This paper presents new geochemical, LA-ICPMS U-Pb zircon dating and LA-MC-ICPMS zircon Hf isotopic results for a biotite plagioclase gneiss from the Taihua Group at the South of Huashan pluton, Shaanxi Province. Geochemical results indicate that the protolith is intermediate-acidic calc-alkaline granitic rock, with low REE content (Sigma REE = 83. 13 x 10(-6)) and high Pb and LILE element contents (e. g. Rb, Ba). The (176)Hf/(177)Hf ratio of zircons from this sample varies from 0. 281258 to 0. 281404 with obviously negative epsilon(Hf)(t) values (-6. 86 similar to -11. 23). The Hf model ages vary from 2. 96 to 3. 24Ga, indicating that the original magma of the protolith derived from Mesoarchean crust. Comparisons show that the biotite plagioclase gneiss of Xiaoqinling area has similar source of Mesoarchean crust with the Taihua Group in Lushan area, but the timing of formation may be different. Structure of zircons, the Th/U ratio and age indicate that the Tailhua Group in the Xiaoqinling area experienced an important thermal event at similar to 1. 91Ga, which has relationship with the global collision event during convergence of Columbia Supercontinent. The Taihua Group of Xiaoqinling area is part of the southern margin of North China craton, but the Taihua Group in different area has distinction in composition, timing of formation and metamorphic age. Therefore, the Taihua Group is the complex and may be at least separated into two units with Neoarchean and Paleoproterozoic ages, respectively.

Publication name	ACTA PETROLOGICA SINICA　Volume:27 　Issue:10 　Pages:3095-3108 　Published:OCT 2011
Author(s)	Shi Yu; Yu JinHai; Xu XiSheng; Tang HongFeng; Qiu JianSheng; Chen LiHui
Corresponding author	SHI Yu  shiyu_61@163.com,jhyu@nju.edu.cn  Nanjing Univ, State Key Lab Mineral Deposits Res, Sch Earth Sci & Engn, Nanjing 210093, Peoples R China
Author(s) from IGCAS	TANG HongFeng

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