The southernmost exposures of Mesozoic dolerites in Coats Land, the Omega dolerites, occur at Whichaway Nunataks. The dolerites are geochemically indistinguishable from the Theron Mountains' dolerites. In both regions high- and low-Ti compositions occur with trace element signatures more akin to island-arc magmas than within-plate tholeiites. From a preliminary Sr isotopic study the Omega dolerites can be classified as Ferrar type. The existence of Ferrar type material in these nunataks suggest that the boundary between the Ferrar and Weddell Sea sub-provinces occurs within the Theron Mountains.