GEOCHEMICAL MODELING OF THE SNC METEORITES: A COMPARISON WITH TERRESTRIAL DIVERGENT MAGMATISM
Rótulo Magmatic, evolution, martian, meteorites, ophiolite, mass, balance
ResumoA modern consensus is that Mars follows the single plate tectonic or stagnant-lid model, however, some lines of evidence disagrees, and make a case for a much more active planet. Recently it was proposed the idea of an mantle overturn from a gravitational instability in Marss the early days, which would significantly deform the lithosphere, making it prone to spreading ridges. Until a successful sample return mission, the best samples from Mars are the martian meteorite collection, composed of crustal rocks ejected by meteorite impact. Given their compositional compatibility with the terrestrial oceanic crustal sequence, the meteorites compose an interesting opportunity to look for evidence of this environment on Mars. Since a comparison between fresh rocks from terrestrial oceanic ridges and the violently shocked meteorites is susceptible to errors, we used ophiolites as an analog. This study compares the SNC meteorites with two representations of ophiolitic belts on Earth using geochemical modeling with trace elements in the Petromodeler® spreadsheet program, in an attempt to look for evidence of divergent magmatism on Mars. All the available numerical data on whole-rock geochemistry of the meteorites were compiled from the Martian meteorite compendium and from the literature. The ophiolitic belts chosen were the mafic-ultramafic Caribbean ophiolite complex, Colombia, and the Oman ophiolite. In order to search for a compatibility between settings, one must fist put the meteorites in order. This was attained using the following criteria: silica content, modal mineralogical composition, anorthite content, and dominant petrographic texture, generating a stratigraphic pile very similar to an expected oceanic crust. The results for the trace element modeling used La vs. Co and Co vs. Cr, representing light rare earth elements and transitional metals, respectively. The results show a very clear pattern for the different settings: a melting followed by a crystalization trend demonstrating the compatibility of the comparison, in which the meteorites follow not only the same stratigraphic order but also the crystallization one. A remaining point that needs to be met is the explanation of how this type of magmatism happened on Mars. The mantle overturn hypothesis doesnt explain the mantle temperature and the crystalization age of the martian meteorites, but it can be satisfied if the ridge is thought of as an inherited structure from the younger planetary days of mantle overturn. The magma generation must then be explained independently from lithospheric movements and rely solely on mantle interactions. On this context, delamination as a theoretical tectonic processes is a good fit and is majorly proposed for the stagnant lid model. It is known that the eclogite lithology can at least experimentally be achieved on Mars which in this case would mean that the main source of the meteorites magmatism would be pyroxenitic. Using the FC3MS parameter, it can be shown a clear direct positive correlation which indicates that the samples derive almost exclusively from a pyroxenitic origin. With geochemical modeling it was also possible to demonstrate a possible geotectonic evolution for the samples and demonstrates that within set parameters, all can be thought in terms of melting from a single type lithology but with different melting proportions. The few that doesnt comply with the trend were modeled as a mixing between the enriched and depleted sources. When one considers the divergent tectonic setting, every new magma batch ascent would display a slightly newer age than the previous, that is, the older meteorites are the most distant from the hypothetical martian ridge, and the youngest ones are the closest. Many articles have proposed a complete guide for the description and classification of ophiolites. Based on these, the samples are compatible with ophiolites not related to subduction and associated with mantle plumes. In conclusion, it is suggested that the martian meteorites are derived from the melting of a eclogite source after delamination, whose magma met a fossil spreading ridge from the early days of planetary formation with a mantle overturn.
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OROSCO RAMOS, D.; MATTE, V. GEOCHEMICAL MODELING OF THE SNC METEORITES: A COMPARISON WITH TERRESTRIAL DIVERGENT MAGMATISM. Anais do Salão Internacional de Ensino, Pesquisa e Extensão, v. 2, n. 14, 23 nov. 2022.