Compositional variations of tourmaline from low to ultrahigh pressure

电气石的组成已被广泛用作形成温度的成岩指示剂，并用于监测地壳和俯冲带环境中的流体驱动过程。然而，有一个更好的量化的tourglass组合物依赖于流体成分的需要，也没有普遍的协议，如果和如何组成的变化tourglass可以潜在地用作地质压力计。我们希望将现有的数据集流体电气石从低到非常高的压力，并将测试的假设，增强K掺入的X-网站的电气石，以及增加纳入四面体协调B到电气石结构的电气石流体和电气石-（K，Na）云母交换实验一系列的压力。如果电气石具有显著量的四面体B，这必然对流体和电气石之间的B同位素分馏具有显著影响，这将被校准。与此同时，我们将通过晶体化学和B同位素分析对来自已知的、先前确定的压力-温度演化区域的低压到高压岩石中的电气石进行研究，以评估电气石可用作地质压力计，而且代表变质作用期间流体的Na-Ca-K浓度的监测器。结合这两个部分，我们期望更好地了解大规模的，长期的B周期在俯冲过程中。

The composition of tourmaline has widely been used as a petrogenetic indicator for temperature of formation and for monitoring fluid-driven processes in the Earth s crust and subduction zone environments. There is, however, a need for a better quantification of tourmaline composition in dependence of fluid composition, and also no general agreement if and how the compositional variability of tourmaline could be potentially used as a geobarometer. We want to extend the available data set for fluid-tourmaline from low to very high pressure and will test the hypothesis of enhanced K incorporation on the X-site of tourmaline as well as increased incorporation of tetrahedrally coordinated B into the tourmaline structure by a series of tourmaline-fluid and tourmaline-(K,Na)mica exchange experiments up to ultrahigh pressure. If tourmaline has a significant amount of tetrahedral B this must have a significant effect on the B isotope fractionation between fluid and tourmaline, which will be calibrated. Parallel to this, we will investigate by crystal-chemical and B isotopic analyses of tourmaline from low to high pressure rocks from areas with well-known, previously determined pressure-temperature evolution in order to assess that tourmaline may serve as a geobarometer and moreover represents a monitor of Na-Ca-K concentrations of fluids during metamorphism. Combining the two parts we expect a better understanding of the large-scale, long-term B cycle during subduction processes.