Origin and tectonic implications of Kangding intrusive complexes in Sichuan Province: Evidence from zircon Hf isotope

Kangding metamorphosed intrusions in Kangding, Mianning and Panzhihua areas of Sichuan Province and Yuanmou area of Yunnan Province were formed in the island arc setting, as shown by the integrated study of petrogenesis and Hf isotopic geochemistry of plutonic rocks ranging from acid to basic ones. Zircons from the mafic plutons have ε_Hf(t) values ranging from -4.2 to +11.0, with their Hf model ages ranging from 742 to 2386 Ma. The felsic plutons have ε_Hf(t) values ranging from -4.9 to +9.4, with their Hf model ages ranging from 967 to 2707 Ma. Magmatic zircons from the Kangding intrusive complexes show similar Hf isotope compositions to those from coeval felsic intrusions on the west margin of the Yangtze Craton, implying their similar magmatic origins. The Kangding intrusive complexes were formed in an oceanic subduction setting, the mafic plutons were derived from depleted mantle sources, whereas the felsic plutons were formed by melting of ancient crustal materials and juvenility crustal materials. According to the Nd isotopic data of the whole rock and the Hf isotopic data of the corresponding zircons in this area, the Hf-Nd decoupling must have resulted from the "zircon effect" and crustal material interaction. Petrology, stratigraphic correlations, tectonic analysis and geochemical evidence suggest that the Yangtze block of South China was located along the margin of the Neoproterozic supercontinent Gondwana rather than at the connection between Australia and Laurentia old land in North America.