han; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" class=MsoNormal>ZE: 14pt; mso-font-kerning: 0pt" lang=EN-US>///The Baiceng basic-ultrabasic dykes in southwest hemas-microsoft-com:office:smarttags" />Guizhou constitute the largest outcrop of Yanshanian basic-ultrabasic rocks in Youjiang fold belt. Two groups of zircon (group A and B) were obtained in the rocks. Group A zircon grains assume the irregular granular form and incomplete broad bands. The SHRIMP U-Pb analysis of 12 zircon grains gave a weighted mean 206Pb/238U age of (84±1) Ma, which is interpreted as the emplacement age of this intrusion. LA-MC-ICP-MS in-situ Lu-Hf isotopic analysis of the same zircon grains gave 176Hf/177Hf ratios ranging from 0.282561 to 0.282719 and the average εHf (84 Ma) of -3.61, suggesting that their parental magmas were mainly derived from a enriched mantle and partly mixed with the lower continental crust rock. These data indicate that Group B zircon grains are captured ones. It is inferred that the Baiceng basic-ultrabasic pluton originated from a mixed melting between an enriched lithospheric mantle and the continental crust rock formed in 409～450 Ma, responding to an extension of lithosphere at 84 Ma or so. hemas-microsoft-com:office:office" />
