THREE LIPS ON TWO AND HALF CRATONS

A north-trending dike exposed on Fingeren nunatak of the Grunehogna craton (in western Dronning Maud Land, East Antarctica) yielded a TIMS U-Pb baddeleyite age of ca. 717 Ma. This age confirms field relationships whereby the dated dike cuts a Borgmassivet sill. Borgmassivet sills and associated Ritscherflya basalts of Grunehogna are time-correlative with ca. 1110 Ma Umkondo magmatism, which is widespread throughout the Archean-age Zimbabwe and Kaapvaal cratons (e.g., Hanson et al., 2006). Grunehogna is considered to be a severed fragment of the Kaapvaal craton, which separated at ca. 185 Ma during the breakup of Pangea. The Kaapvaal craton is sutured with the Zimbabwe craton, together representing the Archean-age components of the composite Kalahari craton. In such a reconstruction the newly dated Fingeren dike approximately aligns with the ca. 724 Ma Mutare swarm of northeastern Zimbabwe. Magmatism associated with a minimum of three large igneous provinces (LIPs) are therefore known to be present across the composite Kalahari craton: Umkondo (Borgmassivet) at ca. 1110 Ma, Mutare (Fingeren) at ca. 720 Ma, and Karoo (Ferrar) at ca. 185 Ma. The presence of these three LIPs, together with correlative lithological units, support interpretations favoring close-knit juxtaposition of Zimbabwe-Kaapvaal-Grunehogna within the framework of the Kalahari craton, during the time interval 1110 Ma to 185 Ma. It is notable that the only other known LIPs of age ca. 720 Ma are the potentially linked Franklin LIP in northern Laurentia, and the Dovyren LIP in southern Siberia. The possibility that the ca. 720 Ma Mutare-Fingeren LIP was adjacent to ca. 720 Ma Franklin and Dovyren LIPs at this time should be considered, although typically the Kalahari craton is placed on the southern side of Laurentia in the supercontinent Rodinia (ca. 1000-700 Ma) (e.g., Li et al., 2008).