Mobility of volatile (H2O & CO2)-bearing melts in the upper mantle: from carbonatite magmatism to the dynamics of kimberlitic eruptions

挥发物(H2O和CO2)在行星内部的动力学和热演化中起着关键作用，并定义了行星表面的宜居条件。因此，了解深层和表层储集层之间的挥发分交换和通量仍然是地球科学界的主要目标。然而，这些过程的定量模拟在很大程度上受到对挥发分熔体的流动性和迁移率缺乏基本限制的限制，而挥发分熔体是挥发分分布的主要传送器。该项目通过将含挥发分熔体的高压密度测量和热力学建模相结合来解决这一关键的知识差距，以获得对地球内部深层挥发循环和相关地球物理过程的定量洞察。在第一个资助期，我们把重点放在富含碳酸盐的熔体上，并限制了水化作用对碳酸盐熔体的密度/流动性、熔体中溶解挥发分的可压缩性以及从俯冲岩性中提取碳酸盐熔体的时间尺度的影响。此外，我们在跨越地幔过渡带以外的岩浆作用的条件下，即高达30 GPa和2300K的条件下，校准了第一个在MgO-CaO-Na2O-K2O-Li2O-H2O-CO2系统中碳酸盐熔体的连续密度模型。在成功的第一个资助期之后，扩展项目将专注于中间的二氧化硅欠饱和富碳熔体，与已被广泛研究的富挥发分的富硅熔体相比，这些熔体的密度数据在相关的地幔条件下几乎不可用。上地幔条件下的碳酸盐岩和金伯利岩熔体的密度数据将在大体积压力机中结合使用同步加速器X射线吸收/射线照相法和沉浮法获得。新的密度数据将使碳酸盐熔体密度模型扩展为全球密度模型，适用于上地幔稳定的含挥发分熔体范围，即从碳酸盐(富含二氧化碳)到碳酸盐玄武岩(富含二氧化硅的熔体)。新模型将能够预测含挥发分熔体的流动性，并模拟熔体在地幔中的迁移/上升/就位，包括含金刚石金伯利岩喷发的动力学及其在固体地幔中的地球物理特征。最终，该项目的结果将使人们对地球深处的挥发性流动和循环有一个新的理解。

Volatiles (H2O and CO2) play a critical role in the internal dynamics and thermal evolution of planetary interiors, and define the habitability conditions at their surface. Understanding the exchanges and fluxes of volatiles between deep and surficial reservoirs thus remain a primary goal of the Earth Sciences community. Yet, the quantitative modelling of these processes is largely limited by the lack of fundamental constraints on the mobility and migration rates of volatile-bearing melts, that are the main conveyors for the distribution of volatiles. This project addresses this critical gap of knowledge by combining high pressure density measurements in volatile-bearing melts and thermodynamic modelling to gain quantitative insights into the deep volatile cycles and related geophysical processes inside the planet. During the first funding period, we focused on carbonate-rich melts and constrained the effect of hydration on the density/mobility of carbonate melts, the compressibility of dissolved volatiles in the melt and the timescale of carbonate melt extraction from subducted lithologies. Moreover, we calibrated the first continuous density model for carbonate melts in the system MgO-CaO-Na2O-K2O-Li2O-H2O-CO2 at conditions that span magmatic processes beyond the mantle transition zone, i.e. up to 30 GPa and 2300 K. After a successful first funding period, the extension project will focus on intermediate silica under-saturated carbon-rich melts for which density data is virtually not available at relevant mantle conditions in contrast to volatile-bearing silica-rich melts that have been extensively investigated. Density data in carbonatite and kimberlite melts at upper mantle conditions will be obtained using a combination of synchrotron X-ray absorption/radiography and sink-float methods in large volume presses. The new density data will enable the extension of the carbonate melt density model into a global density model for the range of volatile-bearing melts stabilized in the upper mantle, i.e. from carbonates (CO2-rich) to carbonated basalts (SiO2-rich melts). The new model will allow predictions of the mobility of volatile-bearing melts and modelling the migration/ascent/emplacement of melts through the mantle, including the dynamics of diamond-bearing kimberlite eruptions, and their geophysical signature in the solid mantle. Ultimately, the results of this project will lead to a new understanding of volatile mobility and recycling in the deep Earth.