Zircon Hf isotopic constraints on the Jurassic-Oligocene magmatic rocks in the Lut-Sistan region, eastern Iran: Implications for the magmatic evolution

SMP41-P10 JpGU-AGU Joint Meeting 2017 Zircon Hf isotopic constraints on the Jurassic-Oligocene magmatic rocks in the Lut-Sistan region, eastern Iran: Implications for the magmatic evolution *Han-Yi Chiu1,2, Sun-Lin Chung1,2, Mohammad Hossein Zarrinkoub3, Hao-Yang Lee1, Kwan-Nang Pang1, Seyyed Saeid Mohammadi3, Mohammad Mahdi Khatib3, Kuo-Lung Wang1 1. Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, 2. Department of Geosciences, National Taiwan University, Taipei, Taiwan, 3. Department of Geology, University of Birjand, Birjand, Iran This study presents new zircon Hf isotopic results for 28 magmatic rocks of Jurassic-Oligocene ages in the Lut-Sistan region to better understand the magmatic evolution of eastern Iran before and after the Lut-Afghan collision. The Middle Jurassic (~168 Ma) granitoids yielded a wide range of zircon εHf(T) values from +8 to -1, revealing the similarity of variable isotopic feature of the coeval magmatic rocks forming along the Sanandaj-Sirjan zone, in agreement with the hypothesis of anti-clockwise rotation of the Lut block. The Early Cretaceous (113-107 Ma) gabbros that belong to the Birjand ophiolite indisputably show depleted mantle-derived zircon Hf isotope compositions of εHf(T) values from +16 to +12 and thus confirm their oceanic crustal origin. Another ~110 Ma diorite without ophiolitic affinity has relatively lower zircon εHf(T) values from +9 to +6, and it also contains abundant inherited zircons that show εHf(T) values between +5 and -2 at ~168 Ma, indicative of the widespread distribution of the Middle Jurassic magmatism in northern part of this region. In the Late Cretaceous, the emplacement of ~86 Ma granitoids also yielded depleted mantle-like zircon Hf isotopes of highly positive zircon εHf(T) values from +17 to +10, and the other granites yielded lower zircon εHf(T) values from +12 to +4 at 74-71 Ma. After the closure of the Sistan ocean during the Late Cretaceous (to Paleocene), the 57-53 Ma granitoids gave zircon εHf(T) values from +12 to +3 in the Early Eocene. Then, the zircon Hf isotopic results of extensive Eocene-Oligocene (46-24 Ma) magmatic rocks show a much variable signature of zircon εHf(T) values between +14 and -2, indicating the heterogeneity of widespread post-collisional magmas during this period. On the whole, the highly radiogenic zircon Hf isotopic features were mostly obtained from dated magmatic rocks in the Lut-Sistan region, similar to our recent observation on the magmatic rocks developed by the Neotethyan evolution in the Urumieh-Dokhtar magmatic arc, which suggest that the depleted-mantle component has played a critical role on the magmatic evolution since at least the Jurassic time. Keywords: Zircon Hf isotopes, Lut-Sistan region, Iran, magmatic evolution ©2017. Japan Geoscience Union. All Right Reserved. - SMP41-P10 -