CONVERGENT GRAVITATIONAL COLLAPSE DRIVES INTRACRATONIC DOME TO DUPLEX TECTONICS IN CENTRAL AUSTRALIA

Defying traditional plate tectonics, the Alice Springs Orogeny (ASO) developed deep within the interior of the Australian continent, far from any plate boundaries, between 450 and 300 Ma. The region NE of the Amadeus basin presents a surprising association of the Entia gneiss dome, exhuming high-grade Paleoproterozoic gneisses alongside a nappe complex comprising high-grade rocks of the Harts Range Metamorphic Complex (HRMC), Paradise Nappes, and their lower-grade Neoproterozoic covers. These isoclinally folded nappes were thrust onto the lower-grade Ruby Gap and White Range duplexes, composed of Amadeus basin sequences. Collectively, these nappes constitute the Arltunga Nappe Complex.

Understanding of the regional geology took a transformative turn when detrital zircon data revealed that the HRMC, into which the Entia dome was emplaced, did not belong to the Paleoproterozoic basement but is instead the metamorphic equivalent of Neoproterozoic to Palaeozoic sediments of the Amadeus Basin. A transect from the Entia Dome to the Ruby Gap duplex reveals conformable structures that juxtapose a high-grade extensional domain (the Entia dome) with a low-grade contractional domain (the Ruby Gap and White Range duplexes), across a transitional zone containing the Bruna décollement zone and the Illogwa shear zone. Exhumation of the Entia Dome and thrusting of the Arltunga Nappe Complex occurred between ~345 and ~310 Ma. The structural continuity and geochronology suggest that these features are synchronous and interrelated.

Numerical experiments support a tectonic model where the dome and nappe complex formed synchronously due to the convergent gravitational collapse of the Paleozoic Harts Range Rift basin. In this model, the Entia dome was emplaced into the 30-40 km deep Harts Range Rift basin, the base of which reached granulite facies metamorphism and melting at ~470 Ma. The density contrast between the Neoproterozoic to Paleozoic sedimentary infill and the metamorphic Paleoproterozoic basement created a strong horizontal pressure gradient, generating significant lateral gravitational stresses acting towards the basin. As the basin's geotherm reached melting conditions, these gravitational forces may have overcome viscous strength, driving centripetal flow, forcing the exhumation of the Entia Dome and the development of gravity nappes at the Earth’s surface.