辽西凌源地区义县组火山岩锆石U—Pb年代学和地球化学特征

对辽西凌源地区义县组的1件流纹岩样品进行锆石U—Pb年代学研究，获得的年龄为（124．4±1．4）Ma，与前人对辽西北票、义县、凌源等地区通过K—Ar、Ar—Ar、U—Pb等定年方法获得的义县组年龄基本一致，时代为早白垩世。7件典型火山岩样品的地球化学研究结果表明，该火山岩的SiO2=65．6％-73．4％，MgO=0．35％～1．23％，Mg^#=16～41，Al2O3=13．40％～16．79％，Na2O=3．54％-4．26％。Sr=（445～774）×10^-6，Yb=（0．51-0．97）×10^-6,V=（7～14）×10^-6,Sr／Y=49-66，LaN／YbN=33-48，高Sr和Sr／Y比值，低Y和Yb，轻重稀土元素分异明显，显示出埃达克岩的地球化学特征，但其Mg^#较低。它们可能是加厚的基性下地壳部分熔融的产物。

U-Pb zircon geochronology and geochemistry of volcanic rocks of the Yixian Formation in the Lingyuan area,western Liaoning,China

Zircon U-Pb dating of a rhyolite sample from the Yixian Formation in the Lingyuan area, western Liaoning, yields an age of 124.4±1.4 Ma, indicating an Early Cretaceous age. The age agrees with the previous results obtained using K-Ar, Ar-Ar and U- Pb methods for the Yixian volcanic rocks in the Beipiao and Lingyuan areas. Geochemical compositions of 7 samples of typical Yixian volcanic rocks from the Lingyuan area show that they consist of trachyte and rhyolite, with SIO2=65.6-73.4%, MGO=0.35-1.23%, Mg#=16-41, Al2O3=13.40-16.79% and Na20=3.54-4.26%. In addition, the volcanic rocks are characterized by enrichment in LREE and depletion in HREE, with high Sr （445-774）×10^-6 and Sr/Y （49-66） and low Y （7-14）×10^-6 and Yb （0.51-0.97）×10^-6 and LaN/ YbN=33-48, showing the geochemical characteristics of adakite. However, they are low in Mg#. The authors suggest that they may have originated by partial melting of the thickened mafic lower crust.