东太平洋海隆(EPR) 13°N 附近含金属沉积物孔隙率研究

研究了采自东太平洋海隆13°N(EPR 13°N)的一个热液成因含金属箱式沉积物岩心E272的孔隙率变化特征。样品孔隙率在70.0%-85.2%之间,顶部层位比底部层位高14%左右。孔隙率随深度增加而指数式单调递减,平均递减梯度约为-0.31%/cm。该岩心上部层位呈红棕色,下部层位呈黄绿色,表明该岩心经历了显著的早期化学成岩作用。前人关于该岩心的元素地球化学,粒度和年代学数据,共同证明该岩心孔隙率随深度变化特征受稳态压缩过程控制。其孔隙率随深度的变化关系符合稳态压缩模型的经验拟合公式。E272顶部沉积物-水界面处溶解物质与海水的交换以离子扩散机制为主,而岩芯内部溶解物质的迁移则可能主要受自下而上的孔隙水流动机制控制,这与岩芯中活动元素含量上部高,下部低的分布模式一致。该研究对将来进一步讨论E272岩心在早期成岩作用中的化学过程具有指导意义。

Study on the porosity of a metalliferous sediment core from the East Pacific Rise 13°N

The porosity of a metalliferous sediment core E272 collected from 13°N East Pacific Rise(EPR 13°N) was studied.The porosity of this core monotonically decreases with increasing depth rangeing from 70.0%-85.2% with difference of about 14% between its top layer and its bottom and an average decreasing gradient of about -0.31%/cm.The red-brown color of the upper layers and yellow-green color of the lower layers of this core indicate early chemical diagenesis has exerted significant influence on this core.A combined analysis of reported geo-chemical,grain-size and chronological data of this core suggests that the porosity of this core might be controlled by steady-state-compaction process.The profile of its porosity versus depth fits well with the steady state compac-tion model.Exchanging mechanism of dissolved materials between bottom sea water and the sediment at the wa-ter-sediment interface is dominated by molecular diffusion,while under that interface,the mechanism controlling the transportation of dissolved materials is the directed flow of the interstitial water from the bottom up,and this is consistent with the profiles of labile elements versus depth of this sediment core.This study is instructive for further study on the chemical diagenesis of this sediment core.