46 Structural Geology (Posters)

Sunday, 1 November 2015
9:00 AM - 5:30 PM
Exhibit Hall

EVOLUTION OF THE MANANTIALES BASIN, SAN JUAN, ARGENTINA:  CONSTRAINING MIOCENE OROGENIC PATTERNS IN THE SOUTH-CENTRAL ANDES

Paper number: 46-36
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

The Manantiales basin is a retroarc foreland basin succession flanked on the west by the Cordillera del Espinacito of the Cordillera Frontal and on the east by the Cordillera del Tigre of the Cordillera Frontal. The basin has been interpreted as a Miocene foreland basin developed in response to Miocene deformation in the east-vergent La Ramada fold and thrust belt. Recent geologic mapping, stratigraphic and structural studies and integrated geochronologic and thermochronologic analyses provide critical constraints on the development of the Manantiales basin.

The Manantiales stratigraphy has been traditionally incorporated into the Miocene Chinches Formation, but recent geochronologic analyses demonstrates that the base of the succession is a previously unrecognized Eocene sequence (Hornillas sucession) with a maximum depositional age of 38.7 ± 0.2 Ma. The redefined Chinches Formation consists of a lower volcanic succession overlain by a thick coarse-grained clastic sequence that records progressive uplift of the western orogenic highland. The initiation of the Miocene succession is constrained by a 16.8 ± 0.2 Ma U/Pb age on a lapilli tuff within the lower volcanic unit, which is coeval with subsidence in the Santa María and Alto Tunuyán basins to the south.

Overlying strata is distinguished by a cyclic sequence of fluvial conglomerate, sandstone and shale. Detrital zircon U/Pb analyses constrain sediment provenance, indicating input from both the Cordillera Principal (JuraCretaceous+Grenville?) and the Cordillera Frontal (PermoTriassic). The dominance of PermoTriassic zircon grains indicate a major contribution from the Choiyoi Group of the Cordillera Frontal, which requires that the Cordillera Frontal was exposed and actively eroding in early Miocene time. Ongoing thermochronologic (U-Th/He) analyses will constrain the pattern of orogenic exhumation and provide constraints on basinal subsidence.