Making a Large Volcano on Mars: Edifice State of Stress of Olympus Mons and Implications for Its Evolution

Abstract:

Olympus Mons volcano on Mars has been mapped in detail by remote sensing instruments from numerous Mars missions. It is characterized by faulting and mass movements, a circumferential scarp, and upper- to mid-flank terraces on the shield. These morphologies have been variously interpreted to be the result of lithospheric flexure, volcanic spreading, or combinations thereof. The evolutionary details and structural history of Olympus Mons are unknown, however. Therefore we aim to understand the role of the combined effects of lithospheric flexure and volcanic spreading in the evolution of the volcano. For this purpose we first re-investigate the structural geology as seen in high resolution satellite imagery. Second, we simulate the deformation of a volcanic cone including elastoplastic rheology and a variable coupling-decoupling behavior at the interface between volcano and lithosphere. We show that terrace-bounding faults on Olympus Mons flanks are thrust faults, and result from compression due to lithospheric flexure that is transferred into the edifice interfering with volcanic spreading. The presence and expression of these faults hence depends on the coupling of volcano and lithosphere, on the time of volcano growth relative to mantle relaxation, and on the edifice cohesion. We further show that a decoupling interface between volcano and lithosphere leads to normal faulting in the edifice center near the transition to the lithosphere, and to basal overthrusting probably correlated to Olympus Mons’ scarp. From a comparison of morphologies observed on Olympus Mons with remote sensing methods and faulting structures resulting from finite element models, we can interpret the state of stress inside the edifice which is crucial to magma ascent.