New insights into nanostructure and geochemistry of bioapatite in REE-rich deep-sea sediments: LA-ICP-MS, TEM, and Z-contrast imaging studies
New insights into nanostructure and geochemistry of bioapatite in REE-rich deep-sea sediments: LA-ICP-MS, TEM, and Z-contrast imaging studies
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DOI：
10.1016/j.chemgeo.2019.02.039
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发表时间：
2019-05
期刊：
影响因子：
3.9
通讯作者：
Jianlin Liao;Xiaoming Sun;Dengfeng Li;Rina Sa;Yang Lu;Zhiyong Lin;Li Xu;R. Zhan;Yuguan Pan-
中科院分区：
文献类型：
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作者：
Jianlin Liao;Xiaoming Sun;Dengfeng Li;Rina Sa;Yang Lu;Zhiyong Lin;Li Xu;R. Zhan;Yuguan Pan-
稀土元素(REE)和Y(Y)，又称稀土元素(REY)，最近在一些远洋沉积物中被发现高度富集，这可能是未来REY的重要来源。然而，它们的浓缩机制仍然存在争议。由于生物成因磷灰石是富稀土深海沉积物中最重要的稀土载体之一，采用化学分析和原子分辨化学成像相结合的方法对其矿物学和地球化学性质进行鉴定是至关重要的。扫描电子显微镜和透射电子显微镜研究表明，生物磷灰石化石主要由定向排列的羟基磷灰石纳米片组成。激光烧蚀-电感耦合等离子体质谱分析表明，稀土元素在所研究的生物磷灰石化石中分布不均匀。测量和模拟分析的浓度剖面表明，在成岩作用早期，主要稀土元素应与来自海水和孔隙水的生物磷灰石化石相结合。Z-衬度成像结果显示，磷灰石中存在两种可能的偶合置换：REE3++ Na+↔ 2Ca2+和/或REE3++ Si4+↔ Ca2++ P5+，区别于陆地上的离子吸收型稀土矿床。我们的研究表明，生物磷灰石化石在成岩作用过程中容易发生蚀变，因此在应用生物磷灰石的稀土元素信号作为古海洋环境重建的指标时，应慎重考虑。
Rare earth elements (REE) and yttrium (Y), termed as REY, are recently found to be extremely enriched in some pelagic sediments, which could be an important resource for REY in the future. However, their enrichment mechanism remains controversial. Because biogenetic apatite is one of the most important REY carriers in REY-rich deep-sea sediment, it is critical to identify its mineralogical and geochemical characteristics by using combined methods ofin situchemical analysis and atomic resolution chemical imaging.Scanning electron microscope and transmission electron microscopy studies reveal that bioapatite fossils mainly consist of aligned hydroxyapatite nano-plates. Laser ablation-inductively coupled plasma-mass spectrometry analyses show that the REY are not uniformly distributed within the studied bioapatite fossils. Concentration profiles from the measurements and modeling analyses indicate that the major REY should be incorporated into the bioapatite fossil from seawater as well as the pore water during the early stage of diagenesis. Z-contrast imaging results reveal the following two possible coupled substitutions in the apatite: REE3++ Na+↔ 2Ca2+and/or REE3++ Si4+↔ Ca2++ P5+, which is distinguished from those ion-absorption-type REE deposits on land. Our study indicates that bioapatite fossils are prone to undergo alteration during diagenesis, and thus cautious examination should be taken when applying REE signal of bioapatite as a proxy for palaeo-ocean environmental reconstruction.