黑龙江省东部佳木斯地区八角山岩体形成时代探讨

Discussion on the age of Bajiaoshan pluton in Jiamusi area,Eastern Heilongjiang Province

佳木斯地块形成与演化一直是地质学者研究的热点之一,笔者对黑龙江省东部佳木斯地区八角山岩体进行了锆石LA-ICP-MS U-Pb测年,结果显示:锆石206 Pb/238 U加权平均年龄为(207.15±0.86)Ma,岩体的形成时代应为晚三叠世。稀土元素特征为轻稀土富集,具正铕异常;微量元素Cr、Th、Sr元素相对富集,而Cs、Zr元素相对亏损。该岩体可能形成于古亚洲洋闭合后的伸展环境。

The formation and evolution of the Jiamusi massif has always been one of the hot spots of geologists.The authors have made zircon LA-ICP-MS U-Pb dating of the Bajiaoshan pluton in Jiamusi area,Eastern Heilongjiang Province.The results show that weighted average age of zircon 206 Pb/238 U is(207.15±0.86)Ma.The formation age of the pluton should be Late Triassic.The REE is characterized by enrichment of LREE with positive Eu anomaly;the trace elements Cr,Th,Sr are relatively enriched,however Cs,Zr are relatively deficient.The pluton may have been formed in an extensional environment after the closure of the paleo Asian Ocean.