U-Pb zircon ages of granites from the southern margin of the Yangtze Block: timing of Neoproterozoic Jinning: Orogeny in SE China and implications for Rodinia Assembly

Neoproterozoic Jinningian Bendong granodiorite and Sanfang and Yuanbaoshan Granites occurred in northern Guangxi, southern margin of the Yangtze Block, SE China and were generally considered to be of orogenic origin, that is the collision between the Yangtze and Huanan Blocks during the Jinning Orogeny. These granites were intruded into the Mesoproterozoic Sibao metamorphic basement, and covered unconformably by the Neoproterozoic Danzhou metasediments. They are dominantly peraluminous (ASI = 1.18-1.29) and have low initial epsilon Nd values of -4.8 to -7.6 indicating derivation from a supracrustal source. With strong enrichment in Rb, K and Th and relatively low Zr, Hf and higher rare earth elements, they are similar to post-collision granites. Zircon U-Pb ages of 819+/-9, 826+/-10 and 824+/-4 Ma were obtained for the Bendong granodiorite and the Sanfang and Yuanbaoshan Granites, respectively, by both SHRIMP and conventional dating methods. The age result precludes the existence of any late Mesoproterozoic (Grenville-age) granitic magmatism in the southern margin of Yangtze Block. Together with previous age determinations of ophiolites along the southern margin of the Yangtze Block, the Jinning Orogeny is referred to the Neoproterozoic orogeny which took place between 1.0 and 0.80 Ga, and likely ended at 0.82 Ga. The granite formation age of similar to 0.82 Ga also supports the basal boundary age of 0.80 Ga for the post-orogenic Sinian System, which is probably stratigraphically correlated with the Adeladean System in South Australia. As the link between Australia-East Antarctica and Laurentia in the configuration of the supercontinent Rodinia, the collision between the Yangtze and Huanan Blocks during the Neoproterozoic Jinning Orogeny probably marks the termination of the Rodinia assembly. (C) 1999 Elsevier Science B.V. All rights reserved.