HR: 10:20h
AN: S41F-01    [PDF]
TI: First-order Crustal Compositional Changes along the Active South American Margin Dominate the Segmented Nature of the Andean Orogen ($15\deg$-$47\deg$S)
AU: * Tassara, A
EM: andres@geophysik.fu-berlin.de
AF: Institut fur Geologische Wissenschaften, Freie Universitat Berlin, Malteser Str. 74-100, Berlin, 12249 Germany
AU: Gotze, H
EM: hajo@geophysik.fu-berlin.de
AF: Institut fur Geologische Wissenschaften, Freie Universitat Berlin, Malteser Str. 74-100, Berlin, 12249 Germany
AB: The Andean Cordillera is a continuous feature along the western margin of South America that has been constructed by a simple common process of ocean-continent collision. However, the Andes show a remarkable continental-scale along-strike segmentation of both the current geotectonic regimen and long-term geological evolution. Here we investigate the hypothesis that differences between the Central ($15\deg$-$33.5\deg$S) and Southern ($33.5\deg$-$47\deg$S) Andes are caused by inherited compositional and hence rheological variations along the South American plate. A quantitative interpretation of elastic thickness (Te) estimates in the framework of a brittle-elasto-ductile rheology demonstrates that Te $<$ 10 km, which characterizes the axis of the Central Andes, is only possible if the bulk crustal composition is felsic, while Te $>$ 35 km along the Patagonian Cordillera segment ($39\deg$-$47\deg$S) of the Southern Andes implies a mafic-intermediate composition. This result is consistent with the available geological, geochemical and geophysical information, and indicates that the weak rheology of the quartz-dominated Palaeozoic basement characteristic of the Central Andean crust has been modified and {\it rigidized} toward the Southern Andes by the development of a stationary Meso-Cenozoic magmatic arc along the Patagonian Cordillera. This compositionally-caused rheological difference along the Andean margin should be consider a key factor in the understanding of the Late Cenozoic geodynamic evolution of the orogenic process.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7205 Continental crust (1242)
DE: 8102 Continental contractional orogenic belts
DE: 9360 South America
SC: Seismology [S]
MN: 2003 Fall Meeting