Tectonic and kinematic study of a strike-slip zone along the southern margin of Central Ovda Regio, Venus: Geodynamical implications for crustal plateaux formation and evolution

The tectonic system of the southern margin of Central Ovda Regio, a crustal plateau which straddles Venus equator, has been interpreted as a dextral strike-slip array, on the basis of evidence clearly identifiable, as are Riedel fracture patterns of different scales, en échelon folds and brittle strike-slip faults. This transcurrent regime developed two main shear belts (Inner and Outer, on respectively thicker and thinner crust), whose minimum dextral displacement has been estimated in 30-50 km. Since the up or downwelling models for plateau formation cannot easily explain tectonic shears of this magnitude along their margins, an alternative hypothesis has been built, which stands on the proposed collisional belt which could form Ovda northern border (King et al., 1998, Lunar Planet. Sci. Conf. 29, 1209; Tuckwell and Ghail, 2002, Lunar Planet. Sci. Conf. 33, 1566). Within this framework, the shear would represent a transcollisional transcurrent zone, similar to the strike-slip zones produced in the foreland of the Himalayas-Tibet collision front. Eastern Ovda would be an independent area of thickened crust, pushed to the SSE by the northern collision, with the deformation concentrated at its margins, and experiencing a shear strain on its southern margin. None of the data, however, either supports nor helps to discard theoretical subduction events as a cause of the collision. On the contrary, image relationships could be interpreted as evidence that the main shear deformation took place during the last global resurfacing event on the planet.