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A total of 56 fission-track ages are reported on 21 apatite, 19 zircon and 2 sphene concentrates from 24 rock samples collected from Toas Island (3) and the Sierra de Perijá (9), Western Venezuela, and from the Santander Massif (12), Eastern Colombia. All apatite ages, set by cooling on uplift, date points on uplift curves. Portions of such uplift curves are late Oligocene (27–22 Ma) in the southeast piedmont of the Sierra de Perijá; early to middle Miocene (19–14 Ma) in the western piedmont and (16–14 Ma) in the central Santander Massif; middle Miocene (13 Ma) in Toas; late Miocene to early Pliocene (7–4 Ma) in the central and northern Santander Massif; and middle Pliocene (3 Ma) in the Sierra de Perijá.

When apatite data for the Venezuelan Andes are added to the above and integrated with regional geologic evidence, it is concluded that Tertiary uplift became progressively greater and occurred at faster rates but through shorter time spans. On an elevation/age plot this should be revealed as a fan-shaped array of uplift curves. Because of inadequate topographic relief at most localities, this cannot be proven but is suggested as a working hypothesis for future verification.

Zircon ages reported here range from about 50 to 126 Ma. When reviewed together with zircon ages from the Venezuelan Andes, it is considered that 8 or 9 ages from the Venezuelan Andes (3), Santander Massif (3), and Perijás (2 or 3) reflect uplift in end- Cretaceous-Paleocene time. Two dates from Toas and the Perijás may give original crystallization ages of felsic volcanics (120–122 Ma). The remaining 23 ages are interpreted as mixed ages related to partial annealing of clocks set in Permian–early Cretaceous time although a pronounced concentration in the range of 85 to 101 Ma raises the possibility of some regional tectono-thermal event at that time. A satisfactory explanation of the latter remains to be found.

The regions referred to above are among the principal tectonic elements of a triangular continental block with apex in Santa Marta, Colombia, and the Oca and Santa Marta–Bucaramanga faults as sides. In this region “Andean” uplift is considered to have been initiated in end-Cretaceous-Paleocene time in response to northwest-southeast compression affecting the Caribbean and South American plates. Progressive compression in the apical direction of the triangle resulted in progressive interlocking of crustal blocks and final major uplift in unison during the Pliocene-Pleistocene(?). The two boundary faults are interpreted as high-angle, oblique-slip type with modest strike-slip component of movement.

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