Mafic dykes and granitoid intrusions were emplaced around the southeastern margins of the Adelaide Foldbelt immediately prior to, during and following the Cambro-Ordovician (ca 500 Ma) Delamerian Orogeny, but are relatively uncommon elsewhere within the foldbelt. They are abundant within a broad NNW- trending zone in the eastern Mount Lofty Ranges and Barossa Valley region where they are associated with a zone of high grade metamorphism. Dykes mainly intrude Cambrian Kanmantoo Group and Normanville Group metasediments but some occur within high grade Precambrian metasediments. Lamprophyric dykes and plugs are common north of Truro east of the main zone of mafic dykes. Liu and Fleming state that mafic dykes intruded at various stages relative to the multiple deformation history of the Delamerian Orogeny. They suggest that some thermal activity occurred at a fairly early stage (pre- to syn-D1) in the tectonometamorphic history of the area. They further consider that the early (pre- to syn-D1) intrusion of mafic dykes is highly suggestive of mafic magmatism (and related mantle upwelling) making a major contribution to the heat budget for early thermal activity (including metamorphism) and granite magma generation within the region. Several locations where the relationships between the dyke intrusions, the various generations of fold structures, and the host lithologies are well preserved are examined during the excursion.