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

زمین شناسی اقتصادی

Article 5, Volume 4, Issue 2 - Serial Number 7, December 2012, Pages 285-301   

Document Type: Research Article

DOI: 10.22067/econg.v4i2.16497

Authors

Ehsan Salati^{* 1}; Mohammad Hassan Karimpour¹; Azadeh Malekzadeh Shafaroudi¹; Mohammad Reza Haidarian Shahri¹; G. Lang Farmer²; Charles R. Stern²

¹Ferdowsi University of Mashhad, Mashhad

²Colorado

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

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