Resumo

JARAMILLO, JOSÉ M; ROJAS LINERO, PILAR  e  GARVER, JOHN I. NEOGENE'S VOLCANISM IN THE CORDILLERA ORIENTAL OF THE ANDES , COLOMBIA . . Earth Sci. Res. J. [online]. 2005, vol.9, n.1, pp.19-28. ISSN 1794-6190.

Volcanic ashes from local volcanic sources cover most of the Cordillera Oriental of the Colombian Andes. These tephra deposits are generally attributed to volcanoes to the west in the in the Cordillera Central . This study provides evidence that a thicker layer of tephra deposits, 20 to 40 m deep, that are most likely derived from newly recognized local volcanic sources in the Cordillera Oriental . The volcanic ashes that we attribute to the Paipa volcano and possibly others as yet unidentifi ed volcanoes in the Cordillera Oriental have new zircon fi ssion -track ages between 3.6 and 4.7 Ma, with a mean of 4.1 ± 0.5 Ma. We have also recognized younger pyroclastic deposits based on stratigraphic correlation. The high thermal gradient associated to these volcanoes could have had a signifi cant impact in the thermal maturation of the organic matter in Cretaceous and Paleogene sediments affecting the timing of oil generation and migration in the Cordillera and the Eastern Foothills, an area of active oil exploration and production. This discovery of young explosive volcanism highlights a serious potential geological hazard. The tephra deposits cover an extensive area of the " Altiplano Condi- boyacense ", indicating that the volcanoes are highly explosive, and potentially dangerous for about 10 million people that inhabit the " Altiplano ", its animals and crops.

Palavras-chave : Neogene Volcanism; Fission Track; Cordillera Oriental; Colombia.

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