Mineralogy of anorthosite veins and host gabbros in the Kal-e-Kafi intrusive body (northeast of Anarak, Isfahan Province, Central Iran)

زمین شناسی اقتصادی

Article 6, Volume 14, Issue 2 - Serial Number 33, 2022, Pages 115-141   

Document Type: Research Article

DOI: 10.22067/econg.2021.68737.1008

Authors

Hanan Salim¹; Ghodrat Torabi^{* 2}; Nargess Nosouhian³

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

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

³Ph.D., Department of Geology, University of Isfahan, Isfahan, Iran

Abstract

Introduction
In the northeastern part of the Isfahan province and 65 km northeast of the Anarak city (Kal-e-Kafi area), an I-type granitoid pluton cross cut the Paleozoic metamorphic rocks and Eocene volcanic rocks. In the contact of this granitoid body with sourrounding rock units, skarn and hornfels have been formed (Ahmadian, 2012; Ranjbar, 2010). The Kal-e-Kafi Eocene intrusive body presents a wide range of mineralogical and petrological compositions, from gabbro to alkali-feldspar granite. Presence of mafic to acidic rocks in this mostly-granitoid body indicates that fractional crystallisation has played an important role during magma evolution. The field and petrographical studies indicate the presence of anorthosite veins within the gabbro section. The mafic and basic parts of this pluton have not been studied yet. The mineralogy and chemistry of rock-forming minerals in the anorthosites and gabbros are the subject of this research study.
 
Analytical Methods
The mineralogical and petrographical studies have been done by using Olympus BH-2 polarizing microscope in the mineralogy laboratory of the University of Isfahan. EPMA and LA-ICP-MS analyses were used to obtain chemical characteristics of rock-forming minerals. Major-elements composition of minerals were performed by JEOL JXA-8800, WDS microprobe electron analyzer with accelerator voltage of 15 kV, current of 15 nmA, diameter of 3 μm, and a counting time of 40 seconds at the Kanazawa University of Japan. 
Natural and synthetic minerals and compounds were used as standards. The ZAF program was used for data correction.
Trace element values of plagioclases and clinopyroxenes were analyzed by LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) using an ArF 193 nm Excimer Laser coupled to an Agilent 7500S at the Earth Science Department of the Kanazawa University, Japan. The diameter of the analyzed points was 110 µm at 10 Hz with energy density of 8 J/cm2 per pulse.
Mineral abbreviations in tables and photomicrographs are adopted from Whitney and Evans (2010).
 
Results and Discussion
The Eocene Kal-e-Kafi pluton includes a wide range of rocks from gabbro to alkali-feldspar granite, which points to an extensive magmatic differntiation. Field relationships indicate presence of at least 4 magmatic phases, and gabbro is the first and oldest phase. The most predominant rock unit in the Kal-e-Kafi intrusive body is granitoid. However,  in the northern parts, the gabbro and anorthosite present substantial exposures. The anorthosites and gabbros are associated with each other in the field. Anorthositic veins with up to 15 cm thickness cut the gabbro.
Gabbro is composed of bytownite and anorthite plagioclase (An= 84 – 94 %; some of them have been altered to bytownite, andesine and oligoclase), clinopyroxene (diopside, Mg#= 0.75), orthoclase (Or_0.88), apatite, magnetite, and prehnite. Anorthosite rock-forming minerals are anorthite plagioclase (An= 89 – 95 %; some anorthite plagioclase have been altered to bytownite and labradorite), sphene and zircon. The main texture of these rocks are granular, intergranular and poikilitic. Field studies suggest that anorthosites are associated with gabbros which have filled the fractures of gabbros.
Very simmilar petrography and chemical composition of plagioclases in the anorthosites and gabbros possibly reveal their cogenetic nature. It seems that the primary magma in the magma chamber, first crystallized the clinopyroxene and plagioclase, which caused formation of gabbros. In the next stage, by occurrence of a tectonic activity, the gabbros have broken and the remaining magma which was rich in plagioclase components, crystallized the anorthosites in the fractures. This reveals that the anorthosites of the study area are the plagioclase rich part of the primary basic magma which have formed the gabbros.
According to the field relationships, it is generally believed that anorthosites are differentiates of gabbroic magmas. The studied anorthosite veins and gabbros of the Kal-e-Kafi area are consanguineous. These anorthosites are perhaps generated by the process of collection of plagioclase crystals from a gabbroic magma under the action of gravity and tectonic activity (filter pressing).
Pyroxene is one of the common minerals. The chemical composition of this mineral provides valuable information about the nature of magma, H2O content, Oxygen fugacity, type of magmatic series, tectonic setting, as well as temperature and pressure of crystallisation (Schweitzer et al., 1979; Leterrier et al., 1982; D’Antonio and Kristensen, 2005).
Chemistry of clinopyroxens within the gabbros of the Kal-e-Kafi  area shows that the parental magma belongs to the sub-alkaline and calc-alkaline magmatic series and these rocks are similar to those of volcanic arcs. The time and place of formation of these plutonic rocks possibly indicate that they are formed by subduction of the Central-East Iranian Microcontinent (CEIM) – confining oceanic crust beneath the CEIM.
 
