Des impacts d'astéroïdes ont-ils pu initier des points chauds et provoquer la dislocation de la Pangée
Résumé
Fifteen major meteorite impacts have hit the Earth between -90 My and -250 My and are reviewed. The purpose of this study is to check if they could have been involved in long-term and/or long distance geophysical effects. Using plate tectonic reconstructions, it appears that, in 11 out of these 15 cases, the original impact positions fall in the vicinity of hotspots or volcanic activities that developed later. In addition, four older impacts, with ages in the range -400 to -250 My, can also be associated with such volcanic events. Moreover, if multiple impacts occurred within few hours, several systems of shockwaves were present at the same time in the crust, coming from different points and travelling in different directions. The waves would have interfered on well-defined loci and left their footprints in the lithosphere. These loci may have initiated the fragmentation of the crust and/or facilitated the outbreak of underlying mantle plume magma. Computations are developed for four events that may have occurred at critical dates in the history of the Earth: -250 My (3 impacts), -214 My (3), -145 My (2) and -90 My (2 impacts). The systems of interferences generated by these impacts reflect most of the break up lines in the Pangea/Gondwana and explain more than 100 000 km of existing rifts, trenches and shorelines. Typical geographical features are direct consequences of these interferences: The Caledonian channel, the Bathurst Inlet, the Rio de la Plata, etc. For all cases, the speed of seismic waves is found to be close to 6.4 km/s. Combinations and relationships between all these effects (hot spots, interferences and magma plumes) could help understand the genesis and the outcome of major events such as the CAMP (-200 My), the Africa-South America separation (-135 My) and the North Atlantic Volcanic Province (-60 My). This whole approach leads to several consequences or “predictions” to be verified: - Suggestions are made for The Hawaiian Island, the Siberian traps, and lake Qinghaï. - A global tectonic motion of North Africa should be involved in order to explain the 90° change of coastline direction in the gulf of Guinea. - The 4000km-long Valles Marineris, on Mars, can also be explained by a double impact and gives a realistic image of effects which could have appended on Earth. - Computations suggest that a fifth event have occurred in -128 My: in addition to the Tookoonooka crater, a second impact crater may exist, half-way between New Caledonia and New Zealand at position 173°E and 28°S.
Domaines
Géophysique [physics.geo-ph]
Origine : Fichiers produits par l'(les) auteur(s)
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