Petrogenesis of (meta-) basalts from the north Qilian orogenic belt, NW China; implications for the Palaeoproterozoic-Mesoproterozoic tectonic evolution of the north Qilian Block

• Published in: Geological magazine 2021-10, Vol.158 (10), p.1795-1810
• Main Authors: Miao Xiuquan, Miao Xiuquan, Liu Yixin, Liu Yixin, Liu Yiwei, Liu Yiwei, Wang Jinrong, Wang Jinrong, Chen Jianlin, Chen Jianlin
• Format: Article
• Language: English
• Subjects: absolute age; alteration; Asia; assimilation; basalts; Beidahe Group; chemical composition; China; Columbia Supercontinent; crust; Far East; fractional crystallization; genesis; Geochronology; igneous and metamorphic rocks; igneous rocks; Lu/Hf; magmas; magmatism; Mesoproterozoic; metabasalt; metaigneous rocks; metamorphic rocks; metamorphism; metasomatism; North China Platform; Paleoproterozoic; partial melting; Petrology; Precambrian; Proterozoic; protoliths; Qilian Mountains; Rb/Sr; Sm/Nd; Tarim Platform; tectonics; upper Precambrian; volcanic rocks; whole rock; Zhulongguan Group
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756821000340

The North Qilian Orogenic Belt is surrounded by the Tarim Craton to the NW and the North China Craton to the NE. The Precambrian continental crust remnants that are distributed in the North Qilian Orogenic Belt are termed the North Qilian Block (NQB), and their tectonic evolution has profound implications for the evolution of the Columbia Supercontinent. Here we present major- and trace-element and Sr-Nd-Hf isotope data for (meta-) basalts from the Beidahe Group (BDHG) and Zhulongguan Group (ZLGG) in the western North Qilian Orogenic Belt, to investigate the tectonic evolution of the NQB during the Proterozoic Eon. The protoliths of Palaeoproterozoic amphibole gneisses and plagioclase amphibolites from the BDHG are calc-alkaline series basalts. These metabasalts show island-arc-basalt affinities with variable Nd and Hf isotopes (εNd(t) = -5.0-0.6 and 2.7-4.3; εHf(t) = -14.2-2.0 and 6.9-8.8) and were generated by partial melting of the asthenospheric mantle that was metasomatized by aqueous fluid and sediment melt in a continental-arc setting. The early Mesoproterozoic ZLGG basalts show features of shoshonite-series basalts and are geochemically similar to ocean-island basalts. These basalts show variable (87Sr/86Sr)i, εNd(t) and εHf(t) values of 0.70464-0.70699, -1-2.6 and -1.5-5.7, and are products of mantle plume magmatism that participated with subducted oceanic crust in an intracontinental rift setting. This study suggests that the NQB underwent tectonic evolution from palaeo-oceanic subduction to intracontinental rifting during the Palaeoproterozoic-Mesoproterozoic eras. Furthermore, the above tectonomagmatic events were in response to convergence-splitting events of the Columbia Supercontinent during the Palaeoproterozoic-Mesoproterozoic eras.