Geochemistry and petrogenesis of the Kolah-Ghazi granitoid assemblage, south of Esfahan

Document Type : Research Article

Authors

• Jamshid Ahmadian ¹
• Hajar Gholamian ²
• Ali Khan Nasr Esfahani ²
• Maryam Honarmand ³

¹ Payame Noor

² Azad University

³ Institute for Advanced Studies in Basic Sciences (IASBS)

10.22067/econg.v10i1.55622

Abstract

Introduction
The Kolah-Ghazi granitoid assemblage is located in the south of Esfahan and in the Sanandaj-Sirjan magmatic-metamorphic zone. The Sanandaj-Sirjan zone is extended for 1500 km from Sirjan in the southeast to Sanandaj in the northwest of Iran and is situated in the west of Central Iranian terrane.
The Sanandaj-Sirjan zone represents the metamorphic belt of the Zagros orogeny which is part of the Alpine- Himalayan orogenic belt. The Kolah-Ghazi granitoid assemblage consists of granodiorite, granites, quartz-rich granitoid and minor tonalite. The aim of this paper is to represent the mineralogy, geochemistry, petrogenesis and tectonic setting of this plutonic assemblage.

Materials and methods
More than 60 samples representing all of the rock units in the study area were chosen for microscopic studies. Then, 22 samples were selected for geochemical studies. The major elements were determined with XRF in the Naruto University, Japan. The trace and rare earth elements were analyzed by ICP-MS in the Acmelab, Canada. The geochemical results are presented in Table 1.

Results and Discussion
The Kolah-Ghazi granitoid assemblage intruded into the Jurassic sedimentary units and overlaid by lower Cretaceous sandstone and conglomerate which suggest Upper Jurassic as the possible age of the Kolah-Ghazi intrusion. Based on the modal studies, this granitoid assemblage is comprised of granite, granodiorite, quartz-rock granitoid and tonalite with different igneous textures including symplectic, myrmekitic, rapakivi, poikilitic and porphyroid. There are some xenoliths, microgranular enclaves and sur micaceous enclaves in the Kolah-Ghazi granitoid assemblage. Xenoliths are mostly derived from Jurassic shale and sandstones which have been trapped in the magma. The sur micaceousenclaves have tonalite composition. The sur micaceous enclaves are biotite-rich rock fragments which display metamorphic texture. The sur micaceous enclaves are classified as restite since they are poor in quartz. The essential minerals in this magmatic assemblage are quartz, plagioclase, alkali-feldspar and biotite as the only ferromagnesian mineral. There was no hornblende in the studied samples. The presence of andalusite, sillimanite and garnet in these rocks point to the sedimentary source of these granitoid melts. Zircon, apatite and opaque minerals occurred as accessory minerals. The secondary minerals included sphene, tourmaline, clay minerals, chlorite and opaque minerals. The Kolah-Ghazi rock samples plot on the granite and granodiorite fields on the geochemical classification diagrams. The geochemistry of these plutonic rocks show peralunimous, high K-calc alkaline features. On the Harker variation diagrams, it can be observed that the Al2O3, FeO, MgO, TiO2 and CaO contents decrease with the increase in SiO2, whereas K2O and Na2O show an ascending trend with increasing SiO2. Moreover, the fractionation of plagioclase and the crystallization of alkali-feldspar caused the observed trends of Rb and Sr in the Harker diagrams. Ba contents decrease with increasing SiO2 which is relevant to the biotite fractionation. All of the analyzed samples show similar patterns in the chondrite-normalized trace elements and the REE diagrams. All samples show LILE and LREE enrichment and HFSE and HREE depletion. The negative anomaly of Sr may be related to the lack of calcic-plagioclase in these samples or suggest the plagioclase rich restite during partial melting of the parental rock. The latter is in agreement with the Eu anomaly that appeared in the REE diagram. All of the Kolah-Ghazi samples show linear trends in the major and trace elements versus SiO2 diagrams and display similar REE patterns suggesting close relationship in the source and magmatic history.
The field, petrography and geochemical evidences such as pegmatit veins in the pluton, biotite rich enclaves, lack of hornblende and titanite, occurrence of metamorphic minerals (e.g., garnet, andalusite and sillimanite), the predominance of ilmenite, A/CNK values (A/CNK >1), and crondom contents (more than 3% in norm) suggest that the Kolah-Ghazi plutonic assemblage can be classified as S-type granitoids. Moreover, all of the Kolah-Ghazi samples plot on the S-type field of the granite classification diagrams (Whalen et al., 1987; Chappell and White, 1992) which is in good agreement with mineralogical evidences.
The sedimentary source, mostly shale and greywacke, can be suggested for Kolah-Ghazi melts according to the Rb/Sr vs. Rb/Ba diagram (Sylvester, 1998). Several discrimination diagrams such as Rb vs. Ta+Yb (Pearce et al., 1984) and R1-R2 (Batchelor and Bowden, 1985) were used to determine the tectonic setting of the Kolah-Ghazi granitoids. The Kolah-Ghazi samples lied between the fields of magmatic arc and syn-collisional granitoids in the discrimination diagrams.
The geochemistry of the studied samples suggest a syntectonic environment for the Kolah-Ghazi granitoids which may be related to the late Cimmerian orogenic phase.

