Petrogenesis of the Taiwushan granite pluton in Fujian Province: Constraints from zircon U-Pb ages and Hf isotopes

The Taiwushan granite pluton, with an outcropped area of about 40km(2), is roughly elongated NE-trending as an irregular stock in the coastal region of SE Fujian Province. Lithologically, this pluton consists mainly of medium to fine-grained granites, with minor porphyraceous biotite granites surrounding the north marginal parts. Zircon LA-ICP-MS U-Pb dating yields an age of 96.9 +/- 1.3Ma (MSWD = 1.09, 2 sigma), indicating that this pluton was generated in the initial stage of Late Cretaceous. Chemically, the Taiwushan granites are enriched in silicon, and depleted in calcium, magnesium and iron. They also have moderately alkaline contents and show weakly peraluminous signature with A/NKC values of 1.01 similar to 1.04 and AKI values of 0.73 similar to 0.92, thus can be grouped into subalkaline and weakly peraluminous granitoids. On trace and REE aspects, the granites are enriched in Cs, Rb, U, Th, Pb and LREE, depleted in Ba, Sr, P, Ti, and show high Rb/Sr ratios and moderately to strongly negative europium anomalies (Eu/Eu* = 0.85 similar to 0.04). They also have lower Zr, Nb, Ce, Y concentrations and lower zircon saturation temperatures (726 similar to 809 degrees C) relative to that of the typical A-type granites. Integrated geological and geochemical data suggest that the Taiwushan pluton should be genetically ascribed to highly fractionated I-type granites. Zircon Hf isotopic compositions of the granites are variable, with epsilon(Hf)(t) values ranging from negative to positive ( - 1.44 similar to 2.78). Correspondingly, they show younger two-stage Hf model ages ranging from 0.98Ga to 1.25Ga with a mean value of 1.06Ga, indicating that large amounts of depleted mantle materials had been involved in magma genesis. Based on a synthesis of geology, geochronology, elemental and isotopic geochemistry, we suggest that the Taiwushan granites were most likely generated via a two-stage process including formation of parental magma by mixing of a depleted mantle-derived magma and an induced crustal-melted felsic magma in the deep crust, and then suffered further differentiation during magma ascent.