Viscous flow and diffusion in highly depolymerized water-rich melts: improvement of experimental methods and implication for natural system

富水强解聚熔体的输运性质仍有争议。到目前为止，还没有实验技术可以用来确定在高温高压下高度解聚的熔体的粘度。这种粘度数据是至关重要的，以了解结晶过程中的动力学过程和喷发过程的自然系统，如含水伟晶岩和声子晶体。落球法（斯托克斯定律）已成功地用于各种条件下的粘度测定。然而，其应用于低粘度熔体主要是有限的可实现的实验持续时间。在项目的第一部分（前12个月），我们开发了一种新的设置，允许在内部加热气体压力容器（IHPV）中快速加热和快速淬火样品，并建立了一个新的垂直定向冷密封压力容器（CSPV）系统，用于快速加热/快速淬火。此外，我们进行了伟晶岩熔体的粘度测定在高（微渗透）和低粘度范围（落球）。初步结果表明，富水伟晶岩熔体的粘度显着低于（高达2 - 3个对数单位）比现有的模型预测。在该项目的第二部分，我们计划使用快速加热和快速淬火装置，以更准确地确定在硅酸盐熔体中的助熔元素，如F，Li（最终B和P）的个别影响。该设置也将被用来确定HFSE（铌和钽）在伟晶岩熔体，这是重要的约束经济HFSE浓度的形成提出的遗传模型的扩散。最后，我们计划确定富水响岩的粘度，这将有助于模拟响岩熔体的上升和脱气。

The transport properties of water-rich strongly depolymerized melts are still under debate. So far no experimental techniques are available to determine the viscosity of highly depolymerized melts at elevated temperatures and pressures. Such viscosity data are crucial to understand kinetic processes during crystallization and eruptive processes of natural systems such as hydrous pegmatites arid phonolites. The falling sphere method (Stokes law) has been successfully used for viscosity determination at various conditions. However, its application to low viscosity melts is mainly limited by the achievable experimental duration. In the first part of the project (first 12 months), we have developed a new set-up allowing rapid heat and rapid quench of samples in internally heated gas pressure vessels (IHPV) and set up a new system of vertically oriented cold seal pressure vessels (CSPV) for rapid heat/rapid quench. Additionally, we have conducted viscosity determinations of pegmatitic melts in the high (micropenetration) and low viscosity range (falling sphere). The preliminary results show that the viscosity of water-rich pegmatite melts is significantly lower (up to 2 - 3 log units) than predicted by available models. In the second part of the project we plan to use the rapid heat and rapid quench devices to determine more accurately the individual effects of fluxing elements such as F, Li (eventually B and P) in silicate melts. The setup will also be used to determine the diffusivity of HFSE (Nb and Ta) in pegmatitic melts, which is of importance to constrain the genetic models proposed for the formation of economic HFSE concentrations. Finally we plan lo delermine the viscosity of water-rich, phonolites which will be useful for modeling ascent and degassing of phonolite melts.