Genesis of Wuduoshan I-S type granite and the constraints on the Early Paleozoic tectonic evolution of the Northern Qinling: Evidence from zircon U-Pb age, geochemistry and Sr-Nd-Hf isotopes

The Qinling orogenic belt, located at the junction zone of the North China plate and the Yangtze plate, has experienced a complex tectonic evolution process, and the mechanism of plate assembly and the collisional time are controversial.In this paper, the geochronology, geochemistry and Sr-Nd-Hf isotopic composition of the Wuduoshan biotite monzogranite in North Qinling studied to constrain the early Paleozoic tectonic evolution of the North Qinling.Two periods of intrusion were identified in Wudaoshan batholith, which is dating 431 Ma and 417 Ma respectively.The rocks are characterized by high silicon(SiO₂ =71.16%~74.22%), alkali and potassium rich(K₂O + Na₂O =7.16%~8.88%, K₂O / Na₂O =0.69~2.34)and peraluminous(A / CNK =1.01~1.19).The total REE content is generally low, and LREE and HREE are strongly fractionated, showing a right dipping distribution pattern and slight negative Eu anomalies.They are characterized by enrichment in large ion lithophile elements(Rb, Th, U), relative depletion in high field strength elements(Nb, Ta, Zr)and Ba and Sr.They belong to "I-S" type granitoids.The Wuduoshan granite has relatively low(⁸⁷Sr/ ⁸⁶Sr)_i values(0.70581~0.71093), and negative ε_Nd(t)values(-6.48 to-3.18), with the corresponding two-stage Nd model age of 1.42 Ga ~1.69 Ga.Most of zircons have negative ε_Hf(t)values(ε_Hf(t)=-6.9~ -0.1), and t_DM2 =1.50~2.34 Ga.The isotopic characteristics indicate that the Wuduoshan granite is the product of partial melting of Paleoproterozoic-Mesoproterozoic crustal material.Combined with the tectonic evolution of Qinling orogenic belt, we concluded that the formation of Wuduoshan granite was related to the collision between Erlangping island arc and North Qinling micro-continent and belongs to syn-collisional and post-conllisional type granite, and the magma source is the ancient crustal material of North Qinling micro-continent.