中国东北鸡西新生代玄武岩源区岩性制约  

Lithology in the Mantle Source of Jixi Cenozoic Basalts from Northeastern China

作　　者：郑志翀 曾罡[1] 张慧丽 刘建强 陈立辉 周中彪 ZHENG Zhichong;ZENG Gang;ZHANG Huili;LIU Jianqiang;CHEN Lihui;ZHOU Zhongbiao(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;Institute of Marine Geology,College of Oceanography,Hohai University,Nanjing 210098,China;Department of Geology,State Key Laboratory of Continental Dynamics,Northwest University,Xi’an 710069,China)

机构地区：[1]南京大学地球科学与工程学院,内生金属矿床成矿机制研究国家重点实验室,南京210023 [2]河海大学海洋学院,海洋地质研究所,南京210098 [3]西北大学地质学系,大陆动力学国家重点实验室,西安710069

出　　处：《高校地质学报》2023年第2期186-200,共15页Geological Journal of China Universities

基　　金：中央高校基本科研业务费专项资金(No.0206-14380114)资助。

摘　　要：新生代火山岩在中国东北地区广泛出露,主要集中于松辽盆地周缘。其中盆地东部多沿抚顺—密山、依兰—伊通断裂带分布,尤其集中于长白山地区,以钠质玄武岩为主。前人研究表明,东北地区的地幔源区存在显著的化学不均一性,暗示这些玄武岩复杂的成因。为进一步查明它们的地幔源区岩性,揭示其岩石成因,文章选择抚顺—密山断裂带北部鸡西地区的玄武岩开展研究工作。研究区玄武岩岩性变化较大,其SiO2含量为44.2~49.6 wt%,MgO含量为6.7~10.6 wt%,在TAS分类图上可进一步细分为碧玄岩、粗面玄武岩及玄武岩三个类别。微量元素上,研究样品呈现不相容元素相对富集的特征,具Nb、Ta的正异常和Pb、Ti的负异常,与洋岛玄武岩的微量元素组成相类似。通过计算研究样品的原生岩浆组成,发现其具有富MgO、贫SiO_(2)和CaO的特征,在透辉石向CATS-橄榄石-石英的投影图上落在贫硅辉石岩的区域内;同时结合玄武岩较高的FC3MS(FeO^(T)/CaO-3×MgO/SiO_(2))值,认为其源区确实存在辉石岩组分的贡献。为进一步证实上述岩性特征,笔者还从玄武岩中挑选了橄榄石斑晶进行分析。结果表明,橄榄石斑晶的Fo值存在较大的变化,高Fo的橄榄石具有比低Fo橄榄石更低的Ca和Mn含量、高的Ni含量及Fe/Mn比值,且高Fo值橄榄石与辉石岩来源熔体结晶的橄榄石组成相似,同样反映其源区存在辉石岩组分的贡献。综上所述,研究认为东北鸡西地区新生代玄武岩的源区确实存在辉石岩组分,是再循环的地壳组分对研究区地幔改造的产物,并在该区幔源岩浆的形成过程中产生了重要的影响。Cenozoic volcanic rocks are widespread in Northeast China,mainly surrounding the Songliao Basin.In the eastern part of the basin,volcanic rocks are distributed along Fushun-Mishan and Yilan-Yitong faults,especially near the Changbai Mountain area,and these volcanic rocks are dominated by sodium basalts.The genesis of these basalts is complex based on their significantly chemical heterogeneity found in the previous studies.Therefore,Cenozoic basalts from Jixi area in the north of Fushun-Mishan fault were selected to further identify the lithology in their mantle source.These basalts show a wide range of SiO_(2)(44.2~49.6 wt%)and MgO(6.7~10.6 wt%)contents,and can be subdivided into basanite,trachybasalt and basalt.In the primitive-mantle normalized incompatible element diagram,they show positive anomalies of Nb and Ta and negative anomalies of Pb and Ti,which is similar to oceanic island basalts.The calculated the primary magmas compositions of these samples are rich in MgO but poor in SiO_(2) and CaO;moreover,they fall in the region of silica-poor pyroxenite on the projections from or towards Diopside into the plane Olivine-Quartz-Calcium Tschermak’s(CATS).The high FC3MS(FeO^(T)/CaO-3×MgO/SiO_(2))values of the basalts again indicate the presence of pyroxenite in their source.Furthermore,the olivine phenocrysts from these basalts are also analyzed,and the high-Fo olivines show lower Ca and Mn contents,and higher Ni contents and Fe/Mn ratios than the low-Fo olivines.The compositions of high-Fo olivines resemble to those olivines crystallized from pyroxenite-derived melt,strongly supporting the presence of pyroxenite in the mantle source.In summary,we highlight that pyroxenitic component,produced during the crustal recycling process,plays an important role in the formation of these mantle-derived magmas in Jixi area.

关 键 词：中国东北 新生代玄武岩 橄榄石 辉石岩 再循环地壳 

分 类 号：P588.1[天文地球—岩石学]