Geochemistry and SHRIMP geochronology of alkaline rocks of the Zijinshan massif in the eastern Ordos basin, China
Yang Xingkea, Chao Huixiaa, N.I. Volkovab, Zheng Menglin c , Yao Weihua d
a Key Laboratory of Western China's Mineral Resources and Geological Engineering, Ministry of Education, Chang'an University, 126 Yanta Road, Xi'an, 710054, China
b Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
c Research Institute of Prospecting and Development, SINOPEC, 20 Xueyuan, Beijing, 100083, China
dResearch Institute of Exploration and Development, Changqing Oilfield Company of CNPC, 151 Weiyang Road, Xi'an, 710021, China
Keywords: Ordos basin; magmatic activity; tectonic thermal event; Early Cretaceous; Zijinshan; SHRIMP chronology
Pages: 751-762
Abstract
Characteristics of geology, petrology, and geochemistry of the Zijinshan massif were studied in the eastern part of the Ordos basin. Geochemical analysis shows that the massif is characterized by high alkali, relatively high Fe, and low Mg and Ca contents. The rocks are undersaturated in SiO2, rich in REE (with no Eu anomaly) and belong to the alkaline-peralkaline series. The geologic history of the Zijinshan massif consists of several stages of magmatism. The obtained isotope-geochronological (U-Pb SHRIMP) data show that the magmatic activity climaxed in the interval 150-110 Ma, while the age of 16 zircon grains fitted a narrower interval, 132-125 Ma, i.e., the Early Cretaceous. The younger age corresponds to the middle and late stages of the evolution of the Ordos basin and agrees with a large Early Cretaceous tectonothermal event in North China. This event led to the large-scale uplift of the eastern flank of the Ordos basin, rise of the Lüliang asthenosphere, and to the formation of a large west-sloping monocline. The U-Pb SHRIMP studies have also revealed magmatic zircons of Carboniferous-Permian age, which evidences the multistage character of the thermal process.
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