Mineral chemistry of clinopyroxene: guidance on geo- thermobarometry and tectonomagmatic setting of Nabar volcanic rocks, South of Kashan

Document Type : Research Article

Authors

• Rezvan Mehvari ¹
• Moussa Noghreyan ¹
• Mortaza Sharifi ¹
• Mohammad Ali Mackizadeh ¹
• Seyed Hassan Tabatabaei ²
• Ghodrat Torabi ¹

¹ Isfahan

² Isfahan University of Technology

10.22067/econg.v8i2.46817

Abstract

Introduction
The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993) and Abbasi (Abbasi, 2012) have been done about the geology of this area.
Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternary travertine and recent alluvium (Emami, 1993). The volcanic and sub volcanic rocks of this area are composed of andesite, trachyandesite, dacite, rhyolite and porphyric pyroxene diorite along with pyroclastic rocks.

Materials and methods
In order to achieve the aims of this work, at first field surveying and sampling were done. Then, thin and polished thin sections were prepared. Some of the samples were selected for microprobe analysis and clinopyroxene minerals were analyzed by using JEOL- JXA-8800 analyzer with a voltage of 20 Kv and a current of 12 nA in the Kanazava University of Japan and Cameca-Sx100 analyzer with a voltage of 15 Kv and a current of 15 nA in the Iranian mineral processing research center, Karaj.

Discussion
On the basis of petrographic investigations, porphyritic, porphyroid, fluidal, amygdaloidal and porphyry with microlitic groundmass are common textures of these rocks. Also plagioclase, clinopyroxene, amphibole, biotite, sanidine and quartz are essential minerals, opaque, zircon and apatite as accessory minerals are observed in the studied rocks. Clinopyroxenes are observed with corona texture that resulted during the uralitization process. On the basis of minerals’ chemistry, pyroxenes are Fe- Mg- Ca type in composition (Morimoto et al., 1988). These clinopyroxenes are augite. Investigations indicate that mineral composition of clinopyroxene can be effectively used to evaluation the P-T conditions during crystallization. Previous research works have proposed several methods such as Soesoo (Soesoo, 1997) and Putrika (Putrika, 2008). Thermobarometric studies of clinopyroxenes reveal that Nabar rocks were formed at temperatures of 900 -1200 ˚C and the pressure of 2-5 kbar. According to the Aoki and Shiba (Aoki and Shiba, 1973) and Helz (Helz, 1973) approaches, the pyroxenes of the studied rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Also according to Helz (Helz, 1973), the water vapor content in the crystallization of clinopyroxenes is more than 10 percent. Using AlIV +Na versus AlIV + 2Ti + Cr diagram which depends on the amount of ferric iron in pyroxenes, we can get oxygen fugacity. Based on this diagram, the pyroxenes which crystalized at high oxygen fugacity, has been situated above the line of Fe3+. Furthermore, Cameron and Papike (Cameron and Papike, 1981) have mentioned to the distances of the samples from the Fe3+ line and noted that further distances of the samples from this line are indicating more oxygen fugacities in their geological setting. On the basis of this diagram samples were located above the line of Fe3+and these rocks are formed in high oxygen fugacities. Pyroxene composition depends on the chemical composition and tectonic setting of the host lava which can be used widely to determine tectonic setting of the rocks. On the basis of approaches of Le Bas (Le Bas, 1962) and Sun and Bertrand (Sun and Bertrand, 1991), the chemical composition of clinopyroxenes shows that the studied rocks are related to calc-alkaline series and orogenic settings.

Results
On the basis of mineral chemistry, pyroxenes are Fe-Mg-Ca type in composition. These clinopyroxenes are augite. Thermometric studies of clinopyroxenes reveal that Nabar rocks are formed at temperatures of 900-1200 ˚C. According to the distribution of aluminum in clinopyroxenes, these minerals were formed at 2-5 k bar pressure and water vapor content of more than 10 percent. Therefore, pyroxenes of the Nabar rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Moreover, the volcanic rocks in Nabar were formed in high oxygen fugacity. The chemical composition of clinopyroxenes reveals that these rocks are related to calc-alkaline series and orogenic settings.

Acknowledgments
The authors wish to thank the University of Isfahan for their financial supports.

