Intra-continental back-arc basin inversion and Late Carboniferous magmatism in Eastern Tianshan,NW China: Constraints from the Shaquanzi magmatic suite |
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Authors: | Hongjun Jiang Jinsheng Han Huayong Chen Yi Zheng Wanjian Lu Gang Deng Zhixiong Tan |
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Affiliation: | 1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China;3. Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640, China;4. Department of Earth Sciences, Sun Yat-sen University, Guangzhou 510472, China;5. No. 6 Geological Party, Xinjiang Bureau of Geology and Mineral Exploration, Hami 839000, China |
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Abstract: | The Yamansu belt, an important tectonic component of Eastern Tianshan Mountains, of the Central Asian Orogenic Belt, NW China hosts many Fe–(Cu) deposit. In this study, we present new zircon U-Pb geochronology and geochemical data of the volcanic rocks of Shaquanzi Formation and diorite intrusions in the Yamansu belt. The Shaquanzi Formation comprises mainly basalt, andesite/andesitic tuff, rhyolite and sub-volcanic diabase with local diorite intrusions. The volcanic rocks and diorites contain ca. 315–305 Ma and ca. 298 Ma zircons respectively. These rocks show calc-alkaline affinity with enrichment in large-ion lithophile elements (LILEs), light rare-earth elements (LREEs), and depletion in high field strength elements (HFSEs) in primitive mantle normalized multi-element diagrams, which resemble typical back-arc basin rocks. They show depleted mantle signature with εNd(t) ranging from +3.1 to +5.6 for basalt; +2.1 to +4.7 for andesite; ?0.2 to +1.5 for rhyolite and the εHf(t) ranges from ?0.1 to +13.0 for andesites; +5.8 to +10.7 for andesitic tuffs. We suggest that the Shaquanzi Formation basalt might have originated from a depleted, metasomatized lithospheric mantle source mixed with minor (3–5%) subduction-derived materials, whereas the andesite and rhyolite could be fractional crystallization products of the basaltic magma. The Shaquanzi Formation volcanic rocks could have formed in an intra-continental back-arc basin setting, probably via the southward subduction of the Kangguer Ocean beneath the Middle Tianshan Massif. The Yamansu mineralization belt might have undergone a continental arc to back-arc basin transition during the Late Carboniferous and the intra-continental back-arc basin might have closed in the Early Permian, marked by the emplacement of dioritic magma in the Shaquanzi belt. |
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Keywords: | Shaquanzi igneous rocks Geochronology Geochemistry Intra-continental back-arc basin Yamansu belt Eastern Tianshan Mountains |
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