Zircon U-Pb age, geochemistry and Hf isotope of the granitoids from Huayang pluton in South Qinling orogen: Constraints on the genesis of Wulong plutons

Huyang pluton is located at the center of the South Qinling orogenic belt in Central China and belongs to Wulong plutons.The granitoid is of weak peraluminous and high-K calc-alkaline nature with A/CNK being 1.01~1.14, Na2O 3.15%~3.83%, K2O3.04%~5.70%, K2O/Na2O 0.84~1.80, and Mg#0.24~0.48. The rocks are enriched in LREE and depleted in HREE with negative Eu anomalies. LA-ICP-MS dating yielded zircon U-Pb ages of 214Ma±2Ma and 228Ma±2Ma, with the zircons separated from medium-grained and fine-grained monogranite respectively; the eHf(t) values are-6.17~2.27,-3.19 on average. The two-stage Hf-isotope model ages(TDM2) range from 1116Ma to 1366Ma, 1464Ma on average. In combination with regional geology and previous research achievements, the authors hold that Huyang pluton was formed by partial melting of the lower crust of Neo- or Meso-Proterozoic epoch, with the addition of a certain proportion of mantle-derived materials. It is also considered that the pluton was formed during the continental collision between North China and South China plates, followed by tectonic transition from compression to extension; in this period, the tectonic setting was converted from syn-collision to post-collision or was at the beginning of the extension of the post-collision period.