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Basin Evolution and Sediment Provenance in the Colombian Andes: Results from Detrital Zircon U-Pb Geochronology

Horton, Brian K.1; Saylor, Joel E.1; Nie, Junsheng 1; Parra, Mauricio 1; Stockli, Daniel F.2; Mora, Andrés 3
1 Department of Geological Sciences, University of Texas, Austin, TX.
2 Department of Geology, University of Kansas, Lawrence, KS.
3 Instituto Colombiano del Petróleo, Ecopetrol, Bucaramanga, Colombia.

New geochronological data for the northern Andes improve Phanerozoic reconstructions of extension, shortening, and basin evolution in the Llanos foreland, Eastern Cordillera, Magdalena Valley, and Central Cordillera of Colombia. U-Pb ages were obtained by LA-ICPMS analyses of detrital zircons from 26 Phanerozoic stratigraphic units and 3 selected granitic intrusions. Dramatic variations in the age of crystalline rocks across northern South America provide an opportunity to discriminate multiple sediment sources, including the 2000-1500 Ma basement shield to the east, 1200-900 Ma and 600-400 Ma basement of the Eastern Cordillera, and 200-50 Ma magmatic-arc rocks and local 1200-900 Ma basement of the Central Cordillera. U-Pb zircon ages from pre-Devonian granites (3 samples) from the Eastern Cordillera indicate magmatism at 600-400 Ma, with inherited zircon ages of 1700-1000 Ma. Detrital zircon age spectra for Paleozoic (4 samples) and Mesozoic (11 samples) strata from the Eastern Cordillera demonstrate a composite source of local basement (Quetame, Floresta, and Santander massifs) and distal eastern basement (Guyana shield). Limited igneous centers also contributed detrital zircons during Jurassic-Cretaceous extension. An early Cenozoic onset for shortening-related uplift appears to be constrained by the initial appearance of detrital zircons in Paleogene strata (3 samples) derived from Cretaceous-Paleogene magmatic-arc rocks uplifted in the Central Cordillera. Detrital zircon ages from Neogene deposits (8 samples) of the eastern foothills and Llanos foreland basin reveal a progressively greater influence of thrust-belt provenance during uplift of the Eastern Cordillera. However, these data do not identify precise source areas because of recycling of extensive Cretaceous clastic units during Eastern Cordillera uplift. Ongoing research is exploring whether detrital zircon U-Pb geochronology can better constrain depositional ages for stratigraphic units in hydrocarbon-bearing regions of the Magdalena Valley and Llanos basin. This study demonstrates the potential of U-Pb geochronology to address problems relating to the timing of deformation relative to hydrocarbon generation and migration, as well as regional stratigraphic correlation.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009