HR: 18:05h
AN: P34A-08    [Abstracts]
TI: Geophysical evidence of an impact crater in northwestern South America
AU: * Hernandez, O
EM: ohernandezp@unal.edu.co
AF: Universidad Nacional de Colombia, Departamento de Geociencias, Edificio Manuel Ancizar Of 335 Ciudad Universitaria, Bogota, D.C 06, Colombia
AU: von Frese, R R
EM: vonfrese@osu.edu
AF: The Ohio State University, School of Earth Sciences 375 Mendenhall, 125 South Oval Mall, Columbus, OH 43210, United States
AU: Khurama, S
EM: skhurama@ingeominas.gov.co
AF: INGEOMINAS, Diagonal 53 # 34-53, Bogota, D.C 06, Colombia
AB: A prominent positive terrain correlated free-air gravity anomaly over regionally depressed topography may identify a mascon centered on (4.15 N, 69.5W) in the Vichada plain, Guiana Shield in Northwestern South America. The topographic depression was recognized by LANDSAT images, showing a complex crater with two rings of 30 km and 50 km of diameter. Being one third of the size of the Chibxulub's impact crater, the 50 km-wide impact crater is the first meteor impact found in Colombia and the biggest impact crater of South America. This structure has been partially eroded by the Vichada River and its topographic expression is obscured by dense vegetation and erosion. Free air gravity anomalies at 20 km altitude from EGM-96 do not show any significant signature. However, concentric positive terrain-correlated free-air gravity anomalies are superposed to the impact crater. Also negative Terrain decorrelated free air gravity anomalies are located at the impact crater structure. MOHO estimates from inverse modeled compensated terrain gravity effects show a shallower MOHO below the impact crater, with a thinning of the continental crust, that could be created as a result of the mantle rebound after the shock waves generated by the impact, creating a mascon, typical of an impact crater structure, with a 40 km-wide, 3 km-high plug of mantle material that had risen up into the Earth's crust. Concentric negative total field magnetic anomalies superposed to the gravity anomalies also support the impact crater model.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 5109 Magnetic and electrical properties (0925)
DE: 8000 STRUCTURAL GEOLOGY
DE: 8015 Local crustal structure
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly