小兴安岭北部八里桥地区碱长花岗岩成因与地质意义  

Petrogenesis and tectonic implication of the alkali-feldspar granite in the Baliqiao area,northern Lesser Xing’an Range

作　　者：苏航 刘旭光 郑涛 刘颖新 SU Hang;LIU Xu-guang;ZHENG Tao;LIU Ying-xin(Heilongjiang Longkuang Resources Development Group Co.,Ltd,Harbin 150036,China;Natural Resources Survey Institute of Heilongjiang Province,Harbin 150036,China)

机构地区：[1]黑龙江省龙矿资源开发集团有限公司,黑龙江哈尔滨150036 [2]黑龙江省自然资源调查院,黑龙江哈尔滨150036

出　　处：《矿物学报》2023年第5期665-673,共9页Acta Mineralogica Sinica

基　　金：中国地质调查局项目(编号:1212011220432)。

摘　　要：小兴安岭八里桥地区位于兴蒙造山带东部兴安地块与松嫩—张广才岭之间的构造带上,区内构造演化复杂,岩浆活动频繁。本文通过对八里桥地区晚古生代碱长花岗岩的年代学和岩石地球化学研究,旨在为兴安地块与松嫩—张广才岭地块碰撞拼合时限提供新的约束。LA-ICP-MS锆石U-Pb定年结果显示,八里桥地区发育的中粒碱长花岗岩形成于(295.3±0.7)Ma,属早二叠世侵入体。碱长花岗岩w(SiO_(2))为75.27%~77.71%,w(Al_(2)O_(3))为11.48%~13.28%,w(Na_(2)O+K_(2)O)为6.96%~8.72%,Na_(2)O/K_(2)O比值为0.27~1.05,A/CNK值在1.00~1.51之间,属过铝质、高钾钙碱性系列岩石。稀土元素总量为116.46×10^(-6)~321.52×10^(-6),ΣLREE/ΣHREE和(La/Yb)N比值分别为3.07~9.65和1.70~6.91,显示轻稀土富集、重稀土亏损的特点;δEu值在0.21~0.34范围内,显示强烈负Eu异常。它们相对富集Rb、U等大离子亲石元素和Zr-Hf等高场强元素,亏损Nb、Ta,具有较高Zr+Nb+Ce+Y总含量,显示出造山后伸展环境“A”型花岗岩的特征。此外,该花岗岩全岩Nd同位素比值较高(εNd(t)=3.66),反映其可能来自与新生下地壳的部分熔融。该套碱长花岗岩的出现代表了兴安地块与松嫩—张广才岭地块碰撞拼合后的伸展事件,指示早二叠世前兴安地块与松嫩—张广才岭地块已经碰撞拼合。The Baliqiao region is located in the transitional belt between the Xing’an and Songnen-Zhangguangcailing Blocks,with multiple-stage of tectonic events and intense magmatism.Geochronology and geochemistry of the alkali-feldspar granite in this region have been presented,aiming to provide constraints on the collisional timing for the two blocks above.LA-ICP-MS zircon U-Pb dating shows it was emplaced at(295.3±0.7)Ma.They have high SiO_(2)of 75.27–77.71 wt%,Na_(2)O+K_(2)O of 6.96–8.72 wt%,and Al_(2)O_(3)of 11.48–13.28 wt%,with variable Na_(2)O/K_(2)O values of 0.27–1.05,A/CNK value of 1.00-1.51,indicative of peraluminous,high-K calc-alkaline affinity.Their rare earth element contents are 116.46×10^(-6)–321.52×10^(-6),with highΣLREE/ΣHREE and(La/Yb)N ratios of 3.07–9.65 and 1.70–6.91,respectively.They have significant negative Eu anomalies(δEu=0.21–0.34).They are characterized by enriched large ion lithophile elements(Rb,U)and Zr-Hf,but depleted in Nb and Ta,with high Zr+Nb+Ce+Y contents.All these features are consistent with anorogenic A-type granite.Besides,their positiveεNd(t)value of 3.66,suggests they might be derived from the remelting of juvenile crust.Such A-type granite may form in the extensional setting after the collision of the Xing’an and Songnen-Zhangguangcailing Blocks,which might have occurred before the Early Permian.

关 键 词：碱长花岗岩 锆石U-PB年龄 地质意义 八里桥 

分 类 号：P579[天文地球—矿物学] P581[天文地球—地质学] P588.12