Cenozoic intraplate tectonics in Central Patagonia: Record of main Andean phases in a weak upper plate

Abstract

Contraction in intraplate areas is still poorly understood relative to similar deformation at plate margins. In order to contribute to its comprehension, we study the Patagonian broken foreland (PBF) in South America whose evolution remains controversial. Time constraints of tectonic events and structural characterization of this belt are limited. Also, major causes of strain location in this orogen far from the plate margin are enigmatic. To unravel tectonic events, we studied the Cenozoic sedimentary record of the central sector of the Patagonian broken foreland (San Bernardo fold and thrust belt, 44º30'S-46ºS) and the Andes (Meseta de Chalia,46ºS) following an approach involving growth-strata detection, U-Pb geochronology and structural modeling. Additionally, we elaborate a high resolution analysis of the effective elastic thickness (Te) to examine the relation between intraplate contraction location and zones of low lithospheric strength. The occurrence of Eocene growth-strata (~44-40 Ma) suggests that

Tectonic Regimes of the Central and Southern Andes: Responses to Variations in Plate Coupling During Subduction

“…Further mechanical variations involve the role of trench sediments in modulating stress transmission across the plate interface (Lamb & Davis, ; Melnick & Echtler, ; von Huene & Ranero, ) and inherited rheological properties of the overriding plate, as related to the extent of pre‐Andean thermal weakening, thickness of South American lithosphere, and composition, age, and strength of Andean crust (Allmendinger et al, ; Giambiagi et al, ; Gianni et al, ; Haschke et al, ; Isacks, ; Kley et al, ; Luo & Liu, ; Mamani et al, ; Wdowinski & Bock, ; Whitman et al, ). Selective removal of lower continental lithosphere and associated igneous processes are also likely to affect the mechanical behavior of the South American Plate (Beck & Zandt, ; Garzione et al, ; Pope & Willett, ).…”

“…Crustal shortening and foreland basin sedimentation (Chubut and Divisadero Groups) commenced at ~110–90 Ma and persisted throughout Late Cretaceous‐Paleocene time (Barcat et al, ; Gianni et al, ; Navarro et al, ; Suárez et al, ). Contractional deformation was distributed over the entire retroarc segment of continental crust (including the San Bernardo fold‐thrust belt), due to possible crustal weakening by earlier extension and reactivation of associated normal faults (Gianni et al, ; Orts et al, ; Savignano et al, ). The inception of regional shortening partially coincided with the main emplacement of the North Patagonian Batholith at ~120–100 Ma, followed by eastward expansion of the calc‐alkaline magmatic arc during slab flattening (Echaurren et al, , ; Pankhurst et al, , ).…”

Constraints on the Neogene growth of the central Patagonian Andes at the latitude of the Chile triple junction (45–47°S) using U/Pb geochronology in synorogenic strata

“…The occurrence of a N-trending, dextral transpressive fault system referred to as the Liquiñe-Ofqui Fault Zone (LOFZ) (Figures 1 and 2), extends ~1,000 km to the north of the CTJ, individualizing a microplate through the present arc front (Hervé, 1994). Cretaceous and Miocene-Pliocene phases of exhumation are recorded through the Patagonian Andes by fission track data (Thomson et al, 2001, Thomson 2002Savignano et al, 2016); while exhumation on the eastern Andean front is determined through recognition and dating of synorogenic strata with late Early-Late Cretaceous, early Eocene and Neogene ages (Orts et al, 2012;Bilmes et al, 2013;Ramos et al, 2015;Gianni et al, 2015Gianni et al, , 2017Echaurren et al, 2016). These events are separated by an episode of extension that started in the late Eocene (Paleocene?)…”

“…These events are separated by an episode of extension that started in the late Eocene (Paleocene?) and peaked in the late Oligocene-early Miocene (Muñoz et al, 2000;Aragón et al, 2011;Orts et al, 2012Orts et al, , 2015Encinas et al, 2015;Gianni et al, 2017).…”

Cretaceous Intraplate Contraction in Southern Patagonia: A Far‐Field Response to Changing Subduction Dynamics?

“…The three plates interact in the Chilean Triple Junction at 46°30 0 S. This point separates the North Patagonian Andes from the Austral Patagonian Andes (Figure 1a). To the east, the~750-to 800-km-long Patagonian broken foreland is located in a low rigidity lithosphere and is characterized by presenting a subtle amount of shortening (3-4%; Echaurren et al, 2016;Gianni et al, 2017). This area is divided into three main zones, the Cañadón Asfalto, San Bernardo, and the Deseado FTBs (Figure 1a).…”