The 1126 Ma volcanic event in the Dechang Area, SW Yangtze Block, and its significance

Abstract Traditionally, the strata of Luonie Valley, Dechang County, SW Sichuan, China, are considered to contain a suite felsic volcanic rocks (the Huili Group) that erupted after c. 1050 Ma. However, we report here new age constraints, elemental and Lu–Hf isotope geochemistry for different older basaltic agglomerate lava, tuff lava basalt from same area, which name Formation. New dating results show upper part Formation formed at 1126.1 ± 9.9 Ma, significantly earlier than deposition Group, but comparable in 1142 16 Ma Laowushan central Yunnan Province. Granite intrusion into dated 1050.7 12.7 provides crucial supporting evidence this depositional age. We also maximum sedimentary 1158 underlying arkose, implying stratigraphic conformity with rock suite. The ? Hf ( t ) values mainly positive, indicating derived depleted mantle slightly stained by crustal materials. characteristics P*, Nb* Zr* anomalies support view. distribution patterns trace rare earth elements indicate an extensional setting. Zr/4–Y–2Nb Th–Nb/16–Zr/117 discrimination diagrams provide understanding. Lithofacies analysis shows wrocks both continental marine facies should be littoral–neritic environment. propose is consistent phase extension preceded convergence Yangtze Block form Rodinia.