Magma ascent and emplacement below floor fractured craters on the Moon from floor uplift and fracture length
Résumé
Floor fractured craters (FFCs) are a class of craters on the Moon that presents deformed, uplifted and fractured floors. These endogenous modifications were likely caused by the emplacement of underlying magmatic intrusions. Here we provide two independent quantitative observations that reflect how the overpressure leading to a crater-centered intrusion varies as a function of crater radius and crustal thickness: the amount of crater floor uplift and the total length of fractures covering the crater floor. Those two observations can be related to the magma overpressure inside the shallow intrusion provided that a significant part of the elastic energy of deformation associated to magma emplacement below the crater is dissipated by the formation of fractures; a condition that seems to be met for a significant number of craters in the Highlands or at the limit between the Highlands and the lunar maria. Here we show that for those FFCs, variations of these two quantities with crater radius and crustal thickness are well predicted by a process of magma ascent caused by crater unloading. By further developing this model and precising its initial conditions, we show that magma storage in the lunar crust is likely to be in the form of vertical dykes emanating from the crust mantle interface. Finally, this study highlights the use of the total fracture length and fracture patterns on FFCs floors as observations that provide insights into the mechanism of magma ascent and emplacement below FFCs and the characteristics of the encasing medium.
Domaines
Planète et Univers [physics]
Origine : Fichiers produits par l'(les) auteur(s)
