孟凡雪, 高山, 柳小明. 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[J]. 地质通报, 2008, 27(3): 364-373.
    引用本文: 孟凡雪, 高山, 柳小明. 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[J]. 地质通报, 2008, 27(3): 364-373.
    MENG Fan-xue, GAO Shan, LIU Xiao-ming. U-Pb zircon geochronology and geochemistry of volcanic rocks of the Yixian Formation in the Lingyuan area, western Liaoning[J]. Geological Bulletin of China, 2008, 27(3): 364-373.
    Citation: MENG Fan-xue, GAO Shan, LIU Xiao-ming. U-Pb zircon geochronology and geochemistry of volcanic rocks of the Yixian Formation in the Lingyuan area, western Liaoning[J]. Geological Bulletin of China, 2008, 27(3): 364-373.

    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

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

    • 摘要: 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,Y=(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。

       

      Abstract: 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 Na2O=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.

       

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