Variable structural controls through time in the Southern Central Andes (~36ºS)

Abstract

ABSTRACT. The Southern Central Andes at 36ºS have been recognized as an orogenic belt where contraction, ac com modated mainly by basement structures, is associated with the inversion of a Late TriassicEarly Jurassic extensional detachment. Based on a structural crosssection, constrained by field data, 2D seismic and borehole information, and the processing of Bouger anomalies, we propose a polyphasic tectonic evolution. In the westernmost sector, along the axis of the Cordillera, NW to NNW basement structures were inverted, being a first order control in the generation of frontal narrow Ntrending thinskinned belts. This slip transfer is controlled by the Late Jurassic main detachment. These structures have low gravity anomalies that cross obliquely the main Andean trend. East of this inversion domain, beneath the frontal thinskinned belts, seismic information reveals that Late Triassic wedgelike depocenters did not experience substantial inversion. To the east doublevergent basement blocks define the Andean emergent orogenic front at these latitudes. These contractional structures truncate gravity anomalies defined by basement discontinuities, indicating that they are not related to tectonic inversion, in contraposition to the westernmost domain. Two contractional phases were distinguished. The oldest is Late Cretaceous in age, as inferred from onlap relations in Upper Cretaceous strata identi fied in seismic lines. These successions have a maximum age of 97 Ma as inferred by UPb in detrital zircons published in previous studies in the area. Contrastingly, the easternmost sector was mainly deformed in Late Miocene times as inferred from less than 18 Ma old synorogenic deposits. Moreover, contractional mechanisms varied through time for each specific sector. While Late Cretaceous contractional tectonics was generated by tectonic inversion and subordinate thinskinned deformation, it is proposed that Late Miocene deformation was controlled mainly by brittleductile transi tions at the upper crust with no major influence of previous structures. This fact can be explained by a higher thermal flux achieved in the retroarc area in the last 17 Ma due to the eastward arc expansion during a shallow subduction regime. RESUMEN. Controles estructurales variables en el tiempo en los Andes Centrales Australes (~36ºS). Los AndesCentrales Australes a los 36ºS han sido reconocidos como una faja orogénica en donde la contracción, principalmente acomodada por estructuras de basamento, está asociada a la inversión de un sistema extensional del Triásico TardíoJurásico Temprano. Basados en una sección estructural, construida a partir de datos de campo, líneas sísmicas 2D, datos de pozo y el procesamiento de anomalías de Bouger, proponemos una evolución tectónica polifásica. En el sector occidental, a lo largo del eje cordillerano, estructuras de basamento con orientación NW a NNW fueron invertidas actuando como un control de primer orden en la generación de fajas frontales de piel fina angostas y de orientación norte. La transferenci...

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…• Malargüe fold-and-thrust belt: [252][253][254][255][256][257][258] • Chos Malal fold-and-thrust belt: [259,260] • Agrio fold-and-thrust belt: [257,261] For this paper the Malargüe fold-and-thrust belt was chosen because it clearly shows the interaction between basin inversion and the involvement of the crystalline basement in compression. The structure of the entire Andean chain along latitude 31 • S is discussed in Section 2.4 (see Figure 12).…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…• Malargüe fold-and-thrust belt: [242][243][244][245][246][247][248] • Chos Malal fold-and-thrust belt: [249,250] • Agrio fold-and-thrust belt: [25,247] For this paper the Malargüe fold-and-thrust belt was chosen because it clearly shows the interaction between basin inversion and the involvement of the crystalline basement in compression. The structure of the entire Andean chain along latitude 31°S is discussed in section 2.4 (see Figure 12).…”

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

“…1) (Kozlowski et al, 1993). This system and the Chos Malal fold and thrust belt to the south, were formed in three contractional pulses, the first occurring in Late Cretaceous, the second in the Paleocene, and the last in early to middle Miocene times (Cobbold and Rossello, 2003;Silvestro and Atencio, 2009;Tunik et al, 2010;Orts et al, 2011). However, the Chos Malal orogenic front is considerably retracted to the west in comparison to the northern segment.…”