Vein controlled crystal size distributions of Barrovian index minerals

Sammanfattning: The concept of index mineral based metamorphic zones was first introduced by George Barrow in 1912, and Barrovian metamorphism is still applied by metamorphic petrologists. Today the importance of metamorphic fluids for driving metamorphic reactions is widely recognised. Even so, the general view is that Barrovian metamorphism is solely controlled by pressure, temperature, and protolith composition. This thesis aims to establish if and how fluids control index mineral formation and distribution during Barrovian metamorphism. To do so, samples from Barrow’s own type locality in Glen Esk, Southeast Scottish Highlands, are used to investigate possible relationships between veining and index mineral distribution. This was done using a combination of petrographic and textural observations and analyses, whole rock chemistry, mineral chemistry, as well as oxygen isotope analyses. These data show a grade dependant association of index mineral distribution and veining: in the chlorite zone and most of the biotite zone, no correlation between veining and index mineral distribution is seen. For the garnet and staurolite zones, index mineral abundance is shown to decrease away from veins. The kyanite zone shows a fairly homogenous kyanite distribution, but also indications of extensive fluid-rock interaction. Based on these observations and the analysis datasets, it is concluded that fluid played a major role in the stabilisation and distribution of the Barrovian index minerals in Glen Esk, and that the fluid control was larger at metamorphic grade.