FRANKLIN-AGE MAFIC DIKES IN WESTERN DRONNING MAUD LAND (ANTARCTICA)

The Fingeren dikes exposed in western Dronning Maud Land (Antarctica) yield consistent ID-TIMS U-Pb baddeleyite and apatite ages of ca. 720 Ma. These weakly tholeiitic mafic dikes intrude ~1130 Ma Ritscherflya strata and 1100 Ma Borgmassivet sills on the Archean Grunehogna craton. Where exposed in the adjacent Meso-Neoproterozoic Maud belt, the dikes crosscut lithologic contacts and structural fabrics in ~1080 Ma high-grade metamorphic rocks. Here the Fingeren dikes are overprinted with a partitioned shear fabric that results in the preservation of primary igneous textures within strain shadows. Grunehogna is regarded as a severed fragment of the Kaapvaal craton, which separated at ~190 Ma during the breakup of Gondwana. Grunehogna and Kaapvaal together with the Zimbabwe craton represent the Archean-age components of the composite Kalahari craton. A reassembled Kalahari indicates that the Fingeren dikes approximately align with the Mutare dikes of northeastern Zimbabwe. In most reconstructions of Rodinia, Kalahari is placed near the present southern end of Laurentia from ca. 1000 to 750 Ma (e.g., Dalziel et al., 2000). In such reconstructions, the Mutare and Fingeren dikes could then be considered contemporaneous with the separation of crustal entities such as East Antarctica and Australia from Kalahari-Laurentia during the breakup of Rodinia. An alternative model is based on known mafic dikes with closely corresponding ages of ca. 720 Ma that are potentially linked to the Franklin LIP in northern Laurentia or to the Irkutsk LIP in Siberia. This model considers the Mutare and Fingeren dikes to be products of the Irkutsk or Franklin LIPs. Whether it is paleomagnetically feasible for Kalahari to have been located proximal to northern Laurentia or Siberia and possibly linked to these LIPs is testable by determining the 720 Ma pole of the Kalahari craton.