Stable Isotope and Textural Evidence on the Mechanisms of Metamorphic Fluid Infiltration Within a Zone of Structurally-Focused High Fluid Flux

Abstract

Dalradian rocks of the SW Scottish Highlands, dominantly comprising interlayered calc-phyllites, psammites and metabasite sills, have been infiltrated by H20-CO2 fluids during regional greenschist facies metamorphism. Three-dimensional, syn-metamorphic fluid fluxes have been mapped on a regional scale using reaction front advection in metabasite sills (Skelton et al., 1994). Fluid flow has been constrained by lithology, and by regional and local structure. Flow was channelled within the 6km thick Ardrishaig phyllites, which embodies the regional upwardfacing Ardrishaig Anticline and within which fluxes increase exponentially towards the axial surface, where maximum fluxes in excess of 103 mam -2 were measured. Fluxes of this magnitude should have caused oxygen isotopic homogenisation of the phyllites. The mechanism by which fluid is preferentially channelled through the axial regions of anticlinal folds remains to be determined. We have undertaken stable isotopic and textural studies of the phyllites and interlayered psammites across the Ardrishaig Anticline structure to seek evidence of isotopic homogenisation and of the mechanisms of fluid flow.