Origin and dynamic significance of Guangtoushan granitic plutons to the north of Mianlue zone in southern Qinling
南秦岭勉略带北光头山花岗岩体群的成因及其构造意义

The granitoid plutons to the north of Mianlue zone in southern Qinling have a cale-alkaline association with a range from diorites through granodiorites to granites, composed mainly of feldspars, quarts, biotites and minor hornblendes with accessory minerals of zircons, apatites, magnetites and sphenes. They have high K, Sr and Zr/Y ratios, as well as LEE and LILE enrichment and poor HFSE, similar to those of post-collisional high-K talc-alkaline I-type granitoids. Moreover, they are characterized by low Y and Yb abundances, high LaN/YbN and Sr/Y ratios and depleted in Nb and Ta. The marie microgranular enclaves, displaying an evidently different rear earth and trace elements than those of host rocks, are quite developed in plutons. All of those give evidence that they were resulted from mixture of two-end magmas derived from mantle and lower crust, which were possibly trigged by lower crustal delamination. High differentiation pluton is high in Fe^tot/Mg and depleted in Sr,Ba,Ti,P, showing characteristics of post-collisional high-K peraluminous subalkalic granitoids transformed to strong differentiation A-type granites in the final stage. Thus, based on the older ages of granitoid plutons outcropped in the west area and younger ages in the east, the west plutons with large amounts of enclaves represented the start of lower crustal delamination, and the higher differentiation talc-alkaline I-type granitoid plutons in the east area indicate a transition from collisional convergence to extension between south and north continental blocks. Where the formation of strong differentiation Jiangjiaping high-K granitic pluton demonstrate that Qinling Orogenic Belt evolved into extension period after main collision and promise a coming of new intraplate period.