Quantifying basalt denudation rates and their contribution to the global carbon dioxide budget using cosmogenic Mn-53

地球表面硅酸盐岩石的化学风化会消耗大气中的二氧化碳，因此有可能影响全球气候。特别是，玄武岩岩石的风化可能是二氧化碳的一个重要汇。我们对控制岩石化学风化速率的理解一直受到限制，因为我们无法测量与陆地形成过程相关的时间尺度上的速率。在过去二十年中，由于陆地宇宙成因核素技术的发展，这种情况有所改善，能够量化剥蚀，从而提取千年和更长时间尺度上的化学风化速率。玄武岩地体在这项工作中受到的关注很少，部分原因是缺乏用于宇宙核素测量的合适的目标元素。然而，最近的进展表明，宇宙成因的Mn-53能够量化铁氧化物的剥蚀速率，这意味着它可以在玄武岩中测量。我们的总体目标是利用这一新能力，并量化玄武岩风化作为全球大气二氧化碳汇的重要性。为了实现这一点，我们将从两个气候不同的环境中收集样本：巴西南部潮湿的巴拉纳洪水玄武岩和干旱的纳米比亚的埃滕代卡洪水玄武岩。这些岩石最初是作为一个整体挤压出来的，但由于大西洋的开放而被一分为二。虽然它们在岩性上是相同的，但它们经历的降雨量非常不同，而且都受到显著的温度梯度的影响。岩石样品中宇宙成因的Mn-53浓度将揭示剥蚀速率，进而揭示气候因素对风化速率的影响。对化学风化和物理风化之间关系的进一步研究，再加上附近非玄武岩岩性的剥蚀速率，将使我们能够对玄武岩的风化速率和控制这些风化的因素有一个广泛的了解。

Chemical weathering of silicate rocks at the Earth's surface consumes atmospheric carbon dioxide and thus has the potential to influence global climate. In particular, the weathering of basalt rocks could be an important sink for carbon dioxide. Our understanding of what controls the chemical weathering rates of rocks has been limited by our inability to measure rates over the timescales that are relevant to land-forming processes. During the last two decades this situation has improved due to the development of terrestrial cosmogenic nuclide techniques, able to quantify denudation and thus extract rates of chemical weathering over millennial timescales and longer. Basaltic terrains have received little attention in this work, due in part to a lack of suitable target elements for cosmogenic nuclide measurements. However, recent progress has shown cosmogenic Mn-53 is able to quantify denudation rates in iron oxides, which means that it can be measured in basalt. Our overall aim is to take advantage of this new ability and to quantify the importance of basalt weathering as a global atmospheric carbon dioxide sink. To achieve this we will collect samples from two climatically diverse environments: the Paraná flood basalts in humid southern Brazil and the Etendeka flood basalts in arid Namibia. These rocks were originally extruded as one body but were split in two and separated due to the opening of the Atlantic Ocean. While they are lithologically the same, they experience very different amounts of precipitation and both are affected by dramatic temperature gradients. Cosmogenic Mn-53 concentrations in the rock samples will reveal rates of denudation and subsequently the influence that climatic factors have on rates of weathering. Additional investigations into the relationships between chemical and physical weathering, coupled with rates of denudation from nearby non-basaltic lithologies, will allow us to develop a broad understanding of the rates at which basalt weathers and the factors that control theserates.