Nous aurons le plaisir d’accueillir Virgile Malarewicz le jeudi 26 février à 13h dans l’amphithéâtre du rez-de-chaussée de l’Institut Pascal, bâtiment 530, pour un séminaire intitulé : ” Mars’ primitive crust explored in the regolith breccia NWA 7533“.
Résumé :
The oldest documented Martian meteorite, the regolithic breccia NWA 7533, offers a unique window into the history of the primitive Martian crust. Its exceptional mineralogical diversity allow us to better constrain a period for which very little direct evidence remains: the pre-Noachian (> 4.0 Ga). New fragments of this meteorite have revealed the first magmatic quartz identified on Mars, constituting lithological fragments of granitic composition. In addition to being the most differentiated rocks detected to date on Mars, isotopic analyses (δ³⁰Si and δ¹⁸O) suggest that they formed from previously altered material. At the same time, systematic chemical and structural characterization of around 100 zircons present in the breccia, dated to more than 4.4 Ga, reveals atypical textures that had not been described previously. These textures are interpreted as traces of early hydrothermal alteration within the Martian crust. All of these observations point to the existence of a primitive Martian crust that was already highly diversified, marked by complex magmatic and hydrothermal processes. These results pave the way for comparisons with the ancient Earth’s crust, particularly regarding the existence of these particular textures on ancient terrestrial zircons.
