Cenozoic building and deformational processes in the North Patagonian Andes |
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| Institution: | 1. Instituto de Estudios Andinos Don Pablo Groeber, UBA–CONICET. Departamento de Ciencias Geológicas, FCEN, Universidad de Buenos Aires, Intendente Güiraldes 2160, Ciudad Universitaria Pabellón II, 1er piso, Buenos Aires C1428EGA, Argentina;2. ENERGIAL S.A., Argentina;3. Dpto. de Geología, F.C.N., Universidad Nacional de la Patagonia “San Juan Bosco”, Ruta Provincial N° 1, Km. 4, (9005) Comodoro Rivadavia, Chubut, Argentina;4. Instituto Geofísico y Sismológico Ing. Volponi, Universidad Nacional de San Juan, Ruta 12, Km 17, CP 5407, San Juan, Argentina |
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| Abstract: | The Oligocene to present evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformational processes that acted through time and relate them to basin formation processes. Seismic reflection profiles reveal the shallow structure of the retroarc area where contractional structures, associated with Oligocene to early Miocene inverted extensional depocenters, are partially onlapped by early to late Miocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40° and 43°30′ S, constrained by surface, gravity and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34%) is determined near 41°30′ S coincidentally with maximum mean topographic values on the eastern Andean slope, where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed towards the foreland. Additionally, eastward shifting of Miocene calc-alkaline rocks occurred at these latitudes, which is interpreted as indicative of a change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data. Younger volcanism and thermal anomalies are explained by slab steepening since early Pliocene, after a mild-shallow subduction setting in the middle to late Miocene, age of the main compressive event. |
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| Keywords: | Andean orogenesis Patagonian Andes Shortening Foreland basin Shallow subduction Arc migration Gravity and magnetic data |
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