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Tephrochronologie de la Colombie centrale (departement d'Antioquia et Abanico de Pereira) : une approche stratigraphique, géochimique, minéralogique et géochronologique (par 14C et traces de fission)

Abstract : ln the Antioquia and Risaralda departments of Central Colombia, the superficial deposits are voleanodetrital. The older ones are indurated, diaclased and faulted. The youngest ones, or " upper tephras ", rarely reach at most a thickness of about 1 m. . ln the Antioquia department (altiplano, and Aburra valley), on the Central Andine Cordillera, heavy mineraIs studies, and zircon fission tracks (FT) and 14C datings show that the deposition of the superficial deposits is not older than the Upper Pliocene. FT dating allows to date various sedimentary deposits (lacustrine sediments, fluvial terraces, " stone line ") and a tectonic event (opening of the Aburra valley). ln the upper tephras, heavy mineraIs determinations allow to derme a stratigraphy for the whole altiplano. FT and 14C dating show that these tephras were deposited between at most 0.44 Ma and 20-30 ka. The Ruiz-Tolima vocanic massif, some 80 km south of the Antioquia department, is active since the Upper Miocene. This is the same age range as recorded in our tephras. Thus the Ruiz-Tolima could be the source of the tephras studied. The FT ages of basement zircons (from saprolites or sediments) are nearly always Upper Cretaceous to Paleocene, testifying of the cooling of their* mother rocks (Antioquenio batholith, its metamorphic host rock or tertiary intrusions). ln one sample, zircons with FT ages of 185 Ma show that since at least that time they were stood below 300°C. ln the Risaralda department, on the west flank of the Central Cordillera, only the upper tephra, were studied, mostly in the " abanico ", - or fan-, of Pereira, immedeiately west of the Ruiz-Tolima massif. lt was not possible to obtain a stratigraphy of these formations for the whole area, which extends westward up to the Western Cordillera. On the abanico de Pereira, the upper tephras are thicker than in the Antioquia department, with younger ages, between more than 14 ka on the Pereira terrace and less than 8 ka ont this terrace and the Otun lake (adjacent to the Ruiz-Tolima), which is to be attributable to its proximity to the voleanic massif
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Submitted on : Wednesday, June 20, 2012 - 3:41:32 PM
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Gloria Toro Villegas. Tephrochronologie de la Colombie centrale (departement d'Antioquia et Abanico de Pereira) : une approche stratigraphique, géochimique, minéralogique et géochronologique (par 14C et traces de fission). Géochimie. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00710305⟩

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