Geometry of Middle to Late Triassic extensional deformation pattern in the Cordillera del Viento (Southern Central Andes): A combined field and geophysical study

Abstract

Combined field and gravimetric-magnetic data reveal a complex pattern of extensional structures superimposed to the late Carboniferous -Early Permian Gondwanan orogen at the inner sectors of the Southern Central Andes, in the westernmost part of the Chos Malal fold and thrust belt at the cordillera del Viento area. W-NW, NW basement structures of regional significance, segmented by minor NE structures are bounding Late Triassic depocenters and structural highs corresponding to the cordillera del Viento rifting, equivalent to the Precuyo cycle. A pattern of roughly N-S trending structures recognized in the field associated with Andean thrusts do not show evidences of previous structural controls, as they cut the magnetic anomalies. Field observations show that W-NW, NW and NE normal structures control changes in Late Triassic sedimentary thicknesses and are associated with synextensional geometries. Our model indicates that Late Triassic rifting in the area would have had a regional W-NW to NW trend being segmented by minor NE structures. Both sets were reactivated during Andean times, acting W-NW and NW structures as transfer zones between decoupled contractional panels and NE structures as frontal contractional structures. N-S contractional structures did not respect rifting architecture cutting through the depocenters and occasionaly exhuming synextensional geometries.Keywords: Synextensional sedimentation, Late Triassic, rifting, Northern Neuquén Precordillera, Andes Resumen La combinacion de datos de campo, junto con magnéticos y gravimétricos, revelan un patrón complejo de estructuras sobreimpuestas al orógeno gondwánico (Carbonífero superior-Pérmico) en el sector interno de la faja plegada y corrida de los Andes Centrales australes, en el área de la cordillera del Viento.Estructuras de basamento W-NW, NW de significancia regional, segmentadas por estruturas menores NE están limitando depocentros y altos estructurales correspondientes al rifting del Triásico Superior de la cordillera del Viento, equivalente de las unidades del ciclo Precuyo.En el campo se reconoce además un patrón de estructuras de rumbo N, asociadas a fallas andinas que no muestran evidencias de un control estrutural previo, ya que las anomalías magnéticas están cortadas por éstas. Las observaciones de campo demuestran que tanto las estructuras W-NW y NW como las NE controlan cambios de espesor de los sedimentos del Triásico Superior y se asocian a geometrías sinextensionales. El modelo propuesto indica que el rifting del Triásico Superior podría haber tenido una geometría elongada según el patrón de estructuras identificadas W-NW a NW, segmentado por estructuras menores NE. Ambas muestran reactivación durante tiempos andinos, las primeras actuando como zonas de transferencia entre sectores que muestran diferentes grados y mecánicas de contracción y las últimas como estructuras frontales contraccionales. Las estructuras contraccionales de orientación N-S no respetan la arquitectura del rift triásico, cortando los depocentros y even...

Retracted: Middle Miocene to Early Pliocene Contraction in the Chos Malal Fold‐and‐Thrust Belt (Neuquén Basin, Argentina): Insights From Structural Analysis and Apatite Fission‐Tracks Thermochronology

“…In the western foothills of the Cordillera del Viento, Paleogene volcanic rocks of the Cayanta Formation rest unconformably over the basement and Mesozoic rocks affected by the Andacollo blind back thrust (ABT; labeled 1′ in Figure a). The ABT has previously been interpreted as an inverted normal fault (Cobbold & Rossello, ; Zapata et al, ), and in the Cordillera del Viento itself, Sagripanti et al () have mapped east dipping normal faults, bounding the synrift deposits (Precuyo Cycle, Upper Triassic, Figure a) and associated these faults with moderate inversion. In order to produce significant enough structural relief to account for the angular unconformity observed below the Paleogene rocks, we interpret the ABT as a shortcut fault derived from the pre‐Andean Mesozoic extensional system.…”

“…A rifting stage, which began in the Late Triassic to Early Jurassic, formed numerous NW‐SE trending half‐grabens (Figure b) (Vergani et al, ). Synrift sediments, known as “precuyanos” deposits (Gulisano et al, ) including the Cordillera del Viento, Milla Millicó, and La Primavera Formations, are exposed on the eastern flank of the Cordillera del Viento, showing a complex architecture and variable stratigraphic thicknesses controlled by normal faults (Sagripanti et al, ). La Primavera Formation, exposed on the eastern slopes of the Cordillera del Viento (Figures b and ), is a volcaniclastic sequence with interbedded marine deposits containing invertebrate fossils (Leanza et al, ).…”

Tectonic Evolution of the Chos Malal Fold‐and‐Thrust Belt (Neuquén Basin, Argentina) From (U‐Th)/He and Fission Track Thermochronometry

“…Tectonics the Cordillera del Viento, Milla Millicó, and La Primavera formations ( Figure 2b). These deposits are exposed on the eastern flank of the Cordillera del Viento and preserve a complex architecture and variable stratigraphic thicknesses controlled by normal faults (Sagripanti et al, 2014). During the Early-Middle Jurassic, subduction initiated along the western Gondwana margin (Franzese et al, 2003) and by the Late Jurassic the Andean magmatic arc was fully developed (Charrier et al, 2007;Ramos, 2010).…”

The structure of the northern Agrio fold and thrust belt (37°30’ S), Neuquén Basin, Argentina

“…Interpretation of poor-quality seismic lines in the study area does not show clear evidence of a significant inversion processes. Comparable conclusions arise from subsurface interpretations (Sánchez et al, 2015;Turienzo et al, 2018) and field observations (Sagripanti et al, 2014) in the Chos Malal FTB, where the Late Triassic-Early Jurassic normal faults were only partially inverted and they preserve their extensional character. Many regional cross-sections have been made along the Agrio and Chos Malal fold and thrust belts in the last three decades, analysing the structural style of the deformed regions of the Neuquén Basin (Fig.…”