![]() ![]() The extensional counterparts of the ridge belts have variously been labeled “fracture belts” or “groove belts” ( 23) and comprise arrays of graben and half graben. 7 – 9).īands of shortening structures that accommodate crustal thickening have been termed “ridge belts” these orogenic systems are primarily composed of folds (that likely overlie thrust faults) and are typically manifest as broad, linear rises (e.g., ref. These zones typically show strains of several percent, corresponding to a few to a few tens of kilometers of crustal extension or shortening (e.g., refs. In places, tectonic structures are pervasively distributed, whereas in other areas strain is concentrated into narrow curvilinear zones. Evidence for crustal extension, shortening, and strike-slip motion is widespread across Venus ( 10, 11, 21). The Venus surface can be divided physiographically into broad highlands, mountain belts, and extensive lowlands, with the latter dominant. Tectonic Deformation in the Venus Lowlands Further, although Venus shows no evidence of Earth-like tectonic plates today, mantle convection might drive some horizontal motion and associated surface deformation ( 10, 11, 16 – 18), possibly facilitated by a weak lower crustal layer arising from the planet’s currently high surface temperature (∼740 K) ( 13, 19, 20). Additionally, recent efforts to reconcile geological and geophysical observations of Venus ( 12) invoke an active, steady-state interior maintained by recycling of the mantle portion of the lithospheric lid ( 13), and even localized lithospheric subduction outward of sites of major mantle upwelling ( 14, 15). However, this perspective is challenged by geological observations of deformation indicative of lateral motions-both isolated instances within the planet’s lowlands ( 7 – 9) and on a much greater horizontal scale in the vicinity of Lakshmi Planum, which appears to have collided as a block with Ishtar Terra ( 10), and regional transcurrent shear zones >1,000 km long between Ovda and Thetis Regiones ( 10, 11). In any case, with a lithosphere coupled to a highly viscous asthenospheric mantle and inhibited from major lateral motion, by this view, Venus has likely behaved as a one-plate planet for at least the last 0.5–1 billion years ( 5, 6). Observations of the planet’s cratering record and inferences about its volcanic history led to the view that Venus exists either in a stagnant lid ( 3) or episodic lid ( 4) tectonic regime, which differ mainly in terms of rates of volcanic and tectonic activity. Given the detection of ever more Earth-mass extrasolar planets at distances from their host stars in the so-called “Venus zone” ( 2), it is increasingly important to understand the geological character and history of our nearest planetary neighbor. The limited but widespread lithospheric mobility of Venus, in marked contrast to the tectonic styles indicative of a static lithosphere on Mercury, the Moon, and Mars, may offer parallels to interior–surface coupling on the early Earth, when global heat flux was substantially higher, and the lithosphere generally thinner, than today.ĭespite close similarities in mass and bulk composition, Earth and Venus have followed different evolutionary paths, at least over recent Solar System history ( 1). Lithospheric stresses calculated from interior viscous flow models consistent with long-wavelength gravity and topography are sufficient to drive brittle failure in the upper Venus crust in all areas where these blocks are present, confirming that interior convective motion can provide a mechanism for driving deformation at the surface. At least some of this deformation on Venus postdates the emplacement of the locally youngest plains materials. We report a globally distributed set of crustal blocks in the Venus lowlands that show evidence for having rotated and/or moved laterally relative to one another, akin to jostling pack ice. ![]() The extent of surface mobility on Venus driven by mantle convection, however, and the style and scale of its tectonic expression have been unclear. However, the Venus surface has been extensively deformed, and convection of the underlying mantle, possibly acting in concert with a low-strength lower crust, has been suggested as a source of some surface horizontal strains. Venus has been thought to possess a globally continuous lithosphere, in contrast to the mosaic of mobile tectonic plates that characterizes Earth. ![]()
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