基于LA-ICP-MS多元素成像技术的早寒武世磷结核成因研究

我国下寒武统底部广泛发育磷结核、磷块岩等富磷沉积,为早寒武世最为重要的化学标志层之一,也代表了隐生宙—显生宙转折期地球表层系统的重大变革。当前对磷来源和富集机制的解释不一。为进一步明确该时期富磷沉积的形成机制,本文利用激光剥蚀电感耦合等离子体质谱联用技术(LA-ICP-MS)对贵州金沙地区牛蹄塘组黑色页岩中的磷结核进行多元素原位微区成像研究。结果表明:磷结核中各元素富集情况清晰地记录了磷结核形成过程中微环境的变化趋势。其中,磷结核内部Ca、P共富集以及Si亏损,指示P富集缘于自生磷灰石生成,P则来自于有机质含氧或厌氧降解释放;Mn、Zn与P共富集于磷结核内部,指示结核形成时的底部水体为含氧水体;As、Mo、V等元素主要富集于围岩或黑色页岩,指示缺氧含H_2S水体形成终止了结核生长。本研究显示,LA-ICP-MS原位多元素成像技术能够获取微区内丰富的地球化学信息,并提供高精度可视化证据,未来将在地质勘探和古环境研究等领域得到更广泛应用。

Study on the Formation Mechanism of Phosphate Nodules in the Early Cambrian Period Using LA-ICP-MS Multi-element Imaging Technology

The phosphorus-rich sediments, including phosphate nodules and phosphate rock, at the bottom of the Lower Cambrian, are widespread in China. These sediments are also considered as one of the most important chemical symbol layers in early Cambrian and also indicate the great change of the Earth''s surface system in the transitional period of Cryptozoic to Phanerozoic. Phosphorus sources and the enrichment mechanism remains a matter of debate. In order to better understand the depositional mechanism of these phosphorus-rich sediments, Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) was used to perform in situ multi-element imaging in the micro areas of phosphate nodules from the black shale of the Niutitang Formation in the Jinsha area of Guizhou Province. The results show that the enrichment of each element in phosphorus tuberculosis clearly records the trend of the microenvironment during the formation of phosphorus tuberculosis. Ca and P are enriched and Si is depleted in the inner layer of the phosphate nodule, which means that the enrichment of P was due to the formation of authigenic apatite. P is derived from organic matter containing oxygen or anaerobic degradation release. The co-enrichment of Mn, Zn with P in the interior indicates an oxic bottom water layer during the formation of the phosphate nodule. The enrichment of As, Mo, V in the surrounding rocks or black shale implies that the reduced bottom water ended the growth of the phosphate nodule. This study shows that LA-ICP-MS in situ multi-element imaging technology can reveal rich geochemical information in the micro-area, which can provide high-precision visualization evidence, and will be widely used in geological exploration and paleo-environmental research.