Evolution of the Manantiales Basin, San Juan: Constraining Miocene Orogenic patterns in the South-Central Andes

MANUELA MAZZITELLI; BRIAN MAHONEY; ELIZABETH BALGORD; LAURA GIAMBIAGI; DAVE KIMBROUGH; ANA LOSSADA; CHAZ MCCANN

Baltimore

Congreso; GSA Metting; 2015

GSA

The study area is in the Southern Central Andes, in the west of San Juan Province, Argentina, at the 32º of Southern Latitude. Is a piggyback basin call Manantiales, from the Miocene, located in the Frontal Cordillera region.The work in the area consisted in mapping, for structural and sedimentary purposes, and the sampling tuffs and volcanic rocks for U-Pb dating.The Chinches Formation has a continuous dipping into the west, with an average strike of N150, and dipping between 8 and 25 to the West. New data from the Chocolate Arenites of the lower portion of the Manantiales section shows an older age than the previous thoughts is 38.68 ± 0.21 Ma instead of 20 Ma. It has a thickness of 140 meters. This is showing a clear hiatus in the sedimentation, and the Chocolate Arenites are not part of the sinorogenic basin.The base of the Chinches Formation is younger than the first data shown, is 16.843 ± 0.23 Ma. This means that is contemporary with other two basins of the area, the Santa María and the Alto Tunuyán basin.There are several evidences that the Frontal Cordillera was always elevated along the west of different basins of the Southern Central Andes, since, at least, 16 Ma ago. The Manantiales basin and the Santa María basin have conglomerates with clasts that are from the Frontal Cordillera and Alto Tunuyán basin has sandstones with a high amount of the same clasts. This means that these Permian-Triassic rocks were all the time an outcrops, giving an important contribution during the formation of the Miocene basins. Each basin had differences in the distance to the source, and that could explain the differences in the grain size.