Signatures of Lithospheric Flexure and Elevated Heat Flow in Stereo Topography at Coronae on Venus

Abstract

Signatures of lithospheric flexure were previously identified at a dozen or more large coronae on Venus. Thin plate models fit to topographic profiles return elastic parameters, allowing derivation of mechanical thickness and surface heat flows given an assumed yield strength envelope. However, the low resolution of altimetry data from the NASA Magellan mission has hindered studying the vast majority of coronae, particularly those less than a few hundred kilometers in diameter. Here we search for flexural signatures around 99 coronae over ∼20% of the surface in Magellan altimetry data and stereo‐derived topography that was recently assembled from synthetic aperture radar images. We derive elastic thicknesses of ∼2 to 30 km (mostly ∼5 to 15 km) with Cartesian and axisymmetric models at 19 coronae. We discuss the implications of low values that were also noted in earlier gravity studies. Most mechanical thicknesses are estimated as <19 km, corresponding to thermal gradients >24 K km−1. Implied surface heat flows >95 mW m−2—twice the global average in many thermal evolution models—imply that coronae are major contributors to the total heat budget or Venus is cooling faster than expected. Binomial statistics show that “Type 2” coronae with incomplete fracture annuli are significantly less likely to host flexural signatures than “Type 1” coronae with largely complete annuli. Stress calculations predict extensional faulting where nearly all profiles intersect concentric fractures. We failed to identify systematic variations in flexural parameters based on type, geologic setting, or morphologic class. Obtaining quality, high‐resolution topography from a planetwide survey is vital to verifying our conclusions.

The Physics of Changing Tectonic Regimes: Implications for the Temporal Evolution of Mantle Convection and the Thermal History of Venus

“…Venus currently shows no clear evidence of Earth‐like plate tectonic activity (e.g ., Schubert et al, ; Solomon et al, ). However, analysis of gravity and topography observations requires active mantle convection upwelling beneath large volcanic rises such as Beta, Atla, and Eistla Regiones, the Devana Chasma rift, and some coronae (Grimm et al, ; Kiefer & Hager, ; Kiefer & Peterson, ; O'Rourke & Smrekar, ; Simons et al, ; Smrekar et al, ; Smrekar & Stofan, ). Tectonic observations of Venus indicate only limited recent surface motions, for example only 10‐20 km of extension at Devana Chasma ( Connors & Suppe, ; Kiefer & Swafford, ; Rathbun et al, ; Solomon et al, ), which is similar to the extension at continental rifts on Earth (see Table 2 of Kiefer & Swafford, ).…”

Normal Faults on Ceres: Insights Into the Mechanical Properties and Thermal History of Nar Sulcus

“…The Nar Sulcus fractures (Figure 1), which are centrally located at 280.11°E, 41.86°S within the Yalode impact crater, display morphologies similar to those of imbricated listric normal faults on the Earth and have topographic profiles suggestive of elastic flexure. Estimates of these parameters through the analysis of flexurally supported topography have previously been done on the Earth (e.g., Kusznir et al, 1991;Lowry & Smith, 1994;Weissel & Karner, 1989), Venus, (e.g., O'Rourke & Smrekar, 2018), Mars (e.g., Grott et al, 2005;Ruiz et al, 2006), Ganymede (Nimmo & Pappalardo, 2004;Nimmo et al, 2002), Europa (Nimmo & Schenk, 2006;Ruiz, 2005), Tethys (Giese et al, 2007), and Enceladus (Giese et al, 2008). When this elastic thickness is combined with an assumed strength profile and strain rate, the mechanical thickness and heat flux present at the site of the newly formed topography can be estimated.…”

“…When this elastic thickness is combined with an assumed strength profile and strain rate, the mechanical thickness and heat flux present at the site of the newly formed topography can be estimated. Estimates of these parameters through the analysis of flexurally supported topography have previously been done on the Earth (e.g., Kusznir et al, 1991;Lowry & Smith, 1994;Weissel & Karner, 1989), Venus, (e.g., O'Rourke & Smrekar, 2018), Mars (e.g., Grott et al, 2005;Ruiz et al, 2006), Ganymede (Nimmo & Pappalardo, 2004;Nimmo et al, 2002), Europa (Nimmo & Schenk, 2006;Ruiz, 2005), Tethys (Giese et al, 2007), and Enceladus (Giese et al, 2008). Despite a plethora of evidence suggesting Ceres' upper layer is rich in water ice (e.g., Buczkowski et al, 2016;Combe et al, 2016Combe et al, , 2019Fu et al, 2017;Hughson et al, 2018;Prettyman et al, 2017;Schmidt et al, 2017;Sizemore et al, 2017Sizemore et al, , 2018, its exact concentration and HUGHSON ET AL.…”

A Global Survey of Lithospheric Flexure at Steep‐Sided Domical Volcanoes on Venus Reveals Intermediate Elastic Thicknesses

“…The curve‐fitting algorithm returns formal uncertainties for all parameters. O'Rourke and Smrekar (2018) used a sophisticated Markov chain Monte Carlo to fit flexural models to topography, but also demonstrated that simpler curve‐fitting algorithms yield equivalent results. We use a Monte Carlo method to propagate the uncertainties on α to estimate the “1‐sigma” uncertainties on the best‐fit elastic thickness.…”