Paper No. 3
Presentation Time: 9:30 AM
THE SPATIAL PATTERN OF SURFACE UPLIFT IN THE CENTRAL ANDES
The early Miocene to present paleoelevation history of the Altiplano plateau of the central Andes has been well studied over the last fifteen years, but almost solely in the northern part of the Altiplano. Here we present stable isotope data that describe the paleoelevation of the southern Altiplano. We focus on the paleoenvironmental record preserved in pedogenic carbonates from well-dated middle-late Miocene (16.3 to 7.1 Ma) sedimentary sections, which record paleo-surface conditions that offer useful proxies for elevation, including paleo-temperature (Δ47
) and paleo-rainwater chemistry (δ18
O). Surface paleotemperatures decreased by 14°C from 16 to 8 Ma in the southern Altiplano relative to low-elevation paleotemperatures, which remained stable through that interval. This surface temperature record indicates a surface elevation increase of 1.5±0.5 km between 16 and 13 Ma and an additional 0.5±0.5 km between 13 and 9 Ma. Paleoelevation estimates based on oxygen isotopes are similar to those based on paleotemperatures from ~16-15 Ma, but under-predict surface elevation since ~13 Ma (including the modern elevation). We interpret this to reflect the evaporative enrichment of oxygen isotopes in rain water and/or soil water due to the increasingly arid conditions.
Previous surface elevation estimates from the northern Altiplano suggest that region experienced 2.5±1.0 km of surface uplift between ~11 and 6 Ma (Garzione et al., 2008). Our results from the southern Altiplano show a similar rate and magnitude of surface uplift, but occurring 7±4 Myr earlier than in the northern Altiplano. This temporal offset also appears in other indicators of surface uplift such as climate (aridity) and sediment accumulation rate. The consistency of the paleoclimate and paleoelevation records suggests that the same mechanism(s) were responsible for the periods of rapid uplift in both parts of the Altiplano, but was active at different times in different regions. Geologically reasonable processes that fit this observed pattern of large magnitude and spatially variable surface uplift include piecemeal removal of dense lower lithosphere and lower crustal flow, possibly in a south-to-north direction.