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

英国西南部克朗沃尔地区的花岗岩及其伴生伟晶岩、长角长石和矿化灰岩构成了一个造山后高度分异的硅质岩浆作用及其伴生热液Sn-W-Cu成矿的典型体系。从科学和经济的角度来看，这些花岗岩的晚期演化，特别是熔融-蒸汽平衡的时间和成分方面，代表了岩浆活动的一个至关重要的阶段。在康沃尔花岗岩体系的挥发性或助熔剂组分中，硼的作用可能是最重要的，也是最不为人所知的。这项工作将记录该环境中硼（如电气石）的丰度和地质关联，并将研究电气石的流体包裹体，这些包裹体可能独特地揭示花岗岩及其伴生脉和寄主岩石中产生的流体的组成和物理状态。此外，对电气石（11B/10B）硼同位素组成的分析将有助于确定花岗岩岩浆的物源（烃源岩）、花岗岩与寄主岩之间的混合程度和流体流动路径（如果发现多个硼储层），并借助同位素分馏的实验校准、压力、温度、温度、温度、温度和温度等。以及电气石结晶不同阶段流体的pH值。本研究为进一步阐明岩浆-热液系统中硼的地球化学循环提供了理论依据。这些结果可能普遍适用于在空间和时间上普遍和广泛分布的类似矿床，并将作为其他矿床效仿的模型。

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.