The distribution of pressure and temperature during Dalradian metamorphism

摘要: The formation of sillimanite in association with the development gneisses and migmatites Grampian Highlands north-eastern Scotland is interpreted as a later superimposition upon slightly earlier metamorphic pattern characterized its higher grades by andalusite kyanite. This subdivided three significant isograds: (i) isograd, along which developed from hydrous mineral assemblages; (ii) kyanite (iii) an andalusite–kyanite dividing zones, are dehydration isograds, virtually isothermal; represents polymorphic inversion to andalusite, P/T slope approximately 12.8 bars/degC. For some 50km southwards coastline Moray Firth on western limb post-metamorphic Boyndie syncline, isograds form parallel traces; parallelism such disparate slopes suggests that isobars isotherms this region were parallel. In central Aberdeenshire isograd diverges appears run Deeside meet south. indicating divergence between isotherms; antiformal monocline ne–sw axes deduced for thermal surface. To explain disposition synmetamorphic monoclinal folding suggested, pressure adjustment was instantaneous sediments depressed deeper levels, but heat content enabled pre-existing isothermal surfaces be preserved.