马里亚纳弧前Conical蛇纹岩泥火山顶自生沉积物特征及其对渗漏流体的指示  

Constrains of seepage fluids based on the characteristics of authigenic deposition from Conical serpentinite mud volcano in the Mariana forearc

作　　者：佟宏鹏 胡海明 陈琳莹 陈多福[1] TONG Hongpeng;HU Haiming;CHEN Linying;CHEN Duofu(Shanghai Engineering Research Center of Hadal Science and Technology,College of Marine Sciences,Shanghai Ocean University,Shanghai 201306,China)

机构地区：[1]上海海洋大学海洋科学学院,上海深渊科学工程技术研究中心,上海201306

出　　处：《海洋地质与第四纪地质》2022年第6期1-10,共10页Marine Geology & Quaternary Geology

基　　金：国家自然科学基金“马里亚纳弧前蛇纹岩泥火山烟囱状自生沉积的成因及深源蛇纹石化流体渗漏活动记录”(41776080),马里亚纳弧前海底蛇纹岩泥火山无机成因甲烷形成水合物的条件及潜力分析(41776050)。

摘　　要：马里亚纳弧前蛇纹岩泥火山顶部海底发育由低温碱性流体渗漏形成的自生沉积物,记录了渗漏流体特征,对俯冲带的物质循环研究有重要意义。但目前对复杂矿物组成的自生沉积物及其所指示的渗漏流体信息仍不清楚。对采自马里亚纳弧前Conical蛇纹岩泥火山的自生沉积物进行了岩石学、矿物学及主量和微量元素分析。结果表明,Conical蛇纹岩泥火山自生沉积物呈疏松多孔状,极易碎,碎块主要呈薄片状和球粒状。薄片状碎块呈白色,主要由针状文石和棱柱状方解石组成,CaO含量较高(49.3%~53.3%),MgO含量较低(2.3%~4.5%)。球粒状碎块呈黄色或白色,为无定形镁硅酸盐,MgO含量较高(25.5%~29.1%),CaO含量较低(0.5%~2.9%)。碳酸盐岩碎块的总稀土含量(ΣREE)为227.2~4136.6 ng/g;无定形镁硅酸盐碎块的ΣREE为115.4~364.9 ng/g,均显示轻微重稀土富集的平坦型配分模式。自生沉积物的稀土配分模式显示,除两个稀土含量相对较高的碳酸盐岩样品外,渗漏流体的贡献高于90%,说明两类样品均形成于较强的渗漏环境,并且碳酸盐及镁硅酸盐可能分别形成于“低硅型”和“高硅型”不同的流体活跃期。Authigenic depositions induced by low-temperature alkaline seepage fluids occur on the top of the Mariana forearc serpentinite mud volcanoes,which are archives of the seepage fluids and are significant for studying the material circulation of the subduction zone.However,little is known about the features of the authigenic depositions composed of multiple minerals and their recording of seepage fluids.In this paper,we investigated the petrology,mineralogy and major and trace element compositions of authigenic depositions collected from Conical serpentinite mud volcano in Mariana forearc.The authigenic depositions from Conical serpentinite mud volcano are loose and extremely friable into lamellar and spherical fragments.The lamellar fragments are white,mainly composed of needle-like aragonite and prismatic calcite,with high CaO contents(49.3%~53.3%)and low MgO contents(2.3%~4.5%).The spherical fragments are yellow or white,made of amorphous magnesium silicate,with high MgO contents(25.5%~29.1%)and low CaO contents(0.5%~2.9%).ΣREE of the carbonate fragments range from227.2 ng/g to 4136.6 ng/g,while theΣREE of the amorphous magnesium silicate fragments are from 115.4 ng/g to 364.9 ng/g.All samples show flat distribution patterns with slight enrichment of heavy rare earth elements.The rare earth element distribution patterns of authigenic depositions indicate that the contribution of seepage fluids is higher than 90%except for two carbonate samples with relatively high rare earth element contents.This suggests that all samples should form in the intense seepage environments,but the carbonates and magnesium silicates may be induced by varied types of seepage fluid,namely,"low-silica type"and"high-silica type".

关 键 词：自生沉积物 稀土元素 主量元素 渗漏流体 蛇纹岩泥火山 马里亚纳弧前 

分 类 号：P736.4[天文地球—海洋地质]