Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two‐dimensional models

Abstract

[1] Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid and recent resurfacing history. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick crust, inconsistent with observations. Partitioning of heat-producing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting $150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature $constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. The basalt density inversion below the olivine-perovskite transition causes compositional stratification around 730 km; breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature $rheological temperature scale lower than T CMB is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start. Core heat flow decreases with time, possibly shutting off the dynamo, particularly in episodic cases.Citation: Armann, M., and P. J. Tackley (2012), Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two-dimensional models,

Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars

“…In this work, we give the first comprehensive chemical, spectroscopic and crystallographic account of the new mineral ahrensite [γ-(Fe,Mg) 2 SiO 4 , IMA-2013-028]. Ahrensite is the Fe end-member of the γ-Mg 2 SiO 4 -Fe 2 SiO 4 series of silicate-spinels, which are critical constituents in the mantles of Earth, Mars, and Venus (e.g., Bertka and Fei, 1997;Stixrude and Lithgow-Bertelloni, 2011;Armann and Tackley, 2012). Since ringwoodite was the first known silicate mineral with the spinel structure, the convention (Mills et al, 2009) is to use ringwoodite as the group name.…”

Habitable Planets: Interior Dynamics and Long-Term Evolution

“…https://doi.org/10.1017/S1743921313013136 342 P. J. Tackley et al surface or shallow crust can be an important heat-transport mechanism and acts as a 'thermostat' on mantle temperature, as seen in the Earth simulations of Nakagawa & Tackley (2012), Mars simulations of Keller & Tackley (2009) and Ogawa & Yanagisawa (2011), Venus simulations of Armann & Tackley (2012), and parameterized models of Kite et al (2009).…”

“…In the Mercury models, stagnant lid convection beneath a relatively thick stagnant lid is clear; by 4.5 billion years this is sub-critical, meaning that the velocity is decaying exponentially with time. The Venus model (a 3D version of one case reported in Armann & Tackley (2012)) is in the episodic lid mode, in which Venus' heat is lost by bursts of plate tectonic activity interspersed by periods of stagnant lid; as a result crust is recycled and builds up above the core-mantle boundary. In the Earth models from Nakagawa & Tackley (2009), plate tectonics occurs, again recycling crust to the CMB.…”

“…Numerical models of various planets in our solar system: Mercury (P.J. Tackley), Venus (a 3D version of a model in Armann & Tackley (2012)), Earth (Nakagawa & Tackley (2009)) and Mars (Keller & Tackley (2009) atmosphere-ocean system (Sleep & Zahnle (2001)). For water it is estimated that Earths interior holds 2-6 ocean masses of water (Ahrens (1989)).…”

Numerical studies of thermal convection with temperature- and pressure-dependent viscosity at extreme viscosity contrasts

“…The parameter values corresponding to other terrestrial planets also indicate that the approximate viscosity variation is of orders 10 20 (Venus) and 10 50 or more (Mars). [11][12][13] Boundary layer analysis and numerical experiments show that temperature dependence of the viscosity leads to an extremely viscous, effectively rigid, cold upper thermal boundary layer, which represents the lithosphere. The resulting "stagnant lid" convection is unlike that seen in the Earth, 14 and the active style of tectonics on Earth is generally thought to be a consequence of weakening at high stress, due either to stress-dependent viscosity or plastic yielding.…”