Gregory - Wodzicki, K.M., 2000, Andean
paleoelevation estimates: A review and critique, Geological Society
of America Bulletin, in press.
Abstract.-- The elevation of the Andean Cordillera is
a crucial boundary condition for both climatic and tectonic studies; the
Andes affect climate because they form the only barrier to atmospheric circulation
in the Southern Hemisphere, and they intrigue geologists because they have
the highest plateau on earth formed at a non-collisional plate margin, the
Altiplano-Puna. Yet until recently, few quantitative studies of their uplift
history existed. This study presents both 1) a review of the quantitative
paleoelevation estimates which have been made for the Central and Colombian
Andes and 2) an examination of the source and magnitude of error for each
estimate. In the Central Andes, paleobotanical evidence suggests that the
Altiplano-Puna had attained no more than a third of its modern elevation
of 3700 m by 20 Ma, and no more than half its modern elevation by 10.7 Ma;
these data imply surface uplift on the order of 2300-3400 m since the
late Miocene at uplift rates of 0.2-0.3 mm/yr. Paleobotanical and geomorphological
data suggest a similar uplift history for the Eastern Cordillera, namely
no more than half the modern elevation present by 10 Ma. There is no evidence
for an exponential increase in uplift rate, as has been interpreted from
fission-track data. These uplift rates mostly reflect mean surface uplift
rather than rock uplift, that is, uplift of material points, because there
has been little dissection of the western Eastern Cordillera south of 19°S
and of the Altiplano-Puna. Thus, the Central Andean Plateau appears to be
young. In the Colombian Andes, paleobotanical data imply rapid uplift of
the Eastern Cordillera between 2 - 5 Ma at rates on the order of 0.6 - 3 mm/yr.
However, some of this uplift is likely rock uplift due to erosionally-driven
isostatic rebound, rather than mean surface uplift.
Figure 5. Paleoelevation estimates for the A) Central Andes, and B) Eastern
Cordillera of Colombia.