Structures and crustal development of the central andes between 21° and 25°S

The Lithospheric Structure of the Central Andes (20–26°S) as Inferred from Interpretation of Regional Gravity

“…550 mGal, yet the derived Bouguer anomaly covers a range of some 750 Reutter et al 1988) in the Central Andes mGal. Although it could be expected that reduction would lead to an overall anomaly decrease, it increases for high mountain regions: e.g.…”

“…They assume that important petrophysical processes (dehydration of oceanic crust, phase transitions etc.) Reutter et al 1988). The densities of the individual segments were inverted by quadratic programming.…”

More constraints to determine the seismic structure beneath the Central Andes at 21°S using teleseismic tomography analysis

“…Gansser, 1973;Ramos, 1999) and represents one of the world's best examples of an area that has been formed under the effects of uplift and magmatism arising from the subduction of an oceanic plate (Nazca Plate) under a continental plate (South American Plate) (e.g. Barazangi and Isacks, 1976;Coira et al, 1982;Reutter et al, 1988;Isacks, 1988;Baby et al, 1992, Gubbels et al, 1993Wigger et al, 1994;Allmendinger et al, 1997). The orogen reaches its greatest width between ~14°S and ~24°S where subduction of the Nazca plate occurs at angles near 20-30° at a rate of 65mm/yr (Cahill and Isacks, 1992;Angermann et al, 1999;).…”

“…Crustal shortening occurring mainly in the Eastern Cordillera (EC) and Subandean region is likely to be responsible for the thickened crust (e.g. Pilger, 1981;Pilger 1983;Isacks, 1988;Reutter et al, 1988;Allmendinger et al, 1997;Sempere et al, 1997;Kley and Monaldi, 1998). Towards the south of the Altiplano a detailed map of crustal thicknesses for the Central Andes based on receiver functions (Yuan et al, 2002) shows that the crustal thickness underneath the southern part of the Puna plateau, is on average 10-15 km shallower than that of the Altiplano.…”

State of In Situ Stress in Northern Chile and in Northwestern Argentina

“…There is evidence that at depths of 30 -60 km within the underthrusting Nazca plate, maximum compressive stress and plate motion correspond in the azimuth of N 85° E and in the dip of 20° E. Focal Seismic activity (Wigger 1988), recent plutonism (Schwarz et al 1986) and volcanism, neotectonics such as thrusting and folding (Schwab 1985, Reutter et al 1988, actual normal and wrench faulting (Okada 1971, Salfity 1985, Scheuber et al 1986, Strecker et al 1989, current uplift of marine terraces (Ratusny & Radtke 1988) and present basin subsidence (Abele 1988) all establish the contemporaneous building of the Andes. An assumed in situ stress field with an E-W directed maximum horizontal compressive stress component deriving from the E-W convergence at the western active margin of the South American plate and from the E-W divergence at its eastern passive margin, would not explain the N-S alignment of alternating uplifted and subsided crustal segments that dominate the Andean morphology.…”