This article presents a stratigraphic definition of the Tip Top Granite, a previously unnamed felsic intrusive belonging to the Lincoln Complex, but identified by new geochronology to be temporally equivalent to the Wertigo Granite and to represent a newly recognised intrusive magmatic event on northeastern Eyre Peninsula. It also presents new whole-rock geochemistry and Nd isotope data on the Tip Top and Wertigo granites, characterises the melt source and tectonic setting of these units and discusses the broader significance of 1790–1770 Ma magmatism in the Gawler Craton. Although broadly equivalent in age and occurring in close proximity, the Wertigo and Tip Top granites represent melting of two geochemically distinct source regions. The Wertigo Granite is derived from a mixed mantle and crustal source and shares geochemical characteristics with the Myola and Tidnamurkana Volcanics, suggesting it may have formed from rift-related melting (asthenospheric upwelling) similar to the inferred environment of these volcanic rocks. In comparison, the Tip Top Granite represents a fractionated S-type granite derived from a lower crustal source equivalent to the Broadview Schist. Given the proximity of the Tip Top Granite to the Wertigo Granite, and their overlap in age, it may be that heat associated with the rift-related melting of the Wertigo Granite led directly to the crustal melting which produced the Tip Top Granite.