Form and extent of the Dufek intrusion, Antarctica, from newly compiled aeromagnetic data
The Dufek intrusion, in the northern part of the Pensacola Mountains, Antarctica, is part of an extensive, Middle Jurassic igneous province that was related to, and emplaced just prior to Gondwana break-up. It has been described as one of the largest layered gabbro intrusions in the world, and is exposed as two non-overlapping gabbro sequences in the Dufek Massif and the Forrestal Range. A new compilation of aeromagnetic data over the Dufek intrusion and surrounding region is based on mapping at two scales, a 2 km grid spacing over the Dufek intrusion, and a 6 km grid spacing over the surrounding region. Advanced processing of the data is used to produce an analytical signal and a terrace map as a basis for a new interpretation. Modelling and interpretation of the data show that the Dufek intrusion is not as extensive as was thought, and that it is more similar in size to the Stillwater Intrusion in North America, than to the Bushveld Complex in South Africa to which it has previously been compared. The reduced size of the Dufek intrusion is due to reinterpretation of an anomaly over Berkner Island, to the north of the Pensacola Mountains, as that of an uplifted basement block rather than a continuation of the Dufek intrusion. The Dufek intrusion is modelled as two separate intrusive phases of a composite intrusion. The main part is a dipping intrusive sheet displaced by a normal fault which accounts for two parallel magnetic anomalies over the Forrestal Range. The minor part forms the Dufek Massif itself, which the magnetic data show was emplaced on a separate trend and is of a shallower origin than the Forrestal phase. Magnetic lineaments on the compilation map are used to establish a possible chronology of events. We suggest that the emplacement of both phases of the Dufek intrusion was preceded by a period of extensional block faulting which uplifted the Berkner Island basement block, and was succeeded by a further period of extensional faulting involving a component of strike–slip deformation during the initial stages of Gondwana break-up.