Multiproxy provenance analysis of Lower to Upper Cretaceous synorogenic deposits in the Southern Andes (34–35°S): Evidence of coeval volcanism during the onset of the Andean orogeny

Abstract

The combination of detrital low-temperature thermochronology with previous U–Pb geochronology, petrological and sedimentological analyses, has proven to be a valuable approach to constrain the provenance of non-marine Lower to Upper Cretaceous synorogenic deposits in the northern Neuquén Basin. This work focuses on the study of the Diamante Formation, a fluvial succession that represents the first synorogenic products of the Andean foreland basin at 34–35°S. The results indicate that the deposition of the Diamante Formation occurred simultaneously with the existence of an active western volcanic arc during the onset of the foreland basin. The facies associations evidence the transition between the backarc and the foreland basin stages as well as the inception of fluvial sedimentation in the foredeep. Petrographic analyses, together with changes in the paleocurrents and the record of limestone clasts suggest a regional detrital source shift. Apatite fission-track analyses (AFT) of a sample collected from the lower part of the Diamante Formation indicate an Albian central cooling age. This sample also evidences a remarkable presence of angular apatite and zircon crystals with subordinated rounded and subangular grains. Zircon fission-track analyses (ZFT) of a sample from the upper part of the Diamante Formation yield two discrete populations of cooling ages, both reflecting source-cooling during the Late Jurassic (∼161 Ma) and the Permian (∼265 Ma). Finally, a comparison between the AFT and the U–Pb maximum depositional zircon-age reveals a short lag time (ca. 3 ma), likely related to the rapid magmatic cooling of a coeval volcanic source at ∼110 Ma (Albian).