辽宁赛马碱性岩体煌斑岩脉特征及成因研究  

Genesis and Characteristics of the Lamprophyre Dike from the Saima Alkaline Complex,Liaoning Province

作　　者：任倩 邬斌 REN Qian;WU Bin(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China)

机构地区：[1]东华理工大学核资源与环境国家重点实验室,江西南昌330013

出　　处：《东华理工大学学报（自然科学版）》2024年第2期146-163,共18页Journal of East China University of Technology(Natural Science)

基　　金：江西省自然科学基金项目(20224ACB213012,20212BAB203003)。

摘　　要：赛马煌斑岩脉与碱性岩(霞石正长岩)紧密共生,为研究煌斑岩脉成因,探讨其与碱性岩的关系,通过岩相学、岩石地球化学与年代学等研究,认为赛马煌斑岩属于钾质钾镁煌斑岩,岩石元素含量具有高Mg、K,低Ti的特征。该岩脉高(^(87)Sr/^(86)Sr)i、低ε_(Nd)(t)及Pb的正异常特征,暗示其来源于俯冲作用改造的岩石圈地幔,上侵过程经历了地壳混染。研究区煌斑岩脉斑晶为氟磷灰石和富镁黑云母,基质为钾长石、钠长石等。其中磷灰石富集S和Mn,指示相对氧化的结晶环境;黑云母成分环带发育,x(Fe^(2+))-x(Fe^(3+))-x(Mg^(2+))比例及钛温度计指示其氧逸度和温度均高于主体碱性岩。此外,黑云母Rb-Sr年龄((224.7±0.1)Ma)与主体碱性岩年龄(224~230 Ma)在误差范围内一致。相似的“年龄、地球化学特征及同位素组成”指示赛马煌斑岩脉与霞石正长岩均来源于富集岩石圈地幔,可能为碰撞伸展构造环境下不同期次岩浆作用的产物。The lamprophyre dikes are spatially associated with the Saima alkaline complex(nepheline syenite),whereas the genesis of lamprophyre and its relationship with the Saima alkaline complex are still unknown.Methods of petrography,petrogeochemistry and geochronology were conducted to solve these issues.The Saima lamprophyre belongs to perpotassic-potassic magnesium lamprophyre characterized by high content of Mg,K and low content of Ti.High initial(^(87)Sr/^(86)Sr)i ratios and negativeε_(Nd)(t)values with positive Pb anomalies in lamprophyre suggested that it originated from subduction-modified lithospheric mantle and probably experienced crustal assimilation during its magma evolution.The phenocryst of Saima lamprophyre is composed of fluorapatite and eastonite and its groundmass consists of subordinate minerals such as potassium feldspar and albite.Fluorapatite phenocrysts are rich in S and Mn,indicating a relatively oxidized crystallization environment.The ratio of x(Fe^(2+))-x(Fe^(3+))-x(Mg^(2+))in compositionally zoned eastonite and the Titanium in biotite thermometer also demonstrate that it formed under relatively oxidized and higher temperature conditions than the Saima nepheline syenite.In addition,the Rb-Sr age of biotite is(224.7±0.1)Ma,which is consistent with the age of the nepheline syenite(224~230 Ma)within the error ranges.Overall,similar formation age,geochemical characteristics and isotopic compositions between both the Saima lamprophyre dikes and nepheline syenite indicate that they were derived from the same enriched lithospheric mantle as products of different magmatism under the post-collision extensional tectonic environment.

关 键 词：煌斑岩脉 碱性岩 赛马碱性岩体 矿物学 地球化学 

分 类 号：P588.13[天文地球—岩石学] P619.2[天文地球—地质学]