Eocene. The Middle Eocene volcanic rocks and Upper Eocene monzonitic stock crosscut the Ashin Ophiolite. This Eocene stock and volcanic rocks contain amphibolite xenoliths with the same mineralogy and petrography. Xenoliths are more abundant in the margin of the monzonitic stock. Gradual decreasing of modal plagioclase content indicates that the xenoliths range from amphibolite (plagioclase + amphibole) to hornblendite (only amphibole) in composition.
Rock-forming minerals of the stock are plagioclase with andesine to labradorite composition (An = 34-60 %), alkali-feldspar with orthoclase composition (Or = 70.8 to 96.1%), diopside clinopyroxene with Mg# = 0.71-0.90, and phlogopite mica with Fe# = 0.3. Opaque minerals are magnetite and titanomagnetite with TiO₂ = 1.6-4.4 wt%. The main textures of samples from this intrusive body are granular, intergranular and poikilitic. Samples from the margin of this stock represent porphyritic texture. The SiO₂ value in the whole rock compositions ranges from 47.9 to 61.65 wt.% (basic to intermediate). The average content of alkalis is 9.75 wt.%). The Kuh-e-Kalut-e-Ghandehari rocks show sodic affinity by higher Na₂O than K₂O, based on the Na₂O/K₂O versus SiO₂ and K₂O/Na₂O versus SiO₂ diagrams (Jaques et al., 1985). The Eocene intrusive and volcanic rocks of this area are similar in terms of mineralogy and texture. Petrography and whole rocks chemical analyses indicate that the studied stock is geochemically composed of gabbro, monzodiorite to monzonite in composition with metaluminous affinity. Monzonite is the predominant rock.
 
Tectonic setting
Various tectonomagmatic discrimination diagrams are used to determine the tectonomagmatic setting of the Kuh-e-Kalut-e-Ghandehari stock. Mineral chemistry and whole rock geochemistry of the Kuh-e-Kalut-e-Ghandehari monzonitic stock indicate a calc-alkaline magmatic series similar to the subduction-related magmas in the normal continental magmatic arcs formed during the mantle metasomatism. According to the the temporal and geological situation, as well as the geochemical characteristics of the Kuh-e-Kalut-e-Ghandehari stock, it is considered as a part of an arc magmatism, related to the subduction of Neo-Tethyan oceanic crust beneath the CEIM (Central–East Iranian Microcontinent) during the Late Mesozoic and Early Cenozoic eras.
 
Acknowledgments
We are grateful to the University of Isfahan and the Department of Geology of Kanazawa University (Japan) for their supports. We are also grateful to anonymous reviewers for their useful comments and suggestions that improved the quality of this paper.
 

Keywords

• Stock
• Eocene
• Monzonite
• Kuh- Kalut Ghandehari
• Ashin Ophiolite
• Central Iran

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References

Aistov, L., Melnikov, B., Krivyakin, B., Morozov, L. and Kiristaev, V., 1984. Geology of the Khur area (Central Iran). Geological Survey of Iran, Tehran, Report 20, 131 pp.

Aghanabati, A., 2004. Geology of Iran. Ministry of Industry and Mines, Geological Survey of Iran, Tehran, 586 pp. (in Persian)

Alavi, M., 1994. Tectonic of the Zagros orogenic belt of Iran: New data and interpretations. Tectonophysics, 229(3–4): 211–238. https://doi.org/10.1016/0040-1951(94)90030-2

Ansari Kish, R., 2020. Petrology of Eocene-Oligocene volcanic rocks in the Band-e-Siah Mountain (NW of Anarak, Isfahan province) (in Persian). M.Sc. Thesis, Isfahan University, Isfahan, Iran, 117 pp.

Berberian, F., Muir, I.D., Pankhurst, R.J. and Berberian, M., 1982. Late Cretaceous and Early Miocene Andean-type plutonic activity in northern Makran and Central Iran. Journal of Geological Society of London, 139(5): 605–614. https://doi.org/10.1144/gsjgs.139.5.0605

Berberian, M. and King, G.C.P., 1981. Toward a paleogeography and tectonic evolution of Iran. Canadian Journal of Earth Science, 18(2): 210–265. https://doi.org/10.1139/e81-019

Davoudzadeh, M., 1972. Geology and petrology of the area north of Nain, Central Iran. Geological Survey of Iran, Report 14, 89 pp.

Deer, W.‌A., Howie, R.A. and J. Zussman., 1992. An introduction to the rock-forming minerals (2nd ed.), Longman London, 696 pp.          

