Magma-Vapor Evolution in Granitic Systems of Cornwall, SW England: The Role of Boron

英格兰西南部克朗沃尔的花岗岩及其伴生的伟晶岩、辉长岩和矿化云英岩，构成了造山后高度分异的硅质岩浆作用和伴生的热液锡钨铜成矿的原型系统。从科学和经济的角度来看，这些花岗岩的后期演化，特别是熔融-蒸汽平衡的时间和成分方面，代表了岩浆作用的一个至关重要的阶段。在康沃尔花岗岩系统的挥发性或助熔剂成分中，硼的作用可能是最重要的，也是最不被了解的。这项拟议的工作将记录这种环境中硼(如电气石)的丰度和地质组合，并将研究电气石的流体包裹体，以独特地揭示花岗岩及其伴生脉体和围岩中产生的流体的成分和物理状态。此外，对电气石(11B/10B)的硼同位素组成的分析将有助于识别花岗岩浆的来源(源岩)、花岗岩与其主岩(如果发现多个硼储集层)之间的混合程度和流体流动的途径，并借助于同位素分馏实验校准，压力，温度，以及电气石结晶不同阶段流体的pH值。这一结果是由首席研究员发展的，以进一步阐明岩浆-热液系统中硼的地球化学循环。这一结果可能普遍适用于在空间和时间上普遍存在的类似矿床，并将作为其他人效仿的典范。

The granites and associated pegmatites, aplites, and mineralized greisens of Cronwall, southwest England, constitute an archetypal system of post-orogenic, highly differentiated silicic magmatism and associated hydrothermal Sn-W-Cu mineralization. The late-stage evolution of these granites, in particular the temporal and compositional aspects of melt-vapor equilibria, represent a critically important stage of magmatism from both scientific and economic perspectives. Among the volatile or fluxing components in the Cornish granite systems, the role of boron may be the most important and least understood. This proposed work will document the abundance and geologic associations of boron (as tourmaline) in this environment, and the tourmaline will be studied for fluid inclusions that may uniquely reveal the compositions and physical states of fluids generated in the granites and associated veins and host rocks. In addition, analyses of the boron isotopic composition of tourmaline (11B/10B) will help to identify the provenance (source rocks) of the granitic magmas, the extent of mixing and pathways of fluid flow between granites and their host rocks (if multiple reservoirs of boron are found), and with the aid of experimental calibration of isotopic fractionation, the pressures, temperatures, and possibly pH of fluids at various stages of tourmaline crystallization. The results of this developed by the principal investigator to further elucidate the geochemical cycle of boron in magmatic-hydrothermal systems. The results may be generally applicable to similar deposits that are common and widespread in space and time, and will serve as a model for others to follow.