SHRIMP zircon U-Pb dating, geochemistry and genesis of early cretaceous basic dykes from the Dabie orogen

This paper aims to constrain the starting time of Early Cretaceous large-scale extensional and mantle properties in Dabie orogen. The SHRIMP zircon U-Pb dating results reveal the Yinshafan gabbro dyke from Jinzhai, North Huaiyang region is 125.8±2.7 Ma, the Dongxinxiang lamprophyre dyke from Dawu, West Dabie is 129.6±2.5 Ma. The Early Cretaceous basic dykes from different regions of the Dabie Orogen show similar geochemical features: These samples have SiO2 ranging from 46.13% to 54.42%, Mg# between 42 and 72, mainly belonging to alkaline series, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), evident depletion in high field strength elements (HFSE, e.g., Nb, Zr and Ti), ISr=0.705 5-0.7094 and highly negative εNd(t) values of about -12.04 to -18.84, TDM=1.60-2.62 Ga. Early Cretaceous crustal extension and large-scale magma eruption in the Dabie orogenic belt began in 130 Ma, and belonged to part of eastern China Late Mesozoic lithospheric thinning extension event. The basic dykes were derived from enriched lithospheric mantle, which originated from North China Craton (NCC) lithospheric mantle contaminated by the deeply subducted Yangtze crust, and maybe have been added in some mantle asthenosphere.