Intra-continental back-arc basin inversion and Late Carboniferous magmatism in Eastern Tianshan, NW China: Constraints from the Shaquanzi magmatic suite

• Published in: Di xue qian yuan. 2017-11, Vol.8 (6), p.1447-1467
• Main Authors: Jiang, Hongjun, Han, Jinsheng, Chen, Huayong, Zheng, Yi, Lu, Wanjian, Deng, Gang, Tan, Zhixiong
• Format: Article
• Language: English
• Subjects: Andesite; back-arc; Basalt; basin; Yamansu; Basins; belt; Eastern; Crystallization; Depletion; Diorite; Eastern Tianshan Mountains; Field strength; Fractional crystallization; Geochemistry; Geochronology; igneous; Intra-continental back-arc basin; Lithosphere; Magma; Mantle; Mountains; Orogeny; Plate tectonics; Radiometric dating; Rare earth elements; Rhyolite; Rocks; rocks; Geochronology; Geochemistry; Intra-continental; Shaquanzi; Shaquanzi igneous rocks; Subduction (geology); Tianshan; Tuff; Yamansu belt; Zircon
• ISSN: 1674-9871; 2588-9192
• DOI: 10.1016/j.gsf.2017.01.008

The Yamansu belt, an important tectonic component of Eastern Tianshan Mountains, of the Central Asian Orogenic Belt, NW China hosts many Fee(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 e305 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 t3.1 to t5.6 for basalt; t2.1 to t4.7 for andesite; _0.2 to t1.5 for rhyolite and the εHf(t) ranges from _0.1 to t13.0 for andesites; t5.8 to t10.7 for andesitic tuffs. We suggest that the Shaquanzi Formation basalt might have originated from a depleted, metasomatized lithospheric mantle source mixed with minor (3e5%) 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 intracontinental 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.