Abstract
The last supercontinent Pangea began fragmenting around 200 Ma to form the present-day continents. The initial stages of the break-up of southern part of Pangea, Gondwana, were marked by extensive mafic magmatism and lithospheric thinning around 180 Ma. Between the then-joined Grunehogna (modern East Antarctica) and Kalahari (southern Africa) cratons, this voluminous magmatism formed the Karoo and Ferrar continental flood basalts, part of the greater Gondwana Large Igneous Province. The Vestfjella mountains of Dronning Maud Land, East Antarctica preserve one of the most extensive Antarctic records of this event and provide a key for reconstructing the pre-breakup configuration of these cratons. Although geochemical and isotopic correlations between Antarctica and Africa are relatively well established, there is limited amount of paleomagnetic constraints from East Antarctica. High-quality data are therefore required to refine plate reconstructions and to better understand the magmatic and tectonic evolution of this part of Gondwana.
During two FINNARP expeditions in the late 90s, more than 400 oriented hand samples were collected from seven nunataks across the Vestfjella region. The dataset includes Jurassic flood basalts (~182-189 Ma) as well as younger intrusive rocks, such as ultrapotassic dykes with ages near 160 Ma. The volcanic suite is compositionally diverse, comprising both low- and transitional-Ti lava types. Several of these lava groups, as well as ferropicritic dykes, have close analogues on the Kalahari craton, highlighting strong intercontinental correlations.
We present new paleomagnetic and rock magnetic results from Jurassic volcanic and intrusive rocks in the Vestfjella region of Dronning Maud Land. Rock magnetic analyses suggest that pseudo-single domain magnetite is the dominant remanence carrier, yielding stable magnetizations. Thermal and alternating-field demagnetization experiments produce both normal and reverse directions. The reversals of the lavas are symmetric and yield a positive reversal test. The resulting polarity stratigraphy shows a shift from normal to reverse directions toward the base of the sequence, closely resembling magnetostratigraphy on the African side of the Karoo flood basalts. The ~182 Ma basalts provide paleomagnetic poles consistent with coeval Karoo data, supporting a close alignment of the Grunehogna and Kalahari cratons at the onset of Gondwana breakup.