大兴安岭多宝山地区晚古生代碱长花岗岩锆石U-Pb年龄：对兴安和松嫩地块碰撞拼合时间的限定

贾旭; 任俊光; 徐文坦; 马虎超; 张超; 石国明

doi:10.12029/gc20220216

大兴安岭多宝山地区晚古生代碱长花岗岩锆石U-Pb年龄：对兴安和松嫩地块碰撞拼合时间的限定

Zircon U-Pb dating of Late Paleozoic alkali-feldspar granite in Duobaoshan, Great Xing'an Range: Constrains on collision and assembly time of Xing'an and Songnen Blocks

摘要

摘要:
研究目的 大兴安岭多宝山地区位于兴蒙造山带东部的兴安地块与松嫩地块之间的构造带上，区内构造演化复杂，岩浆活动频繁，本文通过对多宝山地区晚古生代碱长花岗岩的年代学和岩石地球化学研究，旨在约束兴安地块与松嫩地块碰撞拼合的时限。
研究方法 开展了LA-ICP-MS锆石U-Pb测年和岩石主微量元素的测试分析工作。
研究结果 测年获得的2件样品的加权平均年龄分别为（300.3±2.0）Ma和（307.3±1.7）Ma，属晚石炭世。岩石具有高硅SiO₂=69.70%~77.42%，相对富铝Al₂O₃＝11.60%~15.05%，富钾和钠(K₂O=4.09%~5.67%; Na₂O=3.13%~4.13%），贫钙和镁(CaO=0.02%~0.8%; MgO=0.02%~0.48%)的特征; 微量元素表现出富集Rb、Th、Zr和Hf，亏损Ba、Sr、Nb和Ta，（Zr+Nb+Ce+Y）含量较高，平均值为529.10×10^-6; 稀土元素配分模式呈右倾，具明显Eu负异常; 同时岩石具有较高的锆石饱和温度，符合A型花岗岩的特征。
结论结合区域构造演化史，认为该期碱长花岗岩为造山期后伸展构造环境下岩浆活动的产物，并指示兴安地块和松嫩地块碰撞拼合的结束。

Abstract:
This paper is the result of geological survey engineering.
Objective The Duobaoshan area of the Great Xing'an Range is located on the tectonic belt between the Xing'an block and the Songnen block in the east of the Xingmeng orogenic belt. In this paper, the chronology and petrogeochemistry of the Late Paleozoic alkali feldspar granites in the Duobaoshan area are used to constrain the time limit of the collision between the Xing'an block and the Songnen block.
Methods In this paper, the zircon U-Pb geochronology and the whole rock geochemistry were carried out.
Results The LA-ICPMS U-Pb ages of zircons from two alkali-feldspar granite samples were (300.3±2.0)Ma and (307.3±1.7) Ma, respectively. Two samples have the similar geochemistry characteristics, with high silicon (SiO₂= 69.70% to 77.42%), relatively high aluminum (Al₂O₃=11.60% to 15.05%), and high alkali (K₂O+ Na₂O=7.22% to 9.80%), low Ca and Mg (CaO=0.02% to 0.8%, MgO=0.02% to 0.48%), enrichment of Rb, Th, Zr and Hf, depleted of Ba, Sr, Nb and Ta, relatively high (Zr+Nb+Ce+Y). In addition, they also have significantly negative Eu anomalies, with the right-leaningdistribution of rare earth elements and high zircon saturation temperature, suggesting both of them are A-type granites.
Conclusions Combined with the regionally tectonical evolution, it is concluded that the alkali-feldspar granite formed at extensional geological background of post-collision regime, marking the end of the collision between the Xing'an block and the Songnen block.

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