Influence of tectonics on the extent of quaternary glaciation in the Andes

Resumo

The extent of Quaternary glaciations varies throughout the Andes. Although the lack of radiometric dating in many places precludes precise assessment of these variations, certain spatial patterns are evident. In the N. Andes (N. of 15ºS) glacial landforms and sediments of only the ultimate and penultimate glaciations (O-isotope stages 2, 4, 6) have been identified. In the Central Andes (15-35ºS) successive glaciations since at least the mid-Quaternary have been progressively less extensive. In the Southern Andes successive glaciations since the greatest glaciation at ca. 1.2 Ma have been progressively smaller; also, the Islas Malvinas 800-1,000 km to the east became glaciated for the first time during the penultimate glaciation and developed an even greater number of nivo-glacial features during the last glaciation. The segmented nature of the oceanic and continental crust along the Pacific-South American subduction zone promotes tectonic independence of parts of the Andean chain. It is argued that variations in the extent of glaciation may be largely explained by Quaternary uplift and subsidence in different places and by precipitation-shadow effects related to elevation and air mass source.