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

Abstract

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 echelon 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, Abstract 1209; Tuckwell and Ghail, 2002, Lunar Planet ScL Conf 33, Abstract 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

Volcanism and tectonism across the inner solar system: an overview

“…Koenig & Aydin (1998) and Fernàndez et al (2010) showed horse-tail terminations, en echelon folds, contractional bends and strike-slip offsets in Lavinia Planitia. Finally, Romeo et al (2005) and Chetty et al (2010) identified conjugate shear zones in Ovda Regio associated with tear-folds and imbricate duplexes. Continental drift may account for the substantial horizontal tectonism required by prominent strikeslip belts (Harris & Bédard 2014b).…”

“…However, the upwelling model cannot explain the widespread contractional tectonics observed at some plateau margins nor the complex compressional -extensional deformation recorded on crustal plateaux within so-called tesserae terrains (Ivanov & Head 1996;Gilmore et al 1998;Romeo et al 2005;Hansen & López 2010). On the other hand, the downwelling hypothesis fails to explain the flat-topped topography of plateaux, and, further, it requires an excessive amount of time for crustal thickening (Lenardic et al 1995;Kidder & Phillips 1996).…”

“…On a planet dominated by vertical tectonism and characterized by widely distributed deformations, there is no space for strikeslip shear belts that have traditionally been highly underconsidered on Venus (e.g. Solomon 1993;McGill et al 2010) despite the apparently straightforward evidence collected so far (Raitala 1994;Brown & Grimm 1995;Ansan et al 1996;Koenig & Aydin 1998;Tuckwell & Ghail 2003;Kumar 2005;Romeo et al 2005;Chetty et al 2010;Fernàndez et al 2010;Harris & Bédard 2014a, b). For example, Brown & Grimm (1995) highlighted en echelon fractures and folds along and within Artemis Chasma.…”

Pulsating continents on Venus: An explanation for crustal plateaus and tessera terrains

“…This interpretation is based on the assumption that the wavelength of each of these types of structures is indicative of the thickness of the brittle crust, being generated with a brittle-ductile transition deepened with time during the cooling of the plateau. However, Gilmore et al (1997Gilmore et al ( , 1998 and Romeo et al (2005) concluded that the deformation phases are first compressional and finally extensional. In this interpretation the extensional structures, including the long-narrow grabens, postdate or are contemporary with the generation of the compres sional structures.…”

“…On the one hand, the weak points of the downwelling model are: (1) a predicted domical shape instead of the flat-topped plateau geometry (Kidder and Phillips, 1996); (2) too much time is required for the thickening by crustal flow (1-4 billion years) (Kidder and Phillips, 1996). On the other hand, the main challenges of the plume hypothesis are: (1) there is no explanation for the extensive contractional tectonics observed (Ghent et al, 2005;Hansen, 2006); (2) the predicted timing of the extensional tectonics contradicts cross-cutting relationships in different locations (Gilmore et al, 1998;Romeo et al, 2005). Although Gilmore et al (1998) argued that the formation of ribbon-tessera terrain requires an excessive geothermal gradient, Ruiz (2007) indicated that the heat flow needed for generating ribbons is reasonable for a plume environment.…”