Dercourt, J., Zonenshain, L.P., Ricou, L.E., Kazmin, V.G., Le Pichon, X., Knipper, A.L. and Pechersky, D.H., 1986. Geological evolution of the Tethys belt from the Atlantic to Pamirs since the Lias. Tectonophysics, 123(1–4): 241–315. https://doi.org/10.1016/0040-1951(86)90199-X

Ghaderi Rehnani, M., 2019. Petrology of Eocene volcanic rocks in the northwest of Zavar (NE of Anarak, Isfahan Province) (in Persian). M.Sc. Thesis, Isfahan University, Isfahan, Iran, 125 pp.

Ghadirpour, M., Torabi, Gh., Ghaderi, M., Bayat, F. and Shirdashtzadeh, N., 2023. Magmatic evolution of the Andesitic Eocene volcanic rocks in the Kuh-e- Kalut-e-Ghandehari (NW of Anarak, Isfahan province), Journal of crystallography and mineralogy, 31(3): 497–508. https://doi.org/10.61186/ijcm.31.3.497

Goli, Z., 2013. Petrology of Eocene volcanic rocks in southwest of Choupanan (NE of Anarak, Isfahan Province) (in Persian). M.Sc. Thesis, Isfahan University, Isfahan, Iran, 150 pp.

Irvine, T.N. and Baragar, W.R.A., 1971. A guide to the chemical classification of the common volcanic rocks, Canadian. Journal of Earth Science, 8(5): 523–548. https://doi.org/10.1139/e71-055

Jamshidzaei, A., Torabi, G., Morishita, T. and Tamura, A., 2021. Eocene dike swarm and felsic stock in Central Iran: Roles of metasomatized mantle wedge and Neo-Tethyan slab. Journal of Geodynamics, 145(1): 101844. https://doi.org/10.1016/j.jog.2021.101844

Jaques, A.L., Creaser, R.A., Ferguson, J. and Smith, C.B., 1985. A review of the alkaline rocks of Australia. Verhandeling van die Geologiese Vereniging van Suid-Afrika, 88(2): 311–334. Retrieved August 1, 2023 from https://pubs.geoscienceworld.org/gssa/sajg/articl e-abstract/88/2/311/122026

Khalili Gelsefidi, R., 2020. Petrology of Eocene volcanic rocks in the Gooreh Mountain (NW of Anarak, Isfahan Province) (in Persian). M.Sc. Thesis, Isfahan University, Isfahan, Iran, 248 pp.

Leake, B.E., Wolley, A.R., Arps, C.E.S., Birch, W.D., Gilbert, M.C., Grice, J.D., Hawthorne, F.C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J., Maresch, W.V., Nickel, E.H., Rock, N.M.S., Schumacher, J.C., Smith, D.C., Stephenson, N.C.N., Ungaretti, L., whittaker, E.J.W. and Youzhi, G., 1997. Nomenclature of Amphiboles, Report of the subcommittee on Amphiboles of the International Mineralogical Association commission on new minerals and mineral names, European Journal of Mineralogy, 9(3): 623–651. https://doi.org/10.1180/minmag.1997.061.405.13

Le Maitre, R.W.P., Bateman, A. Dudek, J.L., Keller, M.J., Le bas, P.A., Sabaine, R. Schmid, H. Sorensen, A. Streckeisen, A.‌R., Woolly, B.R. and Zanettin, B., 1989. A classification of igneous rocks and glossary of term. Blackwell, Oxford, 195 pp. https://www.researchgate.net/publication/234448684.

Maniar, P.D. and Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geological Society of America Bulletin, 101(5): 635–643. http://dx.doi.org/10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2

Mohajjel, M., Fergusson, C.L. and Sahandi, M.R., 2003. Cretaceous-Tertiary convergence and continental collision, Sanandaj-Sirjan zone, western Iran. Journal of Asian Earth Science, 21(4): 397–412. https://doi.org/10.1016/S1367-9120(02)00035-4

Morimoto, N., 1989. Nomenclature of pyroxenes, Contributions to Mineralogy and Petrology 27(1): 143–156. https://doi.org/10.2465/minerj.14.198

Muller, D. and Groves, D.I.,1997. Potassic igneous rocks and associated gold-copper mineralization,

Springer, Berlin, 398 pp. Retrieved August 1, 2023 from https://link.springer.com/book/10.1007/978-3-319-92979-8

Nabavi, M.H. and Houshmandzadeh, A., 1990. Geological Map of Anarak, scale 1:250000. Geological Survey of Iran.

