Records of apatite for multiple injections of magmas in adakitic plutons: A case study of Mesozoic plutons in the Shatanjiao region of the Tongling ore cluster, south China

Unraveling the multi-stage magma evolutionary history is essential for enhancing the understanding of the formation of adakitic rocks. In this study, the adakitic affinity, magma source, and magma evolution process of the apatite and zircon from the porphyric granodiorite of the Yaojialing pluton, Shatanjiao region of the Middle-Lower Yangtze River Metallogenic Belt (MLYRB) were studied. Compared with the non-adakitic rocks, apatite grains from the Shatanjiao and Yaojialing plutons have higher Sr/Y, Eu/Eu*, and La/Yb ratios, which display the typical feature of the adakitic rocks. Zircon Lu-Hf isotopes and apatite Sr-Nd analyses suggest that the adakitic rocks in the Yaojialing and Shatanjiao plutons originated from the same magma source and are products of multi-stage magmatism. Additionally, these rocks might have derived from a mixed melt produced by the partial melting of an oceanic slab containing different portions of oceanic basalts, oceanic sediments, and ancient metamorphic rocks of the Yangtze Block. The calculated temperatures for the porphyric granodiorite from the Yaojialing pluton are within the range of 600-700 degrees C, which is the lower estimation of the melt and similar to the granodiorite from the Shatanjiao pluton. The Ce4+/Ce3+ ratios range from 55 to 1042 (average value is 677) and increase from early-to late-stage magma. The increased Ce4+/Ce3+ ratios could be likely caused by the amphibole fractional crystallization, which indicates a high oxygen fugacity of the melt.