Earliest Paleoproterozoic arc magmatism in the western Yangtze Block, South China and its geological implications

Abstract

The Archean – Early Paleoproterozoic tectono-magmatic history of the Yangtze Block is inadequately constrained owing to the scarcity of coeval magmatic outcrops. Herein, we report on the Earliest Paleoproterozoic (2498 ± 17 Ma) meta-diabase dike in the Bajiaojing area of the western Yangtze Block, which may represent the oldest known mafic magmatism in the block. Whole-rock geochemical and mineral chemical proxies (e.g., U/Nb, Sc/Yb, and La/Yb) demonstrated that the Bajiaojing meta-diabase was likely emplaced in a continental arc setting. Positive zircon εHf(t) values (> 8) and incompatible elemental ratios (e.g., Gd/Yb, Sm/Yb, and Lu/Hf) further indicated that the mafic dike was derived from a depleted asthenospheric mantle source, which was modified by fluid and sediment from the subducting slab. The subduction-related modification also accounted for the compositional heterogeneity in the mantle source, which was observed in the wide range of Zr/Nb (1.05–4.38), Ce/Pb (6.11–81.59), and Nb/U (7.96–78.72) values. By combining the Precambrian evolutionary history of the Yangtze Block, we determined that an essential magmatic episode occurred in the Earliest Paleoproterozoic that was likely linked to crustal growth in the block. Therefore, the 2.5 Ga magmatism represented by the Bajiaojing meta-diabase was a potential provenance for the synchronous detrital zircons from Precambrian basement rocks.