Filu-Có plateau: the largest impact crater field of Bajada del Diablo strewnfield, Patagonia, Argentina

ACEVEDO, R.D.; PONCE, J.F.; ROCCA, M.; RABASSA, J.; CORBELLA, H.

Santiago de Chile

Congreso; GEOSUR 2007; 2007

Universidad de Chile

Filu-Có plateau: the largest impact crater field of Bajada del Diablo strewnfield, Patagonia, Argentina   Acevedo, R.D. *1, Ponce, J.F.1, Rocca, M.2, Rabassa, J.1,3, Corbella, H.4,5   (1) CADIC-CONICET, C.C. 92, 9410 Ushuaia, Tierra del Fuego, Argentina (2)  The Planetary Society (3)  Universidad Nacional de la Patagonia-San Juan Bosco, Sede Ushuaia (4) CONICET and Museo Argentino de Ciencias Naturales “B.Rivadavia”, Buenos Aires, Argentina (5) Universidad Nacional de la Patagonia Austral, Río Gallegos, Argentina * Presenting Author’s email: acevedo@arnet.com.ar   Only 8 meteorite crater strewnfields were known on Earth until today: Gilf Kefir (Egypt), Campo del Cielo (Argentina), Sikhote Alin (Russia), Henbury (Australia), Wabar (Saudi Arabia), Kaalijarvi (Estonia), Chiemgau (Germany) and Morasco (Poland). Bajada del Diablo, in central northern Patagonia, Argentina, should be added now to that list. Bajada del Diablo was described for the first time by one us (H.C.) in 1987, though with reserves about its origin. Recent remote sensing analysis and field studies have shown that Bajada del Diablo is undoubtedly one of the largest strewnfields in the world. It is located in a remote area of Patagonia, close to Gan-Gan, Chubut Province. This amazing strewnfield contains more than 100 almost circular, crater-type structures with diameters ranging from 100 to 500 m in width and 30 to 50 m in depth. It is composed of three separated impact craters fields, which formed simultaneously. The original crater field was eroded by Pleistocene fluvial processes, thus three major, separate areas were defined. Our work has been concentrated in one of these impact craters fields, which is located on the Filu-Có plateau, NE from the other two. The craters do not present a classic elliptical distribution. The studied area (60 km2) is composed of (1) a volcanic plateau of late Miocene basalts and trachybasalts of the Quiñelaf Volcanic Complex, (2) coarsely stratified sedimentary breccias, conglomerates and sands of a contiguous Pliocene pediment which extends around most of it, and (3) Pleistocene fluvial deposits forming terraces and network channels. This area includes at least 48 impact craters found both on the Miocene plateau and the Pliocene pediment, but they are absent on the Pleistocene fluvial landforms. Crater structures are similar in both target rocks, although showing different behavior. They are simple rings, bowl-shaped with raised rimrock. Basaltic boulders have been deposited as a ring-shaped pile and ejecta is found towards the NE flanks. They present a hummocky bottom, with dry ponds and lakes in the center, but the craters do not show raised central peaks. The rocks within the craters have strong and stable magnetic signature. No meteorite fragments or other diagnostic landmarks have been founded yet. The craters have been partially filled-in by debris flows from the rim and wind-blown sands in recent times. The origin of these crater fields may be related to multiple fragmentation of one asteroid which broke up before impact, perhaps travelling across the space as a rubble pile. When entering the Earth atmosphere, the impactors were projected in a theoretical shallow input angle between 15º to 25º from the horizontal, smashing against the surface. Alternatively, the multiple collision of comet fragments could explain the formation of these crater fields. The layout of the ejecta that moves preferably in the downrange direction indicates a high velocity impactor coming from SW towards NE. Based on field geological and geomorphological data, the age of this event is estimated to be post-Pliocene and pre-middle Pleistocene.