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You are here: Home » Online First » Volume 13, 2018 - Number 1 » ZIRCON U-Pb AGES, GEOCHEMICAL CHARACTERISTICS, HF ISOTOPE CHARACTERIZATION AND REGIONAL IMPLICATIONS OF THE CHANG7 TUFF IN RUJIGOU AREA, HELAN MOUNTAINS, Carpathian Journal of Earth and Environmental Sciences, February 2018, Vol. 13, No. 1, p. 121 – 134; DOI:10.26471/cjees/2018/013/012


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Yong YANG1, Kaisheng AN2, Jiawei CUI1 & Fei LIU3
1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, China;
2No.5 Oil Production Plant of PetroChina Changqing of Oilfield Company, Xi’an, China;
3No.2 Oil Production Plant of PetroChina Changqing of Oilfield Company, Xi’an, China;
*Corresponding author. E-mail address: 1cuijiawei1@163.com


ZIRCON U-Pb AGES, GEOCHEMICAL CHARACTERISTICS, HF ISOTOPE CHARACTERIZATION AND REGIONAL IMPLICATIONS OF THE CHANG7 TUFF IN RUJIGOU AREA, HELAN MOUNTAINS, Carpathian Journal of Earth and Environmental Sciences, February 2018, Vol. 13, No. 1, p. 121 – 134; DOI:10.26471/cjees/2018/013/012

Full text

Abstract:

A Chang7 tuff interval (CTR) was found in Rujigou area, Helan Mountains. It is located outside of the range of the Chang7 tuffs in Ordos Basin (CTO) as determined by previous researchers. The aim of this paper is to determine the magmatic origin and tectonic setting of the CTR by analyzing the zircon U-Pb ages, geochemical characteristics and Hf isotope characterization. LA-ICP-MS zircon U-Pb data show CTR crystallized in the 231.2 ± 1.4 Ma. The U-Pb dating results are within the age interval of 242~205 Ma for the CTO. The CTR and CTO have similar geochemical characteristics and Hf isotope characterization. Therefore, they are the product of volcanic eruption in the same tectonic setting. Due to the wider coverage, the CTR should correspond to the most intense volcanic eruption in the Qinling orogenic belt. A preliminary analysis of the geochemical composition of the CTR suggests a rhyodacite parental magma from volcanic arc-related setting. The volcanic arc setting was related to the subduction of A'nyemaqen–Mianlue Ocean. Geochemical composition suggests Chang 7 tuffs mainly resulted from a partial melting process of lower crustal rocks at depths of 15-35 km. The two-stage Hf-isotope model ages of CTR range from 1.3 Ga to 1.5 Ga. This indicates that the CTR mainly originated from the Mesoproterozoic growth of the crust in the west Qinling orogenic belt.



Keyword: Zircon U-Pb age, Geochemistry, Hf isotope, Tuff interval, Yanchang Formation, Helan Mountains


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