Characteristics of Rare Earth Elements of Zircons from Mesozoic Volcanic Rocks in Luanping Region, Hebei

Zircon,whichisrichinU,Thanddeficientincommonlead,andhashighstabilityandthehighest envelopedtemperatureofisotopicsystem[1,2],isan idealisotopicdatingobjectinmagmaticrocks.Inthe recentyears,theLA ICP MSmethod,asanewtest ingmethodwhichhassprangupsincetheendo…

Characteristics of Rare Earth Elements of Zircons from Mesozoic Volcanic Rocks in Luanping Region, Hebei

Rare earth elements of the zircons from the Mesozoic volcanic rocks in Luanping region, Hebei, were analyzed the results reflect that the average values of δEu and (Lu/Gd)N are 0.49 and 21.8 respectively in the zircons from the top part of Tiaojishan Formation;but the average values of δEu and (Lu/Gd)N are 0.15, 0.06, 0.09 and 14.51, 15.66, 16.25 respectively in the zircons from the lower, and upper part of the Tuchengzi Formation and the bottom bed of the Zhangjiakou Formation. The results show that the characteristics of the zircons from the Tuchengzi Formation are coincident with those of the zircons from the Zhangjiakou Formation, but are different from those of the zircons from the Tiaojishan Formation, and imply that the Tuchengzi Formation has close relation with the Zhangjiakou Formation. Combining the results above with the former isotopic dating results of the volcanic rocks, the authors draw the conclusions as follows: The Tuchengzi Formation not only has a long interval period with the Tiaojishan Formation, but also is very different from the Tiaojishan Formation in zircon geochemical characteristics. The Tuchengzi Formation not only is nearly continuous with the Zhangjiakou Formation in time, but also is coincident with the Zhangjiakou Formation in geochemistry of zircons. The results imply that the Tuchengzi Formation and the Zhangjiakou Formation were formed in the same geological background, that is, there are not the boundary of the J3-K1 and the interface of the transition of tectonic framework between the Tuchengzi Formation and the Zhangjiakou Formation in the Luanping region. The research shows that the (Lu/Gd)N, δEu are two important parameters which are relatively stable in the analysis of zircons from Crust-source;but the values of ∑LREE of zircons from Crust-source change greatly, especially the abundance of La element, so some ratios of rare earth elements related with La (or ∑LREE) are not usable in determining the characteristics of zircons.