摘要
The variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process.Based on geochronology,whole-rock and mineral chemistry,this paper reveals two different granites in the Northern Qinling migmatite complex,which reveal obvious differences in source region and melting condition.The older granodiorite(402±0.8 Ma)displays typical Na-rich adakite affinity,i.e.,high Na_(2)O/K_(2)O(2.04 to 2.64)and Sr/Y(96 to 117)ratios,they have relative evolved isotopic compositions(ε_(Nd)(t)=-0.52 to-0.04;zirconε_(Hf)(t)=-0.06 to+7.78).The younger leucogranite(371±2 Ma)displays higher SiO_(2)(72.32 to 73.45 wt%),lower(TFeO+MgO+CaO+TiO_(2))contents(<2 wt%)and depleted Sr-Nd-Hf isotopic compositions(i.e.,ε_(Nd)(t)=+2.6 to+3.0;zirconε_(Hf)(t)=+5.94 to+14.12),as well as high 10000×Ga/Al and TFe O/Mg O ratios,indicating that they represent highly fractionated I-type granites that derived from melting of juvenile crust.The variations in source rocks and melting condition of the two granites indicating a tectonic switch from compression to extension in 400 to 370 Ma,this switch is later than that in the eastern section of the North Qinling,indicating a scissor collision process between the South Qinling and North China Craton(NCC)in Devonian era.
基金
supported by the National Natural Science Foundation of China(Grant Nos.41102037,41421002)
the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.201324)
research grant of State Key Laboratory of Continental Dynamics(Grant No.SKLCD-04)。
