Rates and mechanisms of element transfer during mineral reactions in the presence of a fluid phase

地球的特点是元素和同位素分布在空间和时间上的高度变化。因此，由此产生的动力学系统需要在非常不同的尺度上（从单个原子到数百公里）进行大量的热量和质量传输，这通常是由不平衡条件驱动的。在地壳岩石中，大部分物质的迁移与矿物反应有关。拟议的项目定量调查过程中发生的矿物反应在碳酸盐系统中的小规模。这一建议的新挑战是非平衡过程的定量参数化，因为其在自然样品中观察到的元素和同位素分区记录包含关于实际路径的信息，即运作机制和到达那里所需的时间。我们假设，实际的反应机制取决于从平衡状态的偏差，并由此产生的分区模式可以定量解决。因此，本项目的目标是评价矿物a成分在沿着任何P-T-X-t-路径上的时空动态演化，开展实验，系统研究共存矿物对之间的元素和同位素交换。实验运行将分析表面过程和成分深度剖析。将建立一个数值模型来预测沿着任何给定的P-T-X-t-路径发生的矿物反应过程中的反应机制和元素及同位素的空间组成。将根据区域含碳酸盐变质岩中的自然观测结果对模型结果进行检验，这些岩石显示出白云石组成的核心周围的铁白云石反应边缘。由此产生的知识提供了必要的时间尺度上的信息，以平衡常用的热（气压）计，这是固有的联系到所有地质年代学方法的扩散封闭的概念。所获得的知识可用于推断和估计元素和同位素通过地壳的迁移率，从而量化它们在地球系统中的循环。

The Earth is characterized by a high variance of element and isotope distribution with respect to space and time. The resulting dynamic system therefore requires substantial transport of heat and mass on very different scales (from single atoms to several hundreds of kilometers), which are typically driven by disequilibrium conditions. In crustal rocks most of the mass transport is related to mineral reactions. The proposed project quantitatively investigates processes occurring during mineral reactions in the carbonate system on a small scale. The new challenge of this proposal is the quantitative parameterization of non-equilibrium processes as its record of element and isotope zoning observed in natural samples contain information on the actual path, i.e. the operating mechanism and the time taken to get there. We hypothesize that the actual reaction mechanism depend on the deviation from the equilibrium state and that resulting zoning patterns can be resolved quantitatively. Hence, the proposed project aims to evaluate the dynamic evolution of mineral a composition in space and time along any P-T-X-t-path. Experiments will be carried out to systematically studying element and isotope exchange between co-existing mineral pairs. Experimental runs will be analyzed for surface processes and by compositional depth profiling. A numerical model will be developed to predict the reaction mechanism and the spatial composition of elements and isotopes during mineral reactions occurring along any given P-T-X-t-path. Modeling results will be tested against natural observations in regional carbonate bearing metamorphic rocks exhibiting reaction rims of ankerite surrounding cores of dolomite composition. The resulting knowledge provide the information on timescales necessary to equilibrate commonly used thermo(baro)meters which are inherently linked to all geochronology methods by the concept of diffusive closure. The gained knowledge can be used to extrapolate and estimate the rates of element and isotope transport through the crust and thus quantify their cycles in the Earth system.