References
Batchelor, R.A. and Bowden, P., 1985. Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chemical Geology, 48(1): 43–55.
Chappell, B.W. and White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt. Transactions of the Royal Society of Edinburgh, Earth Sciences, 83: 1–2.
Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks. Journal of Petrology, 25(4): 956–983.
Sylvester, P.J., 1998. Post-collisional strongly peraluminous granites. Lithos, 45(1-4): 29–44.
Whalen, J.B., Currie, K.L. and Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95(4): 407–419.

Keywords

• calc-alkaline
• S-type granite
• Jurassic
• Kolah-Ghazi
• Sanandaj-Sirjan

20.1001.1.20087306.1397.10.1.6.9

---

References

Batchelor, R.A. and Bowden, P., 1985. Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chemical Geology, 48(1): 43–55.

Chappell, B.W. and White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold Belt. Transactions of the Royal Society of Edinburgh, Earth Sciences, 83: 1–2.

Collins, W.J. and Richards, S.W., 2008. Geodynamic significance of S-type granites in circum-Pacific orogens. Geology, 36(7): 559–562.

Darvishzadeh, A., 1991. Geology of Iran. Neda publication, Tehran, 901 pp.

Kretz, R., 1983. Symbols for rock forming minerals. American Mineralogist, 68(1–2): 277–279

Kuster, D. and Harms, U., 1998. Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review. Lithos, 45(1–4): 177–195.

Middlemost, E.A.K., 1985. Magma and magmatic rocks: An Introduction to igneous petrology. Longmans, London, 266 pp.

Nabavi, M.H., 1976. Introduction to geology of Iran. Geological survey of Iran publication, Tehran, 135 pp.

Nakamura, N., 1974. Determination of REE, Ba, Mg, Na and K in carbonaceous and ordinary chondrithes. Geochemica Cosmochimica Acta, 38(5): 757–775.

Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks. Journal of Petrology, 25(4): 956–983.

Peccerillo, A. and Taylor, S.R., 1976. Geochcmistry of Eocene calc-alkaline volcanic rocks from the Kasta monon area, Northern Turkey. Contribution to Mineralogy and Petrology, 58: 63–81.

Rollinson, H.R., 1993. Using geochemical data: evaluation, presentation, interpretation. Longman Scientific and Technical, New York, 352 pp.

Saunders, A.D., Tarney, J. and Weaver S.D., 1980. Transverse geochemical variations across the Antarctic Peninsula: implications for the genesis of calc-alkaline magmas. Earth and Planetary Science Letters, 46(4): 344–360.

Shand, S.J., 1951. The study of rocks. Cambridge university press, London, 236 pp.

Streckeisen, A., 1976. To each plutonic rocks its proper name. Earth-Science Review, 12(1): 1–33.

Sun, S.S. and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: A.D. Saunders and M.J. Norry (Editors), magmatism in ocean basins. Geological Society of London, London, Special Publication, 42: pp 313–345.

Sylvester, P.J., 1998. Post-collisional strongly peraluminous granites. Lithos, 45(1-4): 29–44.

Tabatabaei-Manesh, S.M., 1994. Investigation of geology and petrology of Kolah-Ghazi intrusion (south, southeast of Esfahan), M.Sc. thesis, university of Esfahan, Esfahan, Iran, 175 pp.

Tillman, J.E., Poosti, A., Rossello, S. and Eckert, A., 1981. Structural evolution of Sanandaj-Sirjan ranges near Esfahan, Iran. American Association of Petroleum Geologists Bulletin, 65(4): 674–68.

Whalen, J.B., Currie, K.L. and Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95(4): 407–419.

Zahedi, M., 1994. Geological map of Shahrkord (Scale: 1/250000). Geological survey of Iran. (1 sheet)