New Insights Into the Stratigraphic and Structural Evolution of the Middle to Late Jurassic Neuquén Basin as Constrained by Detrital Zircon (U-Th)/(He-Pb) and Apatite (U-Th)/He Ages

Abstract

The stratigraphy and thermal history of the Middle to Upper Jurassic Cuyo Group in the Neuquen basin has been of academic and hydrocarbon-industry interest with established source-rock and reservoir potential (e.g. Octogono and Don Ruiz fields). The discovery of syn-depositional faulting, inferred from structurally-controlled stratal thickness variations in the Cuyo Group have raised questions related to the tectonic and depositional setting, stratigraphic age, sediment provenance and the timing and magnitude of deformation during and after its deposition. All crucial components to define the basin evolution and petroleum play. To address some of these questions we employed zircon (U-Th)/(He-Pb) double dating and apatite (U-Th)/He in detrital grains from Los Molles and Lajas formations, southwest from Zapala, Argentina. The Lajas Formation detrital zircon U-Pb and (U-Th)/He (zHe) analysis yields concordant Late Jurassic (avg. 155±4 Ma.) ages thus constraining its depositional age younger than previously proposed. Equally important the abundance of non-volcanic zHe ages equivalent to the Los Molles and Lajas Formations depositional ages suggest fast fault-induced exhumational rates in the basin vicinity during deposition. This is in direct conflict with the conventionally reconstructed Middle to Late Jurassic tectonics. The sediment provenance analysis confirms that both formations are part of the same source-to-sink system, showing that both were primarily fed by similar, proximal exhuming sources (both show dominant Permo-Triassic and Middle Jurassic zircon U-Pb populations with zHe ages that span from Permian to Jurassic in age). The youngest Jurassic ages were likely sourced from the volcanic arc to the west although intracratonic late Jurassic volcanism in the southern regions is another plausible origin. Detrital zHe analysis show three significant tectono-cooling events in the Cuyo strata (1) middle Triassic, (2) Triassic-Jurassic and (3) Late Jurassic, thus recording characteristic signatures from sources that were tectonically active during early Neuquén rifting and oblique contractional stages. Additionally, Early Miocene (U-Th)/He apatite ages deliver new insights on the timing of local Andean structural deformation and its influence on the Cuyo post-depositional thermal history. Those are key aspects when reconstructing the maturation, migration and trap elements in the Los Molles and Lajas petroleum system in southern Neuquén Basin.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016