Admittance survey of type 1 coronae on Venus

Abstract

[1] In this study, we analyze Magellan gravity and topography data for Type 1 coronae on Venus to estimate crustal thickness (Z c ), elastic thickness (T e ), and apparent depth of compensation (Z L ). We examine the free-air admittance for all 103 Type 1 coronae (defined as having greater than 50% complete fracture annuli) that are resolved in the gravity data. A spatio-spectral method is used to calculate a localized admittance signature of each corona from a global admittance map. This method extracts spectral information from a region in space whose area is varied as a function of degree to make it large enough to yield robust results at every individual wavelength. Elastic flexure models with either bottom-or top-loading compensation are used to fit the data. The estimated lithospheric flexural parameters span the range obtained for other topographic features on Venus, suggesting that the lithosphere on which coronae form is variable. We find no significant difference in lithospheric properties between Type 1 and 2 coronae. Fifty-four percent of all coronae are consistent with local isostasy, which may indicate that they are no longer active. Very few coronae with dome or plateau morphologies have a bottomloading signature or the small T e and large Z L expected if a mantle plume were present. Approximately 71% have Z L estimates less than 70 km, indicating that compensation probably occurs within the crustal layer. We find no systematic relationship between T e or Z c and corona diameter, as would be expected for the spreading-drop model of formation.

Gravity and Topography of the Terrestrial Planets

“…However, the majority of these investigations have fit only the admittance or coherence functions, but not both simultaneously (e.g., Anderson and Smrekar, 2006;Barnett et al, 2000Barnett et al, , 2002Hoogenboom et al, 2005Hoogenboom et al, , 2004Lawrence and Phillips, 2003;McKenzie, 1994;McKenzie and Nimmo, 1997;Simons et al, 1994Simons et al, , 1997Smrekar, 1994;Smrekar et al, 2003;Smrekar and Stofan, 1999). The robustness of the inverted parameter values, the fidelity of the gravity model, and the appropriateness of the loading model are all difficult to assess in these studies.…”

Themis Regio, Venus: Evidence for recent (?) volcanism from VIRTIS data

“…The bottom-loading model provides a good fit to the spectrum for Themis Regio at wavelengths between 700 and 1500 km, giving an elastic thickness value of 35 ± 5 km and an apparent depth of compensation of 95-105 km. The gravity signature of several of the largest coronae have been examined individually, along with Mielikki Mons ( Hoogenboom et al, 2004;Brian et al, 2004 ). All of these features have a very low elastic thickness, with an allowed range of 0-16 km.…”

The geological evolution of Atai Mons, Venus: a volcano–corona ‘hybrid’

“…An elastic flexure model is fitted to the local admittance data from which the above parameters can be estimated. For a more detailed description of the method used the reader is referred to Hoogenboom et al (2004).…”

“…We have conducted a gravity analysis for Atai Mons using the method of Hoogenboom et al (2004) to estimate crustal thickness (Z c ), elastic thickness (T e ) and apparent depth of compensation (Z L ). Gravity data were obtained by Döppler radio tracking of the Magellan spacecraft during Cycles 4 and 5, and part of Cycle 6, after the primary mapping phase of the mission had been completed (Sjogren et al 1997).…”