Folding, thrusting and development of push-up structures during the Miocene tectonic inversion of the Austral Basin, Southern Patagonian Andes (50°S)

ENRIQUE ZERDASS; MAXIMILIANO NAIPAUER; VICTOR A. RAMOS; ANDREA CONCHEYRO; MATÍAS GHIGLIONE; ISABELLA O. CARMO

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 vol. 699 p. 102 - 120

0040-1951

Rift and post-rift sections of the Austral Basin inthe Southern Patagonian fold and thrust belt were examined in outcrop and in 2Dseismic reflection sections to evaluate geometric and kinematic aspects of theextension and subsequent inversion. The syn-rift section is composed of daciticlava flows of the El Quemado Complex (Jurassic), the lowermost unit of thebasin. The coastal sandstones of the Springhill Formation(Tithonian-Berriasian) and marine shales of the Río Mayer Formation(Berriasian-Albian) are thought to be sag units. However, field data suggestthat these units are also part of the syn-rift successions, as evidenced byextensional growth strata in the lower levels of the Río Mayer Formation. Adacitic flow that is texturally and compositionally similar to those of thesyn-rift phase and that is termed here the Río Guanaco dacite is interfingeredwith the basal strata of the Río Mayer Formation and has a U-Pb zirconcrystallization age of c. 141 Ma (Berriasian). The outcropping section wasinverted by compression in the early Miocene, according to structural andisotopic data of adjacent areas, producing a broad anticline with inverted andfossil extensional faults as well as newly generated thrusts. At the seismicscale, most of the extensional master faults present negligible reverse slip,and shortening was accommodated in hanging wall push-up structures. Thissituation is interpreted as a result of the competent metamorphic basement andvolcanic syn-rift section, inducing frictional lock-up of the master faults.