Geochemical and geochronological constraints on the suture location between the North and South China blocks in the Dabie Orogen, Central China

Abstract

The Dabie orogen is a collision zone between the North China block (NCB) and South China block (SCB), and a famous ultrahigh pressure metamorphic belt in the world. Location of the suture between the NCB and SCB in the Dabie orogen is still a controversial issue. We identify that the metabasaltic volcanic rocks from the Dingyuan Formation of the Beihuaiyang zone located in the northernmost Dabie orogen have typical geochemical feature of island arc basalt, e.g. negative Nb, Ti and P anomalies in trace elemental spidergram and high LREE, Ba and Pb abundance. Their Sm-Nd and Rb-Sr whole-rock isochron ages are 446±23Ma and 444±31Ma, respectively. These ages are consistent with the age of the island arc volcanics in the North Qinling belt that was the south active continental margin of the NCB in the Paleozoic. These data, together with the similarity in metamorphic history between the Dingyuan Formation and North Qinling belt, suggest that the Dingyuan formation is a Paleozoic magmatic arc on the south margin of the NCB. The Nd isotopic model ages of the Devonian metasediments from the Foziling flysch formation of the Beihuaiyang zone (TDM = 1.7 to 1.9Ga) are younger than those of the northern Paleozoic sediment cover of the SCB (TDM = 1.9 to 2.1Ga). It suggests that more Phanerozoic volcanic material, which could be derived from the active continental margin of the NCB, was involved into the flysch formation. The Huwan tectonic melange zone located to the south of the Dingyuan Formation was formed in Triassic. The eclogites involved in this melange zone were formed in the Carboniferous (301 ± 13 Ma). Their protoliths could be middle Paleozoic oceanic crust or late Proterozoic to early Paleozoic island arc basalt. All these data together with the recent discovery of the Triassic eclogites in the Northern Dabie Zone place important constraints on the suture location between the NCB and SCB. It should follow the Huwan tectonic melange zone in the west and the boundary between the Northern Dabie zone and the Beihuaiyang zone in the east.