The structure of the Southern Central Andes (Chos Malal fold and thrust belt).

TURIENZO, MARTÍN; SÁNCHEZ, NATALIA; LEBINSON, FERNANDO; DIMIERI, LUIS

The Evolution of the Chilean-Argentinean Andes

Springer

Lugar: Cham; Año: 2018; p. 411 - 441

The Chos Malal fold and thrust belt, formed during the Andean orogeny,is characterized by the involvement of both the Paleozoic basement and Mesozoicstrata of the Neuquén Basin in deformation. Two detailed structural cross-sections,built based on field mapping and subsurface information, allow to characterize thestructural style of this orogenic belt where close interaction between large thickskinnedstructures (1st order) and complex thin-skinned structures (2nd, 3rd and4th order) related to the presence of multiple detachments in the sedimentarycover is recognized. The largest thrusts form basement-involved duplex structures,with a lower detachment located at a depth of about 12-14 km and an upperdetachment in the Jurassic evaporites of the Auquilco Formation. Displacementtransmitted by these basement sheets in the inner zone of the Chos Malal fold andthrust belt produces a wide region with thin-skinned deformation, which containssecond order fault-bend folds that transfer deformation to the overlying AgrioFormation shales (Early Cretaceous) giving rise to third order folds and thrustsinvolving this unit. In the outer zone the basement-involved thrusts have lessdisplacement and form monoclines and a complex thin-skinned deformationrestricted to the deformation front, possibly caused by buttressing effect exertedby the overlying Miocene volcanic sequences. This impediment in forwarddeformation leads to an important out of sequence faulting, whose displacement iscompensated by a passive-roof backthrust along the Cretaceous evaporites of theBajada del Agrio Group forming a triangle zone. Second order anticlines underthis triangle zone, where the seismic data is of low quality, constitute importanthydrocarbon oil fields such as El Porton and Filo Morado. Understanding theclose relationship between the structures of different order cropping out in theinner zone of the Chos Malal fold and thrust belt is important to interpret thesubsurface structures forming hydrocarbon oil fields in the outer zone as well as toidentify other complex structures that may lead to new exploration opportunities.