Cenozoic building and deformational processes in the NorthPatagonian Andes

ORTS, D.L.; FOLGUERA, A.; GIMENEZ, M.; RUIZ, F.; ROJAS VERA, E.; LINCE KLINGER, F

JOURNAL OF GEODYNAMICS

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 86 p. 26 - 41

0264-3707

The Oligocene to present evolution of the North Patagonian Andes is analyzed linking geological andgeophysical data in order to decipher the deformational processes that acted through time and relatethem to basin formation processes. Seismic reflection profiles reveal the shallow structure of the retroarcarea where contractional structures, associated with Oligocene to early Miocene inverted extensionaldepocenters, are partially onlapped by early to late Miocene synorogenic deposits. From the constructionof five structural cross sections along the retroarc area between 40◦and 43◦30S, constrained by surface,gravity and seismic data, a shortening gradient is observed along Andean strike. The highest shorteningof 18.7 km (15.34%) is determined near 41◦30S coincidentally with maximum mean topographic valueson the eastern Andean slope, where basement blocks were uplifted in the orogenic front area, and thedeepest and broadest synorogenic depocenters were formed towards the foreland. Additionally, eastwardshifting of Miocene calc-alkaline rocks occurred at these latitudes, which is interpreted as indicative ofa change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated throughinversion of gravity models that made possible to infer Moho attenuated zones. These coincide withthe occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomaliessuggested by shallowing of the Curie isotherm calculated from magnetic data. Younger volcanism andthermal anomalies are explained by slab steepening since early Pliocene, after a mild-shallow subductionsetting in the middle to late Miocene, age of the main compressive event.