Geochemical, age, and isotopic constraints on the location of the Sino–Korean/Yangtze Suture and evolution of the Northern Dabie Complex, east central China

The Northern Dabie Complex in east central China lies between the Sino–Korean plate to the north and the Yangtze plate to the south. The Northern Dabie Complex has been variously proposed to represent a Paleozoic magmatic arc on the Sino–Korean plate, an exhumed piece of subducted Yangtze plate crust, or crust produced almost entirely by Cretaceous extension-related magmatism. Trace element compositions of Northern Dabie Complex orthogneisses and granites show arc signatures similar to those of ultra-high-pressure rocks in the central Dabie, but no mineralogical evidence of ultra-high-pressure metamorphism is present in the samples investigated here. Field relationships, textures, major and trace element compositions, and ion microprobe U-Pb zircon protolith crystallization ages reveal three distinct types of gneiss: diorite gneiss xenoliths (770 6 26 Ma, 95% confidence limit), those within first-genation highly deformed migmatitic grey gneisses (747 6 14 Ma), and those cross-cut by secondgeneration Cretaceous weakly foliated felsic gneisses (127 6 4 Ma). Unfoliated Cretaceous granites (117 6 11 Ma, monazite Th-Pb age 5 117 6 1 Ma) intrude secondgeneration gneisses. Cretaceous second†Corresponding author e-mail: john.c.ayers@ vanderbilt.edu. generation gneisses and granites yield zircon inheritance ages of ca. 2 Ga, 700–800 Ma, and (rarely) 227–271 Ma, indicating that the Northern Dabie Complex is not simply a Cretaceous extensional terrane. The 700–800 Ma zircon ages are similar to those of granitic gneisses from the central ultra-highpressure zone (698 6 47 Ma) and are characteristic of the Yangtze craton. «Nd values suggest that Cretaceous rocks in the Northern Dabie Complex formed by partial melting of basement with very low «Nd and not by melting of first-generation or diorite gneisses. Nd-depleted mantle model ages are consistent with the time of formation of the Yangtze craton at 1.4–2.5 Ga. The Northern Dabie Complex is interpreted to be an extension of the Yangtze craton that was unaffected by ultra-high-pressure metamorphism. The Sino–Korean/Yangtze suture must lie to the north of the Northern Dabie Complex.