摘要
全球新生代高镁安山岩多分布于活动大陆边缘和岛弧环境,而板内高镁安山岩出露较少。近年来,在松辽盆地西侧的五岔沟地区和北侧的逊克、门鲁河地区以及俄罗斯远东地区相继发现了喷发于20.6~0.3 Ma(新近纪—第四纪)的板内高镁安山岩。这些板内高镁安山岩的发现对于探讨地幔中再循环地壳物质的属性和命运具有重要意义。文章报导了在松辽盆地东侧的牡丹江地区新发现的古近纪高镁安山岩(喷发于49.2~36.3 Ma)。这些火山岩SiO_(2)含量为54.75~58.95 wt%,Mg^(#)为45.18~51.72,属于高镁安山岩。牡丹江高镁安山岩属于亚碱性系列,岩性为玄武安山岩和安山岩,主量元素组成变化范围较小。基于岩相学观察和MELTS软件模拟计算,牡丹江高镁安山岩的矿物结晶顺序为:斜长石和斜方辉石斑晶较早结晶,之后斜方辉石、单斜辉石和钛铁氧化物等基质矿物结晶。MELTS软件模拟结果指示在岩浆演化过程中结晶出的矿物未脱离岩浆体系,岩石成分代表了相对原始的岩浆成分。文章利用斜方辉石—熔体测压法计算出牡丹江高镁安山岩的结晶压力为169~570 MPa,相当于5.6~18.8 km的深度。利用斜方辉石—熔体和熔体两种测温法计算出其结晶温度为1109~1181℃,与东北其它地区新生代高镁安山岩(逊克、门鲁河和五岔沟)的结晶温度基本一致(1132~1192℃),高于岛弧安山岩的结晶温度(950~1050℃)。利用斜长石—熔体测水法计算出其喷发前熔体水含量为0.3~1.0 wt%,与东北其它地区新生代高镁安山岩熔体喷发前水含量基本一致(0.3~1.4 wt%),明显低于岛弧安山岩(2~9 wt%)。因此,牡丹江高镁安山岩在化学组成、岩相学特征、岩浆物理属性(温度和水含量)以及演化特征上都与东北其它地区发现的新生代高镁安山岩基本一致,属于板内高镁安山岩。牡丹江高镁安山岩的发现表明,这类板内高镁安山岩岩浆作用从始新世一直持续到更新世,在东北地区广泛分布。
Cenozoic high-Mg^(#)andesites(HMAs)are generally distributed in the active continental margin and island-arc setting,but they are rare in the intraplate setting.In recent years,intracontinental HMAs erupting at 20.6-0.3 Ma(Neogene-Quaternary)have been found in Wuchagou of western Songliao Basin and Xunke,Menluhe and Russian Far East of northern Songliao Basin.The discovery of these intracontinental HMAs is important to understand the nature and fate of recycled crustal materials in the mantle.Here we,for the first time,report Paleogene HMAs erupting at 49.2-36.3 Ma in Mudanjiang area,eastern Songliao Basin.These volcanic rocks have SiO_(2) contents of 54.75-58.95 wt% and Mg^(#)values of 45.18-51.72,falling into the scope of HMAs.They are mainly basaltic andesites and andesites belonging to subalkaline series with a small variation of the major element compositions.Based on petrographic observation and MELTS_Excel calculation,plagioclase and orthopyroxene phenocrysts were crystal phases at the earliest stage and mineral phases in the groundmass(such as orthopyroxene,clinopyroxene and titanomagnetite)appeared successively.The results of MELTS_Excel calculation indicate that the crystal phases have not been separated from the magma system and the composition of these rocks can represent the primary magma composition.The crystallizing pressures of the Mudanjiang HMAs are 169-570 MPa by using the orthopyroxene-melt barometer,suggesting a depth of 5.6-18.8 km.The crystallizing temperatures of these rocks are 1109-1181℃ by using the orthopyroxene-melt and melt thermometers,which are consistent with other Cenozoic HMAs(Xunke,Menluhe and Wuchagou)in northeast China(1132-1192℃)and are higher than island-arc andesites(950-1050℃).The pre-eruptive melt H_(2)O contents vary from 0.3 to 1.0 wt% calculated by the plagioclasemelt hygrometer,which are in the range of Cenozoic HMAs in other parts of northeast China(0.3-1.4 wt%),yet tend to lower H_(2)O than island-arc andesite(2-9 wt%).Therefore,the chemical composition,petrographic characteristics,magmatic physical properties(temperature and H_(2)O content)and evolutionary characteristics of the Mudanjiang HMAs are similar to Cenozoic HMAs found in other areas of Northeast China,which all belong to intracontinental HMAs.The discovery of Mudanjiang HMAs suggests that these intracontinental HMA-type magmatism continued from Eocene to Pleistocene and are distributed throughout northeast China.
作者
熊巧
曾罡
郑志翀
张慧丽
周中彪
王小均
刘建强
陈立辉
XIONG Qiao;ZENG Gang;ZHENG Zhichong;ZHANG Huili;ZHOU Zhongbiao;WANG Xiaojun;LIU Jianqiang;CHEN Lihui(State Key Laboratory for Mineral Deposites Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;Department of Geology,Northwest University,Xi’an 710069,China)
出处
《高校地质学报》
CAS
CSCD
北大核心
2023年第2期161-173,共13页
Geological Journal of China Universities
基金
国家自然基金项目(42130310,41672049)资助。
关键词
高镁安山岩
板内岩浆作用
岩浆演化
high-magnesium andesites
intracontinental volcanism
magmatic evolution
