Zircon U-Pb age and Hf isotopic composition of the Xiaozhangjiakou ultramaric pluton in northern Hebei.

采用离子探针(SHRIMPⅡ)测得小张家口基性-超基性岩体中的锆石主要有220±5Ma和491±7Ma两组年龄,以及一个很老的继承锆石年龄2453Ma。年龄为220±5Ma的一组锆石(A组)具有典型的岩浆型振荡环带,这组年龄应代表该岩体的侵位年龄。A组锆石的~(176)H/~(177)Hf比值从0.282557到0.282690,ε_(Hf)(220Ma)=-2.9～+1.66。年龄为491±7Ma的一组锆石(B组)具有变质成因的蝴蝶结构(Butterfly structure)和熔蚀边,属于继承锆石。B组锆石的~(176)Hf/~(177)Hf比值从0.282239到0.282483,ε_(...We obtained two groups of zircon U-Pb ages of 220 5Ma (group A) and 491 7Ma (group B), and a very old age 2453Ma for the Xiaozhangjiakou mafic-ultramafle pluton in northern Hebei province, China. The age of group A zircons (220Ma) is interpreted as the emplacement age of this intrusion based on the typical oscillatory zoning of zircons, indicative of igneous origin. They show Hf-176/Hf-177 ratios ranging from 0.282557 to 0.282690 and epsilon(HF) (220Ma) = -2.9 similar to + 1.66. The group B zircons (similar to 491Ma) are interpreted as inherited zircons as they have typical "butterfly structure" and erosions. They show significantly varied Hf-176/Hf-177 ratios ranging from 0.282239 to 0.282483 and epsilon(Hf) (490Ma) = -8.6 similar to 0.06. The zircon with Pb-207/Pb-206 age of 2453Ma is interpreted as a captured zircon from the Paleoproterzoic basement of the North China Craton. The new Hf isotopic data suggest that the Xiaozhangjiakou mafic-ultramafic pluton originated from partial melting of a mixture between an enriched subcontinental lithospheric mantle and a depleted asthenospheric mantle, responding to an extension of lithosphere at around 220Ma, which induced upwelling and interaction of asthenosphere with the above enriched lithospheric mantle. The group B zircons were probably entrapped in the Xiaozhangjiakou pluton during magma ascent from the enriched mantle source or the lower continental crust.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000246956900005&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)2203583-5902