The Onset of Gondwanide Orogeny in Eastern Australia: Insight From the Provenance of Syn‐Orogenic Strata in the New England Orogen (Australia)

Abstract

AbstractThe last major episode of cordilleran‐style tectonism in eastern Australia was the late Paleozoic‐early Mesozoic Gondwanide Orogeny. When exactly this deformation commenced and what caused this phase of orogenesis is still debated. Using previous stratigraphic and sedimentological data from pre‐orogenic to syn‐orogenic strata, integrated with new detrital zircon U‐Pb geochronology, we investigated the onset of the Gondwanide Orogeny in the northern New England Orogen (Gogango Overfolded Zone, eastern Australia). The lowermost syn‐orogenic strata display evidence of rapid base‐level change coeval with increasingly abundant and more proximal mass‐wasting deposits, which reflect a shift to static loading‐induced subsidence and the establishment of a ∼1,600‐km long foreland basin system. The syn‐orogenic strata contain abundant detritus sourced from syn‐depositional magmatism, alongside an up‐section increase in detritus derived from uplifted older rocks of the New England Orogen. Detrital zircons show maximum depositional age of ∼276 Ma from immediately above the sequence boundary, and ∼269 Ma from an overlying formation. These results confirm previous suggestions that tectonic forcing of the orogenic hinterland affected subsidence and sedimentation patterns in the easternmost part of the basin during the middle Permian, >11 Myr prior to deformation in the western part of the foreland basin. The onset of the Gondwanide Orogeny in eastern Australia, and in other sectors of the Gondwanan margin, likely resulted from a tectonic switch from crustal extension to contraction, which was driven by increased convergence rates due to a plate reorganization event following the final assembly of Pangea.