References
Abbasi, S., 2012. Petrography and petrology of intermediate rocks in the East Nabar area (SW of Kashan). M.Sc. Thesis, University of Isfahan, Isfahan, Iran, 177 pp.
Aoki, K. and Shiba, I., 1973. Pyroxenes from lherzolite inclusions of Itinome- Gata, Japan. Lithos, 6(1): 41-51.
Cameron, M. and Papike, J.J., 1981. Structural and chemical variations in pyroxenes. American Mineralogist, 66(1-2): 1-50.
Emami, M.H., 1993. Geological Map of Kashan, scale 1:100,000. Geological Survey of Iran.
Helz, R.T., 1973. Phase relations of basalts in their melting ranges at p H2O=5kb as a function of oxygen fugacity, Part I, Mafic phases. Journal of Petrology, 14(2): 249-302.
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.
Morimoto, N., Fabrise, J., Ferguson, A., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K. and Gottardi, G., 1988. Nomenclature of pyroxene. Mineralogical Magazine, 52(367): 535-555.
Putrika, K.D., 2008. Thermometers and barometers for volcanic systems. Reviews in Mineralogy and Geochemistry, 69(1): 61-120. Ridolfi, F., Renzulli, A. and Puerini, M., 2010. Stability and chemical equilibrium of amphibole in calc- alkaline magmas: an overview, new thermobarometric formulations and application to subduction – related volcanoes. Contributions to Mineralogy and Petrology, 160(1): 45-66.
Soesoo, A., 1997. A multivariate analysis of clinopyroxene composition: empirical coordinates for the crystallization P-T estimations. Geological Society of Sweden, 119(1): 55-60.
Sun, C.M. and Bertrand, J., 1991. Geochemistry of clinopyroxenes in plutonic and volcanic sequences from the Yanbian Proterozoic ophiolites (Sichuan province, China): Petrogenetic and geotectonic implications. Schweiz Mineralogische Petrologische Mitteilungen, 71(2): 243-259.

Keywords

• Clinopyroxene
• Thermobarometry
• Tectonomagmatic
• Nabar
• Urumieh- Dokhtar

20.1001.1.20087306.1395.8.2.12.3

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References

Abbasi, S., 2012. Petrography and petrology of intermediate rocks in the East Nabar area (SW of Kashan). M.Sc. Thesis, University of Isfahan, Isfahan, Iran, 177 pp.

Aghanabati, S.A., 1994. Geology of Iran. Geology Survey of Iran, Tehran, 586 pp.

Andersen, D.J., Lindsley, D.H. and Davidson, P.M., 1993. QUILF: A Pascal program to assess equilibria among Fe- Mg- Mn- Ti oxides, pyroxenes, olivine and quartz. Computers and Geosciences, 19(9): 1333-1350.

Aoki, K. and Shiba, I., 1973. Pyroxenes from lherzolite inclusions of Itinome- Gata, Japan. Lithos, 6(1): 41-51.

Beccaluva, L., Macciotta, G., Piccardo, G.B. and Zeda, O., 1989. Clinopyroxene composition of ophiolite basalts as petrogenetic indicator. Chemical Geology, 77(3-4): 165-182.

Blevin, P.L., 2004. Redox and compositional parameters for interpreting the granitoid matallogeny of Eastern Australia: Implications for gold- rich ore system. Resource Geology, 54(3): 241-252.

Botcharnikov, R.E., Koepke, J., Holtz, F., McCammon, C. and Wilke, M., 2005. The effect of water activity on the oxidation and structural state of Fe in a ferro- basaltic melt. GeochimicaetCosmochimicaActa, 69(21): 5071-5085.

Burnham, A.D. and Berry, A.J., 2014. The effect of oxygen fugacity, melt composition, temperature and pressure on the oxidation state of cerium in silicate melts. Chemical Geology, 366(1): 52-60.

Cameron, M. and Papike, J.J., 1981. Structural and chemical variations in pyroxenes. American Mineralogist, 66(1-2): 1-50.

Carmichael, I.S.E. and Ghiorso, M.S., 1986. Oxidation- reduction relations in basic magma: a case for homogeneous equilibria. Earth and Planetary Science Letters, 78 (2-3): 200-210.

Deer, W., Howie A. and Zussman J., 1992. Anintroduction to the rock forming minerals. Longman, London, 760 pp.

