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A magmatic origin for floor-fractured craters in the Southern Highlands of Mars

Alexandra Le Contellec1 , Chloé Michaut1,2, Virginie Pinel3, Damian Walwer4,Francesco Maccaferri5

  • Affiliations: 1Laboratoire de Géologie de Lyon : Terre, Planète, Environnement, ENS de Lyon, Université Claude Bernard Lyon 1, 69007 Lyon, France; 2Institut Universitaire de France; 3ISTerre, Université Savoie Mont-Blanc, Université Grenoble-Alpes, Chambéry, France; 4California Institute of Technology; 5INGV, Sezione di Bologna, Italy.

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 252

  • Programme No: 1.4.12

  • Theme 1 > Session 4

Abstract

Lunar floor-fractured craters (FFCs) possess fractured and uplifted floors and result from shallow, crater-centered, sill-like intrusions. FFCs have been observed on Mars, mainly in the Southern hemisphere, where the crust is thicker and of enigmatic composition. However, the complex geologic history of Mars makes it difficult to assess with certainty their magmatic origin as interaction with groundwater or ice could produce similar structures. Here, we study a set of FFCs located in the Martian Highlands. We show that their floor uplift evolves following the square root of the total length of their floor fractures, as predicted from a physical model of fracture formation from a sill intrusion, similarly to lunar FFCs. This suggests that these FFCs are of magmatic origin. On the contrary, extrusion of mafic magma is observed in the interior of Jezero, a crater located in the same region of Mars, though on a thinner crust. In both cases, the process is crater-centered, suggesting that the magma is negatively buoyant in the crust. We use a model of dyke propagation in an elastic crust, considering the stress field caused by the crater unloading, to study the dyke path below the crater. We demonstrate that a simple difference in crustal thickness can explain the horizontal deflection of dykes into sills below FFCs and the extrusion of magma in the interior of Jezero. We finally show that the crust must be lighter by 100-150 kg m3 than the magma for FFCs to form in the Highlands.