A ‘Barrovian’ isograd Ky50 based on the coexistence with kyanite and staurolite of biotite M/FM = 50 forms a SW–NE trending loop extending from Deeside into Perthshire; fault displacement of the southern limb suggests a north-westerly dip with high grade overlying low grade. The recumbent thermal anticline so delineated represents syn-metamorphic thermal disturbance, possibly due to the introduction of warm material with the upward and southward translation of the Tay nappe. In the ‘Moray’ zones, the putative pattern of isograd outcrop based on the argument that the andalusite-kyanite isograd marks the boundary between prograde hydration reactions and prograde dehydration reactions delineates a thermal trough correlated with the predominantly post-metamorphic Boyndie Syncline.

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