Abstract
The early Mesozoic extensional processes recognized in SW Gondwana have been related to a supercontinent precursor break-up phase, the gravitational collapse of a late Paleozoic orogen, changes in subduction dynamics or the impact of a thermal anomaly. However, intraplate extension is still lacking accurate temporal constraints for the area devoid of the influence of subduction-related extensional processes that affected its margin between mid-Permian and Early Cretaceous times. Evidence from this intraplate extensional phase is found in the Cara Cura – Reyes depocenter of the Neuquén basin located in west-central Argentina. Field and seismic evidence allowed identifying synextensional growth geometries, and zircon U-Pb SHRIMP dating of volcanic rocks revealed ages of 198.8 ± 2.0 Ma and 195.4 ± 1.0 Ma for the oldest and youngest exposed synrift deposits. These allowed limiting the mechanical subsidence phase to the Sinemurian, which was followed by a Pliensbachian – Toarcian hiatus separating it from the postrift deposits. These deposits are characterized by a series of marine transgressive-regressive cycles separated by sedimentation gaps, constrained in this sector to the Bathonian – Callovian and the Kimmeridgian. When inserted into the broader realm of the Neuquén basin, a diachronic development for both the synrift and postrift deposits is evident, although the synrift-postrift transition occurred at ca. 190 Ma. The correlation of these events along SW Gondwana supports a common tectonic evolution which, at the same time, allows correlating the hiatus detected in postrift sedimentation of the Cara Cura – Reyes depocenter with Jurassic intraplate contractional events. The shift in the intraplate tectonic regime coincides with a radical change in Gondwana's absolute motion, being northwards during extension, and southwards during contraction, after the opening of the Central Atlantic Ocean. Therefore, upper-plate dynamics seems to have played a first-order role during the opening of the Neuquén basin.
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