The Tongbai area of the eastern Qinling belt in China includes granulite-grade metamorphic assemblages (Qinling Complex) which were previously regarded as Arcbean to early Proterozoic in age and belonging to the southern margin of the North China plate (craton). Our petrological and geochemical data characterize these rocks as two-pyroxene granulites and garnet granulites which formed at temperatures of 757ø-840øC and pressures of about 9.5 kbar and are now found as xenoliths in granodioritic gneisses. The protoliths of these rocks were granodiorites and tholeiitic basalt or gabbro. The 207pb/206pb ratios derived from evaporation of single zircons yield ages of 470-+20 and 470-•-_14 Ma, respectively, for the basic granulites which we interpret to reflect the time of protolith emplacement. These are intruded by a 435+ 14 Ma granodioritic gneiss post-dating granulite formation. A metaquartzite sample contains detrital zircons as old as 2555_+8 Ma. Two samples of granitoid gneiss from the Tongbai Complex S of the Qinling granulites have single-zircon 207pb/206pb evaporation ages of 776_+8 and 746_+10 Ma, respectively, and document late Proterozoic igneous activity. We suggest that the Qinling granulites document an important and hitherto unknown phase of early Silurian crustal thickening following subduction and continental collision and that both the Qinling and Tongbai Complexes were part of the southern margin of the North China craton prior to this event and record late Proterozoic igneous activity. INTRODUCTION AND REGIONAL GEOLOGY OF THE TONGBAI AREA The Tongbai area is part of the Qinling-Dabie mountains in China and is situated in the border region of Henan and Hubei provinces, bounded in the NE and NW by the Hehuai plain and the Nanyang basin, respectively, and to the south and SE by the Suixian mountainous area of Hubei province. Geologically, it is a constituent pan of the Qinling-Dabie orogenic belt (Figure 1) . This belt occurs as a narrow WNW striking zone of strongly folded rocks between the North China and Yangtze blocks and is characterized by a complex composition and intense polyphase deformation and metamorphism. This is due to a long evolutionary history beginning in the lateProterozoic with rifting and graben formation, followed by ocean opening, Devonian and, finally, collision between the North China and Yangtze plates in the middle Triassic (Figure 2) [Zhang et al., 1988a; Ren et al., 1991]. The central Qinling belt, including the Tongbai region, can be divided into five principal tectonic units. From north to south (Figure 1) they are as follows. Northern thrust zone: This zone (I in Figure 1) is essentially made up of a southward directed nappe complex composed chiefly of middle to late Proterozoic Kuanping group rocks consisting of greenschist facies metabasalts intercalated with clastic rocks, impure marbles, and quartz mica schists. Z. Q. Zhang et al. [1991] obtained Sm-Nd whole rock isochron ages of 975_+39 Ma and 920-+59 Ma, respectively, for "greenschists" (presumably, altered basalt...