INVESTIGADORES
PONCE Juan Federico
congresos y reuniones científicas
Título:
. Bajada del Diablo, Patagonia, Argentina: The impact of a split comet?
Autor/es:
ACEVEDO, R.D.; PREZZI, C.; ORGEIRA, M. J.; RABASSA, J.; CORBELLA, H.; PONCE, J.F.; MARTINEZ, O.; VÁSQUEZ, C.; SUBÍAS, I.; GONZÁLES, M.; ROCCA, M.
Lugar:
Londres
Reunión:
Encuentro; 74th Annual Meeting of the Meteoritical Society; 2011
Resumen:
An impact origin has been proposed for the almost 200 circular
structures found in Bajada del Diablo (42 46¢ to 43 S and 67 24¢ to 45¢
W), Patagonia, Argentina [1], some of them partially obliterated by
erosion or sediment accumulation, which range in diameter from 100 m
up to 400 m.
The circular structures have been identified in two rock types: the
Quin elaf eruptive complex (Miocene basalts) and Pampa Sastre
Formation (Pliocene basaltic conglomerate).
Geological and geomorphological strong evidences of involvement
on both geologic entities more over the Pleistocene pediment gravels and
sands has been interpreted as the cause of the impact but lack either
pieces of the impacting body like meteorites or definitive signs of shock
metamorphism. Only samples of breccias randomly spread were collected.
In neither case, however, was detected there any evidence of coesite. Most
important diagnostic elements collected so far are tiny Fe-Ni lawrencitebearing
microspheres of 300 microns in average diameter, presumably
originated by the impact, buried under post-impact sedimentary coverage.
To strengthen the hypothesis of impact through the geophysical
survey magnetometric record of magnetic anomalies were performed. The
magnetic anomalies show a circular pattern with magnetic lows in the
circular structures floors. Furthermore in the circular structures rims,
high-amplitude, conspicuous and localized (short wavelength) anomalies
are observed. Such large amplitude and short wavelength anomalies are
not detected out of the circular structures. For all used frequencies, the
electromagnetic profiles show lower apparent electrical conductivities in
the circular structures floor, while the rims present notably higher values.
Curvature attributes, analytic signal, horizontal gradient and Euler
solutions were calculated for the magnetic data. 2.5 D magnetic models
were developed across each one of the studied circular structures. Our
results suggest that in the circular structures floors up to 12 m of Pampa
Sastre conglomerate would have been removed. On the contrary, the
circular structures rims exhibit high-amplitude, localized magnetic
anomalies and higher apparent electrical conductivities, which would be
related to the anomalous accumulation of basalt boulders and blocks
remanently magnetized. The fact that such high-amplitude anomalies are
not present out of the surveyed circular structures supports this
hypothesis. The geomorphological, geological and geophysical features of
the studied circular structures can only be explained by means of an
extra-terrestrial projectile impact.
Even Fe-Ni microspheres with lawrencite and breccias have been
found inside craters, nevertheless, the absence of direct evidences of a
disintegrated asteroid opens the possibility to consider the event of a split
comet with an ice nucleus hitting the patagonian surface in Pleistocene
times.