Pirnia, T., Saccani, E., Torabi, G., Chiari, M., Gorecan, S. and Barbeo, E., 2020. Cretaceous tectonic evolution of the Neo-Tethys in Central Iran: Evidence from petrology and age of the Nain-Ashin ophiolitic basalts. Geoscience Frontiers, 11(1): 57–81. https://doi.org/10.1016/j.gsf.2019.02.008

Rieder, M., Cavazzini, G., D’Yakonov, Yu. S., Frank-Kamenetskii, V.A., Gottardi, G., Guggenheim, S., Koval, P.V., Muller, G., Neiva, A.M.R., Radoslovich, E.W., Robert, J.L., Sassi, F.P., Takeda, H., Weiss, Z. and Wones, D.R., 1998. Nomenclature of the micas, The Canadian Mineralogist, 36(3): 905–912. https://doi.org/10.1346/CCMN.1998.0460513

Sarjoughian, F., Ahmadian, J. and Kananian, A., 2015. The composition of the major minerals in the Nasrand intrusive rocks and its dikes. Petrology 21(6): 35–54. (in Persian) Retrieved August 1, 2023 from  https://ijp.ui.ac.ir/article_16202_e34f7b5bac19bdb188651619bb1deaf5.pdf

Sayari, M., 2006. Petrology of Eocene volcanic rocks in north of Anarak area (NE of Isfahan province) (in Persian). M.Sc. Thesis, Isfahan University, Isfahan, Iran, 119 pp.

Serra-keel, J., Hottinger, L.,  Caus, E., Drobne, K., Ferrandez, C., Jauhri, A., Less, G., Pavlovec, R., Pignatti, J., Maria Samso, J., Schaub, H., Sirel, E., Strougo, A., Tambareau, Y., Tosquella, J. and Zakrevskaya, E., 1998. Larger foraminiferal biostratigraphy of the Tethyan Paleocene and Eocene. Bulletin of Geological Society of France 169(2): 281–299. Retrieved August 1, 2023 from https://pubs.geoscienceworld.org/sgf/bsgf/article-abstract/169/2/281/88097/Larger-foraminiferal-biostratigraphy-of-the

Shahabpour, J., 2007. Island-arc affinity of the Central Iranian volcanic belt. Journal of Asian Earth Science, 30(5–6): 652–665. https://doi.org/10.1016/j.jseaes.2007.02.004

Shirdashtzadeh, N., Furnes, H., Miller, N., Luise Dantas, E., Torabi, Gh., 2022. Subduction inItiation of the Neo-tethys ocean in central Iran based on U-PB geochronology, geochemical and ND isotope data of the Ashin ophiolIte. Ofioliti, 47(2): 155–171. https://doi.org/10.4454/ofioliti.v47i2.557

Shirdashtzadeh, N., Torabi, G., Meisel, T., Arai, S., Bokhari, S.N.H., Samadi, R. and Gazel, E., 2014. Origin and evolution of metamorphosed mantle peridotites of Darreh Deh (Nain Ophiolite, Central Iran): implications for the Eastern Neo-Tethys evolution. Neues Jahrbuch für Geologie und PaläontologieAbhandlungen, 273(1): 89–120. https://doi.org/10.1127/0077-7749/2014/0418

Soesoo, A., 1997. A multivariate statistical analysis of clinopyroxene composition: empirical coordinates for the crystallization P-T estimations. Geological Society of Sweden (Geologiska Föreningen), 119(1): 55–60. https://doi.org/10.1080/11035899709546454

Takin, M., 1972. Iranian geology and continental drift in the Middle East. Nature, 235(21): 147–150. https://doi.org/10.1038/235147a0

Torabi, G., 2004. Petrology of Anarak area ophiolites (NE of Isfahan province, Iran). Ph.D. Thesis, Tarbiat Modarres University, Tehran, Iran, 240 pp.

Torabi, G., 2006. Petrology of volcanic shoshonites in south of Ashin, and age determination of igneous carbonates by using the fission track method (west of Anarak, North-east of Isfahan province). Journals of University of Isfahan, Basic Sciences, 25(3): 1–13. (in Persian) Retrieved August 1, 2023 from https://sid.ir/paper/55884/en

Whitney, D.‌L. and Evans, B.‌W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95(1): 185–187. https://doi.org/10.2138/am.2010.3371

Yavuz, F., 2013. Win Pyrox: A windows program for pyroxene calculation classification and thermobarometry. American Mineralogist, 98(7): 1338–1359. https://doi.org/10.2138/am.2013.4292