LATE PROTEROZOIC TO EARLY PALEOZOIC TECTONISM IN DRONNING-MAUD-LAND, ANTARCTICA - SUPERCONTINENTAL FRAGMENTATION AND AMALGAMATION

The Mid-Proterozoic-Early Palaeozoic tectonic development of western Dronning Maud Land is examined in the light of recent proposals that suggest geological continuity between Laurentia and Gondwana during the Middle Proterozoic (the SWEAT hypothesis). Gondwana amalgamation from the remaining constituents followed fragmentation and rifting of Laurentia from this supercontinent, culminating in a Late Cambrian orogeny at c. 500 Ma. The Mid-Proterozoic-Early Palaeozoic tectonic development of western Dronning Maud Land was significantly different to that observed in the Transantarctic Mountains, and the c. 500 Ma event in particular is characterized by: (1) a regional isotopic resetting event at c. 470 Ma, (2) scarce coeval magmatism, comprising only one major intrusion of alkaline affinity, and volumetrically small 'S-type' granitic sheets derived from local anatexis of gneisses, (3) structural deformation considerably less intense than during the preceding Kibaran (1100 Ma) orogeny, comprising relatively open to gentle folding, (4) reactivation of thrusting initiated during the Kibaran orogeny, with associated metasomatism. It is concluded that the effects of the Late Cambrian (c. 500 Ma) event are consistent with crustal thickening through large-scale underplating, rather than subduction-related processes as seen in the Ross orogeny of the Transantarctic Mountains. It is also concluded that Gondwana amalgamation occurred along suture lines not currently exposed in outcrop in Dronning Maud Land. These data neither contradict nor support the SWEAT hypothesis as currently argued.