The mechanisms controlling the release, transport, and isotopic composition of trace elements during weathering

风化过程中控制微量元素释放、运输和同位素组成的机制

• 批准号: 2598400
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2598400
• 关键词: mechanisms; controlling; release; transport; isotopic

The long-term carbon cycle of the Earth is dominated by the effects of mineral weathering, coupled with carbonate precipitation and the burial and oxidation of organic carbon. These processes are the key control on atmospheric concentrations of carbon dioxide and oxygen on million-year timescales (Holland, 1978). Long term climate records imply that chemical weathering acts as a negative feedback against metamorphism and volcanism, stabilising atmospheric CO2 to maintain a habitable environment (Walker, 1981) and much research has gone into quantifying the intensity of weathering processes and their associated fluxes of key cations and alkalinity through the Earth's surface environment.The lithium isotopic system is a potentially powerful tracer of silicate weathering, with advantages over other elements such as strontium and osmium, as there are minimal effects on 7Li from carbonate weathering, the presence of evaporites and biological processes (Pistiner and Henderson, 2003). The isotopic fractionation between 6Li and 7Li is driven by the formation of secondary clay minerals, which preferentially incorporate 6Li and drive waters to be isotopically heavier than the rocks they drain (Huh, 2001). The balance between denudation of silicate rocks, dissolution of primary silicates, clay formation and eventual redissolution of secondary clays gives a characteristic combination of the concentration and isotopic state of Li in river systems (Pogge von Strandmann, Dellinger and West, 2021), and the ratio of the weathering rate to the denudation rate is considered to be the intensity of silicate weathering (Dellinger, 2015).While trace element concentrations and isotopic compositions in river systems are readily measured, and a qualitative understanding of the link between these measurements and weathering intensity is well developed, there is insufficient understanding of the key mechanistic processes which generate these signatures. A fundamental complication of drawing environmental interpretations from this data is that chemical and isotopic trends are created by the processes which affect individual minerals and specific sites within their structures at the atomic level, which can behave in different ways (Hindshaw, 2019). A quantitative understanding of weathering in natural environments therefore requires improved knowledge of partitioning, isotope fractionation factors and the physical processes which distribute lithium (Pogge von Strandmann, Dellinger and West, 2021).

地球的长期碳循环主要受矿物风化的影响，加上碳酸盐沉淀和有机碳的埋藏和氧化。这些过程在百万年的时间尺度上是控制大气中二氧化碳和氧气浓度的关键因素(Holland，1978)。长期的气候记录表明，化学风化起到了防止变质作用和火山作用的负反馈作用，稳定了大气中的二氧化碳，以维持一个宜居的环境(Walker，1981)，许多研究都在量化风化过程的强度及其相关的关键阳离子和碱度通过地球表面环境的通量。锂同位素系统是潜在的强大的硅酸盐风化示踪剂，与其他元素如锶和锶相比具有优势，因为碳酸盐风化、蒸发岩的存在和生物过程对7Li的影响很小(Pistiner和Henderson，2003)。6Li和7Li之间的同位素分馏是由次生粘土矿物的形成驱动的，次生粘土矿物优先结合6Li，并驱动水的同位素比它们排放的岩石更重(Huh，2001)。硅酸盐岩石的剥蚀、原生硅酸盐的溶解、粘土的形成和次生粘土的最终再溶解之间的平衡给出了河流系统中Li的浓度和同位素状态的特征组合(Pogge von Strandmann，Dellinger和West，2021年)，风化速率与剥蚀速率的比率被认为是硅酸盐风化的强度(Dellinger，2015)。虽然河流系统中的微量元素浓度和同位素组成很容易测量，并且对这些测量和风化强度之间的联系有很好的定性理解，但对产生这些特征的关键机制过程缺乏足够的了解。从这些数据中得出环境解释的一个基本复杂性是，化学和同位素趋势是由在原子水平上影响个别矿物及其结构中的特定位置的过程造成的，这些过程可以以不同的方式表现(Hindshaw，2019)。因此，要定量了解自然环境中的风化作用，需要更好地了解分配、同位素分馏系数和分配锂的物理过程(Pogge von Strandmann，Dellinger和West，2021)。