Geophysical signatures compatible with an impact origin

PREZZI, CLAUDIA BEATRIZ; MARÍA JULIA ORGEIRA; MARTÍNEZ, OSCAR; ACEVEDO, ROGELIO; PONCE, FEDERICO; GOLDMANN, GASTÓN; MAGNERES, IGNACIO

Jornada; 2das. Jornadas de Geociencias para la Ingeniería; 2015

Bajada del Diablo is located in the Northern Patagonian Massif, Chubut, Argentina. The study area includes at least 66 circular structures found in Miocene olivine basalts of the Quiñelaf Eruptive Complex and in the Late Pliocene/Early Pleistocene Pampa Sastre conglomerates. An impact origin has been proposed for these circular structures. With the aim of further investigate the proposed impact origin topographic, gravimetric, magnetic, resistivity, paleomagnetic and electromagnetic surveys in two circular structures (?8? and ?G?) located in Pampa Sastre conglomerates and in basalts of the Quiñelaf Eruptive Complex were carried out. The new geophysical results support the hypothesis of an impact origin. Particularly, the 3D forward gravity model developed for circular structure ?8? suggests that Pampa Sastre conglomerates could have been ejected and/or displaced during excavation by the impact of an extra-terrestrial projectile. The 3D forward gravity model developed for circular structure ?G? suggests the possible existence of: 1) anomalous accumulation of fractured blocks of basalts in the rims of the structure and/or, 2) calcrete and/or compacted, clay-rich sediments filling the center of the structure in the absence of a lake and/or, 3) allochthonous coherent layered melt sheets in the circular structure fill or as dykes, veins and veins networks in the autochthonous circular structure basement. The paleomagnetic results obtained in circular structure ?G? show that the primary magnetization, acquired during cooling of the lavas, was preserved in all the sampled blocks. Thus, the actual attitude of the distinct rim basalt blocks is a consequence of a process that affected the basalts after their emplacement, consistently with an impact. However, the confirmation of such an origin through the findings of shock metamorphism evidences and/or the recovery of meteorites remains elusive. Bajada del Diablo should be envisaged as a focus of further research, which could provide novel information about impact events.