U-Pb zircon geochronology, Sr-Nd isotope geochemistry, and petrogenesis of oxidant granitoids at Keybarkuh, southwest of Khaf

Document Type : Research Article

Authors

• Ehsan Salati ¹
• Mohammad Hassan Karimpour ¹
• Azadeh Malekzadeh Shafaroudi ¹
• Mohammad Reza Haidarian Shahri ¹
• G. Lang Farmer ²
• Charles R. Stern ²

¹ Ferdowsi University of Mashhad, Mashhad

² Colorado

10.22067/econg.v4i2.16497

Abstract

Keybarkuh area is located 70 km southwest of Khaf, Khorasan Razavi province. The study area is situated in northeastern Lut block. The rock units in the area are Paleozoic metamorphic rocks and Cretaceous to Tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. Based on magnetic susceptibility, the intrusive rocks are divided into oxidant and reduced series. In this study, the oxidant intrusions are discussed. These intrusions are mostly high-K to shoshonitic and also meta-aluminous type. Their magma formed in subduction magmatic arc and they belong to I-type granitoid series. Enrichment of Large Ion Lithophile Elements (LILE) such as Rb, Cs, K, Ba, and Th relative to High Field Stength Elements (HFSE) such as Nb, Zr, and Ti supported the idea. Enrichment of Light Rare Earth Elements (LREE) and depletion of Heavy Rare Earth Elements (HREE) are also typical of subduction magmatism. Negative anomalies of Eu/Eu* can be attributed to the presence of residual plagioclase in a mantle source and contamination of magma by reduced continental crust. The amount of Nb > 11 ppm, lower ratio of Zr/Nb < 2, the initial 87Sr/86Sr isotope ratio (> 0.706), initial 143Nd/144Nd (> 0.512) and εNd (< -3.5) indicate that magma contaminated by reduced continental crust. Hornblende biotite granodiorite porphyry dated using U-Pb zircon geochronology at 43.44 Ma (Middle Eocene). Based on calculated TDM, magma derived from ancient slab with 820 Ma age in the Keybarkuh area, was affected by the highest continental crust contamination during its ascent.

Keywords

• Keybarkuh
• subduction
• oxidant series intrusions
• radiogenic isotope
• zircon geochronology

20.1001.1.20087306.1391.4.2.7.0

---

References

[1] آقانباتی ع.، "زمین شناسی ایران"، سازمان زمین شناسی و اکتشافات معدنی کشور، (1383)، ٦٠٦ ص.

[2] Tirrul R., Bell I. R., Griffis R. J., Camp V. E., "The Sistan suture zone of eastern iran", Geolc. Soc. Am. Bull 94 (1983) 134-156.

[3] Camp V., and Griffis R., "Character, genesis and tectonic setting of igneous rocks in the Sistan suture zone, eastern Iran", Lithous, Issn 0024-4937, v. 15 (1982) 221-239.

[4] Tarkian M., Lotfi M., Baumann A., "Tectonic, magmatism and the formation of mineral deposits in central Lut, East of Iran", Geol. Survey of Iran, Rep. No. 57 (1983) 357-383.

[5] Jung D., Keller J., Khorasani R., Marcks Chr., Baumann A., Horn P., "Petrology of the Tertiary magmatic activity the northern Lut area, East of Iran", Ministry of mines and metals, GSI, geodynamic project (geotraverse) in Iran, No. 51 (1983) 285-336.

[6] Ishihara S., "The magnetite-series and ilmenite-series granitic Rocks", Mining Geology 27 (1977) 293-305.

[7] Ishihara S., "The granitoid series and mineralization", Economic Geology, 75th Anniv (1981) 458- 484.

[8] بلوریان غ.، صفری م.، "نقشه زمین شناسی 1:100000 زوزن"، سازمان زمین شناسی و اکتشافات معدنی کشور (1384).

[9] Middlemost Eric A. K., "Naming materials in the magma/igneous rock system", Earth Sci Rev 37 (1994) 215-224.

[10] Peccerillo A., Taylor S. R., "Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey", Contributions to Mineralogy and Petrology 58 (1976) 63–81.

[11] Shand S. J, "Eruptive rocks.Their genesis, composition, classification and their relation to ore-deposits", 1969 (facs. of 3rd ed. 1947). Hafner, New York (1947) 488.

[12] Pearce J. A., Haris N. B. W., Tindle A. G., "Trace element discrimination diagrams for the tectonic interpretation of granitic rocks", Jour. Of Petrology, 25, part 4 (1984) 956- 983.

[13] Taylor S. R., McLenan S. M., "The continental crust, its composition and evolution, an examination of the geochemical record preserved in sedimentary rocks", Blackwell, Oxford (1985) 312.

[14] Boynton W. V., "Cosmo chemistry of the rare earth elements: Meteorite studies, In Rare Earth Element Geochemistry (P. Henderson, ed.), (Developments in Geochemistry 2)", Elsevier, Amsterdam (1985) 115-1522.

[15] Wilson M., "Igneous petrogenesis", Uniwin Hyman, London (1989).

[16] Martin H., "Adakitic magmas: modern analogues of Archaean granitoids", Lithos 46 (1999) 411-429. PII: S0024-4937(98)00076-0.

[17] Gust D. A., Arculus R. A., Kersting A. B., "Aspects of magma sources and processes in the Honshu arc", The Canadian Mineralogist 35 (1977) 347-365.

[18] Sun S-s., and McDonough W. F., "Chemical and isotopic systematic of oceanic basalts: implication for mantle compositions and processes", In: A.D. Saunders and M.J. Norry (eds). Magmatic in the ocean basins. Geological Society. London. Special Publication 42 (1989) 313- 345.

[19] Williams I. S., "Response of detrital zircon and monazite, and their U-Pb isotopic systems, to regional metamorphism and host-rock partial melting, Cooma Complex, southeastern Australia", Australian Journal of Earth Sciences, 48 (2001) 557-580. DOI: 10.1046/j.1440-0952.2001.00883.x

[20] Rubatto D., Williams I. S., and Buick I. S., "Zircon and monazite response to prograde metamorphism in the Reynolds Range Central Australia", Contributions to Mineralogy and Petrology, 140 (2001) 458-468.

[21] Rubatto D., "Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism", Chemical Geology, 184 (2002) 123-138. PII: S0009-2541(01)00355-2.

[22] Cherniak D. J., Watson E. B., "Pb diffusion in zircon", Chemical Geology, 172 (2000) 5-24. DOI:10.1016/S0009-2541(00)00233-3.

[23] Depaolo D. J., "Neodymium isotopes in the Colorado front range and crust-mantle evolution in the Proterozoic", Nature 291 (1981) 193-196.

[24] Depaolo D. J., "Neodymium Isotope Geochemistry: An Introduction", Springer, New York, (1988).

[25] کریم پور م. ح.، ملکزاده آ.، ج لنگ فارمر .، چالرز استرن.، "پتروژنز گرانیتوئیدها، سن سنجی زیرکن به روش U-Pb، ژئوشیمی ایزوتوپ های Sr-Nd و رخداد مهم کانی سازی ترشیاری در بلوک لوت، شرق ایران"، مجله زمین شناسی اقتصادی، جلد4، شماره1، دانشگاه فردوسی مشهد، (1391) ص 1- 27.

[26] Zindler A., Hart S. R., "Chemical geodynamics", Ann Rev Earth Planet Sci 14 (1986) 493- 571.