主要地质储库钾同位素不均一性研究与基准值标定

Potassium is an important element that is ubiquitously occurring on Earth, and its isotopes have the potential of tracing distribution and cycling of potassium and the alkaline group elements between different geological reservoirs. In the past few years, advances in mass spectrometry had enabled high precision K isotope analysis, initiating a rapid expansion in the research field of potassium stable isotope geochemistry. However, currently the isotopic heterogeneity and isotopic baseline of potassium in major geological reservoirs (i.e., mantle and crust) are still not well understood, which is becoming a limiting factor for further development of potassium isotopes as a tracing tool and its applications to geological problems. This proposed project aims at setting up a high precision analytical method for K isotopes in China, and using this method to obtain high precision K isotope data for different representative mantle- and crust- sourced rocks, to elucidate the isotopic heterogeneity of potassium in mantle, and to better constrain the isotopic baseline of potassium in Earth's mantle and crust. The behavior of potassium isotopes during several typical magmatic processes will also be investigated in this proposed project.

钾是一个广泛分布的重要元素，钾的稳定同位素能帮助我们理解钾甚至碱金属族元素在各种地质体之间的分配与循环。在过去的几年里，高精度的钾同位素分析技术取得突破，为钾同位素地球化学研究的迅猛发展打开了一个窗口。但是，当前对主要地质储库钾同位素不均一性和基准值的了解依然不充分，这限制了钾同位素作为地球化学示踪剂的进一步发展和针对具体地质问题的应用。本项目拟在国内完全建立高精度钾同位素分析方法，并对有代表性的幔源岩石、大洋和大陆玄武岩、以及具有代表性的地壳岩石进行高精度钾同位素分析，从而厘清地幔的钾同位素不均一性，更好地制约地壳与地幔两个重要储库的钾同位素基准值，并研究一些典型岩浆过程中的钾同位素行为。

本项目旨在更好地理解主要地质储库钾同位素不均一性和进一步标定其基准值，为钾同位素作为地球化学示踪剂的进一步发展和针对地质问题的应用奠定基础。在此项目的资助下，在南京大学依托新引进的Nu1700 碰撞反应池多接收等离子质谱仪 （CC-MC-ICP-MS）建立了高质量的 K 同位素分析方法。探索了两种不同的K同位素分析技术路线，对δ41K的长期外部重现性优于±0.07‰（热焰+高分辨模式）或±0.06‰（碰撞反应池模式）。对一系列地质储库样品，包括河水、黄土和页岩、近海沉积物、洋岛玄武岩、花岗岩、伟晶岩等超过两百个样品进行了高精度K同位素测量，获得大量数据，对上地壳火成岩、地表沉积物、和水圈的K同位素不均一性进行了进一步的限定。系统研究了表生风化过程和岩浆结晶过程的K同位素分馏行为。发表K分析方法论文两篇，地质样品K同位素研究论文三篇，K同位素地球化学综述论文一篇。标注本项目基金号（41873004）论文10篇，其中第一标注论文1篇，第二标注论文4篇。相关K同位素研究论文发表在国际一流期刊包括PNAS，Analytical Chemistry和Science China Earth Sciences等国内一流期刊上。