Acknowledgments
The authors thank the University of Isfahan for financial supports.

Keywords

Plagioclase; Clinopyroxene; Anorthosite; Gabbro; Eocene; Kal-e-Kafi; Central Iran

References

Ahmadian, J., 2012. Geochemistry, Mineral Chemistry and Petrology of Kal-e Kafi Ore- bearing intrusive bodies, E Anarak pages. Ph.D. Thesis, Tarbiat Modarres University, Tehran, Iran, 264 pp. (in Persian with English abstract(

Ahmadian, J., Haschke, M., McDonald, I., Regelous, M., Ghorbani, M.R., Hashem Emami, M. and Murata, M., 2009. High magmatic flux during Alpine-Himalayan collision: Constraints from the Kal-e-Kafi complex, central Iran. Geological Society of America Bulletin, 121(5–6): 857–868. https://doi.org/10.1130/B26279.1

Ahmadian, J., Sarjoughian, F., Lentz, D., Esna-Ashari, A., Murata, M. and Ozawa, H., 2016. Eocene K-rich adakitic rocks in the Central Iran: implications for evaluating its Cu–Au–Mo metallogenic potential. Ore Geology Reviews, 72: 323–342. https://doi.org/10.1016/j.oregeorev.2015.07.017

Aistov, L., Melnikov, B., Krivyakin, B. and Morozov, L., 1984. Geology of the Khur Area (Central Iran), Explanatory text of the Khur quadrangle map 1:250,000. Geological Survey of Iran,Tehran, 132 pp.

Anderson, J.L., 1996. Status of thermo-barometry in granitic batholiths. Earth Science Reviews, 87(1–2): 125–138. https://doi.org/10.1017/S0263593300006544

Aoki, K. and Shiba, I., 1973. Pyroxene from lherzolite inclusions of Itinomegata. Japan. Lithos, 6(1): 41–51. https://doi.org/10.1016/0024-4937(73)90078-9

Ashchepkov, I.V. and André, L., 2002. Pyroxenite xenoliths in picrite basalts (Vitim Plateau): origin and differentiation of mantle melts. Russian Geology and Geophysics, 43(4): 343–363. Retrieved May 09, 2021 from https://repository.geologyscience.ru/bitstream/handle/123456789/29776/Ashc_02.pdf?sequence=1&isAllowed=y

Charlier, B., Namur, O., Bolle, O., Latypov, R. and Duchesne, J.C., 2015. Fe-Ti-V-P ore deposits associated with Proterozoic massif-type anorthosites and related rocks. Earth Science Reviews, 141(1): 56–81. https://doi.org/10.1016/j.earscirev.2014.11.005

Delor, C.P. and Rock, N.M.S., 1991. Alkaline-ultramafic lamprophyre dykes from the Vestfold Hills, Princess Elizabeth Land (East Antarctica): Primitive magmas of deep mantle origin. Antarctic Science, 3(4): 419–432. https://doi.org/10.1017/S0954102091000512

Fuhrman, M.L. and Lindsley, D.H., 1988. Ternary-feldspar modeling and thermometry. American Mineralogist, 73(3–4): 201–215. Retrieved May 09, 2021 from https://pubs.geoscienceworld.org/msa/ammin/article-abstract/73/3-4/201/42101/Ternary-feldspar-modeling-and-thermometry?redirectedFrom=fulltext

 Green, D.H., Falloon, T.J., Eggins, S.M. and Yaxley, G.M., 2001.  Primary magmas and mantle temperatures. European Journal of Mineralogy, 13 (3): 437–452. https://doi.org/10.1127/0935-1221/2001/0013-0437

