Pressure–temperature evolution and thermal regimes in the Barrovian zones, Scotland

posted on 21.06.2016 by Sarah H. Vorhies, Jay J. Ague

We constrain the PT evolution of the Barrovian metamorphic zones from the southwestern to the northeastern coasts of Scotland using thermobarometry and pseudosection analysis based on mineral composition data, garnet zoning profiles and 2D garnet maps. Twenty-five samples were investigated from the garnet to the sillimanite zones. In the western half of the field area there was relatively high-P metamorphism (0.9–1.1 GPa) followed by near-isothermal decompression. In and around the Barrovian type area of Glen Clova maximum pressures were also high (c. 0.8–0.9 GPa); however, peak-T conditions were driven by a brief (of the order of 1 Ma or less) thermal pulse or pulses during exhumation at c. 0.6 GPa. Pressures at peak-T conditions along the eastern coast were the lowest observed, c. 0.4–0.5 GPa. These rocks were probably affected by the same thermal pulse activity evident around Glen Clova. All three regions initially developed during regional metamorphism associated with thermal relaxation of tectonically overthickened crust. The eastern part of the sequence, including Glen Clova, is fundamentally different from the western part because it required additional advective heat input to achieve peak thermal conditions. This heat was probably supplied by synorogenic magmas (e.g. Newer Gabbros) and the associated elevated crustal heat flow.