Geochemical characterization of tubular alteration features in subseafloor basalt glass
Geochemical characterization of tubular alteration features in subseafloor basalt glass
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DOI：
10.1016/j.epsl.2013.05.012
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发表时间：
2013-07
影响因子：
5.3
通讯作者：
Emily Knowles;H. Staudigel;A. Templeton
中科院分区：
文献类型：
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作者：
Emily Knowles;H. Staudigel;A. Templeton
有许多迹象表明，海底玄武岩目前可能含有大量活性微生物细胞，并以物理和化学玄武岩玻璃蚀变的形式包含古代生命的生物特征。不幸的是，技术上的挑战使我们无法在原位观察这些蚀变特征的形成和矿化，或在实验室中再现管状玄武岩蚀变过程。因此，综合分析矿化小管中残留的物理和化学痕迹是目前破译玻璃蚀变记录的最佳方法。我们已经使用了一些高分辨率的光谱和显微镜的方法来探测的玄武岩玻璃管蚀变特征的地球化学和矿物学特征，从一套海底钻芯，涵盖了一系列不同的收集位置和年龄。通过将三种不同的基于同步辐射的X射线测量-X射线荧光微探针映射，XANES光谱和μ-XRD -与聚焦离子束铣削和透射电子显微镜相结合，我们已经空间分辨了主元素和微量元素分布，以及Fe的氧化态，确定了Fe，Mn和Ti在微米尺度上的配位化学，并将次生矿物限制在这些特征中。管状蚀变特征的特征是与新鲜玻璃相比，Fe 2+、Mn 2+和Ca 2+的强烈损失，残余Fe的氧化以及Ti和Cu的积累。充填蚀变区的主要相是以2：1粘土为主的含铁硅酸盐，其次是铁和钛的氧化物，以及部分氧化的锰硅酸盐相。管状蚀变特征中观察到的这些地球化学模式在过去5-100 Ma形成的不同样品中具有可比性，这表明微尺度矿化过程在整个海洋盆地和整个时间内是常见和一致的。Ti和Cu的分布在管状矿化和裂隙充填矿物之间是不同的，从而描绘了流体-岩石相互作用的顺序阶段。管状蚀变中保存的粘土和氧化物矿化的化学性质代表了一种常见的前体状态（例如钛的积累），这种状态尚未经历过在许多较老的管状蚀变变质实例中观察到的重结晶（例如钛铁矿的形成）。
There are numerous indications that subseafloor basalts may currently host a huge quantity of active microbial cells and contain biosignatures of ancient life in the form of physical and chemical basalt glass alteration. Unfortunately, technological challenges prevent us from observing the formation and mineralization of these alteration featuresin situ, or reproducing tubular basalt alteration processes in the laboratory. Therefore, comprehensive analysis of the physical and chemical traces retained in mineralized tubules is currently the best approach for deciphering a record of glass alteration. We have used a number of high-resolution spectroscopic and microscopic methods to probe the geochemical and mineralogical characteristics of tubular alteration features in basalt glasses obtained from a suite of subseafloor drill cores that covers a range of different collection locations and ages. By combining three different synchrotron-based X-ray measurements – X-ray fluorescence microprobe mapping, XANES spectroscopy, and μ-XRD – with focused ion beam milling and transmission electron microscopy, we have spatially resolved the major and trace element distributions, as well as the oxidation state of Fe, determined the coordination chemistry of Fe, Mn and Ti at the micron-scale, and constrained the secondary minerals within these features. The tubular alteration features are characterized by strong losses of Fe2+, Mn2+, and Ca2+compared to fresh glass, oxidation of the residual Fe, and the accumulation of Ti and Cu. The predominant phases infilling the alteration regions are Fe3+-bearing silicates dominated by 2:1 clays, with secondary Fe- and Ti-oxides, and a partially oxidized Mn-silicate phase. These geochemical patterns observed within the tubular alteration features are comparable across a diverse suite of samples formed over the past 5–100 Ma, which shows that the microscale mineralization processes are common and consistent throughout the ocean basins and throughout time. The distributions of Ti and Cu are distinct between tubular mineralization and the crack-filling minerals and thus delineate sequential stages of fluid–rock interaction. The preserved chemistry of clay and oxide mineralization in the tubular alteration then represents a common precursor state (e.g. Ti accumulation), that has not yet undergone recrystallization (e.g. titanite formation) as observed in many older, metamorphosed examples of tubular alteration.