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

ZERFASS H.; RAMOS, V.A.; GHIGLIONE, M.; NAIPAUER, M.; BELOTTI, H.J.; CARMO, I.O.

TECTONOPHYSICS

ELSEVIER SCIENCE BV

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

0040-1951

Rift and post-rift sections of theAustral Basin in the Southern Patagonian fold and thrust belt were examined inoutcrop and in 2D seismic reflection sections to evaluate geometric andkinematic aspects of the extension and subsequent inversion. The syn-riftsection is composed of dacitic lava flows of the El Quemado Complex (Jurassic),the lowermost unit of the basin. The coastal sandstones of the SpringhillFormation (Tithonian-Berriasian) and marine shales of the Río Mayer Formation(Berriasian-Albian) are thought to be sag units. However, field data suggest thatthese units are also part of the syn-rift successions, as evidenced by extensionalgrowth strata in the lower levels of the Río Mayer Formation. A dacitic flowthat is texturally and compositionally similar to those of the syn-rift phaseand that is termed here the Río Guanaco dacite is interfingered with the basalstrata of the Río Mayer Formation and has a U-Pb zircon crystallization age ofc. 141 Ma (Berriasian). The outcropping section was inverted by compression inthe early Miocene, according to structural and isotopic data of adjacent areas,producing a broad anticline with inverted and fossil extensional faults as wellas newly generated thrusts. At the seismic scale, most of the extensional masterfaults present negligible reverse slip, and shortening was accommodated in hangingwall push-up structures. This situation is interpreted as a result of the competentmetamorphic basement and volcanic syn-rift section, inducing frictional lock-upof the master faults.