Gondwanan continental collision drives gravitational spreading and collapse of the ancestral East Antarctic mountains

Abstract

Continent-continent collisions develop mature orogenic systems over tens of millions of years, creating a thermally weakened mid-crustal infrastructure layer (15–50 km deep) that flows laterally from the thickened mountain ranges or plateaus. This gravitational spreading or ‘channel flow’ of a partially molten infrastructure layer beneath a rigid superstructure layer occurs during and after mountain building, dispersing high-temperature orogenic crust over length scales of 102–103 km into the orogenic foreland. In the Prydz Belt, East Antarctica, heterogeneous high-temperature Ediacaran–Cambrian orogenic crust and magmatic rocks formed during Gondwana amalgamation, but the architecture of the collisional orogen and location of key sutures remains controversial. We propose a new model classifying the orogenic crust into infrastructure and superstructure based on the record of Ediacaran–Cambrian deformation and metamorphism. The superstructure rocks are variably deformed and generally of lower metamorphic grade, overlying high-grade infrastructure rocks rich in former anatectic melts. These orogenic domains are separated by the Grove decoupling horizon shear zone. We suggest the high-grade infrastructure rocks of the Prydz Belt were dispersed from a thickened orogenic core near the ancestral Gamburtsev Subglacial Mountains via a mid-crustal channel spreading up to ∼103 km. Kinematic data from the infrastructure suggest that gravitational spreading was impeded and guided by rigid Archean provinces. The timing and evolution of the orogenic system is interpreted from new and compiled U-Pb-Hf-isotope data from detrital zircon grains most likely sourced from the ancestral mountains. The zircon Hf-isotope record is consistent with ocean closure and continental collision having occurred in the late Neoproterozoic at c. 650–600 Ma. The orogenic system had matured by c. 580 Ma with gravitational spreading peaking at c. 560–500 Ma and waning by c. 490 Ma. Our model is broadly applicable to studies of gravitational spreading in orogenic systems and aims to provide tectonic context for the East Antarctic lithosphere, improving understanding of the timing and location of key sutures in Gondwana amalgamation.