Basement-cover interaction in the mountain front of the Northern Neuquén fold and thrust belt (37º10’ – 37º40’ S), Argentina

Abstract

The deformation front of the Neuquén fold and thrust belt (~37°30′S) comprises kilometer-scale basement-involved anticlines, related to development of the Las Yeseras and Pampa Tril thrust systems, connected with awide frontal syncline. The interpretation of more than 70 seismic lines led to the construction of a time-structuremap at top of the Cuyo Group (Middle Jurassic), which shows a structural high east of the Tromen volcanoproduced by the superposition of thick-skinned structures. Moreover, data from 35 oil wells constrain the along-strike variations in structural reliefs. The structural relief of the Las Yeseras anticline increase from north tosouth, between ~1000 m and 2000 m, while the structural relief of the Pampa Tril anticline reaches its max-imum height of 3700 m in the north and decreases southwards to only 1600 m height and then disappears. Threestructural cross-sections based on surface and subsurface information show the overall structural style domi-nated by north-trending basement-involved anticlines, with subhorizontal backlimbs and maximum structuralreliefs around 3–4 km, associated with thick-skinned thrust systems and without significant participation ofinverted normal faults. Calculated thick-skinned shortenings are ~8.3 km (14.8%) in the north and ~4 km(7.8%) in the south, which principally reflects the decreasing displacement of the Pampa Tril thrust system.Along-strike structural changes were locally controlled by WNW transfer zones that can be interpreted as SSW-dipping preexisting normal faults with minor positive inversion. Thin-skinned structures that form oil fields atdepth are genetically associated with the thick-skinned thrust systems, thus the understanding of basement-coverinteraction in the mountain fronts will aid to future hydrocarbon explorations and to comprehend the me-chanisms of Andean mountain building.