Spatial and temporal characterization of progressive deformation during orogenic growth: Example from the Fuegian Andes, southern Argentina

Abstract

Superposed structural fabrics in the easternmost Fuegian Andes reveal two distinct, non-coaxial deformation phases across the transition from the orogenic core to the thrust-fold belt. Each phase is characterized by different metamorphic conditions and consistently different orientations, which allow the structural correlation between the orogenic core and the internal thrust-fold belt. The first deformation phase was coeval with regional metamorphism reaching upper greenschist facies, and featured simple shear deformation of the basement (Paleozoic and Jurassic) and cover (Cretaceous) in the top of the underthrusting South American plate. The second phase developed during collision of the orogenic wedge with the Río Chico Arch, a promontory in the underthrusting plate; this phase was characterized by thrust sheet emplacement and formation of a crustal duplex, with rock uplift and consequent low to very-low grade metamorphism. Buttressing against the Río Chico Arch is responsible for the change in shortening orientation that distinguishes both phases. of the magmatic arc and the cratonic margin, with deformation of the Paleozoic-Early Cretaceous rocks between them. In the Fuegian Andes, arc-continent collision involved cratonward obduction of the oceanic crust of the back-arc basin, and subduction (underthrusting) of the cratonic margin (Fig. 1D) (Klepeis et al., 2010). Thrusting and stacking of upper crustal rocks in the top of the lower plate formed a major antiformal stack that propagated toward the foreland into a thrust-fold belt (Fig. 1D) (Torres Carbonell and Dimieri, 2013). The latter includes the Rocas Verdes fill, as well as

The Fuegian thrust-fold belt: From arc-continent collision to thrust-related deformation in the southernmost Andes

“…2 and 3) comprises slates with a marine protolith, that may interfinger southwards with the Yahgan Formation (Olivero and Malumián, 2008;Martinioni et al, 2013). South of Lago Fagnano, the contact with the underlying Lemaire Formation is a few meters below a north-northeast-dipping detachment surface (Torres Carbonell and Dimieri, 2013;Cao, 2019; this work), whilst at Península Mitre this contact is a south-dipping reverse fault (Torres Carbonell et al, 2017b). Its top is not well defined due to lack of stratigraphic definition north of Lago Fagnano.…”

“…In southern Península Mitre, the D1 CB structures and metamorphic grades in the Lemaire and Beauvoir formations are similar to those between Lago Fagnano and Canal Beagle, with a NW-SE structural trend (Torres Carbonell et al, 2017b) Previous constraints on the age of the D1 CB structures were limited to their inclusion in the "main phase of deformation" ("mid" Cretaceous in Bruhn, 1979;Dalziel and Palmer, 1979), and the statement that they affected rocks not younger than the Campanian-?Maastrichtian Bahía Thetis Formation (Torres Carbonell et al, 2017b).…”

“…3) that roughly defines the mountain front in Tierra del Fuego. Previous structural work in the internal thrust-fold belt has been published by Klepeis (1994), Zanella et al (2014) and Torres Carbonell et al (2013b, 2017b. The structure of the internal thrust-fold belt will be addressed in the following sections together with new structural and stratigraphic data from this region.…”

“…D1 CB is characterized by ductile NE-vergent folds and axial-plane foliations associated with low-grade regional metamorphism, and with the development of shear zones with mylonitic foliations in sectors of localized higher strains (Fig. 8a, Kranck, 1932;Bruhn, 1979;Dalziel and Palmer, 1979;Torres Carbonell and Dimieri, 2013;Torres Carbonell et al, 2017b;Cao et al, 2018;Cao, 2019). Between Canal Beagle and Lago Fagnano, D1 CB folds range from tight or isoclinal in the Lapataia and Lemaire formations, to tight or very tight folds with NE vergence, usually classes 1C to 2, in the Yahgan and Beauvoir formations.…”

Stress Field Evolution of the Southernmost Andean Cordillera From Paleostress Analysis (Argentine Tierra del Fuego)

“…Contours indicate foreland sediment thickness in kilometers (Biddle et al, ; Galeazzi, ). (c) Cross‐section x ‐ y of the Central Belt, the Magallanes‐Fagnano Fault System, and the Fuegian Thrust and Fold Belt modified from Torres Carbonell, Cao, and Dimieri ().…”