Tectonic control on hydrocarbon generation in the northwestern Neuquen Basin, Argentina

The petroleum systems of the Malargtie fold-thrust belt in the northwestern Neuquen Basin, Argentina, comprise multiple reservoir and seal rocks and three major source rocks of the Lower Jurassic (Los Molles Formation [Fm.]), the lower Tithonian to lower Valanginian (Vaca Muerta Fm.), and the lower Hauterivian to lower Barremian (Agrio Fm.). The thermal history of the Mesozoic source rocks has been reconstructed using one-dimensional and two-dimensional modeling. The most important factors that affected the source-rock maturation are the timing of maximum Late Cretaceous to Paleogene burial and the heat flow during back-arc extension. We postulate that synclines have been buried over longer periods and source-rock maturation ceased earlier in antidines, accordingly. Hydrocarbon generation from the Vaca Muerta Fm. and Agrio Fm. has started during the Campanian. Despite late-stage magmatic activity causing local thermal perturbations, the models suggest that the thermal field has been dominated by conductive heat transport and that heat flow has been a response to the evolution from back-arc extension to orogenic shortening. High heat flows of 85 mW/m(2) during back-arc extension between the latest Cretaceous and Paleogene have been modeled. Two main source pods supply hydrocarbons until the present. They are related to structurally deep footwall positions of thrust faults, active since the Late Cretaceous, and to deep frontal syndines, having formed through late-stage thick-skinned tectonics since the Neogene. Modeling of hydrocarbon fluid type is consistent with existing oil fields exhibiting light and medium oils with API between 22 degrees API and 39 degrees API, charged from early- to peak-mature source rocks.