What can Olympus Mons tell us about the Martian lithosphere?

Nicola C Taylor,Jessica H Johnson,Richard A Herd,Catherine E Regan

doi:10.1016/j.jvolgeores.2020.106981

Nicola C Taylor, Jessica H Johnson + Show 2 more

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https://doi.org/10.1016/j.jvolgeores.2020.106981

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Abstract

Under gravitational loading, a volcanic edifice deforms, and the underlying lithosphere downflexes. This has been observed on Earth, but is equally true on other planets. We use finite element models to simulate this gravity-driven deformation at Olympus Mons on Mars. Eleven model parameters, including the geometry and material properties of the edifice, lithosphere and underlying asthenosphere, are varied to establish which parameters have the greatest effect on deformation. Values for parameters that affect deformation at Olympus Mons, Mars, are constrained by minimising misfit between modelled and observed measurements of edifice height, edifice radius, and flexural moat width. Our inferred value for the Young's modulus of the Martian lithosphere, 17.8 GPa, is significantly lower than values used previously, suggesting that the Martian lithosphere is more porous than generally assumed. The best-fitting values for other parameters: edifice density (2111 – 2389 kg.m–3) and lithosphere thickness (83.3 km) are within ranges proposed hitherto. The best-fitting values of model parameters are interdependent; a decrease in lithosphere Young's modulus must be accompanied by a decrease in edifice density and/or an increase in lithosphere thickness. Our results identify the parameters that should be considered within all models of gravity-driven volcano deformation; highlight the importance of the often-overlooked Young's modulus; and provide further constraints on the properties of the Martian lithosphere, namely its porosity, which have implications for the transport and storage of fluid throughout Mars' history.

Highlights

Gravitational loading from a volcanic edifice causes the underlying lithosphere to downflex
We suggest that similar trade-offs exist between other model parameters, but the effects that some model parameters have on lithospheric flexure have not been quantified, so these trade-offs have not been studied
We suggest that the width of the flexural moat can be used to estimate lithosphere thickness, but cannot place tight constraints on edifice density; comparing the modeled and observed edifice morphology could reduce the range of permissible values for edifice density

Summary

Introduction

Gravitational loading from a volcanic edifice causes the underlying lithosphere to downflex. Olympus Mons, Mars, provides an interesting paradigm for studying lithospheric flexure because of its immense size. Tectonic plate movement on Mars possibly never started (O’Rourke and Korenaga, 2012; Leone, 2017), or ceased early in the planet’s history (Frey et al, 2002). This enabled Olympus Mons to grow to dimensions that dwarf volcanoes on Earth, and has preserved an extensive history of volcanic activity. Dorman and Lewis, 1970; Watts, 2001) to provide constraints on values for properties that affect lithospheric flexure at Olympus Mons Previous studies have used a range of techniques, including analog, analytical and numerical modeling (e.g. Byrne et al, 2013; Musiol et al, 2016), geochemical analyses of meteorite samples (e.g. Baratoux et al, 2014), crater counting (e.g. Isherwood et al, 2013), and gravitational admittance surveys (e.g. Dorman and Lewis, 1970; Watts, 2001) to provide constraints on values for properties that affect lithospheric flexure at Olympus Mons

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