Anatomy of the Kuunga Orogen in East Antarctica

The Kuunga Orogen in East Antarctica essentially lies buried below the ice sheet, and therefore remains the most poorly exposed and enigmatic Gondwana-forming orogen. Paleomagnetic constraints from India and Australia imply that a Neoproterozoic plate boundary bisecting East Antarctica accommodated some 3000-5000 km of relative plate motion. However, evidence for typical plate boundary processes in the Antarctic geological record (e.g., arc/subduction-related magmatism, high-P metamorphism) during this time remains equivocal.

Here we explore the spatial extent and timing of Neoproterozoic-Cambrian tectonics associated with the amalgamation of eastern Gondwana using new and published geological datasets. We suggest the boundary between crust originally of ‘Indian’ and ‘Australian’ affinity can be resolved into two plate-boundary segments in East Antarctica, representing two contrasting tectonic regimes: (1) a strike-slip/transpressional margin delineated by a series of NNW-trending lineaments in Queen Mary-Wilhelm II-Wilkes lands, and (2) a near-orthogonal convergent margin that consumed the “Mawson Ocean” basin, now recorded by significantly thickened (60 km) crust and lithosphere (200 km) through the Antarctic interior, incorporating the Gamburtsev Subglacial Mountains region.

We suggest that, based on key changes in Hf-isotopic character of detrital zircon, cryptic Neoproterozoic arc magmatism in the interior of Antarctica commenced from c. 720 Ma, continent-continent collision was underway by c. 620-600 Ma, and that the plethora of c. 550-500 Ma U-Pb ages mostly mark the final stages of collision, slab break-off failure and orogenic collapse. These new constraints provide an opportunity for improved plate models for the Neoproterozoic and the transition from the supercontinent Rodinia to Gondwana.