U-Pb ages and Lu-Hf isotopes of detrital zircons from the southern Qinling Orogen: Implications for Precambrian to Phanerozoic tectonics in central China

Abstract

The Qinling Orogen, central China, was constructed during the Mesozoic collision between the North China and Yangtze continental plates. The orogen includes four tectonic units, from north to south, the Huaxiong Block (reactivated southern margin of the North China Craton), North Qinling Accretion Belt, South Qinling Fold Belt (or block) and Songpan Fold Belt, evolved from the northernmost Paleo-Tethys Ocean separating the Gondwana and Laurentia supercontinents. Here we employ detrital zircons from the Early Cretaceous alluvial sediments within the Qinling Orogen to trace the tectonic evolution of the orogen. The U-Pb ages of the detrital zircon grains from the Early Cretaceous Donghe Group sediments in the South Qinling Fold Belt cluster around 2600-2300 Ma, 2050-1800 Ma, 1200-700 Ma, 650-400 Ma and 350-200 Ma, corresponding to the global Kenorland, Columbia, Rodinia, Gondwana and Pangaea supercontinent events, respectively. The distributions of ages and εHf(t) values of zircon grains show that the Donghe Group sediments have a complex source comprising components mainly recycled from the North Qinling Accretion Belt and the North China Craton, suggesting that the South Qinling Fold Belt was a part of the united Qinling-North China continental plate, rather than an isolated microcontinent, during the Devonian-Triassic. The youngest age peak of 350-200 Ma reflects the magmatic event related to subduction and termination of the Mian-Lue oceanic plate, followed by the collision between the Yangtze Craton and the united Qinling-North China continent that came into existence at the Triassic-Jurassic transition. The interval of 208-145 Ma between the sedimentation of the Early Cretaceous Donghe Group and the youngest age of detrital zircons was coeval with the post-subduction collision between the Yangtze and the North China continental plates in Jurassic.