Dynamics of Lithospheric Overturns and Implications for Venus's Surface

Abstract

Across the solar system, planetary surfaces and specifically their volcano-tectonic structures offer windows into the dynamic evolution of planetary interiors. Volcanism and tectonism rejuvenate the planetary surface depending on the rate and style of magmatic and tectonic processes. While the present Earth's surface is, at the large scale, dominated by ocean-plate tectonics (Crameri et al., 2019), other bodies' surfaces are either dominated by extensive volcanism (e.g., Io) or show very little to no sign of recent activity. The latter is the case for the classical stagnant-lid bodies, Mars, Mercury, and the Moon, which feature a strong immobile lithosphere; the global-scale convection is or was (if convection ceased at some point) restricted to the Abstract Venus is currently characterized by stagnant-lid mantle convection, but could have previously experienced episodes of global resurfacing due to lithospheric overturn. Using numerical models of Venus's interior, we attempt to explain Venus's surface characteristics in the context of interior evolution and to understand how Venus's tectonic history has diverged from Earth's. For both the stagnant-and the episodic-lid regime, we explore the role of reference mantle viscosity; for the latter regime, we also explore the role of the lithospheric yield stress. Our stagnant-lid models predict thicker crust and younger surface than typically inferred from cratering statistics. When considering resurfacing episodes, the yield stress influences the frequency of overturns, which limits crustal thickness to better agree with previous independent estimates. Surface age is variable and depends on overturn frequency and resurfacing rate between overturns but reaches larger values just before an upcoming overturn event compared to values in the stagnant-lid cases. Both regimes predict substantial lateral variations in surface age, instead of an end-member uniform surface age indicating the cessation time of the last overturn, because ongoing volcanic resurfacing is spatially heterogeneous and dominates over tectonic resurfacing. Reviewing the crater-based surface age variations suggests that the model-predicted age spreads in the episodic scenario could be consistent with Venus's cratering record. Moreover, we find that a small fraction of crust can resist recycling during overturns. These outcomes indicate that overturn events may allow for surface age variations that reproduce Venus's surface better than stagnant-lid models. Plain Language Summary In contrast to Earth, Venus currently does not feature plate tectonics inhibiting effective crustal recycling into the planetary interior. Yet, its surface features only few and almost randomly distributed craters, which suggests a globally young and more homogeneous surface age than on other planetary surfaces. To date, it remains unclear whether these surface characteristics are generated in an equilibrium style of resurfacing due to volcanism or whether largescale tectonic overturns are required to explain the observations. Her...

Evidence for a Locally Thinned Lithosphere Associated With Recent Volcanism at Aramaiti Corona, Venus

“…As a result, a repeated or episodic occurrence of catastrophic global resurfacing is predicted (Turcotte, 1993). More recently, a resurfacing model has been proposed that is episodic but does not result in global resurfacing (Uppalapati et al., 2020). In this model spatially heterogeneous volcanic resurfacing dominates over tectonic resurfacing, allowing spatial variations in surface age.…”

Regional-Scale Lithospheric Recycling on Venus via Peel-Back Delamination

“…The young surface age implies that the most recent overturn event happened in the last 250-750 Myr, and the CR hypothesis attributes the mostly unmodified crater population to low levels of tectonic or volcanic activity during the fol--3-manuscript submitted to JGR: Planets lowing quiescent period (Herrick, 1994;Schaber et al, 1992). Convection models from previous studies support the CR hypothesis by producing cyclic global overturn events under certain conditions (Armann & Tackley, 2012;Crameri & Tackley, 2016;Moresi & Solomatov, 1998;Reese et al, 1999;Rolf et al, 2018;Weller & Kiefer, 2020;Uppalapati et al, 2020).…”

Reviewing subduction initiation and the origin of plate tectonics: What do we learn from present-day Earth?

“…Recent study further suggests that subduction initiation may have occurred on Venus (Davaille et al, 2017). However, such overturn/subduction, if it existed, may have been local and short lasting (Fowler and O'Brien, 1996; Davaille et al, 2017; Uppalapati et al, 2020). On Earth, water release during subduction may lubricate the interface between plates (Gerya et al, 2008; Zheng and Chen, 2016; Sobolev and Brown, 2019), which could decouple the subducting plate and the overriding plate and stabilize the subduction system.…”

“…Mantle convection on most other terrestrial planets and moons is probably in stagnant lid regime: the strong stagnant lid has remained on the surface for billions of years while the underlying mantle has been vigorously convective (Korenaga, 2013; Stern et al, 2018). Venus's dynamic evolution is believed to be characterized by the episodic style of mantle convection: long‐lasting stagnant‐lid periods are interrupted by short, dramatic periods of global overturns (Moresi and Solomatov, 1998; Reese et al, 1999; Armann and Tackley, 2012; Uppalapati et al, 2020).…”