Late Palaeozoic tectonic evolution of the southern Central Asian Orogenic Belt: Constraints from the Early Permian magmatism in the northern Alxa area. Issue 5 (26th February 2023)

• Record Type: Journal Article
• Authors: Deng, Wenbing; Shao, Zhaogang; Xu, Haijing; Chen, Xuanhua
• Is Part Of: Geological journal. Volume 58:Issue 5(2023)
• Page Start: 1760
• Page End: 1775
• Publication Date: 2023-02-26
• Subjects: Central Asian Orogenic Belt -- Early Permian -- geochemistry -- geochronology -- northern Alxa area -- tectonic evolution; Geology -- Periodicals; 551
• DOI: 10.1002/gj.4692
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : The northern Alxa area is the southernmost part of the central segment of the Central Asian Orogenic Belt and is located in a crucial junction to unravel the geological evolutionary history of the Palaeo‐Asian Ocean. Here, we present an integrated study of whole‐rock geochemistry, zircon U–Pb geochronology and zircon–Hf isotope on Early Permian igneous rocks from the Zhusileng–Hangwula Belt of the northern Alxa area. Three syenogranites, two monzogranites and one granodiorite are identified as peraluminous, (high‐potassium) calc‐alkaline I‐type granites. The zircon dating results show that they were formed during the Early Permian (291–285 Ma). Geochemically, these rocks show enrichments in light rare‐earth elements (LREEs), large‐ion lithophile elements (LILEs) and negative Nb–Ta anomalies, as well as low A/CNK values. Furthermore, the syenogranites have almost positive zircon ε Hf ( t ) values (−0.4 to +4.8) and Early Palaeoproterozoic–Mesoproterozoic Hf model ages (1, 768–1, 296 Ma), indicating that they were probably derived from juvenile crustal components, mixed with ancient continental crust. The monzogranites have markedly positive zircon ε Hf ( t ) values (+11.2 to +13.5) and Neoproterozoic–Cambrian Hf model ages (716–513 Ma), suggesting that they were generated by rapid reworking of newly formed juvenile material. The granodiorite shows positive zircon ε Hf ( t ) values (+4.0 to +7.0) and Mesoproterozoic Hf model ages (1, 368–1, 090 Ma), implying that the granodiorite was probably derived from the partial melting of the juvenile crust. Our geochronological, geochemical and isotopic data, combined with published data, unravel that a crustal thinning event that was simultaneous with more input of mantle materials in the northern Alxa area, implies that a subduction‐related extensional environment occurred in the Zhusileng–Hangwula Belt which is probably due to the slab rollback of the Paleo‐Asian Ocean during the Late Carboniferous–Early Permian. Abstract : The new geochronological, geochemical and isotopic data of the Early Permian granitoids imply that a subduction‐related extensional environment occurred in the Zhusileng–Hangwula Belt of northern Alxa area which is probably due to the slab rollback of the Palaeo‐Asian Ocean during the Late Carboniferous–Early Permian.