Metamorphism of the Lower Palaeozoic rocks of the Leadhills district, southern Scotland, 1:50K sheets 15E & 23E

Systematic studies of metapelitic grade linked with the geological re-survey of the Southern Uplands have been used to generate a series of contoured metamorphic maps which currently cover nearly two-thirds of the Lower Palaeozoic terrane. These studies have used X-ray diffraction (XRD) measurements of clay mineral reaction progress, particularly white mica (illite) crystallinity, to delineate zones of diagenesis and low-grade metamorphism in the imbricated Ordovician and Silurian strata. Although the regional pattern revealed by metapelitic zonal sequences shows considerable variations in metamorphic trends, patterns of increasing grade from older into younger strata suggest that accretionary burial was the main cause of regional metamorphism (Merriman & Roberts, in press). These patterns also reflect the different levels of exhumation of the terrane, by both normal movement on reactivated thrust faults and differential block movement on north-north-west-trending faults.