Evidence of Jurassic extension in NW Argentina: Characterization of fault-related strata at the Salta Group base using sandstone provenance and zircon U–Pb geochronology

Abstract

The present-day structure of the Eastern Cordillera in NW Argentina is governed by structural and lithological heterogeneities inherited from preceding deformation phases, which influence the localization of newly-formed faults and the inversion of pre-existing structures. The Salta Rift Basin formed during a Late Jurassic-Cretaceous extensional phase and created a dominant structural and stratigraphic imprint in NW Argentina that is particularly evident within the Eastern Cordillera, where uplift and exhumation have exposed the Salta Group syn-rift succession. Although in general, the Salta Group rests upon Paleozoic rocks, locally the Tacurú Group forms an intermediate succession, consisting of interfingering eolian sandstones and proximal fault-related conglomerates with a Jurassic maximum depositional age. This succession might be the key to unraveling the Mesozoic history of NW Argentina, prior to the deposition of the Salta Group. The conglomerates represent the earliest deposits related to extension in the western Lomas de Olmedo sub-basin, which is also documented in predominantly Jurassic zircon (U–Th-Sm)/He cooling ages of the rift shoulders. The detrital zircon U–Pb age signature and sandstone provenance of the Tacurú Group conglomerates differs strongly from the Salta Group syn-rift strata, which show a more regional signal. These variations and the angularity of the unconformity may be connected to a rotation of the extension direction in the western Lomas de Olmedo sub-basin.