Zircon SHRIMP dating and geochemical characteristics of Taohuashan granites in Huarong County, northern Hunan

Abstract： The Taohuashan granitic pluton in northern Hunan which intruded into Middle Proterozoic Lengjiaxi Formation is composed of early fine-grained sparsely-porphyritic hornblende biotite granodiorite， fine- and medium-grained porphyritic biotite monzonitic granite, medium- and fine-grained sparsely-porphyritic two-mica monzonitic granite and late fine-grained biotite-two-mica monzonitic granite. Zircon SHRIMP dating of the granites yields an age of (140.3±3.8) Ma, belonging to Late Jurassic. The granites belong to the peraluminous High-K calc-alkaline series with SiO2 being 71.10%～73.00% and K2O/Na2O 1.09～1.66. The rocks are enriched in large-ion lithophile elements and depleted in high field-strength elements, with the data Rb/Sr=0.23～1.95, ∑REE=175.1～259.9, δEu=0.55～0.82, （La/Yb）N=13.52～43.71, εNd=-8.1～-10.1）, T2DM=1.59～1.75 Ga. Studies show that the Taohuashan granites belong to muscovite-bearing peraluminous granitoids whose materials were derived from Precambrian basement. The rocks were formed with the weakening of the stress in late collision period, suggesting that northern Hunan has entered into an extensional period since 140Ma BP.