南海IODP 349航次U1434站位海相红层成因——来自漫反射光谱与X荧光光谱的制约

The Genesis and Geological Implications for Oceanic Redbeds of the South China Sea in U1434 of IODP Expedition 349——the Constraint from Diffuse Reflectance and X-Ray Fluorescence Spectroscopy

提出IODP349航次首次在南海发现的大洋红层,与ODP124航次苏禄海、苏拉威西海大洋红层以及三水盆地陆相红层相似,都具有直接覆盖于大规模岩浆岩之上的特征,对于揭示红层与岩浆热事件的关系具有重要意义。自上而下采集U1434站位灰绿色—红棕色海相沉积序列进行测试分析,并设计实验模拟沉积—成岩过程中氧逸度和地热温度对红层色素形成的控制作用,通过红色与非红色沉积、实测与实验样品的对比分析,探讨红层成因机制及其地质意义。采用漫反射光谱、荧光光谱分析以及二价铁滴定测试,量化分析了海相沉积与实验样品的颜色红度值、针铁矿、赤铁矿与不同价位铁元素的含量,得到以下新认识:U1434站位红色—非红色海相沉积均形成于较高的氧逸度条件,水体氧化还原环境的差异并不是控制红色与非红色沉积的主要因素; U1434站位大洋红层直接覆盖大洋玄武岩,起源于沉积—成岩阶段的高地温作用;陆相红层和白垩纪海相红层均分布于相应时期的构造—岩浆活动带,暗示了红层对地质热事件具有重要的指示意义。

We presented a new finding that the occurrences of oceanic redbeds in the South China Sea(SCS) first discovered from Expedition 349 are similar to those in Sulu Sea and Celebes Sea from Expedition 124, as well as to the continental redbeds in Sanshui Basin of China, all directly covering massive magmatic rocks with significance for revealing the connections between oceanic redbeds and magma thermal events. We measured the samples collectted from marine sedimentary with colors ranging from celadon to rufous in U1434 of IODP Expedition 349, and analyzed the influence of oxygen fugacity and geothermal temperature on the formation of pigment in redbeds. By comparing red-nonred sediments and experimental samples, we discussed the redbed genesis and its geological implications. We obtained the red values, the content of goethite, hematite and quantivalent Fe in marine sediments and experiment samples through the analysis of diffuse reflectance and fluorescent spectroscopy and Fe^2+ in titration test. The results showed that,(1) Red and non-red marine sediments are formed at high oxygen fugacity environment in U1434 of IODP Expedition 349, and difference in oxidation-deoxidation environment was not the controlling factor on red and non-red sediments;(2) The oceanic redbeds directly covering basalts in U1434 of IODP Expedition 349 originated from high geothermal temperature during sedimentary-diagenesis process;(3) And we found that continental redbeds and Cretaceous oceanic redbeds formed in different geological periods are closely associated with tectonic-magmatic active belts, showing that redbeds have significance in indicating geological thermal events.