ABSTRACT
The Qinling orogen represents the convergence zone between North China and Yangtze cratons. The North and South Qinling, which are separated by the Danfeng-Shangnan megasuture, have been considered to be the active continental margin of North China block and the passive margin of Yangtze blocic respectively, during the Neoproterozoic and Early Palaeozoic time. Nd model ages of crust-derived rocks indicate that the crust of both the northern and southern Qinling belts were formed during the Proterozoic (2.2–0.8Ga), with the Neoarchaean basement existing only in the South Qinling. The ε Nd (t) vs. age plot for mantle-derived rocks reveals that the upper mantle beneath North Qinling was in a stable and strongly depleted state (ε Nd= +7.3 - +6.3) during the entire Proterozoic, whereas the upper mantle beneath South Qinling had developed nearly parallel to the evolutionary line of the depleted mantle from the Palaeo- to Mesoproterozoic. The South Qinling is similar to the Yangtze block in their lithospheric history and property. North Qinling with its own distinctive evolutionary trends of crust and mantle was most likely a separate microcontinent. The identification of crust/mantle recycling in the ancient convergence zone reveals the subduction of oceanic crust and the lateral crustal accretion in North Qinling during Early Neoproterozoic. The vertical crustal accretion accompanied by mafic magma underplating at about 1000 Ma ago in South Qinling was evidenced by the alkaline bimodel nature of the Yaolinghe and Yunxi volcanic rock series, and the source rock of the Indosinian granites.
