大兴安岭中段白音高老组流纹岩年代学、地球化学及其地质意义

对大兴安岭中段(阿尔山—柴河地区)白音高老组流纹岩进行了年代学、地球化学详细测试,结果表明:白音高老组流纹岩LA—ICP—MS锆石U—Pb表面年龄值为124.8~135.6 Ma,加权平均年龄值为127.0±0.5 Ma,形成时代为早白垩世;岩石主体属高硅高钾弱过铝质钙碱性系列;稀土元素配分模式图呈右倾型,轻重稀土分馏明显((La/Yb)N=3.12~10.28,平均7.57),铕弱负异常(δEu=0.18~0.73,平均0.53);大离子亲石元素Rb、Th、U相对富集,Ba、Sr明显亏损,高场强元素Zr较为富集,Ti强烈亏损。根据区域对比并结合他人研究成果,认为大兴安岭中段白音高老组流纹岩形成于早白垩世板内伸展环境,与太平洋板块俯冲关系密切。

Chronology,geochemistry of rhyolites from Baiyingaolao Formation in the middle part of Da Hinggan Mountains and its tectonic implications

The testing results of chronology and geochemistry of rhyolites from Baiyingaolao Formation in the middle part of Da Hinggan Mountains indicate that the zircon U- - Pb age is 124. 8 ～135. 6 Ma，with weighted aver- age age of 127. 0 ±0. 5 Ma，belonging to Early Cretaceous． The rocks belong to high- SiO2 ，high- K peraluminous calc alkaline series． The ＲEE pattern is rightward sloping with significant fractionation of LＲEE and HＲEE ( (La/ Yb) N =3. 12 ～10. 28，average as 7. 57) and slight negative Eu anolies． The rhyolites are characterized by enrich- ment in LILE (Ｒb，Th，U) and Zr，depletion in Ba，Sr and Ti． Combined with regional comparison，the au- thors consider that the Baiyingaolao Formation rhyolites formed in Early Cretaceous extension setting，which is clos- ey related with the subduction of Pacific plate．