摘要
近年来一些研究在岛弧岩浆中发现了蛇纹岩组分,这表明俯冲至弧下的蛇纹岩不仅为地幔楔提供流体,而且可以通过部分熔融参与岛弧岩浆形成。然而,蛇纹岩在地幔楔中的熔融行为及其在俯冲带物质循环中的作用仍未进行深入研究。因此,本研究选择3种蛇纹岩样品:蚀变原岩分别为二辉橄榄岩(SE2)和方辉橄榄岩(SE3)的天然蛇纹岩,以及模拟含有大量滑石的合成蛇纹岩样品(SEQ),在700~1300℃和4 GPa的温度压力条件下进行了模拟实验,限定了蛇纹岩的熔融温度,分析了实验产生的熔体成分。研究发现,不同类型蛇纹岩的固相线存在显著差异,SE3、SEQ和SE2蛇纹岩的固相线分别为900~960℃、960~1100℃以及1150~1200℃。这3种蛇纹岩的固相线均高于俯冲板片上表面的温度,要求蛇纹岩通过底辟作用进入地幔楔以发生部分熔融。根据实验结果,本研究认为SE2和SEQ蛇纹岩可以在地幔楔底部相对较低的温度条件下(960~1100℃)即发生熔融,产生科马提质岩浆;而在上覆地幔楔更高温度条件下(>1200℃),SE2蛇纹岩可以发生更广泛、更高程度的部分熔融,产生玻安质岩浆。
Recent studies have identified serpentinite components in arc magmas,suggesting that subducted serpentinites contribute not only fluids to the mantle wedge but also participate in arc magma formation through partial melting.However,the melting behavior of serpentinites in the mantle wedge and their role in the material cycle of subduction zones remain underexplored.We selected three types of serpentinites:natural serpentinites altered from harzburgite(SE2)and lherzolite(SE3),and synthetic serpentinite(SEQ)containing talc.Experiments were conducted under 700~1300℃and 4 GPa,to constrain the melting temperature of serpentinites and analyze the composition of the melts.Results show that the solidi among different serpentinite types vary greatly from each other.The solidi of SE3,SEQ,and SE2 are between 900~960℃,960~1100℃,and 1150~1200℃,respectively.These solidi are higher than the surface temperatures of subducting slab,thus requiring serpentinites diapir into the mantle wedge to melt.Therefore,SE2 and SEQ serpentinites can melt at the bottom of the mantle wedge under relatively lower temperature conditions(960~1100℃),producing komatiitic magmas,whereas in the overlying mantle wedge,SE2 serpentinite undergo more extensive and higher degrees of partial melting at higher temperature conditions(>1200℃),generating boninitic magmas.
作者
胡佳森
张国良
HU Jiasen;ZHANG Guoliang(Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China;University of Chinese Academy of Sciences,Beijing 100049,China;Center for Ocean Mega-Science,Chinese Academy of Sciences,Qingdao 266071,China)
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2024年第2期157-170,共14页
Marine Geology & Quaternary Geology
基金
中国科学院战略性先导科技专项(B类)子课题:“印太交汇区海盆岩浆过程和地幔组成”(XDB42020302)
国家自然科学基金项目“西太平洋板块俯冲体系岩浆过程中深部碳循环研究”(91858206)。
关键词
蛇纹岩
俯冲带
高温高压实验
高镁岩浆
科马提岩
serpentinite
subduction zone
high-temperature and high-pressure experimentation
high-Mg magmas
komatiite
