小兴安岭西北部早——中侏罗世TTG花岗岩年代学、地球化学特征及构造意义

发布时间：2018-09-14 15:21

【摘要】：通过对出露于小兴安岭西北部白石砬子地区中生代花岗岩的研究,查明该地区存在一套由英云闪长岩-花岗闪长岩-石英闪长岩和少量闪长岩为组合的花岗岩,锆石U-Pb LA-ICP-MS测年分别获得(171.1±1.3)、(173.9±3.9)、(178.3±1.5)和(169.1±6.2)Ma的岩体侵位年龄,证明其形成于早—中侏罗世。通过岩石地球化学方法判别该花岗岩组合具有高Al_2O_3型T_1T_2G_1花岗岩特征,整体具有富硅、富铝,钠质,贫铁、镁、钛,属于偏铝质-弱过铝质钙碱性系列,富集轻稀土,相对亏损重稀土,富集Rb、Ba、Th、U、Sr等大离子亲石元素,相对亏损Nb、Ta、Zr、Hf等高场强元素,Eu具有轻微负异常的特点,与安第斯I型花岗岩具有相似性。其低Sr/Y值、(La/Yb)N值,弱或无负δEu异常等特征反映源区残留相矿物以角闪石、辉石为主,有少量斜长石,石榴石可能有少量残留。岩体露头有闪长质岩浆与英云(花岗)闪长质岩浆两种不完全机械混合的现象,反映可能存在两个以上的不同源区。另外,岩体不规则侵入元古宙地层(兴华渡口群和落马湖群)和岩浆中残留有大量早期捕获锆石,说明在岩浆上升侵位过程中与围岩发生同化混染作用。综合研究认为,该早—中侏罗世TTG岩浆形成与蒙古—鄂霍茨克洋的闭合作用密切相关,反映侏罗纪蒙古—鄂霍茨克洋存在向南侧微陆块的俯冲作用。
[Abstract]:Based on the study of Mesozoic granites exposed in Baishilazi area, northwest of Xiaoxinganling, it is found that there is a set of granitic rocks, composed of quartz diorite and quartz diorite, which are composed of quartz diorite and quartz diorite in this area. Zircon U-Pb LA-ICP-MS dating obtained (171.1 卤1.3), (173.9 卤3.9), (178.3 卤1.5) and (169.1 卤6.2) Ma emplacement ages, respectively, indicating that they were formed in the Early-Middle Jurassic. The granite assemblage is characterized by high Al_2O_3 type T_1T_2G_1 granite, and is characterized by silicon-rich, aluminum-rich, sodium, iron, magnesium and titanium, which belongs to the metaluminum-weak peraluminous calc-alkaline series and is enriched in light rare earths. Relative depletion of heavy rare earths, enrichment of large ion lithophile elements such as Rb,Ba,Th,U,Sr, and relative depletion of high field strength elements, such as Nb,Ta,Zr,Hf, show slight negative anomalies, which are similar to those of Andean I-type granites. Its low Sr/Y value, (La/Yb) N value and weak or no negative 未 Eu anomalies indicate that the residual minerals in the source region are mainly amphibole and pyroxene, with a small amount of plagioclase and a small amount of garnet residues. There are two incomplete mechanical mixing phenomena of diorite magma and Yingyun (granitic) diorite magma in outcrop of rock mass, which indicates that there may be more than two different sources. In addition, the irregular intrusion of the rock body into the Proterozoic strata (Xinghua Dukou Group and the Shimahu Group) and a large amount of early captured zircon remained in the magma, indicating that assimilation and contamination occurred with the surrounding rock during the magmatic uplift emplacement. It is considered that the formation of the TTG magma in the early and Middle Jurassic is closely related to the closure of the Mongolia-Okhotsk Ocean, which reflects the subduction of the Jurassic Mongolia-Okhotsk Ocean towards the southern microcontinental block.
【作者单位】：中国地质大学(北京)地球科学与资源学院;中国地质调查局沈阳地质调查中心;
【基金】：中国地质调查局地质调查项目(12120114055701) 国家自然科学基金项目(41502063,41574093)~~
【分类号】：P588.121

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