Integrating Experiments With Observations at Oldoinyo Lengai; Insights Into Alkalic Magmatic Processes

世界上唯一的碳酸岩火山，坦桑尼亚的伦盖火山，岩浆的形成和喷发，继续使地球科学家感到惊奇和困惑。岩浆起源于地幔，但导致其独特的低温熔岩的过程仍不清楚。形成它的过程是什么？该项目将对这座火山的熔岩进行实验和分析，以从根本上了解地球岩浆改变成分并最终喷发的一般过程。以前的工作人员假设，这些岩浆反映了一种不相容反应，这种反应最终形成两种岩浆，一种是硅酸盐，一种是碳酸盐。这些研究人员将沿着在高压和高温下进行铁同位素比分析的新技术，以评估这一假设。具体来说，他们将进行实验，以测量两个共存的不混溶熔体之间的Fe同位素分馏因子。此外，他们将进行热梯度实验，以评估这一过程对形成喷发岩石中观察到的成分演化序列的可能作用。 该团队将使用新的断层X射线成像技术来评估这些实验中的熔体分布，以帮助限制Ol'doinyo Lengai周围观察到的电磁特征。使用U系列不平衡技术将使我们能够约束的时间和过程的岩浆形成的热梯度实验结果用于评估一个新的模型不平衡的产生。所获得的信息将有助于了解与大陆裂谷火山活动有关的危害。

The formation and eruption of magma from the world's only carbonatite volcano, Ol Doinyo Lengai in Tanzania, continues to amaze and perplex earth scientists. The magma originates as mantle derived but the processes leading to its unique, low temperature lava remain undefined. What is the process that forms it? This project will undertake experiments and analyses of lavas from this volcano to gain fundamental insight into the general processes by which Earth's magmas change composition and ultimately erupt.Previous workers have hypothesized that these magmas reflect an immiscibility reaction that occurs to ultimately form two magmas, one silicate and one carbonatite. These researchers will perform the new technique of Fe isotope ratio analyses along with laboratory experiments at high pressure and temperature to assess this hypothesis. Specifically, they will perform experiments to measure the Fe isotopic fractionation factor between 2 coexisting immiscible melts. Furthermore, they will perform thermal gradient experiments to assess the possible role of this process on forming the compositional evolution sequence observed in erupted rocks. The team will use new tomographic X-ray imaging techniques to assess the melt distribution in these experiments to help constrain observed electromagnetic signatures around Ol'doinyo Lengai. Use of U-series disequilibria techniques will allow us to constrain the timing and processes of magma formation with the thermal gradient experiment results used to assess a new model for disequilibria generation. The information obtained will help to understand the hazards associated with continental rift volcanism.