Deep seismic imaging of a polydeformed accretionary orogen: Crustal architecture and evolution of the central Lachlan Orogen, East Gondwana margin

The central Lachlan Orogen of eastern Australia, a key component of the Cambrian to Triassic Tasmanides, records a complex history of crustal evolution along the proto-Pacific margin of East Gondwana. We present an integrated interpretation of 506 km of newly acquired deep crustal seismic reflection data, combined with geological, geochronological and other geophysical datasets, constraining the subsurface architecture and geological evolution of the Hermidale-Cobar-Yathong region. Seismic imaging reveals west-vergent, crustal-scale fold and thrust structures within the Hermidale Terrane, formed during the Upper Ordovician to early Silurian Benambran Orogeny. These structures predate the late Silurian to Devonian Cobar Basin and Yathong Trough and record greater than 35% crustal shortening, whereas the Devonian Tabberabberan Orogeny and subsequent events produced only ∼ 15% shortening and largely exploited the pre-existing architecture. The Benambran Orogeny was thus the dominant phase of deformation in the region. Integration of new geochronological data with the seismic interpretation also reveals several kilometres of Cambrian strata beneath the predominantly Ordovician surface geology, deposited over a mixed oceanic and continental substrate, the latter interpreted as rifted or attenuated Delamerian crust. This finding strengthens stratigraphic correlations with successions in Victoria and supports continuity of the East Gondwana margin through the Cambrian and Ordovician, while highlighting a marked divergence in structural style and mineral endowment along strike. Long-lived, crustal-penetrating thrusts and inversion faults offer new perspectives on metal source regions and migration pathways, with implications for the distribution of minerals critical to clean-energy technologies.