In situ U-Pb geochronology of Hadean zircon xenocryst(4.1~3.9Ga) from the western of the Northern Qinling Orogenic Belt
北秦岭西段冥古宙锆石(4.1~3.9Ga)年代学新进展

One zircon xenocryst with a concordant 207Pb/206Pb age of 4079±5Ma was reported by Wang et al. (2007) from volcanic rocks in the western of the Northern Qinling Orogenic Belt. In recent study on those old xenocrysts, about 3,000 zircon grains are separated from the same rock outcrop and have been analyzed by LA-ICPMS. Two metamorphic zircon xenocrystic cores gave concordant 207Pb/206Pb ages of 4008±29Ma and 3908±45Ma, respectively. The occurrence of 4.0Ga metamorphic zircon provided evidence that the metamorphism occurred as old as 4008Ma. The lithologic characteristics of the host rocks contain Hadean zircons are clearly defined as pyroclastic lava, not volcanic lava, as previously believed.