Zircon U-Pb geochronology and geochemistry of post-collisional granitic porphyry from Yuantoushan, Nileke, Xinjiang.

The Yuantoushan biotite granitic porphyry intrusion is located at the southern Nileke. Copper mineralization prevalently occurs within the intrusion, especially in the shattered zone. The granite has typical porphyritic texture, where phenocrysts are composed of alkali feldspar and biotite, and matrix is mainly composed of feldspar, biotite, quartz and minor sulfide. Trace element patterns for the granite are significantly depleted in HSFE, Nb, Ta, P, Ti and enriched in Pb and LILE ( except Sr), indicating products of arc magmatism. Zircon U-Pb age for the granite is 269 +/- 3Ma. According to its geochemical features, we inferred that the granite were derived from a source mainly is composed of the lower continental crust materials with minor mantle substance and the lower continental crust has similar geochemical features with arc magma. In addition, the Yuantoushan granite has high (Sr-87/Sr-86)(i) ratios (0. 706054 to 0. 709228) and Pb contents (5. 05 x 10(-6) similar to 32. 5 x 10(-6)) indicate the occurrence of contamination of continental crust materials during its emplacement. The involvement of fertilized materials from the melting-assimilation-storage homogenization (MASH) zones, which settled in the bottom of lower continental crust, induced the primary magma of the Yuantoushan intrusion enriched in water and metals. The geochemical data of the Yuantoushan granite indicates it was formed at post-collision setting and controlled by a delamination of mantle lithosphere. The delamination could be induced by the collapse of Central Asian Orogenic Belt or by the activity of Tarim mantle plume.