Helz, R.T., 1973. Phase relations of basalts in their melting range at P (sub H₂O) = 5kb as a function of oxygen fugacity: part I. mafic phases. Journal of Petrology, 14(2): 249–302. https://doi.org/10.1093/petrology/17.2.139

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

Koroll, H., Evangelakakkis, C. and Voll, G. 1993. Two feldspar geothermometry: A review and revision for slowly cooled rocks. Contributions to Mineralogy and Petrology, 114(1): 510–518. https://doi.org/10.1007/BF00321755

Le Bas, M.J., 1962. The role of aluminum in igneous clinopyroxenes with relation to their parentage. American Journal of Science, 260(4): 267–288. https://doi.org/10.2475/ajs.260.4.267

McDonough, W.F. and Sun, S.S., 1995. The composition of the earth. Chemical Geology, 120(3–4): 223–253. https://doi.org/10.1016/0009-2541(94)00140-4

Namdar Mohammadi, T., 2009. Study of copper-molybdenum mineralization and related alterations in the Kal-e-Kafi intrusive body - northeast of Anarak. MSc thesis in Geology, Petrology, University of Payame Noor, Isfahan, Iran, 162 pp. (in Persian with English abstract)

Nazari, G.‌H., Torabi, G., Arai, S. and Morishita, T., 2019. Lower Oligocene Calc-Alkaline Spessartitic Lamprophyres from Central Iran (East of Anarak Area); an Evidence from the Eastern Branch of Neotethys Subduction-Related Mantle Enrichment. Geotectonics, 53(6): 786–805. https://doi.org/10.1134/S0016852119060098

Ranjbar, S., 2010. Petrological and mineralogical research on the skarns in the Kal-e-Kafi area (NE of Anarak, Isfahan province), M.Sc. Thesis in Petrology, University of Isfahan, Isfahan, Iran, 135 pp. (in Persian with English abstract)

Romanko, E., Kokorin, Yu., Krivyakin, B., Susov, M., Morozov, L. and Sharkovski, M., 1984. Outline of metallogeny of Anarak area (Central Iran): explanatory text to metallogenic map, 1:250000. Moscow, Geological Survey of Iran, Tehran, Technoexport Report 19, 136 pp.

Salim, H., 2019. Mineralogical characteristics of plagioclase and clinopyroxene in the gabbros and anorthosites from the Kal-e-kafi intrusion (Northeast of Anarak, Isfahan pro Salim ince, Central Iran). M.Sc. Thesis, University of Isfahan, Isfahan, Iran (in Persian with English abstract), 150 pp.

Sargazi, M. and Torabi, G., 2019. Petrography and mineral chemistry of the Eocene granodiorites in the Toveireh area (Southwest of Jandaq, Isfahan province). Journal of Economic Geology, 10(2): 449–470. (in Persian with English abstract) https://dx.doi.org/10.22067/econg.v10i2.60825

Schweitzer, E.L., Papike, J.J. and Bence, A.E., 1979. Statistical analysis of clinopyroxene from deep-sea basalts. American Mineralogist, 64(5–6): 501–513. Retrieved May 09, 2021 from https://pubs.geoscienceworld.org/msa/ammin/article-abstract/64/5-6/501/41015/Statistical-analysis-of-clinopyroxenes-from-deep?redirectedFrom=PDF

Torabi, G., Arai, S. and Abbasi, H., 2014. Eocene continental dyke swarm from Central Iran (Khur area). Petrology, 22(6): 617–632. https://doi.org/10.1134/S086959111406006X

Torabi, G., Morishita, T. and Arai, Sh., 2019. Two types of plagiogranite from Mesozoic Ashin Ophiolite (Central Iran): a mark of tectonic setting change from Jurassic to Cretaceous. Geotectonics, 53(1): 110–124. http://doi.org/10.1134/S0016852119010084

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

Woodruff, L.G., Nicholson, S.W. and Fey, D.L., 2013. A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites: U.S. Geological Survey, Reston, 47 pp. https://doi.org/10.3133/sir20135091

Yakovenko, V., Chinakov, I., Kokorin, Yu. and Krivyakin, B., 1981. Report on geological prospecting in Anarak area (Kal-e Kafi- Khuni locality), V/O Technoexport, Moscow, Report 13, .293 pp.

Zakipour, Z. and Torabi, G., 2021. Metamorphism of peridotites from Kal-e-Kafi area (Isfahan Province, Central Iran). Advanced Applied Geology, 11(1): 136–156. (in Persian with English abstract) https://doi.org/10.22055/aag.2020.29597.1989