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 (NDC) in east central China lies between the Sino-Korean plate to the north and the Yangtze plate to the south.  It 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 NDC orthogneisses and granites show arc signatures similar to those of UltraHigh-Pressure (UHP) rocks in the central Dabie, but no mineralogical evidence of UHP metamorphism is present in the samples investigated here.  Field relationships, textures, compositions, and ion microprobe U-Pb zircon protolith crystallization ages reveal three distinct types of gneiss: diorite gneiss xenoliths (770 ± 26 Ma 95% confidence limit), within first generation highly deformed migmatitic grey gneisses (747 ± 14 Ma), cross-cut by second generation Cretaceous weakly foliated felsic gneisses (127 ± 4 Ma).  Unfoliated Cretaceous granites (117 ± 11 Ma, monazite Th-Pb age=117 ± 1 Ma) intrude second generation gneisses.  Cretaceous second generation gneisses and granites yield zircon inheritance ages of ~2 Ga, 700-800 Ma and (rarely) 227-271 Ma, indicating that the NDC is not simply a Cretaceous extensional terrane.  The 700-800 Ma zircon ages are similar to those of granitic gneisses from the central UHP zone (698 ± 47 Ma) and are characteristic of the Yangtze craton. e_Nd values suggest that Cretaceous rocks in the NDC formed by partial melting of basement with very low e_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 NDC is interpreted to be an extension of the Yangtze craton unaffected by UHP metamorphism.  The Sino-Korean/Yangtze suture must lie to the north of the NDC.