Abstract

New petrological observations from a volcanic unit at the base of the Jurassic sequence in the Alta Guajira region (Colombia) are consistent with the presence of a continental volcanic arc and the development of an intra-arc basin in the area. Fault-bounded Jurassic sedimentary basins in the Alta Guajira region were initiated during the early Jurassic (180 Ma) with silicic volcanism in the axis of a magmatic arc and later filled with a thick volcano-sedimentary sequence. The Jurassic silicic volcanic rocks at the base of the basin (Riodacita de Ipapure–Cerro La Teta) are observed as isolated remnants of andesite, dacite, and rhyolite. These lithologies are characterized geochemically by a calc-alkaline character, enrichment in light rare earth elements, Nb-Ta depletion, and Eu negative anomaly indicating a converging tectonic-setting origin, possibly in a continental volcanic arc related to early subduction. The unit marks the beginning of a continental-arc basin that was a sediment depocenter since the middle Jurassic in the area.