The North Patagonian orogenic front and related foreland evolution during the Miocene, analyzed from synorogenic sedimentation and U/Pb dating (~42ºS).

MIGUEL RAMOS; JONATHAN TOBAL; LUCIA SAGRIPANTI; ANDRES FOLGUERA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 1 p. 1 - 20

0895-9811

Miocene sedimentary successions of the ~Nirihuau and Collon Cura formations east of the El Maiten Beltconstitute a partial record of the Andean exhumation, defining a synorogenic infill of the ~Nirihuau Basinin the foothills of the North Patagonian fold and thrust belt. Gravimetric and seismic data allowrecognizing the internal arrangement and geometry of these depocenters that host both units, separatinga synextensional section previous to the Andean development at these latitudes, from a series of syncontractionalunits above. A series of progressive unconformities in the upper terms shows the synorogeniccharacter of these units corresponding to the different pulses of deformation that occurredduring the middle Miocene. New UePb ages constrain these pulses to the ~13.5e12.9 Ma interval andallow reconstructing the tectonic history of this region based on the detrital zircon source populations.The UePb maximum ages of sedimentation give to the ~Nirihuau Formation in particular a younger agethan previously assumed. Additionally, synsedimentary deformation in strata of the upper exposures ofthe Collon Cura Formation associated with contractional structures and UePb ages allow identifying ayounger paleoseismogenic pulse in ~11.3 Ma. Thus, based on these data and a compilation of previousdatasets, a tectonic evolution is proposed characterized by a contractional episode that migrated eastwardlysince ~19 to 15 Ma producing the Gastre broken foreland and then retracted to the eastern NorthPatagonian Precordillera, where out-of-sequence thrusts cannibalized the wedge top zone in the ElMaiten belt at ~13.5e11.3 Ma.