安徽狮子山矿田南洪冲岩体形成时代及成因机制研究

Nanhongchong pluton in Shizishan ore-field, Anhui province, is spatially close to those Yanshanian plutons that have metallogenic relations with important copper-iron-gold-sulfur deposits. Zircon U-Pb LA-ICPMS dating yields an age of 141.2 ± 1.6Ma, which meets the ages of other plutons in the ore-field and suggests the magmatism event occurred between late Jurassic and early cretaceous. Nanhongchong pluton was metaluminous calc-alkaline granodiorite characterized by high alkali (Na₂O > K₂O). Rb, Ba, Sr, Th and U were enriched, while Nb, Ta and Ti were depleted. REE showed strong LREE enrichment with (La/Yb)_N ratios of 21.07∼24.28 and the absence of Eu anomaly with δEu values of 0.92∼1.03. Isotope geochemical study revealed initial ⁸⁷Sr/⁸⁶Sr ratios were 0.70792∼0.70793 while ε_Nd(t) values were -9.5 ∼ -9.1, and Nd model ages (1.67 ∼ 1.71 Ga) were Mesoproterozoic. The characteristics above in accord with former relevant data indicate that the mixed magma derived from enriched mantle, intruded and fractionated in a crustal extension-thinning tectonic environment while assimilated a proportion of the crust. Particularly, the magma in Shizishan ore-field was rather evolved when Nanhongchong pluton formed and fractional crystallization was the dominant process then, which suggested moderately diverse magmatism.