Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: Evidence from detrital zircon U–Pb ages and Hf isotopic composition

Abstract

The North Qinling terrain reveals a different geological history from the North China block to the north and the South Qinling micro-continental block to the south. The timing of events and geochemical features of the North Qinling terrain are essential for understanding the evolution of the Qinling orogenic belt that joins the North and South China blocks. This study presents detrital zircon ages and Hf isotopic compositions from the Guandaokou Group, a cover sequence of the North China block, and from the Kuanping Group, an upper basement sequence of the North Qinling terrain. The youngest detrital zircon U–Pb ages constrain the initiation of sedimentation in the Guandaokou Group to 1.85 Ga and the maximum depositional age of the Kuanping Group to ~ 640 Ma. Zircon U–Pb ages and Hf data testify to a major phase of magmatism in the North Qinling terrain at ~ 1000–900 Ma. The magmatic rocks were largely produced from reworking of early Paleoproterozoic (~ 2.5–2.0 Ga) crust with minor contribution of late Paleoproterozoic (~ 1.7 Ga) juvenile material. This age record differs in time from the two important thermal events of ~ 1.85 Ga and ~ 2.5 Ga, widely manifested in the North China block. The North Qinling terrain can thus be regarded as a separate micro-continent with a pre-Neoproterozoic evolution different from that of the North China block. The final assembly of the North Qinling terrain to the North China block took place after about 640 Ma.