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的分布在空间和时间上有很大的变化。因此，由此产生的动力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，大部分的物质搬运与矿物反应有关。拟议的项目定量地研究了在碳酸盐体系中发生的矿物反应过程。这个提议的新挑战是非平衡过程的定量参数化，因为它在自然样品中观察到的元素和同位素分带记录包含了实际路径的信息，即运行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对平衡态的偏离，并且由此产生的分带模式可以定量地解决。因此，提议的项目旨在评估矿物组成在空间和时间上沿任何p -t- x -t路径的动态演化。实验将系统地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工艺和成分深度剖面。将开发一个数值模型来预测沿任何给定的p -t- x -t路径发生的矿物反应的反应机制和元素和同位素的空间组成。模拟结果将与区域含碳酸盐变质岩的自然观测结果进行对比，这些变质岩显示白云岩组成的岩心周围有铁白云岩的反应边缘。由此产生的知识提供了平衡常用热（气压）表所必需的时间尺度信息，热（气压）表通过扩散闭合的概念与所有地质年代学方法内在地联系在一起。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运输速率，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.