基于LA-ICP-MS多元素成像技术的早寒武世磷结核成因研究

发布时间：2018-09-11 14:11

【摘要】：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。
[Abstract]:Phosphorus rich deposits such as phosphorus nodules and phosphorite are widely developed in the bottom of the Lower Cambrian in China. They are one of the most important chemical markers of the early Cambrian and represent the great changes of the Earth's surface system during the transition period of the crypto-Phanerozoic period. Current explanations of phosphorus sources and enrichment mechanisms are not uniform. In order to further clarify the formation mechanism of phosphorus-rich deposition in this period, the multielement in-situ microimaging of phosphorus nodules in the black shale of Niutetang formation in Jinsha area, Guizhou Province was studied by laser denudation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results show that the enrichment of various elements in phosphorus nodules clearly records the trend of microenvironment changes during the formation of phosphorus nodules. Among them, Ca,P co-enrichment and Si depletion in phosphorus nodules indicate that P enrichment is due to autogenous apatite formation and P is derived from organic matter containing oxygen or anaerobic degradation release of Mn-Zn and P co-enriched in phosphorus nodules. It indicates that the bottom water of nodule formation is mainly enriched in surrounding rock or black shale, and that the formation of anoxic water containing H2S terminates the growth of nodules. This study shows that LA-ICP-MS in situ multielement imaging technique can obtain abundant geochemical information and provide high accuracy visual evidence in microarea. It will be widely used in geological exploration and paleoenvironmental research in the future.
【作者单位】：贵州大学资源与环境工程学院;中国石油勘探开发研究院油气地球化学重点实验室;北京大学地球与空间科学学院造山带与地壳演化教育部重点实验室;
【基金】：国家自然科学基金资助项目(41530317,41472089) 中国石油天然气股份有限公司重点资助项目(2016A-0204,2016A-0205) 贵州省地勘基金项目(2016-09-1)
【分类号】：P512.2;P534.41

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