Ishtar Terra highlands on Venus raised by craton-like formation mechanisms

Abstract

The Ishtar Terra highlands on Venus consist of Lakshmi Planum, an Australia-sized crustal plateau with an average elevation of ~4 km that is comparable to that of the Tibetan Plateau, surrounded by elongated mountain belts with elevations of around 10 km, taller than the Himalayas. The region is floored by thick crust that is comparable to that of cratons on Earth. On Earth, plateaus and mountain belts result from the collision of tectonic plates. However, the origin of Ishtar Terra remains enigmatic because Venus lacks Earth-like plate tectonics. Here we use three-dimensional thermo-chemo-mechanical computational simulations of Venus-like mantle convection to show how magmatism and tectonics emerge from mantle dynamics. The simulations show that a lithosphere weakened as a result of high initial hydration or high surface temperatures enhances convective thinning and decompression melting, favouring the emplacement of a thick magmatic crust on top of a deep residual depleted mantle. The stiffer residual root deflects mantle flow outwards, leading to the formation of fold belts around the buoyant lithosphere that are consequently uplifted into a plateau and preserved from further deformation. The modelled topography, crustal thicknesses and gravity is consistent with observational constraints of Ishtar Terra. Our findings suggest that plateau formation on Venus may operate similarly to craton formation on the hot early Earth, before the onset of plate tectonics. Venusian highland terrains such as Ishtar Terra formed from melting beneath thinned lithosphere that created a stiff mantle root in a mechanism akin to craton formation on the early Earth, according to three-dimensional computational simulations.