Ebrahimi, L., 2013. Petrology and petrography of volcanic rocks in the East of Nabar (SW of Kashan). M.Sc. Thesis, University of Isfahan, Isfahan, Iran, 138 pp.

Emami, M.H., 1993. Geological Map of Kashan, scale 1:100,000. Geological Survey of Iran.

France, L., Ildefonse, B., Koepke, J.andBech, F., 2010. A new method to estimate the oxidation state of basaltic series from microprobe analyses. Journal of Volcanology and Geothermal Research, 189(3-4): 340-346.

Helz, R.T., 1973. Phase relations of basalts in their melting ranges at p H2O=5kb as a function of oxygen fugacity, Part I, Mafic phases. Journal of Petrology, 14(2): 249-302.

Javadi, F., 2012. Petrology and Geochemistry of east NabarSkarn at the southwest of Kashan (Urumieh- Dokhtar Zone). M.Sc. Thesis, University of Isfahan, Isfahan, Iran, 125 pp.

Laubier, M., Grove, T.L. and Langmuir, C.H., 2014. Trace element mineral/melt partitioning for basaltic and basaltic andesitic melts: An experimental and laser ICP-MS study with application to the oxidation state of mantle source regions. Earth and Planetary Science Letters, 392(2): 265-278.

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.

Lepage, L.D., 2003. ILMAT: An excel worksheet for ilmenite- magnetite geothermometry and geobarometry. Computers and Geosciences, 29(5): 673-678.

Lindsley, I., 1983.Pyroxene thermometry. American Mineralogist, 68 (5-6): 477-493.

Miekayle, R., Noghreyan, M., Mackizadeh, M.A., Taghipour, B. and Tahmasebi, Z., 2010. Minerals chemistry and geochemistry of propylitic alteration in Astanehgranitoid (southwest of Arak). Iranian journal of crystallography and mineralogy, 18(1): 93-104.

Moretti, R., 2005. Polymerization, basicity, oxidation state and their role in ionic modeling of silicate melts. Geophysics, 48(4-5): 583-608.

Morimoto, N., Fabrise, J., Ferguson, A., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K. and Gottardi, G., 1988. Nomenclature of pyroxene. Mineralogical Magazine, 52(367): 535-555.

Nimis, P. and Taylor, W.R., 2000. Single clinopyroxen ethermobarometry for garnet peridotites. Part I. Calibration and testing of a Cr-in-Cpx barometer and an enstatite-in-Cpx thermometer. Contributions to Mineralogy and Petrology, 139 (2): 541-554.

Nisbet, E.G. and Pearce, J.A., 1977. Clinopyroxene composition in mafic lavas from different tectonic setting. Contributions to Mineralogy and Petrology, 63(2): 149-160.

Ottonello, G., Moretti, R., Marini, L. and Zuccolini, M.V., 2001. Oxidation state of iron in silicate glasses and melts: A thermochemical model. Chemical Geology, 174(1-3): 157-179.

Putrika, K.D., 2008. Thermometers and barometers for volcanic systems. Reviews in Mineralogy and Geochemistry, 69(1): 61-120.

Ridolfi, F., Renzulli, A. and Puerini, M., 2010. Stability and chemical equilibrium of amphibole in calc- alkaline magmas: an overview, new thermobarometric formulations and application to subduction – related volcanoes. Contributions to Mineralogy and Petrology, 160(1): 45-66.

Schweitzer, E.L., Papike, J.J. and Bence, A.E., 1979. Statistical analysis of clinopyroxenes from deep-sea basalts. American Journal of Sciences, 64(5-6): 501-513.

Shelly, D., 1993. Igneous and metamorphic rocks under the microscope. Chapman and Hall, London, 630 pp.

Soesoo, A., 1997. A multivariate analysis of clinopyroxene composition: empirical coordinates for the crystallization P-T estimations. Geological Society of Sweden, 119(1): 55-60.

Sun, C.M. and Bertrand, J., 1991. Geochemistry of clinopyroxenes in plutonic and volcanic sequences from the Yanbian Proterozoic ophiolites (Sichuan province, China): Petrogenetic and geotectonic implications. Schweiz Mineralogische Petrologische Mitteilungen, 71(2): 243-259.

Whiteney, D.L. and Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95‌(1): 185-187.