Chronology And Genesis Of The Taibai Granitoid Pluton From The North Qinling

The Taibai pluton is located in the north side of Shangdan suture in the North Qinling. Field relationship and zircon U-Pb dating suggest that the pluton consists of the early Silurian Wulixia pluton, the late Triassic Honyahe pluton and the early Cretaceous Xiabanshi pluton. The main lithology of the Wulixia pluton are gneissic porphyritic biotite monzonitic granite and gneissic biotite monzonitic granite, Zircon LA-ICPMS dating for the gneissic biotite monzonitic granite yielded age of 431±2Ma. The Honyahe pluton consists of biotite monzonitic granite and fine-grained biotite granodiorite with Zircon U-Pb ages of 214±2Ma and 212±3Ma, respectivly. The Xiabansi pluton constitutes Coarse-grained biotite granite with zircon U-Pb age of 130±1Ma.The gneissic porphyritic biotite monzonitic granite and gneissic biotite monzonitic granite of the Wulixia pluton are enriched in silicon, alkali and high aluminum content, showing characteristics of high potassium calc-alkaline series and weakly peraluminous I-A transitional type granites; Biotite monzonitic granite of the Honyahe pluton is also high potassium calc-alkaline series and weakly peraluminous I-A transitional granites with enrichment of silicon, alkali and high aluminum content, but Si O2 content of the fine-grained biotite granodiorite is relatively low, enriched in alkali and high aluminum content, showing high potassium calc-alkaline series and metaluminous I-A transitional granites. Coarse-grained biotite granite of the Xiabansi pluton is enriched in silicon, alkali and high aluminum content, suggesting high potassium shoshonite series and weakly peraluminous high differentiation I type granite.The granitic rocks of Taibai pluton show enrichment of LREE relative to HREE with relativeflat HREE pattern, high LREE/HREE [(La/Yb)N=9.05~107.33] ratios and weak Eu anomaly(δEu=0.38~1.21), indicating enriched in large ion lithophile elements(K、Rb、Ba、Sr、Pb) and depleted in high-field strength elements(Nb、Ta、P). On the isotopic composition, The Wulixia pluton whole rock ISr=0.701935, εNd(t)=-4.98, tDM2=1.58 Ga, Zircon Hf isotope εHf(t)=2.93~8.18(average value is 4.83), tDM2=0.90~1.23Ga(average value is 1.11Ga), The Honyahe pluton whole rock ISr=0.702754, εNd(t)=-8.02, tDM2=1.65 Ga, Zircon Hf isotope εHf(t)=-7.10 ~-0.74(average value is-3.52), tDM2=1.29~1.70Ga(average value is 1.47Ga), The Xiabansi pluton whole rock ISr=0.705506, εNd(t)=-6.00, tDM2=1.41 Ga, Zircon Hf isotope εHf(t)=-10.21~-1.11(average value is-5.54), tDM2=1.26~1.84Ga(average value is 1.54Ga). Geochemical and Sr-Nd-Hf isotopic characteristics suggest that the Proterozoic crust(Kuanping group and Qinling group) is the main source of the Wulixia pluton, Honyahe pluton and Xiabansi pluton, meanwhile, there are also some juvenile components, and the juvenile components decreases from early to later(Wulixia pluton→Honyahe pluton→Xiabansi pluton), young components participation decreased slowly. Combined with the regional geology and magmatic evolution, the Wulixia pluton formed in a collision stage, the Honyahe pluton formed in a post-collision and the Xiabansi pluton formed in a intraplate during transformation of compressional to extensional tectonic environment related to the subduction of the Pacific plate to Eurasian plate lithospheric stretching thinning.