Mesozoic- Pleistocene fission-track ages on rocks of the Venezuelan Andes and their tectonic implications.

Abstract

A total of 45 fission-track ages are reported on 22 apatite, 21 zircon, and 2 sphene concentrates from 23 rock samples from the Venezuelan Andes. Apatite ages ranging from approx 1.4-24.0Ma are all interpreted as cooling ages related to uplift and erosion of cover rocks. Updoming of isotherms is inferred and discussed. On the basis of the apatite ages, it is suggested that uplift of the Andes involved first uplift of the leading (NW) margin in the Oligocene to Miocene, followed by uplift of the trailing (SE) margin in the late Miocene, and in turn by rapid uplift of the central Andes in Pliocene-Pleistocene time. Zircon ages range from approx 60-172Ma with a strong grouping in the range of a..