大兴安岭柴河白音高老组流纹岩锆石U-Pb定年及成因探讨

Zircon U-Pb Dating and Petrogenesis of the Baiyingaolao Formation Rhyolites in Chaihe Area,Great Xing'an Range

为了研究大兴安岭中段柴河地区白音高老组流纹岩的形成时代和岩石成因,进行了锆石U-Pb同位素年龄测试和地球化学研究.LA-ICP-MS锆石U-Pb定年结果显示,白音高老组流纹岩形成于年龄为129~137 Ma的早白垩世.岩石地球化学研究表明,白音高老组流纹岩具有高硅富碱、贫钙镁的特征;稀土丰度总量m（∑REE）=121.35×10-6~194.92×10-6,轻重稀土分馏明显,m（La）/m（Yb）N=12.2~21.7,Eu负异常（δ_（Eu）=0.39~0.61）,微量元素以富集Rb,Ba,Th,K,亏损Nb,Sr,P,Ti为特征;白音高老组流纹岩原始岩浆来源于上地壳岩石的部分熔融.

Zircon U-Pb istopic dating and geochemical analysis were used to study the formation age and petrogenesis of the rhyolites in Baiyingaolao Formation. LA-ICP-MS dating results show that the Baiyingaolao formation rhyolites in Chaihe area form in early cretaceous from 129 to 137 Ma. The geochemical study results show that the rhyolites have the characteristic of high silicon and rich alkalis, poor calcium and magnesium. The total REE amount ranges from 121.35 × 10^-6 to 194. 92 × 10^-6. Fractionation of LREE and HREE is obvious[ m（La）/m（Yb）N = 12.2 21.7], and Eu has negative anomalies（δEu =0. 39 ~0. 61 ）. The trace elements are characterized evidently by enrichment of Rb, Ba, Th, K and depletion of Nb, Sr, P, Ti. Original magma of Baiyingaolao formation rhyolites is chiefly derived from partial melting of up crust rocks.